Synch MotorProject Feb2009

8/2/2019 Synch MotorProject Feb2009

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ANALYSIS AND BEHAVIOUR OF 5.6MW SYNCHRONOUSMOTOR FOR EXHAUST FAN DRIVE

A Project Report submitted To

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY,HYDERABAD.Of

BACHELOR OF TECHNOLOGY IN

ELECTRICAL AND ELECTRONICS ENGINEERINGSubmitted By

K.SANTHOSH KUMAR REDDY 05G01A0223B.KISHORE 05G01A0204B.POORNA PAVAN KUMAR 05G01A0213

Under the esteemed guidanceOf

A. HEMASEKAR, M.TechAssociate. Professor.

SRI VENKATESA PERUMAL COLLEGE OF ENGG. & TECH., PUTTUR R.V.S. NAGAR, K.N. ROAD, PUTTUR-517583

(AFFILIATED to JNTU, HYDERABAD)ISO 9001:2000 CERTIFIED INSTITUTION

2008-2009


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CERTIFICATE

This is to certify that the project report entitled ANALYSIS ANDBEHAVIOUR OF 5.6MW SYNCHRONOUS MOTOR FOR EXHAUST FAN

DRIVE that is being submitted by K.SANTHOSH KUMAR REDDY,

B.KISHORE, B.POORNA PAVAN KUMAR in partial fulfillment of the

requirements for the award of the degree of Bachelor of Technology in

ELECTRICAL & ELECTRONICS ENGINEERING to the Jawaharlal Nehru

Technological University is a record of bonafide work carried out by him under our

guidance and supervision.

Under the esteemed guidance of


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ANALYSIS AND BEHAVIOUR 5.6MWSYNCHRONOUS MOTOR FOR EXHAUST

FAN DRIVEB.TECH

IN

ELECTRICAL AND ELECTRONICS ENGINEERING

Submitted by

K. SANTHOSH KUMAR REDDY 05G01A0223

B. KISHORE 05G01A0204

B. POORNA PAVAN KUMAR 05G01A0213

SRI VENKATESA PERUMAL COLLEGE OF ENGINEERING & TECHNOLOGY

Under the esteemed guidance of Mr..

SINTAR PLANTVISAKHAPATNAM STEEL PLANT

TO

RASTRIA ISPAT NIGAM LIMITEDVISAKHAPATNAM


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CERITIFICATE

This is to certify that project work entitled as ANALYSIS AND

BEHAVIOUR OF 5.6MW SYNCHRONOUS MOTOR FOR EXHAUST FAN DRIVE is

a bonafide record of work done by K.SANTHOSH KUMAR REDDY, B.KISHORE,

B.POORNA PAVAN KUMAR students of SRI VENKAESA PERUMAL COLLEGE OF

ENGINEERING & TECHNOLOGY in partial fulfillment of the requirement under the

guidance and supervision in VISAKHAPATNAM STEEL PLANT.

VisakhapatnamDate: Under the esteemed guidance of


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ACKNOWLEDGEMENT

We here by take this opportunity to express our sincere gratitude to thefollowing eminent personalities whose aid and advice helped us to complete this project

work successfully without any difficulty.

We express our profound gratitude to Mr. C.V. S. Prabhakar of

T&DC for according permission to pursue a project in the plant.

We are thankful to Mr.., Sinter Plant who has been with

us all through the project to spend his valuable time and to share his knowledge. We

would also like to thank Mr. who has specially taken interest.

As a token of our feeling, we would like to acknowledge our sincere

regards to our internal guide Mr. A. Hemasekar for allowing us to take up a project in

a working plant. We are also thankful to faculty member.


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ABSTRACT

Main purpose of the project report is to study and analysis the behavior of the

synchronous motors which are used in sinter plant. In sinter plant, the sinter mix is

converted into blocks (60mm) require for the blast furnace.

5.6 MW synchronous motors are used to maintain constant vaccum under the

sinter machine (furnace). These motors are operating at 5.6 MW and 11KV and also at

different range power factors


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INTRODUCTION TO VSP:

Visakhapatnam Steel Plant is a symbol of the technical corporation

between India and Russia. Some of the technological highlights of Visakhapatnam

Steel Plant are:

Visakhapatnam Steel Plant is the only shore based integrated steel plant

in our country. The decision to set up an integrated steel plant at Visakhapatnam by

the Government of India was taken in the Parliament on 17th April, 1970 and on 20th

January, 1971, the then Prime Minister, and Smt. Indira Gandhi laid the foundation

stone fulfilling the long cherished dream of the people of Andhra Pradesh. Theconstruction of VSP is taken up by steel authority of India (SAIL). With economic

and Technical Corporation of rest while Union of Soviet Socialist Republics.


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Visakhapatnam is a fast growing city and a railway junction station in

the Eastern Ghats and the coast of Bay of Bengal. It is the district headquarters.

Visakhapatnam is the home for several heavy industries in the Public Sector like

BHPV, Hindustan Zinc, Hindustan Shipyard, HPCL etc. It also houses establishmentslike NSTL, Eastern Naval Command, NAD, Visakhapatnam Port Trust, and Centre

for naval architecture etc. Visakhapatnam Steel Plant is located 15 Kms to the South

West of the Visakhapatnam Port. It lies between the Northern boundary of the

National Highway No. 5 from Madras to Kolkata and 7 Kms to the South West of

Howrah Madras railway line.

1.1. Coke Oven and Coke Chemicals Plants:

Coke oven plant consists of three coke oven batteries of 67 ovens each

with useful coke chamber volume of 41.6 cubic meters. Each battery is of 7 meters

height. It produces coke in the sizes of 25 to 70 mm which meet the coke requirement

of the Blast Furnaces. The annual capacity of the three batteries is 2.261 mt. During

production operation the CO gas (carbon monoxide) generated is used in the Coke

chemical plants to extract different Bi-products like Benzyl, Ammonium Sulphate,Tar products etc. After extracting all the valuable products the remaining gas is used

as energy source.

1.2 Blast Furnace (BF):

There two Blast Furnaces named "GODAVARI" and "KRISHNA", each

of 3200 cubic meter useful volume. Here hot metal is produced from the raw

materials like iron ore (Lump), sinter, coke and limestone etc. The annual capacity of

this facility is 3.4 mt. From molten hot metal pig iron / steel is produced.

1.3 Steel Melting Shop:


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There are three nos. of LD converters each of 133 cubic meters with a

capacity to produce 3 mts of liquid steel. The production capacity of a plant is its

capacity to produce liquid steel. VSP is a 3 mt plant. SMS also has six numbers of

four strands continuous casting machines to produce blooms. 2.82 mt of blooms can be cast annually. In this shop hot metal from BF is received in the mixer, kept for

temporary storage and transferred to converter where charging takes place in presence

of 99.5% pure oxygen. After Argon rinsing the molten steel is moved from here to the

six strand continuous casting machines. Blooms are formed which form the input

material for the mills. Blooms are also taken as input to small steel making industries.

1.4 Rolling Mills :

There are three rolling mills in VSP.

Light & Medium merchant mills: It includes the billet mill and bar mill. It

has a two strand rolling mill. It produces billets, bars and structures. The

annual capacity is 1.857 mts of billets and 7.1 mts of bars & structures.

Wire Rod mill: It is a high speed four strand continuous mill. The mill

is designed to produce wire rods in plain rounds and ribbed bars (5.5 to 12.7

mm diameter). The annual capacity of wire rods production is 0.8 mt.

Medium and Merchant mill: This mill produce squares 12 to 65mm,

flats 30 to 150mm, channels and angles etc. This mill has an annual

capacity of 0.85 mt of bars and structures.

1.5 Thermal Power Plant:

The production capacity is 240 MW from the four turbo generators each

of 60 Mw capacity. There are nos. of Turbo blowers each having a capacity of 6067

NM3 / min of cold blast. Power is also generated from BPTS (back pressure turbine

station) and GETS (gas expansion turbine station) in VSP in small quantities.


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Water needs of the plant are met from the Yeleswaram reservoir

specially constructed for the plant along with the 150 km long walled canal and the

Kanithi balancing reservoir in VSP towns. VSP has a large township with all modern

amenities like hospitals, schools, clubs, function halls, shopping centers, and parks for children, good roads and protected drinking water. The products manufactured by

VSP are pig iron, steel billets, wire rods.

SINTER PLANT

Sintering:Sinter is a hard & porous ferrous material obtained by agglomeration of

iron Ore fines, coke breeze, lime stone fines, metallurgical wastes viz. flue dust, mill

scale, Ld slag etc. sinter is a better feed material to Blast Furnace in comparison to ore

lumps and its usage in Blast furnace help in increasing productivity, decreasing the coke

rate & improving the quality of hot metal produced. Hot sinter discharged from

sintering machine is crushed to 25 mm- 50 mm size and cooled before dispatching to

Blast Furnaces .

The dust laden air from the machines are cleaned in scrubbers & electrostatic

precipitators to reduce the dust content to 100 mg/ level before allowing to escape into

the atmosphere and thus helping in maintaining a clean & dust free environment.

History of Sintering

Iron ore fines (0-10 mm) which were a result of mechanized mining could not be

charged in a Blast furnace because they reduce the permeability of burden in a blast

furnace. These iron fines that were generated at mines could not ignored because of their

i) Huge quantity and

ii) High iron content.


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To use these fines effectively in a Blast furnace many processes were developed.

Sintering being one of them and widely in integrated steel plants.

Raw materials used in sintering:

Various raw materials used in sintering process are

i) Iron ore fines (0-10 mm).

ii) Coke - used as fuel.

iii) Limestone & Dolomite - to maintain required sinter basicity.

iv) Sand - to maintain required sinter basicity.

v) Metallurgical wastes - to use wastes effectively and thus reduce the cost

of sintering.

vi) Lime - to enhance the process of sintering.

Sintering process1) Preparation of various raw materials.

2) Mixing & Blending.

3) Mixing with sinter returns in presence of water to form green balls.

4) Charging on to the machine.

5) Ignition and suction.

Technical parameters of Sinter Machine:

Type : Dwight Lloyd

Total grate area : 312 m2

Effective / Sintering area : 276 m

Length between sprockets : 93.4 m

Width of the machine : 4 m

No. of pallets : 135

Number of wind boxes : 26

Drive arrangement : Left hand

Wind box arrangement : Right hand


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Speed of machine pallets : 1.5 to 8 m/min

Capacity of the machine : up to 450 TPH

Bed height : 500 mm

Height of bed layer : 40 mm

Processing in sinter plant

First the raw material is stored in the yard (RMB)

RMB SMPP SMSP BF

IRON LUMP ORE 25 MM BF (LIQUID FORM)

SMPP SINTER MACHINE PELTIZING PLANT

SMSP SINTER MACHINE SCREENING PLANT

BF BLAST FURNACE

ABOUT PROJECT:

Sinter plant consists of two sinter machines of 312sqmeter grate area each. We deal with 5.6MWSYNCHRONOUS MOTORS.

SYNCHRONOUS MOTORSIntroduction

A synchronous motor is electrically identical with an alternator or

a.c. generator. Most synchronous motors are rated between 150kw and 15MW and

run at speeds ranging from 150 to 1800r.p.m.

Some characteristic features of a synchronous motor are worth nothing:


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It runs at synchronous speed while running it maintains a constant speed.

The only way to change its speed is to vary the supply frequency

(because Ns=120f/p).

It is not inherently self-starting. It has to be run up to synchronous speed by

some means, before it can be synchronized to the supply.

It is capable of being operated under a wide range of power factors, both

lagging and leading. Hence, it can be used for power correction purposes,

in addition to supplying torque to drive loads.

Constructional features

The construction of the synchronous motors is essentially the same

as the construction of the salient pole alternator. In fact, such an alternator may

be run as an ac motor. It is similar to the drawing. Synchronous motors have the

characteristic of constant speed between no load and full load. They are capable

of correcting the low power factor of an inductive load when they are operated

under certain conditions. They are often used to drive dc generators. Synchronous

motors are designed in sizes up to thousands of horsepower. They may be

designed as either single-phase or multiphase machines.


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To understand how the synchronous motor works, assume that the

application of three-phase ac power to the stator causes a rotating magnetic field

to be set up around the rotor. The rotor is energized with dc (it acts like a bar

magnet). The strong rotating magnetic field attracts the strong rotor fieldactivated by the dc. This results in a strong turning force on the rotor shaft.

The rotor is therefore able to turn a load as it rotates in step with the rotating

magnetic field.

It works this way once its started. However, one of the disadvantages

of a synchronous motor is that it cannot be started from a standstill by applying

three-phase ac power to the stator. When ac is applied to the stator, a high-

speed rotating magnetic field appears immediately. This rotating field rushes past

the rotor poles so quickly that the rotor does not have a chance to get started.

In effect, the rotor is repelled first in one direction and then the other. A

synchronous motor in its purest form has no starting torque. It has torque only when it

is running at synchronous speed.

A squirrel-cage type of winding is added to the rotor of a

synchronous motor to cause it to start. It us so named because it is shaped and


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looks something like turnable squirrel cage. Simply, the windings are heavy copper

bars shorted .

Application and operation Synchronous motors are like induction motors in that they both

have stator windings that produce a rotating magnetic field. Unlike an induction

motor, the synchronous motor is excited by and external DC source and,

therefore, requires slip rings and brushes to provide current to the rotor.

In the synchronous motor, the rotor locks into step with the

rotating magnetic field and rotates at synchronous speed. If the synchronousmotor is loaded to the point where the rotor is pulled out of step with the

rotating magnetic field, no torque is developed, and the motor will stop. A

synchronous motor is not a self-starting motor because torque is only developed

when running at synchronous speed; therefore, the motor needs some type of

device to bring the rotor to synchronous speed.

Synchronous motor uses a wound rotor. This type of rotor contains

coils of wire placed in the rotor slots. Slip rings and brushes are used to supply

current to the rotor.


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Synchronous motor starting

Synchronous motor may be started by a DC motor on a common

shaft. When the motor is brought to synchronous speed, AC current is applied

to the stator windings. The DC field excitation to the rotor of the synchronous

motor. The load may now be placed on the synchronous motor. Synchronous motors

are more often started by means of a squirrel-cage winding embedded in the

face of the rotor poles. The motor is started as an induction motor and brought

to ~95% of synchronous speed, at which time direct current is applied, and the

motor into synchronism is called the pull-in torque.

As we already know, the synchronous motor rotor is locked into

step with the rotating magnetic field and must continue to operate at synchronous

speed for all loads. During no-load conditions, the center lines of a pole of the

rotating magnetic field and the DC field pole coincide(Figure 1a). As load is

applied to the motor, there is a backward shift of the rotor pole, relative to the

stator pole(Figure 1b). There is no change in speed. The angle between the rotor and

stator poles is called the torque angle.

(a) If the mechanical load on the motor is increased to the point where the rotor

is pulled out of synchronism, the motor will stop. The maximum value of torque


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that a motor can develop without losing synchronism is called its pull-out

torque.

5.6MW SYNCHRONOUS MOTOR AT SINTER PLANT IN VSP. Our sinter plant consists of two synchronous motors. Each synchronous

motor consists of two exhausters. Each exhauster consists of four motors.

The four motors are one main motors and one stand by motor and

(pair of Jacking motors). The stand by motor is used when the main motor is

in use. The Jacking motor is used to lift the motor up to 1mm.

We already known that the synchronous motor is not self-starting. It s

synchronous motor is started without the help of prime mover should be

started with the help of prime mover. But in sinter plant the synchronous motor

is started without the help of prime mover.

ELECTRICAL CIRCUIT ANOLOGY

(1) Power Circuit:The power flows in the circuit as shown in the single line diagram.


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In the above diagram from LBSS the power is transformed to LCSS (load

centre substation) i.e. 11kv & 6.6kv. That 11kv is the supporting system for

synchronous motor.

(2) Control & Interlocking circuit:

The control and interlocking circuits are of two types.

They are

(a) Safe interlocking and operation.


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(b) Handling the switchgear.

The various types of switchgears are as follows:

(a) Isolators(b) Circuit Breakers

(c) MCCBS

(d) Contactors

(e) Overload relays

(f) Push buttons

Isolators:

Isolators are employed only for isolating circuit when the current

has already been interrupted. They ensure that the current is not switched in to

the circuit until everything is in order. These are operated under No-load condition.

They do not have specified current breaking or current making capacity. The

isolators in some cases are used for breaking charging current of transmission

lines.

Circuit Breakers:

Circuit Breakers are mechanical devices designed to close or open

contact members thus closing or opening of an electrical circuit under normal

and abnormal conditions. Automatic circuit breakers, which are usually employed

for the protection of electrical circuit, are equipped with a trip coil connected to

a relay or other means, designed to open the breaker automatically under

abnormal conditions.

The circuit breaker performs the following duties:

(1) It carries the full load current continuously without overheating or damage.

(2) It opens and closes the circuit on no load.


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(3) It makes and breaks the normal operating current.

Overload relay: Overload may be caused either due to partial breakdown of

windings insulation or due to excessive load on the power supply system.

In case an over load protection is provided for motors such a

protection might disconnect the motor from the system due to momentary

troubles outside the power station.

Push Buttons:

The push buttons are those which are used to start and stop the

device. In most cases these push buttons are only in use.

(3) Protection circuit:

These are two types of protections. They are

(a)Switchgear protection

(b)Drive protection

Earthing is the main protection. The various protections required for a 3-phase

motor when one of the phases is tripped as shown in figure.

As shown in above fig when one of the phases is tripped the following

protections are to be required.

They are:


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(1) Over load

(2) Single phasing

(3) Under voltage

(4) Stalling protection

Switch Gear protection is inherently available with switchgear for many applications.

Note: These protections are required only to minimize the damage or avoid the

damage. But zero percent damage cannot be achieved with these protection.

(4) Annunciation and Indication:

The following feature comes under the Annunciation and Indication.They are

Understand the status of equipment (i.e. on/off condition)

Trip status

Corrective actress

(5)Integration with other networks:

It is the integration between two blocks. That is it is the inter

relation between the process done in the two blocks. The network that done in

the both blocks are integrated.

Synchronous Motors

Single phase synchronous motors are available in small sizes for applications

requiring precise timing such as time keeping, (clocks) and tape players . Though battery

powered quartz regulated clocks are widely available, the AC line operated variety has


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better long term accuracy-- over a period of months. This is due to power plant

operators purposely maintaining the long term accuracy of the frequency of the AC

distribution system. If it falls behind by a few cycles, they will make up the lost cycles

of AC so that clocks lose no time.

Above 10 Horsepower (10 kW) the higher efficiency and leading power factor

make large synchronous motors useful in industry. Large synchronous motors are a few

percent more efficient than the more common induction motors. Though, the

synchronous motor is more complex.

Since motors and generators are similar in construction, it should be possible to

use a generator as a motor, conversely, use a motor as a generator. A synchronous

motor is similar to an alternator with a rotating field. The figure below shows small

alternators with a permanent magnet rotating field. This figure below could either be

two paralleled and synchronized alternators driven by a mechanical energy sources, or

an alternator driving a synchronous motor. Or, it could be two motors, if an external

power source were connected. The point is that in either case the rotors must run at the

same nominal frequency, and be in phase with each other. That is, they must besynchronized. The procedure for synchronizing two alternators is to (1) open the switch,

(2) drive both alternators at the same rotational rate, (3) advance or retard the phase of

one unit until both AC outputs are in phase, (4) close the switch before they drift out of

phase. Once synchronized, the alternators will be locked to each other, requiring

considerable torque to break one unit loose (out of synchronization) from the other.
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Synchronous motor running in step with alternator:

If more torque in the direction of rotation is applied to the rotor of one of the

above rotating alternators, the angle of the rotor will advance (opposite of (3)) withrespect to the magnetic field in the stator coils while still synchronized and the rotor

will deliver energy to the AC line like an alternator. The rotor will also be advanced

with respect to the rotor in the other alternator. If a load such as a brake is applied to

one of the above units, the angle of the rotor will lag the stator field as at (3), extracting

energy from the AC line, like a motor. If excessive torque or drag is applied, the rotor

will exceed the maximum torque angle advancing or lagging so much that

synchronization is lost. Torque is developed only when synchronization of the motor is

maintained.

In the case of a small synchronous motor in place of the alternator

Figure above right, it is not necessary to go through the elaborate synchronization

procedure for alternators. However, the synchronous motor is not self starting and must

still be brought up to the approximate alternator electrical speed before it will lock

(synchronize) to the generator rotational rate. Once up to speed, the synchronous motor

will maintain synchronism with the AC power source and develop torque.


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Sine wave drives synchronous motor:

Assuming that the motor is up to synchronous speed, as the sine wave

changes to positive in Figure above (1), the lower north coil pushes the north rotor pole,

while the upper south coil attracts that rotor north pole. In a similar manner the rotor

South Pole is repelled by the upper south coil and attracted to the lower north coil. By

the time that the sine wave reaches a peak at (2), the torque holding the north pole of

the rotor up is at a maximum. This torque decreases as the sine wave decreases to 0 V DC

at (3) with the torque at a minimum.

As the sine wave changes to negative between (3&4), the lower south

coil pushes the south rotor pole, while attracting rotor north rotor pole. In a similar

manner the rotor North Pole is repelled by the upper north coil and attracted to the

lower south coil. At (4) the sine wave reaches a negative peak with holding torque again

at a maximum. As the sine wave changes from negative to 0 V DC to positive, the process

repeats for a new cycle of sine wave.

Note, the above figure illustrates the rotor position for a no-load

condition (=0 o). In actual practice, loading the rotor will cause the rotor to lag the

positions shown by angle . This angle increases with loading until the maximum motor


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torque is reached at =90 o electrical. Synchronization and torque are lost beyond this

angle.

The current in the coils of a single phase synchronous motor pulsates

while alternating polarity. If the permanent magnet rotor speed is close to the frequency

of this alternation, it synchronizes to this alternation. Since the coil field pulsates and

does not rotate, it is necessary to bring the permanent magnet rotor up to speed with an

auxiliary motor. This is a small induction motor similar to those in the next section.

Addition of field poles decreases speed:

A 2-pole (pair of N-S poles) alternator will generate a 60 Hz sine wave

when rotated at 3600 rpm (revolutions per minute). The 3600 rpm corresponds to 60

revolutions per second. A similar 2-pole permanent magnet synchronous motor will

also rotate at 3600 rpm. A lower speed motor may be constructed by adding more pole

pairs. A 4-pole motor would rotate at 1800 rpm, a 12-pole motor at 600 rpm. The style

of construction shown is for illustration. Higher efficiency higher torque multi-pole

stator synchronous motors actually have multiple poles in the rotor.


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One-winding 12-pole synchronous motor

Rather than wind 12-coils for a 12-pole motor, wind a single coil with

twelve interdigitated steel poles pieces as shown in Figure above . Though the polarity

of the coil alternates due to the applied AC, assume that the top is temporarily north, the

bottom south. Pole pieces route the south flux from the bottom and outside of the coil to

the top. These 6-souths are interleaved with 6-north tabs bent up from the top of the

steel pole piece of the coil. Thus, a permanent magnet rotor bar will encounter 6-pole

pairs corresponding to 6-cycles of AC in one physical rotation of the bar magnet. The

rotation speed will be 1/6 of the electrical speed of the AC. Rotor speed will be 1/6 of

that experienced with a 2-pole synchronous motor. Example: 60 Hz would rotate a 2-

pole motor at 3600 rpm, or 600 rpm for a 12-pole motor.

The stator (Figure above ) shows a 12-pole Westclox synchronous clock

motor. Construction is similar to the previous figure with a single coil. The one coil

style of construction is economical for low torque motors. This 600 rpm motor drives

reduction gears moving clock hands.
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If the Westclox motor were to run at 600 rpm from a 50 Hz power

source, how many poles would be required? A 10-pole motor would have 5-pairs of N-

S poles. It would rotate at 50/5 = 10 rotations per second or 600 rpm (10 s -1 x 60

s/minute.)

The rotor (Figure above ) consists of a permanent magnet bar and a

steel induction motor cup. The synchronous motor bar rotating within the pole tabs

keeps accurate time. The induction motor cup outside of the bar magnet fits outside and

over the tabs for self starting. At one time non-self-starting motors without the

induction motor cup were manufactured.

A 3-phase synchronous motor as shown in Figure below generates an

electrically rotating field in the stator. Such motors are not self starting if started from a

fixed frequency power source such as 50 or 60 Hz as found in an industrial setting.

Furthermore, the rotor is not a permanent magnet as shown below for the multi-

horsepower (multi-kilowatt) motors used in industry, but an electromagnet. Large

industrial synchronous motors are more efficient than induction motors. They are used

when constant speed is required. Having a leading power factor, they can correct the

AC line for a lagging power factor.

The three phases of stator excitation to produce a single resultant magnetic

field which rotates f/2n times per second, where f is the power line frequency, 50 or 60

Hz for industrial power line operated motors. The number of poles is n. For rotor speed

in rpm, multiply by 60.

NS = 120f/pWhere: N S = rotor speed in rpm

f = AC line frequency p = number of poles per phase
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The 3-phase 4-pole (per phase) synchronous motor (Figure below ) will

rotate at 1800 rpm with 60 Hz power or 1500 rpm with 50 Hz power. If the coils are

energized one at a time in the sequence -1, -2, -3, the rotor should point to the

corresponding poles in turn. Since the sine waves actually overlap, the resultant fieldwill rotate, not in steps, but smoothly. For example, when the -1 and -2 sine waves

coincide, the field will be at a peak pointing between these poles. The bar magnet rotor

shown is only appropriate for small motors. The rotor with multiple magnet poles

(below right) is used in any efficient motor driving a substantial load. These will be slip

ring fed electromagnets in large industrial motors. Large industrial synchronous motors

are self started by embedded squirrel cage conductors in the armature, acting like an

induction motor. The electromagnetic armature is only energized after the rotor is brought up to near synchronous speed.

Three phase, 4-pole synchronous motor

Small multi-phase synchronous motors (Figure above ) may be started

by ramping the drive frequency from zero to the final running frequency. The multi-

phase drive signals are generated by electronic circuits, and will be square waves in all

but the most demanding applications. Such motors are known as brushless DC motors.

True synchronous motors are driven by sine waveforms. Two or three phase drive may

be used by supplying the appropriate number of windings in the stator. Only 3-phase is

shown above.
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Electronic synchronous motor

The block diagram (Figure above ) shows the drive electronics associated

with a low voltage (12 V DC) synchronous motor. These motors have a position sensor

integrated within the motor, which provides a low level signal with a frequency

proportional to the speed of rotation of the motor. The position sensor could be as

simple as solid state magnetic field sensors such as Hall Effect devices providing

commutation (armature current direction) timing to the drive electronics. The position

sensor could be a high resolution angular sensor such as a resolver , an inductosyn

(magnetic encoder), or an optical encoder.

If constant and accurate speed of rotation is required, (as for a disk drive) a

tachometer and phase locked loop may be included. (Figure below ) This tachometer

signal, a pulse train proportional to motor speed, is fed back to a phase locked loop,

which compares the tachometer frequency and phase to a stable reference frequency

source such as a crystal oscillator.

A Phase locked loop controls synchronous motor speed
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Motor driven by square waves of current, as provided by simple Hall

Effect sensors, is known as a brushless DC motor. This type of motor has higher ripple

torque variation through a shaft revolution than a sine wave driven motor. This is not a

problem for many applications. Though, we are primarily interested in synchronousmotors in this section.

Motor ripple torque and mechanical analog.

Ripple torque, or cogging is caused by magnetic attraction of the rotor

poles to the stator pole pieces. (Figure above ) Note that there are no stator coils, not

even a motor. The PM rotor may be rotated by hand but will encounter attraction to the

pole pieces when near them. This is analogous to the mechanical situation. Would

ripple torque be a problem for a motor used in a tape player? Yes, we do not want the

motor to alternately speed and slow as it moves audio tape past a tape playback head.

Would ripple torque be a problem for a fan motor? No. Windings distributed in a belt

produce a more sinusoidal field.


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If a motor is driven by sine waves of current synchronous with the

motor back emf, it is classified as a synchronous AC motor, regardless of whether thedrive waveforms are generated by electronic means. A synchronous motor will generate

a sinusoidal back emf if the stator magnetic field has a sinusoidal distribution. It will be

more sinusoidal if pole windings are distributed in a belt (Figure above ) across many

slots instead of concentrated on one large pole (as drawn in most of our simplified

illustrations). This arrangement cancels many of the stator field odd harmonics. Slots

having fewer windings at the edge of the phase winding may share the space with other

phases. Winding belts may take on an alternate concentric form as shown in Figure

below .

Concentric belts
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For a 2-phase motor, driven by a sine wave, the torque is constant

throughout a revolution by the trigonometric identity:

sin2 + cos 2 = 1

The generation and synchronization of the drive waveform requires amore precise rotor position indication than provided by the Hall Effect sensors used in

brushless DC motors. A resolver or optical or magnetic encoder provides resolution of

hundreds to thousands of parts (pulses) per revolution. A resolver provides analog

angular position signals in the form of signals proportional to the sine and cosine of

shaft angle. Encoders provide a digital angular position indication in either serial or

parallel format. The sine wave drive may actually be from a PWM, Pulse Width

Modulator, a high efficiency method of approximating a sine wave with a digitalwaveform. (Figure below ) Each phase requires drive electronics for this wave form

phase-shifted by the appropriate amount per phase.

PWM approximates a sine wave .

Synchronous motor efficiency is higher than that of induction motors. The

synchronous motor can also be smaller, especially if high energy permanent magnets

are used in the rotor. The advent of modern solid state electronics makes it possible to

drive these motors at variable speed. Induction motors are mostly used in railway


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traction. However, a small synchronous motor, which mounts inside a drive wheel,

makes it attractive for such applications. The high temperature superconducting version

of this motor is one fifth to one third the weight of a copper wound motor. [1] The

largest experimental superconducting synchronous motor is capable of driving a navaldestroyer class ship. In all these applications the electronic variable speed drive is

essential.

The variable speed drive must also reduce the drive voltage at low speed

due to decreased inductive reactance at lower frequency. To develop maximum torque,

the rotor needs to lag the stator field direction by 90 o. Any more, it loses

synchronization. Much less results in reduced torque. Thus, the position of the rotor needs to be known accurately. And the position of the rotor with respect to the stator

field needs to be calculated, and controlled. This type of control is known as vector

phase control. It is implemented with a fast microprocessor driving a pulse width

modulator for the stator phases.

The stator of a synchronous motor is the same as that of the more popular

induction motor. As a result the industrial grade electronic speed control used withinduction motors is also applicable to large industrial Synchronous motors.

If the rotor and stator of a conventional rotary synchronous motor are

unrolled, a synchronous linear motor results. This type of motor is applied to precise

high speed linear positioning. [2]

A larger version of the linear synchronous motor with a movable carriage

containing high energy NdBFe permanent magnets is being developed to launch aircraft

from naval aircraft carriers
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Protection of relays:

The Modern electric Power system consists of several elements

such as generators, transformers, station bus bars, transmission lines, and other

associated equipment, It is imperative to protect these elements from differenttypes of faults, which are likely to occur sooner or later.

The Protective relays can be advantageously used to detect the improper

behavior of any element of the power systems and initiate corrective measures.

Protection is most complex and elaborate because of following reasons.

(1) Motor is a costly equipment and one of the major links in a power

system.

(2) Motor is not a single equipment but is associated with the unit

transformers, auxiliary transformer, station bus bars, excitation system,

prime mover, voltage regulating equipment, cooling system etc. The

Protection of motor is therefore to be coordinated with the associated

equipment.

(3) The Motor capacity has sharply risen in recent years from 50MW to

250MW with the result that loss of even a single machine may cause

overloading of the associated machines in the system and eventual system

instability.

The basic function of protection applied to motor is therefore to

reduce the outage period to a minimum by a rapid discriminative clearance

of faults. Since the motor will continue to supply power to a stator winding

fault until its field excitation is suppressed. It is therefore necessary that the

field is opened, fuel supply to the prime mover is stopped and sometimes

breaking applications also becomes imperative.

The protection used for a particular motor depends on the

switchgear employed for its control. In general two basic protections are

provided for every motor which are


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(a) Thermal overload protection

(b) Short circuit protection.

General faults occur: Stator Winding Faults :

Such faults occur mainly due to the insulation failure of the stator

coils. The main types of stator winding faults are

(a) phase to earth fault

(b) phase to phase fault

(c) Inter turn faults involving turns of the same phase winding.

The Stator Winding faults are the most dangerous and are likely to

cause considerable damage to the expensive machinery. So automatic

protection is absolutely necessary to clear such faults in the shortest possible

time in order to minimize the extent of damage.

Phase to phase faults and phase inter-turn faults are less common,

these usually developed in to an earth faults. Inter-turn faults are more difficult

to be detected.

The effect of earth fault in the stator is twofold:

(a) Arcing to core, which welds laminations together, causing eddy current

hot spots on subsequent use. Repairs to this condition involves

expenditure of considerable money and time.

(b) Severe heating the conductors damaging them and the insulation with

possible fire breaks.

Rotor circuit faults:

Faults in the rotor circuit may be either earth faults or inter-turn faults,

which are caused by severe mechanical and thermal stresses.


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The field system is normally not grounded and therefore, a single

fault between field winding and rotor body due to insulation break down does

not give rise to any fault current. However, a second earth fault will shortcircuit some part of the rotor winding and may there by develop an

unsymmetrical field system, giving unbalanced force on the rotor. This can cause

severe vibration of the rotor with possible damage to the bearings. Thus a single

earth fault can be tolerated for a while but it should not be allowed to

continue.

Rotor earth fault protection is provided in case of largemotors. Owing to a fault, there may be an unbalanced in the three phase stator

current. According to the theory of symmetrical components, unbalance three

phase currents have a negative sequence components, which rotates at

synchronous speed in a direction opposite to the direction of rotation of rotor.

So double the frequency currents are induced in the rotor. this cause severe

vibration, but the overheating problems is more acute.

SYNCHRONOUS MACHINE TESTING WITH ALL-TESTINSTRUMENTATION

In order to further understand the application of motor circuit testing and

analysis on synchronous electric motors synchronous machines), it is important to have


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a brief overview of the operation of a synchronous motor, most common faults,

common test methods, how the ALL-TEST IV PRO 2000 works with large

synchronous motors, basic steps for analysis of synchronous stators and rotors, and,

expected test results. In this paper, we will discuss these various aspects, referencingother materials for additional details. About Synchronous Machines Large synchronous

motors have two basic functions:

The first is to improve the electrical power factor in a plant. In any plant

with large inductive loads, such as motors and transformers, current begins to lag

behind voltage (poor power factor). When this becomes severe enough, the plant

requires significantly larger amounts of current to perform the same amount of work.This can cause voltage sag and overheating of electrical components. A synchronous

motor can be used in such a way as to cause little to no impact on power factor, or can

be used to cause current to lead voltage to correct power factor problems.

The second method of operation is to absorb pulsating loads, such as

reciprocating compressors. Once asynchronous motor has achieved synchronous speed,

it has coils which lock in step with the electric motor s rotating magnetic fields from thestator. If a torque pulse occurs (such as at the top of a reciprocating compressor stroke),

the motor may come out of synch with the rotating fields. When this occurs, a special

winding on the rotor called an amortisseur winding (see synchronous construction

below) absorbs the energy from the torque pulse, keeping the rotor in synch. The basic

construction of a synchronous motor is straight forward.

There are three sets of windings, a stator, a rotor, bearings, and either

a generator (brushless) or a static exciter (brush-type). The windings consist of: A

standard three phase winding, very similar to a standard induction electric motor; A set

of field coils, which are DC coils made of round wire for small machines and

rectangular or ribbon wire on larger machines; And an amortisseur winding, which is


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similar to an induction motor rotor squirrel cage. The starting methods for both the

brush-type and brushless synchronous motors are similar. The starting circuit will be

different for both. Following is a description of the basic mode of operation, followed

by a brief description of the differences:During the starting phase of a synchronous motor, it acts much the same

as a standard induction motor. The stator receives an electrical current and a rotating

magnetic field is developed (the speed = (120 * applied frequency) / # of poles). This

field generates a current in the amortisseur winding, which is used to develop starting

torque by generating its own magnetic field which interacts with the stator magnetic

field in the air gap and causes the rotor to follow the stator magnetic fields. As the rotor

starts to catch up to the stator fields, DC current is injected into the rotor field coils,creating north and south magnetic pairs (rotor coils are always found in pairs). These

lock in step with the stator magnetic fields and follow at the same speed as the stator

fields, where as a standard induction motor always lags behind. In a brush machine, the

DC source for the rotor fields usually comes from a static (electronic) starter, which

converts a supplied AC power to DC. In most cases, the output DC is varied through the

starting cycle. The drive may also be set up to short out the field coils of the machine to

avoid rotor saturation and the resulting extremely high currents on the stator. Once the

rotor begins to turn, DC is supplied to assist the motor in developing torque. The DC

voltage is supplied through a pair of slip rings and brushes. In a brushless machine, a

DC generator is installed directly on the shaft of the synchronous motor.

As the synchronous motor starts, the generator provides very little DC through

its commutator. As the speed increases, the DC voltage also increases, helping the

motor generate torque then lock in step at synchronous speed. In this type, there are also

machines that have a generator mounted on the shaft of the rotor that feeds a separate

control. This is used to first short the windings and then control the amount of DC fed

to the rotor, just as the brush machine.


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Most Common Synchronous Motor Faults:

Large synchronous motors tend to be well built and sturdy. They are

often overbuilt with material to withstand the severe loads that are applied. The most

common failures for industrial synchronous machines, in order, are: Bearings due togeneral wear and contamination Rotor fields due to high temperatures, these will often

burn up from the inside out Amortisseur windings mostly in reciprocating loads.

Because of the amount of energy absorbed, and short, making it easier for the rotor to

fall out of synch. Stator windings - general wear and contamination. Stator windings in

synchronous machines tend to be firmly wound and heavily insulated. Almost all of

the winding faults that occur in a synchronous motor start between conductors in the

rotor or stator coils. Common Test Methods, Strengths and Weaknesses Following arethe traditional test methods for evaluating the condition of a synchronous motor:

Insulation resistance testing :

Using applied DC voltages as specified by IEEE 432000, a potential is

placed between the stator windings and ground. These measures only direct faults

between the stator windings and the stator frame. Is also performed through the slip

rings on a brush type machine. Polarization Index: Is a 10 minute to 1 minute ratio of insulation resistance. This has been traditionally used as a method to gage the condition

of the insulation between the stator windings and frame. As with insulation resistance

testing, this can also be performed through the slip rings on a brush type machine. As

stated in IEEE 43-2000, this test method is only truly valid on pre-1970 insulation

systems. High potential testing: Most common on large machines is DC high potential

testing which is performed at a value of twice the motor nameplate voltage plus 1000

volts, times the square root of 3. On an existing insulation system, this value is often

reduced to 75% of the potential voltage. This test highly stresses the insulation system

and is potentially damaging (per IEEE Std s 388 and 389).


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This type of test should never be applied to the rotor windings of a

synchronous motor. Surge Comparison testing: Evaluates the turn to turn condition of

the stator only by comparing the waveforms of two windings when a fast rise time pulse

of twice the voltage plus 1000 volts. If there are correctable issues, such ascontaminated windings, this test may damage the motor windings.

Partial Discharge testing:

Is a non-destructive test method that measures radio frequencies from

discharges in voids within the insulation system of the motor windings. This is effective

for trending on machines that are over 6.6 kV and only provide a brief warning from 4

kV. It does not detect any rotor faults. Motor Current Signature Analysis: Was designed

for rotor testing of induction motors. Has limited applications on synchronous motorsand cannot detect faults in de-energized equipment.

Voltage Drop Test:

Requires that the motor is disassembled, A 115 AC voltage is applied to

the rotor windings and the voltage drop is measured with a volt meter across each coil.

If there is a short, the voltage drop will vary more than 3%. The above list does not

include equipment for mechanical testing of synchronous motors. About the ALL-

TEST.

The ALL-TEST IV PRO 2000 is a simple electronic instrument that

performs in much the same manner as a multimeter, except that it provides a series of

readings that cover the AC parameters of the motor circuit. It is a data collector and

tester that sends a low voltage DC signal for simple resistance testing, in the same

manner as a milli-Ohm meter, and a low voltage, high frequency AC signal for AC

readings. The instrument then uses a series of balanced electrical bridges to provide test

results in engineering units of resistance, impedance, inductance, phase angle,

current/frequency response and an insulation resistance test to ground. The primary

differences between electronic testing of power equipment versus traditional power

methods are: A more complete view of the motor circuit, including influences from

changes in the condition of rotor field coil insulation.


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One instrument for a large range of equipment size. The test is limited

only to the simple resistance range of the instrument (0.001 Ohm to 999 Ohms). Non-

destructive no harmful voltage is applied. Easier data interpretation A few simple rules

for data interpretation (See data interpretation below).Hand held vs. equipment that mayweigh from 40 to well over 100 lbs. Internal power source for the instrument.

. As an insulation system ages, or if the insulation system is contaminated

and it is effecting the integrity of the insulation, the electrical circuit of the motor

changes. Because the rotor is an integral part of the circuit, changes to the electrical

integrity of the rotor circuit and insulation system are directly reflected through the

stator windings, as well. This allows both immediate troubleshooting and long-termtrending of the motor. Unique test information allows the ALL-TEST to view enough

parameters of the insulation system to detect and isolate: Shorted stator windings

Shorted rotor fields broken amortisseur winding bars Air gap eccentricity Winding

contamination (rotor and stator)Ground insulation faults For further details on how

these tests are performed and detected, see Guideline for Electronic Static Winding.

Basic Steps for the Analysis of Synchronous Machines with ALL-TEST the

steps for testing synchronous machines are similar to those for evaluating the condition

of standard induction motors. However, because there are field coils on the motor rotor,

a few additional steps are involved when troubleshooting a fault. When testing a

synchronous machine from the motor control center or starter: De-energize the

equipment. Ensure that secondary sources of power are also de-energized. Perform the

standard ALL-TEST IV PRO 2000 tests on the stator following the menu prompts on

the instrument. Evaluate the test results (See Expected Test Results)

If a fault is indicated, begin troubleshooting:

1. Adjust the position of the rotor, as much as possible, up to 45 degrees (any

movement will do if the rotor is difficult to turn, but no less than 5 degrees).


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2. Re-perform the tests and review the readings. If the fault has shifted, or changed

by more than a digit, then the fault most likely is located in the rotor.

3. If the fault remains stationary (does not change with rotor position), then

disconnect the leads at the motor terminal box and retest. If a fault is stillindicated, it is most likely in the stator, if not, it is most likely in the cable.

The average test time, other than troubleshooting, is approximately 3-5

minutes. When testing a disassembled synchronous machine, it is important to

remember that the readings will be very different without the rotor in place:

Perform the ALL-TEST IV PRO Auto test on the stator and evaluate the test results.

This will provide an immediate indication of any faults.For the rotor test:

1. Perform the Auto test and compare to a past reading; or,

2. Perform the Auto test and compare to an identical rotor; or,

3. Perform the Auto test across each field coil instead of a voltage drop test.

4. All parameters for all three should meet the evaluation limits.

Because of the style of testing, these results can be trended and compared

between like machines. Other applications for motor circuit testing include evaluation

and acceptance, and predictive maintenance. Expected Test Results Fault patterns are

very straight-forward and apply regardless of equipment size, within the test range of

the ALL-TEST. Following is a brief overview of the test measurements and their results

for basic trouble shooting: Simple resistance measurements are an indicator of high

resistance connections, loose connections or broken conductors in the circuit. This test

is important, especially if the resistance problem is in one spot as, based upon I2R, a

resistive spot will put out a great deal of heat energy (in Watts). For instance, a 0.5 Ohm

resistance across a point in a circuit that is seeing 100 Amps would give off: (100Amps)

(0.5 Ohms) =5,000 Watts (5kW) worth of energy. This is about the same energy used to

turn 6 horsepower worth of electric motor.


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Inductance measurement:

Is an indicator of magnetic strength of a coil and the influence of other

coils on one coil. It is impacted by the number of turns in a circuit, the dimensions of the coils and the inductance of other coils. This measurement, by itself, is only a good

indicator of the condition of the amortisseur winding and rotor eccentricity. Inductance

will only show a shorted winding if it is severe. Impedance measurement: Is the

measurement of the complex resistance in the circuit. It can be used, much

like inductance, for checking the amortisseur winding and rotor condition. However,

when used along with inductance, it can be used to detect overheated windings and

winding contamination quickly. By viewing the relationship of inductance and

impedance between each phase: If the inductance and impedance are relatively parallel,

then any inductive and impedance unbalance is in the relationship between the rotor and

stator (rotor position); if they are not parallel, then there is an insulation problem such

as insulation breakdown or winding contamination. Phase angle and I/F

(Current/Frequency): Are both indicators of insulation faults between turns in the stator

or rotor.

SIZING AND PERFORMANCE OF AN IDUCTION MOTOR AND A

PERMANENT MAGNET SYNCHRONOUS MOTOR IN SERVODRIVES

The two most commonly used motor types in servo applications are the

permanent magnet synchronous motor (PMSM) and the induction motor (IM). The

purpose of this chapter is to provide information about the dimensioning and the


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performance of these two motor types in dynamically demanding servo applications. As

it was stated in the first chapter, the focus is on the 1100 kW power range. The goal is

to study how the dimensioning of servomotors differs from industrial motor design, and

further, to find out how the dimensioning of a high performance PMSM relates to thedimensioning of a comparable IM. According to Vas (1998), a servomotor should meet

the following requirements

High air gap flux density

High power-to-weight ratio

Large torque-to-inertia ratio

Smooth torque operation (also at low speeds)

Accurate torque control at zero speed High-speed operation

High overloading torque

High efficiency and high power factor

Compact design

Nearly all the requirements seem to prefer a PMSM instead of an IM,

with the exception of a requirement of the high-speed operation, which might be

problematic due to limited field weakening capability of PMSMs. In somewhat older

literature (for instance Vas 1998) when comparing a permanent magnet synchronous

motor to an induction motor, it is often claimed that an induction motor can have a

higher air gap flux density. This is a quite obsolete argument, because with modern high

energy density magnets, air gap flux densities well beyond 1 T are possible, even

without the flux concentration. Of course, the induction motor can be dimensioned.

OPERATING CHARACTERISTICS:

TORQUES

A synchronous motor must be always designed taking into account driven

load characteristics, in addition to torques and inertia.

a) Starting torque


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It is the torque that the motor must supply to drive the standstill load

resistant torque, that is, it is the load starting torque.

b) Pull-in Torque

It is the torque that the motor must supply to reach the correct speed,where the excitation field application will take the motor to the synchronism (pull-in

torque).

c) Pull-out Torque under Synchronism

It is the torque that the motor must supply to keep the motor under

synchronism in case of momentary overloads (pull-out torque).

Syncs MotorsStarting characteristic curve of a synchronous motor at full voltage

If the specified motor torque, at 95% of the synchronous speed is equal tothe load pull-out torque, this motor cannot supply this torque at 98% of the synchronous

speed and then such motor will not synchronize.

This way, to ensure motor starting and synchronism, careful analysis of

the starting torque curve along with load resistant torque curve must be carried out.


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Asynchronous Starting

1. The main starting method applied on synchronous motor starting is the

asynchronous starting through a squirrel cage with the short-circuited winding

rotor or connected to a resistance, usually called starting resistance or dischargeresistance.

2. Through asynchronous starting, the rotor accelerates at a speed very close to the

synchronous speed, with a slight slip in reference to the rotating field. On this

point, a direct current is applied to the rotor winding and then taking the motor to

synchronism.

3. On brush-supplied machines, a field application relay is used, while on brushless

motors a discharge electronic circuit is applied, which is installed attached to arotating disc. This electronic circuit and the field application relay are intended

to manage the synchronous motor starting sequence, since the rotor short circuits

up to the field current application.

4. A synchronous motor starts exactly like an induction motor and then it

accelerates the load up to the point where the motor torque becomes the same as

the load resistant torque. Usually this point occurs with 95% of the synchronous

speed or above that, and on this condition, the excitation voltage is applied to the

motor, and the rotor synchronizes, that is, it will accelerate the combined rotor

and motor inertia plus the load inertia up to precise Synchronous speed.

5. Driven load characteristics will determine acceleration and synchronism

conditions.

6. On high resistant torque loads, the amortisseur winding must make the motor

and load torque accelerate at a time period higher than that for a shorter resistant

torque.

The proper amortisseur winding design requires precise knowledge of the load

resistant torque.

1. Based on the synchronous motor starting characteristic curve, starting torque

decreases as it gets close to the synchronous speed.


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2. On load applications with resistant torque parabolic curve and considering that at

98% of the synchronous speed, the value of such torque is equal to the load rated

torque, the motor is required to supply a torque equal or higher than the load

torque on this point.

EXCITATION TYPES

Synchronous motors require a DC power supply to power the field

winding (rotor winding), which is usually done through slip rings and brushes (Static

Exciter) or through a brushless rotating exciter.

1. Static exciter (with brushes)

1. Synchronous motors supplied with static exciter are fitted with slip rings and brushesthat allow current powering of the rotor poles through slip contacts.

2. The DC power supply for the poles must come from a AC/DC converter and static

controller. The static exciter is much used on VFD applications.

2. Brushless exciter

1. Synchronous motors with brushless excitation system are fitted with a rotating

exciter, normally installed on the backside of the motor.


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2. The exciter operates as an AC generator with the rotor attached to the motor shaft. It

is fitted with a three phase winding and the stator consists of alternating poles (north

and south) and powered by an independent DC source.

3. This three phase winding is connected to bridge rectifiers. The voltage generated onthe rotor is rectified and intended to power the motor field winding. The amplitude of

such field current can be controlled through the rectifiers that power the exciter stator

field. Synchronous motors with brushless excitation require low maintenance

cost once they are not fitted with bushes.

4. Since they are not built with slip electric contacts, avoiding sparking, synchronous

brushless excitation motors are recommended for explosive atmosphere applications.

Sequence of operation of synchronous motor in sinter plant:In 4 breakers are Q1.1, Q1.2, Q1.3, Q1.4 are connected to 11kv supply

and motor. In Q1.3 is connected to auto transformer why because it is not a self starting.

Step 1: B1 off, B2 off, B3 off, B4 off


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Step 2: 11kv supply healthy motor protection panel healthy static excitation healthy

fan ready to start check it.

Step 3: B4 is on, B1 off, B2 off, B3 off

Step 4: B1 off, B2 off, B3 on, B4 off Step 5: B1 on, B2 off, B3 on, B4 on

Step 6: After present time & sub synchronous speed B1 on, B2 off, B3 off, B4 on

Step 7: Slip frequency relay actuation closes field circuit breaker

Step 8: B1 on, B2 on, B3 off, B4 on

Step 9: Machine synchronized at full voltage

SPECIFICATIONS OF SYNCHRONOUS MOTOR IN SINTER PLANTFrame - IDL 7650-8FE73z

KW - 5600

KVA - 7183

PF - 0.8 Lead

Rpm - 1000

Exc.Volts - 149

Insln. Class - F

Phase - 3

Hz - 50

Connection - Star

Ambient Temp - 50 oc

Stator amp - 377

Exc.amp - 389

Specification - Is 4722

Duty - Continuous

Deg of Prot - IP 55

S.L.No - 47119 A 425 -11-d

Year 1989 WT 29200 KG


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OPERATING INSTRUCTIONS OF EXHAUSTERS

1. While starting of exhausters

Start lubrication pump and motor cooling fan.

Ensure water pressure is sufficient.

Ensure damper is in closed condition and fan brake is released.

Ensure return oil is coming.

Start the jacking oil pump.

Inform electrical and LBSS-1.

After electrical clearance is given, start exhausters.

Ensure jacking oil pump is stopped after synchronization.

Open damper to a min of 5%.

2. While Running of Exhausters

Observe current and power are within the limits if not adjust damper

opening accordingly.

Observe temperatures scanners for stator and fan temperatures.

Inspect oil levels and lubrication oil pumps.

Check cooling water pressure.

Inspect motor cooling fan running.

3. Stopping Exhausters


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Inform LBSS-1.

Close exhausters damper.

Stop exhausters.

Ensure jacking oil pump is running as soon as exhauster is stopped.

Apply brakes before fan reverse.

Run lubrication pump for 2hrs after stopping exhausters.

4. In case of Exhausters tripping or single exhauster running

Look for fault indication on control desk in case of tripping.

Inform control room (sinter machine).

Follow same steps as stopping exhausters.

In case of single exhauster ensure brake is applied and damper is fully

closed for exhauster which is not running.

Starting of Exhausters (Normal Starting)

1. The exhauster should be in standstill condition. All control supplies on OCD,

MPP, SEE and MCC should be on (can be judged by seeing indication lamps

and relay flags resetting), 415V, 3- power supplies to SEE and MCC should be

on, and 11KV supply at LBSS-1 bus should be available as indicated by

voltmeter on OCD.

2. Fan ready to start signal should come at operators desk. Also operator should

come from that the different auxiliary requirements have been fulfilled, brake is

released, and damper is in closed condition.


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3. Motor winding temperature (channel 1 to 6 of motor scanners) should be less

than 70 0 C in each channel.

4. Should ensure the following starting duty is not violated. 2 cold starts and 1 hot

start spaced at 15 minutes plus one start in every hour in 24 hours a day. This

should normally be covered up along with point no.3 above.

5. Field should be kept Manual channel at SEE panel.

6. No fault signals should exists on SEE panel and MPP.

7. MSTR should be reset. All other relays should normally get reset except

AUXB91 which should not be reset in case of exhausters 1 and 2 i.e., first stageexhausters. Relays net getting reset should be recorded in Logbook.

8. In case of exhausters 1 and 2, the CTMM relays I 1(t) and I th should be defected

while starting by giving paper insulation at that contacts of these protections.

9. Power clearance to be taken from LBSS-1 personnel and they should be asked to

make the start permit switch of the particular exhauster ON if clearance exists.

Before making ON DMP personnel should ensure that the control supplies atMCCBS are ON and springs are changed. If the exhauster does not start within

15 minutes of taking clearance from SEE for starting.

10. On making ON the permit switch, motor ready to start signal should appear

on OCD.

11. While starting Exhauster no.1, the operator should be asked to close the damper

of exhauster no.4 by more than 50% and vice versa. Similarly relationshipexists between exhauster no.2 and exhauster no.3 and the same procedure

should be followed while their starting.

12. Operator can now start the exhauster after taking clearance from SMB control

room personnel.


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13. Once the start command is given the following sequence of operations will take

place (B4 will be ON even before starting).

I. B1 .. OFF

B2 .. OFF

B3 .. ON

B4 .. ON

II. B1 .. ON

B2 .. OFF

B3 .. ONB4 .. ON

Machine starts running as induction motor at reduced voltage.

III. After rotor reaches to nearby synchronous speed, the stator current falls

down (approximately within 100 to 110 seconds of starting), then

B1 .. ON

B2 .. OFF

B3 .. ONB4 .. ON

FCB closes through SEE. IF FCB does not close through SEE, it should

be made CB manually by PB at SEE.

IV. B2 will switched OFF through FCB after present time and B2will close.

B1 .. ON

B2 .. ONB3 .. OFFB4 .. ON

This is machine synchronized condition at full stator voltage.


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ADVANTAGES:

Due to their special operating characteristics, synchronous motor

applications usually result in economical and operational advantages to end users.Included in the economical advantages of using synchronous motors are:

1. High efficiency

2. Power supply factor correction

In addition to that, there are other specific operational advantages of using

synchronous motors as follows:

1. Special starting characteristics

2. Constant speed under load variation3. Reduced maintenance cost

High Efficiency

Associated to the initial purchasing cost of a synchronous motor, further gains resulting

from low operational cost should be also considered. On those cases, where just the

efficiency aspect is taken into account when specifying a motor, a synchronous motor

with SF=1.0 is usually the solution. When the reactive power (kVAr) is not required

and only the actual power (kW) is applicable, the power supply current is minimized

resulting in lower stator winding loss I2R. Once the required field current is the

minimum applicable, there will be lower field winding loss I2R. Except for those cases

where high torque is required, the low stator winding losses allow a synchronous motor

with SF=1.0 to be designed in lower size if compared to a synchronous motor with

SF=0.8 of equal power rating. Hence, synchronous motor efficiencies with SF=1.0 are

normally higher than induction motor efficiencies of equal power rating. Comparison

between efficiency levels of synchronous motors with PF= 0.8, PF=1.0 and induction

motors.

Power Factor Correction


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Electric power systems are based not only on the generated active power supply

in kW, but also on the power factor on which it is generated Whenever the load power

factor is below the specified values, the consumer may be subject to penalties. These

penalties (fines) occur due to the fact that the low power factor results in increase of required reactive power (kVAr) and, as a consequence, increases of the power supply

transmission and generation equipment capacity. On industries, inductive reactive load

are predominant. These are usually low size or low speed induction motors. Such loads

require considerable portion of reactive power (kVAr) as magnetization current. Other

than applying bank of capacitors to supply the power supply with reactive power,

synchronous motors are normally used for such purpose. Power factor of synchronous

motors can be easily controlled as they are fitted with an independent excitation source.This way, power factor can be increased without generating reactive power (motor with

PF=1.0) or generate required reactive power (motor with SF=0.0). So depending on the

application, a synchronous motor can supply the required power with substantial power

reduction on the whole system.

Special Starting Characteristics

Large ball mills for iron mines, cement plants and compressors are few examples

of applications that required high starting torque (150 to 200 % of the rated torque).

Due to power supply system limitations, low starting currents

(Locked rotor) are usually required. A combination of high torque with low starting

current can be better achieved with the application of synchronous motors without

affecting operating characteristics. Starting current reduction can be usually achieved

with a special design of stator and amortisseur windings. Starting the motor with

reduced voltage is also an alternative applied so as to have the current reduced,

although, with torque reduction.


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Constant Speed

Independently of load variations and as long as the load is maintained within themotor pull-out torque limitation, the synchronous motor average speed is kept constant.

This occurs due to the fact that the rotor poles remain locked in relation to the rotating

magnetic field that is generated by the stator winding. Then, synchronous motor speed

is kept constant either on overload variations or on voltage drop cases, in addition to

following pull-out torque limitations. On certain applications such as on pulp and paper

mills, the constant speed results in superior uniformity and quality of the supplied

product.

Reduce Maintenance Cost

Since they do not require slip electric contacts for their operation, BRUSHLESS

synchronous motors are not manufactured with brushes or with slip rings. Hence,

maintenance, inspection and cleaning on these components are not required.

APPLICATIONS OF SYNCHRONOUS MOTORS

Synchronous motors are manufactured specifically to meet every application

requirements.

They are used on all types of industry including:

Mining (crushers, mills, conveyor belts and others)

Steel plants (laminating machines, fans, pumps, compressors)

Pulp and paper (extruders, chippers, compressors, grinders)

Sewage systems (pumps)


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Chemical and Petrochemical (compressors, fans, exhausters)

Cement (Crushers, mills, conveyor belts)

Rubber (extruders, mills, mixers)

Fixed speedSynchronous motor applications with fixed speed are recommended due to low

operational cost once they offer high efficiency and can be used as synchronous

compensating machines for power factor correction. Recommended motors for this

application are those with brushless excitation.

Variable speed

Synchronous motors with variable speed are recommended for applications with high

torque, low speed and wide speed adjusting range. Depending on load and environmentcharacteristics, motor construction for such applications can be supplied with or without

brushes. Due to their higher efficiency level, reduced size and higher output rating

capacity, synchronous motors can replace DC motors on high performance applications.

On several cases, a motor with lower torque values compared to standard values can be

actually applied. This brings positive reduction on motor starting current, resulting in

less electric system troubles on starting, along with reduction on mechanical thrusts

resulting from motor winding. For a correct design and application of Weg synchronous

motors, we recommend to supply complete application data.

Applications of synchronous motor in sinter plant:

To drive induced drought fans to create vaccum up to 1600mm.

The speed of synchronous motor is 1000rpm the further details are as

follows.

Motor - 5.6KW

Power factor - 0.8 lead

Stator voltage - 11000V

Excitation voltage - 149V


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Stator current - 377A

Voltage - 11KV

The starting time of synchronous motor is 150sec that it takes to reachup to 1000rpm with auto transformer starting.

CONCLUSION

This project work is proved to a good opportunity for studying where as

accepts related to synchronous motors and associated equipment we could better

understand about starting method of synchronous motor and synchronizing concept. It

has become possible for us to see the power factor variation of a synchronous motor

under different loading conditions and also different field variations.

Also we have studied various accepts oblique precautions and protections

to be taken into consideration before starting, while synchronization and also under

steady state conditions This project has helped us in updating our knowledge with

Synch MotorProject Feb2009

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Transcript of Synch MotorProject Feb2009