Topic 2 Industrial Distribution Equipment

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BEF 44903INDUSTRIAL POWER SYSTEMS

By: Engr. Dr. Kok Boon Ching (JEK 2014)

OUTLINES

Introduction Distribution Transformer Switchgear Power Cables Protective Devices Motor Control Centre (MCC)

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Introduction

Main equipment in IPS:

Distribution Transformer

Switchgear Power Cable

Compensation Protective DevicesMotor Control

Centre

Overview of IPS

Incoming Distribution Transformer

Main Switchgear

12 kVTransformer132kV 11kV

12 kV

Switchboard 1440V

Switchboard 2440V

DB 1 DB 2MCC 1440V

MCC 2440V

DB 1440V

DB 2440V

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INTELLIGENT INDUSTRIAL COMMUNICATION AND POWER NETWORK CONCEPT

Distribution Transformer (Overview)Main Parts: Core and magnetic

circuit (thin and cold-circuit (thin and coldrolled grain-oriented steel laminations)

Windings either copper or aluminum (HV/ LV/ multiple secondary windings)g )

Tank for liquid-immersed transformers and an enclosure for dry-type transformers

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Distribution Transformer (Construction)

Basic core and coil configuration (Core Type) Typical type in distribution transformers

Distribution Transformer (Construction)

Basic core and coil configuration (Shell Type) Developed for very-high-magnitude short-circuit

applications such as generator step up transformersapplications such as generator step-up transformers

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Distribution Transformer (Tap changer)

Tap Changer in Distribution Transformer: Off-circuit Tap

C Load Tap Changer Usually placed on the primary winding in

order to minimise the current to be switched as larger current is energised at secondary in distribution transformer.

Off-circuit tap is used in industrial power system with 4 full capacity taps (5 positions) on primary (HV) in which provided 2.5%/ step. The transformer must be de-energized before the tap changer mechanism is operated.

Distribution Transformer (Tap changer)

Load Tap Changer (LTC) are usually used with oil-immersed transformers connected to the

tilit l t lt l l diutility power supply at a voltage level exceeding 34.5 kV.

Typical voltage variation is 10%, thus the tap changer is provided with an equivalent range of voltage regulation of 10% in 16 or 32 steps.

What is the %/ step for each type?

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Distribution Transformer (Types)

Types of distribution yptransformers

Oil-Filled (I d)

Nonflammable Li id Fill d Dry-Type(Immersed) Liquid-Filled Dry Type

Distribution Transformer (Oil-filled)

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Distribution Transformer (Oil-filled)

Oil-filled transformers up to 2500 kVA are of two types:

PERMANENTLY SEALED TANK

Widely used as maintenance free. The hermetically-sealed prevents oxygen, nitrogen or moisture contact with the oil which can degrade the transformer performance

TANK WITH A CONSERVATOR

As the winding heats up and cools down, the air is expelled from or drawn into the transformer through the conservator. It can be repaired at the site

Types of oil used: mineral oil, synthetic oil (chlorinated diphenyl/ askarel), and silicon oil.

transformer performance. repaired at the site.

Distribution Transformer (Oil-filled maintenance)

Maintenance of oil-filled transformers: oil dielectric strength and acidity should be checked

llannually. If the dielectric strength is less than 50 kV for 1

min or the acidity is above 0.4, the oil should be replaced or filtered.

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Distribution Transformer (Oil-filled cooling methods)

Cooling method in a distribution transformer is designated by 4 letters:

O, K or L, G N, F, D A, W N, F Internal

cooling Circulation mechanism External i l ti

1 23 4

medium mechanism for the internal cooling medium

cooling medium

circulation mechanism for the external cooling medium

Distribution Transformer (Oil-filled cooling methods)

ONAF

ONAN

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Distribution Transformer (Dry-type)

Distribution Transformer (Dry-type)

In industrial plants, dry-type transformers are used for lighting, unit substations, and variable-frequency drives.Three different types of construction: Three different types of construction: Vacuum-pressure impregnation in polyester or

silicone varnish. Less expensive, needs clean environment, and mechanically weak against through-fault current.

Cast coil or cast resin. Mechanically short-circuit f d t th i di il t i iproof due to the winding coils are cast in a resin.

VPI epoxy sealed or encapsulated. Winding coils are sealed with epoxy and thus is mechanically strong against through-fault currents.

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Distribution Transformer (Dry-type insulation)

Distribution Transformer (Typical ratings)

Primary (kV)

Secondary (kV)

Rating (kVA)

Construction Type

Impedance range (%)

3 33 380 440 V 150, 250, 300, 400, 500, 630, Oil-filled and Dry- 3 73 33 380 440 V 150, 250, 300, 400, 500, 630, 750, 1,000, 1,250, 1,600,

2,000, 2,500

Oil filled and Drytype

3 7

10 12 3 7.2 4,000, 5,000, 6,300, 7,500, 10,000

Oil-filled 5 10

20 24 3 12 4,000, 5,000, 6,300, 7,500, 10,000

Oil-filled 5 10

33 36 3 12 4,000, 5,000, 6,300, 7,500, 10,000

Oil-filled 5 10

66 3 36 4,000, 5,000, 6,300, 7,500, Oil-filled 5 1566 3 36 4,000, 5,000, 6,300, 7,500, 10,000, 16,000

Oil filled 5 15

132 3 110 4,000, 5,000, 6,300, 7,500, 10,000, 16,000, 25,000,

40,000, 50,000

Oil-filled 5 20

10 33 3 11 4,000, 5,000, 6,300, 7,500, 10,000, 16,000, 20,000

Dry-type 5 10

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Distribution Transformer (Dry vs. Oil-filled)

Availability of Dry-type transformers are available in certain ratings

onlyDry-type do not require any maintenance except y

rating

Cost and locationMaintenance

only.any maintenance except dust-free. Oil-filled (except permanently sealed) needs more maintenance.

Fire/ Building/ Electricity

regulations

Oil-filled is 20 30% cheaper. Oil-filled is suitable

for outdoor and indoor installation. Dry-type is only

for indoor installation only.

Oil-filled is restricted to these regulations. Some locations like basement and top floor is permitted to dry-type only. Insurance is higher for oil-filled.

Switchgear

Main Switchgear

Functions of a Switchgear

1. Electrical protection (P)Switchgear12 kV

1. Electrical protection (P)2. Electrical isolation (I) of sections of

an installation3. Electrical control (C) the local or

remote switching

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Functions of Switchgear

Protection Overload currents Short circuit currents Insulation failureProtection

Isolation

Insulation failure Undervoltage

Isolate faulty section Isolate energised

section for maintenance

Functional switching

Control Functional switching Emergency switching Emergency stopping Measurements

Main Components in Switchgear

Incoming Feeders Front Panel

Busbar

CB Fuses

Isolator/ Disconnector

Contactor

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Basic Magnitudes in Switchgear

Voltage [rated voltage > operating voltage, insulation level (rated power-frequency withstand voltage for one minute peak voltage (due to lightning)]minute, peak voltage (due to lightning)]

Current [rated current, operating current, short time withstand current (1sec or 3sec), peak withstand current]

Frequency Short circuit power

Power Cables

2 common types of cables used in IPS:

Used in most of the area such as feeder, motor load and between switchboard

Power cables

Used in various protection and control systems. Example: connection

Control cables

and distribution board. Larger size and higher ampacity.

pbetween instrument transformer and relay or any digital control systems. Smaller in size as well as the ampacity.

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Power Cables

Power Cables

Types of conductor in a cable:

1 21Solid conductors

Normally, solid conductors are available up to size 6

American wire gauge (AWG), max. 4/0 AWG.

2Stranded conductor

Most systems use concentric stranding.

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Power Cables

Power cables are classified with respect to insulation as follows: Laminated type: This type of cable uses paper,

varnished cambric, polypropylene, or other types of tape insulation material. Insulation formed in layers, typically from tapes of paper or other materials or combination of them. An example of this type of cable is the paper insulated lead-covered (PILC) cable.

Extruded type: This type of cable uses rubber and rubber-like compounds, such as polyethylene (PE), cross-linked polyethylene (XLPE), ethylene propylene rubber (EPR), etc., applied using an extrusion process for the insulation system.

Power Cables

Selection of the cable insulation should be made on the basis of the applicable phase-to-phase voltage:

100% level: Cables in this category may be applied where 100% level: Cables in this category may be applied where the system is provided with relay protection which normally clears ground faults within 1 min. This category is usually referred to as the grounded systems.

133% level: Cables in this category may be applied where the system is provided with relay protection which normally clears ground faults within 1 h. This category is usually referred to as the low resistance grounded or ungroundedreferred to as the low resistance grounded, or ungrounded systems.

173% level: Cables in this category may be applied where the time needed to de-energize the ground fault is indefinite. This level is recommended for ungrounded and for resonant grounded systems.

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Power Cables

Three main criteria in cable sizing:1. Short circuit current withstand capacity2. Continuous current capacity (Ampacity)3. Starting and running voltage drops in cable

Power Cables (Criteria 1)

Short circuit current withstand capacity This criteria is applied to determine the

minimum cross section area of the cable, so that cable can withstand the short circuit current.

Failure to check the conductor size for short-circuit heating could result in permanent damage to the cable insulation and could also result into fire. In addition to the thermal stresses, the cable may also be subjected to significant mechanical stresses.

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Short circuit current withstand capacity The maximum temperature reached under short

circuit depends on both the magnitude and duration of the short circuit current.

The quantity (I2t) represents the energy input by a fault that acts to heat up the cable conductor.


Short circuit current withstand capacity The minimum cable size due to short circuit

temperature rise:

where,

.......... (Eqn. 1)K

tIA SC

2

,

A = Minimum required cross section area in mm2t = The duration of the short circuit in secondK = Short circuit temperature rise constant

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Short circuit current withstand capacity The temperature rise constant (K) according to

IEC 60364-5-54:

..(for copper conductors)

1

12

5.2341226

TTTInK

TT

1

12

1.2281148

TTTInK ..(for aluminium conductors)


Short circuit current withstand capacity Boundary conditions of initial and final

temperature for different insulation is as:

Insulation material

Final temperature, T2 (C) Initial temperature, T1(C)

PVC 160 70Butyl Rubber 220 85XLPE/ EPR 250 90

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Short circuit current withstand capacity The common value for K is given as:

Material Copper Aluminium

Insulation PVC Butyl RubberXLPE/ EPR PVC

Butyl Rubber

XLPE/ EPR

(K) 1 sec. current rating in Amp/ mm2

115 134 143 76 89 94

(K) 3 sec current 66 77 83 44 51 54(K) 3 sec. current rating in Amp/ mm2

66 77 83 44 51 54


Short circuit current withstand capacity The value of constant K has been determined

for Eqn. 1. The value of t is to be determined next.

The short circuit current is varies with time and the calculation process can be complicated. To simplify the process, the cable can be sized based on the interrupting capability of the circuit breakers/ fuses that protect them.

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Short circuit current withstand capacity The fault clearing time (tc) of the breakers/

fuses per ANSI/IEEE C37.010, C37.013, and UL 489 are: For medium voltage system (4.16 kV) breakers, use

5-8 cycles For starters with current limiting fuses, use cycle

F l lt b k ith i t di t / h t For low voltage breakers with intermediate/short time delay, use 10 cycles

For low voltage breakers with instantaneous trips, use 1-2 cycles


Short circuit current withstand capacity Consider a feeder serving large motor which is

being fed from LV 415V or 400V switchgear having a circuit breaker with separate multifunction motor protection relay (For this calculation it is assumed to be SIEMENS made 7SJ61).

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Short circuit current withstand capacity The minimum faults withstand duration

necessary (instantaneous setting) for cable:

No. Parameters Time (ms)1 Relay sensing/ pickup time 202 Tolerance/ Delay time 103 Breaker operating time 404 Relay overshoot 205 Safety margin 30

Total time in (ms) 120


Short circuit current withstand capacity Therefore the cable (XLPE, Aluminium) selected for a

i it b k t ll d t f d i 415Vcircuit breaker controlled motor feeder in 415V or 400V switchgear shall be suitable to withstand the maximum rated fault current of 50kA for at least 120msec.

However, an allowance of 40 msec in the opening time of circuit breaker is a wise consideration due to the

i f t b f ti i iaging, frequent number of operation, increase in contact resistance of circuit breaker and to cover the variation due from manufacturer.

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Short circuit current withstand capacity Hence the cable selected for a circuit breaker

controlled motor feeder in 415V or 400V switchgear shall be suitable to withstand the maximum rated fault current of 50kA for at least (120 + 40) = 160msec.

A = (ISC x t)/K = (50000 x 0.16)/94 = 2212.766mm2

Next standard cable size: = 240 mm2


Continuous current carrying capacity This criteria is applied so that cross section of

the cable can carry the required load current continuously at the designed ambient temperature and laying condition.

Ampacity is defined as the current in amperes that a conductor can carry continuously under the conditions of surrounding medium in which the cables are installed.

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Continuous current carrying capacityCable ampacity given as in IEEE -399, section 13:

kARR

TTTTIcaac

dac 2

1

'int

''

Tc allowable conductor temperature (C)Ta ambient temperature (either soil or air) (C)Td temperature rise of conductor due to dielectric heating (C)T t t i f th d t d t i t f h ti f dj t blTint temperature rise of the conductor due to interference heating from adjacent cables (C)Rac electrical ac resistance of conductor including skin effect, proximity and temperature effects (/ft)Rca effective total thermal resistance of path between conductor and surroundingambient to include the effects of load factor, shield/ sheath losses, metallic conduitlosses, effects of multiple conductors in the same duct etc (thermal- ft, C-cm/W).


Continuous current carrying capacity From the above equation it is clear that the rated

current carrying capacity of a conductor is depending on the following factors: Ambient temperature (air or ground) Grouping and proximity to other loaded cables, heat

sources etc.M th d f i t ll ti ( b d b l d) Method of installation (above ground or below ground)

Thermal conductivity of the medium in which the cable is installed

Thermal conductivity of the cable constituents

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Continuous current carrying capacity Ampacity deration factor is defined as the

product of various rating factors which accounts for the fraction decrease in the ampacity of the conductor: K1= Variation in ambient air temperature for cables laid in air /

ground temperature for cables laid underground. K2 = Cable laying arrangement.y g g K3 = Depth of laying for cables laid direct in ground. K4 = Variation in thermal resistivity of soil.

Ampacity deration factor (K) = K1 x K2 x K3 x K4


Continuous current carrying capacity (K1) Rating factors for variation in ambient air

temperature:

Rating factors for variation in groundtemperature:

Air Temp. (C) 20 25 30 35 40 45 50 55Rating Factor 1.81 1.41 1.10 1.05 1.00 0.95 0.89 0.84

temperature:Ground Temp. (C)

20 25 30 35 40 45 50

Rating Factor 1.12 1.08 1.04 0.96 0.91 0.87 0.82

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Continuous current carrying capacity (K2)

Arrangement 1 Arrangement 2Arrangement 1 Arrangement 2

a a

25mm 25mm

300mm 300mm


Continuous current carrying capacity (K2) Rating factors for multi-core cables laid on open

racks in air (arrangement 1):

No. of racks

No. of cables per rack1 2 3 6 9

1 1.00 0.98 0.96 0.93 0.922 1.00 0.95 0.93 0.90 0.893 1.00 0.94 0.92 0.89 0.886 1.00 0.93 0.90 0.87 0.86

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Continuous current carrying capacity (K2) Rating factors for multi-core cables laid on open

racks in air (arrangement 2):

No. of racks

No. of cables per rack1 2 3 6 9

1 1.00 0.84 0.80 0.75 0.732 1.00 0.80 0.76 0.71 0.693 1.00 0.78 0.74 0.70 0.686 1.00 0.76 0.72 0.68 0.66


Continuous current carrying capacity (K2) Rating factors for single core cable in trefoil

circuits laid on open racks in air:

No. of racks

No. of cables per rack1 2 3

1 1.00 0.98 0.962 1.00 0.95 0.933 1.00 0.94 0.926 1.00 0.93 0.90

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Continuous current carrying capacity (K2) Rating factors for groups of multi-core cables

laid direct in ground, in horizontal formation:

Spacing No. of cables in group2 3 4 6 8

Touching 0.79 0.69 0.62 0.54 0.5015 cm 0.82 0.75 0.69 0.61 0.5730 cm 0.87 0.79 0.74 0.69 0.6645 cm 0.90 0.83 0.79 0.75 0.7260 cm 0.91 0.86 0.82 0.78 0.76


Continuous current carrying capacity (K2) Rating factors for grouping of multi-core cables

laid direct in ground in tier formation:

Spacing No. of cables4 6 8

Touching 0.60 0.51 0.4515 cm 0.67 0.57 0.5130 cm 0.73 0.63 0.5745 cm 0.76 0.67 0.5960 cm 0.78 0.69 0.61

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Continuous current carrying capacity (K2) Rating factors for grouping of single core cable

laid in trefoil circuits laid direct in ground in horizontal formation:Spacing No. of circuits in group

2 3 4 6 8Touching 0.78 0.68 0.61 0.53 0.48

15 cm 0 81 0 71 0 65 0 58 0 5415 cm 0.81 0.71 0.65 0.58 0.5430 cm 0.85 0.77 0.72 0.66 0.6245 cm 0.88 0.81 0.76 0.71 0.6760 cm 0.90 0.83 0.79 0.76 0.72


Continuous current carrying capacity (K3) Rating factors for depth of laying for Cables laid

direct in the ground:

Cable size Depth of laying (cm)75 90 105 120 150 180

up to 25 sq. mm.

1.00 0.99 0.98 0.97 0.96 0.95

25 to 300 1 00 0 98 0 97 0 96 0 94 0 9325 to 300 sq. mm

1.00 0.98 0.97 0.96 0.94 0.93

above 300 sq. mm.

1.00 0.97 0.96 0.95 0.92 0.91

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Continuous current carrying capacity (K4) Rating factors for variation in thermal resistivity

of soil (multi-core cables laid direct in ground):

Nominal area of

conductor in sq. mm

Rating factors for value of Thermal Resistivity of Soil in C cm / Watt

100 120 150 200 250 300

25 1.24 1.08 1.00 0.91 0.84 0.78

35 1.15 1.08 1.00 0.91 0.84 0.7750 1.15 1.08 1.00 0.91 0.84 0.7770 1.15 1.08 1.00 0.90 0.83 0.76


Continuous current carrying capacity (K4) Rating factors for variation in thermal resistivity

of soil, three single core cables laid direct in the ground (three cables in trefoil touching):

Nominal area of

conductor in sq. mm

Rating factors for value of Thermal Resistivity of Soil in C cm / Watt

100 120 150 200 250 300

25 1.19 1.09 1.00 0.88 0.80 0.74

35 1.20 1.09 1.00 0.88 0.80 0.7450 1.20 1.09 1.00 0.88 0.80 0.74

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Continuous current carrying capacity (Example)

Input Required Sourcep qRated kW of Load (Assume it as 160 kW motor) Mechanical/ Process

Load listMotor Data (PF and efficiency, considering PF of 0.85 and motor efficiency of 95%)

Motor Data sheet by manufacturer

Type of Cable to be used (Considering Aluminium, XLPE, 3 core cable)

Project technical specification

Electrical design ambient temperature (Considering electrical design ambient temperature of 50 C)

Project technical specificationdesign ambient temperature of 50 C) specification

Laying condition (Assume laid in open racks in air, assuming 3 Nos. of cable rack with number of cables/ rack to be 6 and cables are laid touching each other)

Cable route layout

Cable ampacity (240mm, 430 A) and deration factors Cable manufacturers catalog


Continuous current carrying capacity (Example)

Calculate the motor current with PF and the efficiency

Rated load current

Calculate K value

K = K1 x K2

Ampacityderation factor Find the cable

ampacity value K x Cable

Ampacity (430A)

Cable Ampacity

I3 > I1 Is the cable size

sufficient to serve the load?

Analysis1

2

3

42 4Hence cable size selected on the basis of continuous current requirement is single run of 3C x 300 Sq mm, Aluminium, XLPE, ampacity = 497A.

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Continuous current carrying capacity (Example) A motor rated at 160 kW controlled by air circuit

breaker fed from main PCC of fault rating 50kA and connected through Aluminum XLPE cable requires a cable size of 3C x 240 Sq mm minimum due to the short circuit rating.

However, the next selected size is 3c x 300 Sq d t th ti t i tmm due to the continuous current requirement.

Next consideration will be the voltage drop criteria.


Starting and running voltage drops in cable This criteria is applied to make sure the cross sectional

f th bl i ffi i t t k th lt darea of the cable is sufficient to keep the voltage drop (due to impedance of cable conductor) within the specified limit so that the equipment which is being supplied power through that cable gets at least the minimum required voltage at its power supply input terminal during both starting and running conditions. Thi i t f d ffi i t ti f th This is to ensure safe and efficient operation of the associated equipment at the supply input terminal.

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Starting and running voltage drops in cable The common standard for voltage drop

11 kV Line11 kV/415V

LV CB

PCC

LOAD

Source

Primary feeder Secondary feeder

-3% -3%

-5%


Starting and running voltage drops in cable Approximation method:

Modified equation for 3phase calculation:

sinXcosRIV LLbdrop

%1001000/sincos3% d VXRILV SV

VS = Supply voltage

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Starting and running voltage drops in cable More accurate equation by considering the

horizontal and vertical domains of voltage drop:

%1001000/sincos31000/sincos3

%22

S

SSd V

NRXILVNXRILVV

N = Number of parallel runs cable


Starting and running voltage drops in cable (Example) Resistance of conductor of 3CX300 mm Sq Al, XLPE cable

= 0.128 Ohms/km (From manufacturers catalog) Reactance of conductor of 3CX300 mm Sq Al, XLPE cable

= 0.071 Ohms/km (From manufacturers catalog) Cable length = 150m (assumed for this calculation) Running power factor of motor = 0.85 Starting power factor of Motor = 0.3 Starting current of motor = 6 times rated current Assuming a voltage drop of 1.5% in the cable for incoming

feeder, that is from (source) to power control center (PCC)

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Starting and running voltage drops in cable (Example) Running voltage drop = ? (From PCC to load) Total running voltage drop = ? (From source to

load)

Starting voltage drop = ? (From PCC to load)Starting voltage drop ? (From PCC to load) Total starting voltage drop = ? (From source to

load)

Protective Devices

The circuit breaker is a device that ensures the control and protection on a network. It is capable of making, withstanding and interrupting operating currents as wellwithstanding and interrupting operating currents as well as short-circuit currents.

The main circuit must be able to withstand without damage: The thermal stress caused by the short-circuit current during 1

or 3 s The electrodynamic stress caused by the peak of short-circuitThe electrodynamic stress caused by the peak of short circuit

current: 2.5 Isc for 50 Hz (standard time constant of 45 ms) 2.6 Isc for 60 Hz (standard time constant of 45 ms) 2.7 Isc (for longer time constant)

The constant load current

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Characteristics of a Circuit Breaker

RATED SHORT-CIRCUIT

RATED Voltage at which the circuit-

Highest (prospective) valueof current that the CB is capable of CIRCUIT

BREAKING CAPACITY (Im)

OPERATIONAL VOLTAGE (Ve)

OVERLOAD RELAY TRIP-

Circuit Breaker

breaker has been designed to operate

Maximum value

Maximum current that the circuit-breaker can carry without tripping

CB is capable of breaking without being damaged

CURRENT or SHORT-CIRCUIT

RELAY TRIP-CURRENT (Ir)

RATED CURRENT (In)

of current that a circuit-breaker can carry indefinitely at a specific ambient temperature

Value that trip the circuit-breaker rapidly on the occurrence of high values of fault current

Characteristics of a Circuit Breaker

Tripping-current ranges of overload and short-circuit protective devices for LV circuit-breakers:

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Circuit Breaker Versus Fuse

Performance Curve of a Circuit Breaker

Overload protection (L)Short-circuit instantaneous protection (I)

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Close/ Open Cycle of Circuit Breaker

Automatic Reclosing Cycle

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Motor Control Centre

MCC440V


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Typically one motor starter controls one

tmotor. When only a few

geographically dispersed AC motors are used, the circuit protection and controlprotection and control components may be located in a panel near the motor.


Motor control centres are simply physical groupings of combination starters in one

blassembly.


Topic 2 Industrial Distribution Equipment

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