1. Introduction to MV Design Guide

7/30/2019 1. Introduction to MV Design Guide

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Building a New Electric World

Introduction to MVequipmentsTraining for internal group

2006


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2T Limantoro Sch. Indonesia . Aug 2005

Introduction to MV equipments

Basic magnitude to define a MV Switchgear:

Voltage

Current

Frequency

Short Circuit power

The Voltage, rated current and rated frequency are

often known in the single line or specification or can

easily be defined

Short circuit power to choose various parts of a

switchgear which must withstand significant

temperature rises and electro dynamic constraint.

Voltage to define the dielectric withstand of the

components such as: CB, insulators, CTs,VTs,etc


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Electrical network can be disconnect, protect and

control by using SWITCHGEAR :

METAL enclosed switchgear divided 3 types:

Metal clad : example: MC set,NEX

Compartmented : example: SM6

Block : example Interface/joggle cubicle.

Introduction to MV equipments


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Metal-enclosed, factory built equipment

VOLTAGE

Operating/service Voltage U (kV): Voltage across the equipment terminals.

example : 22kV, 3.3kV,

Rated Voltage Ur (kV) : (nominal Voltage)

Max rms (root mean square) value of the voltage that

equipment can withstand under normal operating

conditions.

The rated voltage (Ur) is always greater than the

operating voltage.

The rated voltage associated with an insulation level

Examples : Rated voltage 24kV, 17.5kV, 12kV and 7.2kV


5/535T Limantoro Sch. Indonesia . Aug 2005


VOLTAGE

Insulation level Ud (kV rms, 1 minute) and Up (kV peak)

This defines the electric withstand of equipment to switching under operation over

voltages and lightning impulse.

Ud: Over voltage due to of internal switchgear, which accompany all changes in

the circuit: opening/closing CB or Switch, breakdown or shorting across an insulator,

etc

Simulated in laboratory by the power-frequency withstand voltage for 1 minute.

Example : Ur : 24kV Ud : 50kVrms/1 min.

Up: over voltage of external switchgear or atmospheric origin occur

when lightning falls on or near a transmission line.

Simulated in laboratory by the lightning impulse withstand voltage.

Examples : Ur : 24kV Up : 125kVp




Standard

Merlin Gerin equipment is conformity with list 2 of the series 1 table IEC60 071 and 60 298.

Insulation level apply to MV swgr at altitudes of less than 1000 meters,20 deg.C, 11 g/m3 humidity and press of 1.013 mbar.

Above this ,derating should be considered.

Rated

Voltage

Rated power-

frequency

withstand voltage

Normal

operating

voltage

kV rms 1minute kV rms kV rms

list 1 list 2

7.2 40 60 20 3.3 to 6.6

12 60 75 28 10 to 11

17.5 75 95 38 13.8 to 15

24 95 125 50 20 to 22

36 145 170 70 25.8 to 36

Rated lightning

impulse

withstand voltage

1.2/50us 50Hz

.

kV peak




Standard

Each insulation level corresponds to a distance in air whichguarantees withstand without a test certificate.

lower than this distance, we need simulation/test in the laboratory tocheck lightning impulse withstand voltage.

Rated

Voltage

Rated power-

frequency

withstand

voltage

Distance live

to earth in air

.

kV rms 1minute kV rms cm

7.2 20 9

12 28 12

17.5 38 16

24 50 22

36 70 32

95

125

170

Rated lightning

impulse

withstand voltage

1.2/50us 50Hz

.

kV peak

60

75




IEC Standard Voltage

20 7.2 60

1217.5

24

36

Ur

957528

38

UpUd

170

12550

70

1.2/50us 50Hz


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Current

The rms value of current that equipment can withstand whencurrent flow without exceeding the temperature rise allowed in

standards.

Temperature rises authorized by the IEC according to the type of

contacts.


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OPERATING Current : I (A)

Calculate from the consumption of the devices connected.

Actual current passes through the equipment.

generally customer provide its value

calculate if we know the power of the load

Exercise:

A switchboard with a 630kW motor feeder and a 1250kVA

xmer feeder at 5.5kV operating voltage, cos j = 0.9 and motor

efficiency h = 90%

How many ampere the operating current of Transformer and

motor?

81.74 A


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Short Circuit Current

Short circuit power depends on :

Network configuration (exp: single source, parallelsource,network, generators)

Impedance of each equipments or devices.(exp: lines, cables,

transformers, motors)

Maximum power that network or source can deliver to an

installation during a fault, expressed in MVA or in kA rms at operating

voltage.(Psc, for instance 500MVA)

Determination of the short-circuit power requires analysis of the

power flows feeding the short circuit in the worst possible case.

What is short circuit level for 500MVA at 20KV ?

14.5kA 13.13kA


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Short Circuit Current


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Minimum short-circuit current: Isc (kA rms.)

Corresponds to a short circuit at one end of the fault point.

This value allows us to choose the setting of thresholds for over current

protection devices and fuses

Example: Isc: 25kA rms

source load

Ith Is

c


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Maximum short-circuit current: Ith (kA rms. 1 s or 3 s)

Corresponds to a short circuit in upstream terminals of the switchingdevice.

This value is defined in kA for 1s or 3 s

It is used to define the thermal withstand of the equipment

Example: Isc: 31.5 kA rms. 1 s or 3 s

source load

IscIt

h


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Peak Value of the max.short circuit current (kA peak)

value of the initial peak in the transient period

I dyn = (kA peak)

I dynamic is equal to :

2.5 x Isc at 50 Hz (IEC)

2.6 x Isc at 60 Hz (IEC)

2.7 x Isc (ANSI) times the short circuit current calculated at a given

point in the network.

Example: Isc : 25kA Idyn: 2.5 x 25= 63.75kA peak (IEC 60 056)

Idyn: 2.7 x 25= 67.50kA peak (ANSI), 25kA at

a given point

This value determines the breaking capacity and closing capacity of CBs and

Switches, as well as the electro dynamic withstand of busbars and switchgear. IEC uses the following values: 8 12.5 16 20 25 31.5 40 kA rms


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The short circuit current depends on the type of equipment

installed on the network (transformers, generators, motors, lines,etc)

Transformer :

To determine the short circuit current across the terminals of atransformer , we need to know short circuit voltage (Usc %)

Usc % is defined by:

1. The voltage xmer is not powered: U=0

2. place the secondary in short circuit

3. gradually increase voltage U at the primary up to the

rated current Ir in the transformer secondary side The value U read across the primary is then equal to Usc

The short circuit Isc = Ir / Usc

Example : Transformer 20 MVA/10kV with Usc: 10%. Upstream

power infinite

Ir = Sr/ (V3 xU no-load) = 20.000/(V3x10) = 1150 A

Isc = Ir / Usc = 1150 / 10% = 11.500A = 11.5kA


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Synchronous Generators : (Alternator and Motor)

To determine the short circuit current across the terminals of a

synchronous generator is very complicated because the internal

impedance of the generator varies according to time

When the power gradually increases, the current reduces passing

through three characteristic periods:

Sub Transient, average duration 10 ms (enabling

determination of the making capacity of the CB and electro

dynamic constraint)

Transient , average duration 250 ms (sets the equipments

thermal constraints) Permanent (value of the short circuit current in steady state)

The short circuit Isc = Ir / Xsc

The most common values for a synchronous generator are:

Example : Generator 15 MVA/10kV with Xd: 20%.

Ir = Sr/ (V3 xU) = 15.000/(V3x10) = 867 A

Isc = Ir / Xd = 867/ 20% = 4.330A = 4.33kA


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Frequency fr (Hz)

Two frequency are usually used throughout the world:

50 Hz in Europe

60 Hz in the USA

several countries use both frequencies indiscriminately

Instrument Voltage Transformer rated 50 can operate at 60Hz

Instrument Current Transformer rated 50 can operate at 60Hz.

But CT with rated 60Hz can not be operated at 50Hz.


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SWITCHGEAR FUNCTION


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DIFFERENT ENCLOSURE TYPE

metal clad

compartment

Block type


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DIELECTRIC WITHSTAND

depends on 3 parameters:

The Dielectric strength of the medium

The Shape of the parts The distance :

ambient air between the live parts

insulating air interface between the live parts

Dielectric Strength of air depends on ambient conditions:

Pollution reducing the insulating performance by a factor


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The Shape of the parts

It is essential to eliminate any peak effect to avoid disastrous effect

on the impulse wave withstand in particular and on the surface ageing of

insulator.

Air Ionization Generate Ozone Breakdown of insulator surface or

skin

Distance between parts

Ambient air between live parts

For installations sometime we can not test under impulse conditions,

the table below gives the minimum distance to comply with in air either

phase to earth or phase to phase .

The table based on IEC 71-2 according to the rated lightning impulse

withstand voltage


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CURRENT TRANSFORMER

To provide a secondary current that is proportional tothe primary current.

Transformation ratio (Kn) :

Kn = I primary/Isecondary = N2/N1

Current transformer must be conformity with IEC 185 and BS3038 and ANSI

One CT comprises one or several primary windings or one or several secondary windings and all being

encapsulated in an insulating resin

Dont leave a CT in open circuit because dangerous voltages for people and equipment may appear

across its terminal

CT defined at 50Hz can be installed on a 60Hz network. The opposite is not correct.

Rated primary Voltage (Upr) > rated insulation voltage

Special case for CT is core balance or ring CT installed on a cable. The dielectric insulation is provided

by the cable and the air located between them. The core balance or ring CT is itself insulated.


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Ifj and h are not known, use

approx value cos j: 0.8 and h = 0.8

Capacitor Feeder :

Derating coefficient of 30% to takeinto account of temp. rise due to

capacitor harmonic

Bus section

The greatest value of current that

can flow in the bus section on a

permanent basis.

Ips = In bus

Standardized values :

10-12.5-15-20-25-30-40-50-60-75 andtheir multiples and factors

CT must be able to withstand 120% the

rated current

f


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Metal-enclosed, factory built equipment CURRENT TRANSFORMER

Example:

A thermal protection device for a motor has a setting range of between 0.6 and 1.2 x Ir (CT).

In order to protect this motor, the required setting must correspond to the motors rated current.

If we assume that Ir for the motor = 45 A, the required setting is therefore: 45A

If we use a 100/5A CT, the relay will never see 45A , because: 100A x 0.6 = 60A > 45A.

If we use a 75/5A CT, the relay will see , 75 x 0.6 = 45 A

The range of setting will be: 0.6 < 45/75 < 1.2 . This CT is suitable.

RATED THERMAL SHORT CIRCUIT CURRENT (Ith)

Value of the installation max. short circuit current and the duration 1s or 3 s.

Each CT must be able to withstand short circuit current both thermally and dynamically until the fault is

effectively cut off.

Ith = Ssc / (U x V3), Ssc = power short circuit MVA

When the CT is installed in a fuse protected, the Ith = apprx. 80 Ir.

RATED SECONDARY CURRENT:

Local use or inside switchgear Isr = 5A

Remote use or long distance Isr = 1A

M t l l d f t b ilt i t


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ACCURACY CLASS

Metering: class 0.5

Switchboard metering : class 1

Over current protection : class 10P or 5P

Differential protection : class X or 5P20

Zero sequence protection: class 5P

REAL POWER OUTPUT

The total (sum) of the consumption of the cabling, protection or metering device connected to the CTsecondary circuit.

Consumption of the cooper cable (losses in the cable):

where :

Consumption of each metering or protecting devices are given in the technical specification

0.0225

0.5625

M t l l d f t b ilt i t


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SAFETY FACTOR (SF)

Safety Factor is protection of metering device in case of a fault

SF will chosen according to the current metering short time withstand current: 5 < SF< 10.

SF is ratio between the limit of rated primary current (Ipl) and the rated primary current (Ipr)

where : Ipl is the value of primary current for which the error in secondary current = 10%

Example: an ammeter is guaranteed to withstand a SC of 10 Ir, I.e. 50A for a 5A (secondary CT/device

input). To avoid ammeter will not be destroyed in the case of primary fault, the CT must be saturated

before 10 Ir in the secondary side. A safety factor of 5 is suitable.

Schneider CTs have a safety factor of 10, however lower SF can be requested.

ACCURACY LIMIT FACTOR (ALF)

Protection application : accuracy limit factor and accuracy class

Example: Definite time OC relay

The relay will function perfectly if : ALF real CT > 2 (Irs / Isr)

where : Irs : relay threshold setting, Isr : rated secondary CT

CT 100A/5A, I relay setting : 5 times , so the ALF = 2 (5x5/5) = 10, Actual ALF CT > 15 or 20

Metal enclosed factory built equipment


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CLASS X (DIFFERENTIAL PROTECTION)

The short circuit current is chosen as

a function of the application:

generator differential

motor differential

Transformer differential

busbar differential



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Metal-enclosed factory built equipment


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VOLTAGE TRANSFORMER

To provide secondary voltage that is proportional to the primary voltage.

IEC Standard 60 186 defines the conditions which voltage transformer must meet.

One VT comprises a primary windings and one or several secondary windings and all

being encapsulated in an insulating resin

RATED VOLTAGE FACTOR (KT)

The rated voltage factor is the rated primary voltage has to be multiplied in order to

determine the max. voltage for which the transformer must comply with the specified

temperature rise and accuracy recommendations.

According earthing system of the network, the VT must be able to withstand this max.

voltage for the time that is required to eliminate the fault.

Generally VT manufactures comply with : VT phase to earth: 1.9 for 8 h and VT phase to

phase : 1.2 continuous.



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Metal enclosed, factory built equipment

RATED PRIMARY VOLTAGE (Upr)

According to the design, VT will be connected :

Phase to earth 22.000V/V3 / 110V/V3, where Upr = U/V3

Phase to phase 22.000 / 110V, where Upr = U

RATED SECONDARY VOLTAGE (Usr)

Phase to phase VT, rated secondary voltage : 100V or 110 V

Phase to Ground VT, rated secondary voltage : 100/V3 or 110V/V3

RATED OUTPUT

The apparent power output that VT can supply the secondary circuit

when connected at rated primary voltage and connected to the nominal

load.

It must not introduce any error exceeding the values guaranteed by the

accuracy class . (S = V3. U. I in 3 phase circuit)

Standardized value are:

10-15-25-30-50-75-100-150-200-300-400-500 VA



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ACCURACY CLASS

The limits of errors guaranteed in terms of transformation ratio and phase under the specified conditions

of both power and voltage.

PROTECTION ACCORDING TO IEC 60 186

Classes 3P and 6P (but in practice only class 3P is used)

The accuracy class is guaranteed for values :

of voltage of between 5% of the primary voltage and the max. value of this voltage which is the

product of the primary voltage and the rated voltage factor (kT x Upr)

For secondary load between 25% and 100% of the rated output with a power factor of 0.8

inductive.



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Transformation Ratio (Kn)

Voltage ratio error

This is the error that the transformer introduces into the voltage measurement

Phase error or phase shift error

This is the phase difference between the primary voltage Upr and the secondary voltage Usr.

the error expressed in minutes of angle

Thermal power limit or Rated continuous power

This is the apparent power that transformer can supply in steady state at its rated secondary

voltage without exceeding the temperature rise limits set by the standards.



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, y q p

PROTECTION INDEX

Protection of people against direct contact and protection of equipment

against certain external influences.

Requested by international standard for electrical installations and

products (IEC 60 529)

The protection index is the level of protection provided by an enclosure

against access to hazardous parts, penetration of solid foreign bodies

and of water.

The IP code is a coding system to indicate the protection index.



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, y q p

PROTECTION INDEX: first index



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y q p PROTECTION INDEX: second index



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PROTECTION INDEX: third index

Definitions

The protection mentions correspond to impact energy

levels expressed in joules hammer blow applied directly to the equipment

impact transmitted by the supports, expressed in terms of

vibrations therefore in terms of frequency and acceleration

The protection indices against mechanical impact can be

checked by different types of hammer: pendulum hammer,

spring-loaded hammer or vertical free-fall hammer (diagram

below).



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PROTECTION INDEX: third index


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Sepam 1000+

Presentation

Sepam 1000+d d li i


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standard applications

For industrial and service

sector site networks

For public distribution

networks

For all voltage levels

S20 substation applicationS i 20


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Series 20

Substation incomer and feeder

applications

Protection functions:

50/51, phase overcurrent

50N/51N, earth fault

46, negative sequence /

unbalance

Logic discrimination

4-cycle recloser

Substation application(S40/S41/S42 t ) S i 40


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(S40/S41/S42types) Series 40

Parallel incomers or closed ring

networks

Isolated or compensated

neutral networks


50/51,50N/51N,46,50BF 67N/67NC,

directional earth fault

67, directional phase

overcurrent

32P, reverse power

I, U, P, E metering

T20 transformer applicationS i 20


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Series 20


50/51, 50N/51N and 46

49RMS, thermal overload

38/49T, temperature

monitoring (8 sensors)

Processing of faults detectedby transformer Buchholz or

thermostat

(MES module required)

Transformer application(T40/T42 t ) S i 40


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(T40/T42 types) Series 40

Parallel transformers

Isolated or compensatedneutral networks

Protection functions: 50/51,50N/51N, 46,50BF 49RMS and 38/49T

67N/67NC, directional earthfault

67, directional phaseovercurrent

I, U, P, E metering

M20 motor applicationSeries 20


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Series 20


50/51, 50N/51N, 46

49RMS

38/49T

Specific functions:

37, phase undercurrent

48/51LR, excessive starting

time and locked rotor

66, starts per hour

specific motor-related function

(MES114)

Motor application(M41 type) Series 40


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(M41 type) Series 40

Isolated or compensated

neutral networks

All the M20 protectionfunctions, plus: 67N/67NC, directional earth

fault 32P, reverse power

27/59, 81L/81H,

Automatic load shedding

I, U, P, E metering

Generator application(G40 type) Series 40


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(G40 type) Series 40


50/51, 50N/51N,46,50BF 49RMS and 38/49T 27/59, 81L/81H,

Specific functions: 50V/51V, voltage restraint

overcurrent 32P, 32Q/40, directional active

and reactive overpower

I, U, P, E measurements

B21 busbar applicationSeries 20


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Series 20

Voltage protection functions:

27/59, phase-to-phase

under/overvoltage 81L/81H, under/overfrequency

59N, neutral voltage

displacement

27D/47, positive sequence

undervoltage and phaserotation direction

27R, remanent undervoltage

27S, 3 phase-to-phase

undervoltages V1,V2,V3

B22 busbar applicationSeries 20


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Series 20

Voltage protection functions:

27/59, 27S, 59N 81L/81H 27D/47, 27R

Loss of mains protection 81R,rate of change of frequency(ROCOF)

fast, reliable detection of lossof mains for substations with generators

in parallel with the mainnetwork

Sepam 1000+Selection guide


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Selection criteria series 20 series 40

Measurements I U U I and U I and U I et U

Specific protection Loss of mains Directional Directional

functions (ROCOF) earth fault earth fault &phase O/C

Applications series 20 series 40

Substation S20 S40 S41 S42

Transformer T20 T40 T42

Motor M20 M41

Generator G40

Busbar B21 B22


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1. Introduction to MV Design Guide

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