Introduction-to-MV-Design-Guide.ppt

Building a New Electric World
Introduction to MV
equipments
Training for internal group
2006

2
T 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

3
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

4
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
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

6
 Standard
Merlin Gerin equipment is conformity with list 2 of the series 1 table IEC
60 071 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

7
 Standard
Each insulation level corresponds to a distance in air which
guarantees withstand without a test certificate.
 lower than this distance, we need simulation/test in the laboratory to
check 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

8
 IEC Standard Voltage
20 7.2 60
12
17.5
24
36
Ur
95
75
28
38
Up
Ud
170
125
50
70
1.2/50us 50Hz

9
Current
The rms value of current that equipment can withstand when
current flow without exceeding the temperature rise allowed in
standards.
Temperature rises authorized by the IEC according to the type of
contacts.

10
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
x’mer 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

11
Short Circuit Current
 Short circuit power depends on :
 Network configuration (exp: single source, parallel
source,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

12
Short Circuit Current

13
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

14
Maximum short-circuit current: Ith (kA rms. 1 s or 3 s)
 Corresponds to a short circuit in upstream terminals of the switching
device.
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
Isc
It
h

15
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 a
transformer , we need to know short circuit voltage (Usc %)
Usc % is defined by:
 1. The voltage x’mer 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 equipment’s
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 X’d: 20%.
Ir = Sr/ (V3 xU) = 15.000/(V3x10) = 867 A
Isc = Ir / X’d = 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

20
DIFFERENT ENCLOSURE TYPE
metal clad
compartment
Block type

21
 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 <10.
Pollution may occur from external dust, lack of cleanliness, breaking
down of an internal surface, pollution & humidity causes electrochemical
conduction which will worsen discharge phenomena.
 Condensation  reducing the insulating performance by a factor 3
 Pressure  related to the altitude, derating performance.
 Humidity  % of humidity can cause a change in insulating
performances. (liquid always leads to a droop in performance)
 Temperature  temp. increases can cause decreases insulation
performance. Thermal shock can be the cause of the micro fissuration
which can lead very quickly to insulator breakdown. Insulator expands by
5 and 15 times more than a conductor.

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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

23
 CURRENT TRANSFORMER
To provide a secondary current that is proportional to the 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
 Don’t 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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 If j and h are not known, use
approx value cos j: 0.8 and h = 0.8
 Capacitor Feeder :
Derating coefficient of 30% to take
into 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 and
their multiples and factors
 CT must be able to withstand 120% the
rated current

25
 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 motor’s 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

26
 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 CT
secondary 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

27
 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 CT’s 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

28
 CLASS X (DIFFERENTIAL PROTECTION)
 The short circuit current is chosen as
a function of the application:
 generator differential
 motor differential
 Transformer differential
 busbar differential

29

30

31

32
 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.

33
 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

34
 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.

35
 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.

36
 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.

37
 PROTECTION INDEX: first index

38
 PROTECTION INDEX: second index

39
 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).

40
 PROTECTION INDEX: third index

42
Sepam 1000+
standard applications
For industrial and service
sector site networks
For public distribution
networks
For all voltage levels

43
S20 substation application
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

44
Substation application
(S40/S41/S42 types) 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

45
T20 transformer application
Series 20
 50/51, 50N/51N and 46
 49RMS, thermal overload
 38/49T, temperature
monitoring (8 sensors)
Processing of faults detected
by transformer Buchholz or
thermostat
(MES module required)

46
Transformer application
(T40/T42 types) Series 40
Parallel transformers
neutral networks
 50/51,50N/51N, 46,50BF
 49RMS and 38/49T
 67N/67NC, directional earth
fault
 67, directional phase
overcurrent

47
M20 motor application
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)

48
Motor application
(M41 type) Series 40
neutral networks
All the M20 protection
functions, plus:
 67N/67NC, directional earth
fault
 32P, reverse power
 27/59, 81L/81H, …
Automatic load shedding

49
Generator application
(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

50
B21 busbar application
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 phase
rotation direction
 27R, remanent undervoltage
27S, 3 phase-to-phase
undervoltages V1,V2,V3

51
B22 busbar application
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 loss
of mains
 for substations with generators
in parallel with the main
network

52
Sepam 1000+
Selection guide
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

53
Basic electrical knowledge is needed to understand MV SWGR

Introduction-to-MV-Design-Guide.ppt

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