CT & VT
CT & VT
CT & VT
Instrument transformers
Presentation 2
Applications and types 4
1
Instrument transformers Presentation
2
Instrument transformers Presentation (cont.)
3
Instrument transformers Applications and types
DE58030EN
b voltage transformers.
These devices carry out the functions of:
b reducing the size of value to be measured
b providing galvanic separation
b supplying the power needed to process
the data, or even for the protection device
to work.
Types
Instrument transformers are of the following types:
Current transformers
Connected on the MV network primary circuit, they supply a reduced current value
to the secondary circuit, proportional to the network current on which they are installed.
There are two types:
b CT: current transformer
b LPCT (Low Power Current Transformer): electronic current transformers.
Voltage transformers
Connected to the MV network primary, they supply the secondary circuit with a reduced
voltage value, proportional to the network voltage on which they are installed.
4
CTs: Current Transformers Selection guide
Technical description
DE52455
5
CTs: Current Transformers Selection guide
Technical description (cont.)
Characteristics (cont.)
Short-time thermal current peak value
This value is standardized from Ith - 1 s at:
b IEC: 2.5 Ith at 50 Hz and 2.6 Ith at 60 Hz
b ANSI: 2.7 Ith 60 Hz.
Accuracy load
The value of the load on which is based the metered current accuracy conditions.
Accuracy power Pn
Apparent power (VA) that the CT can supply on the secondary for the rated
secondary current for which the accuracy is guaranteed (accuracy load).
Usual values 5 - 7.5 - 10 - 15 VA (IEC).
Accuracy class
Defines the limits of error guaranteed on the transformation ratio and on the phase
shift under the specified conditions of power and current. Classes 0.5 and 1 are used
for metering class P for protection.
Current error ε (%)
Error that the transformer introduces in the measurement of a current when the
transformation ratio is different from the rated value.
Phase shift or phase error ψ (minute)
Difference in phase between the primary and secondary currents, in angle minutes.
Table of current transformer characteristics
Characteristics Rated values
Rated voltage (kV) 7.2 12 17.5 24 36
Insulation level:
b power frequency withstand (kV) 1 min 20 28 38 50 70
b lightning impulse withstand (kV - peak) 60 75 95 125 170
Frequency (Hz) 50 - 60
Primary current Ipn (A) 25 - 50 - 75 - 100 - 200 - 400 - 600...
Short-time thermal current Ith (1 s) 12.5 - 16 - 20 - 25 - 31.5 - 40 - 50 kA
or
40 - 80 - 100 - 200 - 300 x In
Secondary current Isn (A) 1-5
Accuracy power Pn (VA) 2.5 - 5 - 7.5 - 10 - 15
6
CTs: Current Transformers Selection guide
Technical description (cont.)
DE58031EN
Metering CT or protection CT
We have to choose a CT with characteristics that are suited to its application.
Metering CT
This requires good accuracy (linearity zone) in an area close to the normal service
current; it must also protect metering devices from high currents by saturating earlier.
Protection CT
This requires good accuracy at high currents and will have a higher precision limit
(linearity zone) for protection relays to detect the protection thresholds that they are
meant to be monitoring.
7
CTs: Current Transformers Selection guide
Technical description (cont.)
Feasability of a CT
We can define the over-current coefficient of the CT:
Ksi = Ith
--------1s
------
Ipn
The lower Ksi, the easier the CT is to produce with a given volume, compatible with
being integrated in a MV cubicle. A high Ksi leads to over-dimensioning of the CT
and makes it difficult to produce.
Ksi order of magnitude CT production
Ksi < 100 Standard
100 < Ksi < 300 Sometimes difficult for certain secondary characteristics
300 < Ksi < 400 Difficult
400 < Ksi < 500 Limited to certain secondary characteristics
Ksi > 500 Sometimes impossible
CT connection
CT with a double (or triple) secondary
A CT can have one or two, and more rarely three, secondaries for the chosen
application (protection and/or measurement).
DE52348
Safety
The CT secondary is used at low impedance (virtually in short circuit).
The secondary circuit should never be left open, since this would mean
connecting across an infinite impedance. Under these conditions, hazardous
voltages for personnel and equipment may exist across the terminals.
Terminal marking
CT connection is made to the terminals identified according to the IEC:
b P1 and P2 on the MV side
b S1 and S2 on the corresponding secondary. In the case of a double output,
the first output is identified by 1S1 and 1S2, the second by 2S1 and 2S2.
DE58033EN
8
CTs: Current Transformers Selection guide
Technical description (cont.)
9
CTs: Current Transformers Selection guide
Technical description (cont.)
FLP = --Ipl
------- (standardized values: 5 - 10 - 15 - 20 - 30)
Ipn
In practice this corresponds to the linearity limit (saturation curve) of the CT.
Example
Protection CT: 100/5 A, 7.5 VA, 5P20.
b rated primary current 100 A
b rated secondary current 5 A
b rated transformation ratio 100/5 A
b accuracy power 7.5 VA
b accuracy class 5P.
Under a load corresponding to the accuracy power of 7.5 VA, the error limit table
gives an error y ± 1% and ± 60 min at Ipn (100 A).
b accuracy limit factor 20.
At a load corresponding to the accuracy power, the error y ± 5%.
10
CTs: Current Transformers Selection guide
Using the order forms
The tables on the following pages allow you to define the current transformer
reference that corresponds to the necessary and required characteristics,
and to place your order.
The selection factors enabling you to find the reference you require are explained
in the example given below for a DIN type metering CT, in reference to the previous
definitions.
Insulation level and frequency Transformation Short-time Power, accuracy class, Type Reference Quantity
ratio thermal current safety factor FS
A/A kA x 1 s
Ur 12 kV 50 / 5 12.5 15 VA cl. 0.5 Fs < 10 AD12 03811366N0
Ud 28 kV - 1 min 16 AD12 03811368N0
Up 75 kV peak
75 / 5 25 AD12 03811371N0
31.5 AD12 03811373N0
fr 50/60 Hz 100 / 5 25 AD12 03811376N0
31.5 AD12 03811378N0
DE58001
DE58002
11
CTs: Current Transformers Order form
DIN standard 12 kV CT -
single and double secondary
DE58002
DE58002
12
CTs: Current Transformers Order form
DIN standard 24 kV CT -
single secondary
DE58004
25 AD21/N1 03811427N0
31.5 AD21/N1 03811430N0
40 AD22/N1 03811433N0
100 / 5 25 AD21/N1 03811436N0
31.5 AD21/N1 03811439N0
40 AD22/N1 03811442N0
200 / 5 25 AD21/N1 03811443N0
AD21 AD22 31.5 AD21/N1 03811445N0
40 AD21/N1 03811447N0
DE58005
DE58004
DE58004
13
CTs: Current Transformers Order form
DIN standard 24 kV CT -
double secondary
ARJD
Dimensions page 21
14
CTs: Current Transformers Order form
24 kV primary conductor support CT -
single secondary
DE58007
DE58006
15
CTs: Current Transformers Order form
24 kV primary conductor support CT -
double secondary
ARJP3
DE58009
ARJA1
Dimensions page 22
16
CTs: Current Transformers Order form
36 kV primary conductor support CT -
single secondary
DE58012
40 ARM6T/N1 03811606N0
400 / 5 40 ARM6T/N1 03811608N0
600 / 5 40 20 VA cl. 0.5 Fs < 10 ARM6T/N1 03811610N0
750 / 5 40 ARM6T/N1 03811612N0
1000 / 5 40 30 VA cl. 0.5 Fs < 10 ARM9T/N1 03811614N0
1250 / 5 40 ARM9T/N1 03811616N0
1500 / 5 40 ARM9T/N1 03811618N0
ARM6T ARM9T 2000 / 5 40 ARM9T/N1 03811620N0
Dimensions page 23 2500 / 5 40 ARM9T/N1 03811622N0
DE58012
40 ARM6T/N1 03811607N0
400 / 5 40 ARM6T/N1 03811609N0
600 / 5 40 ARM6T/N1 03811611N0
750 / 5 40 ARM6T/N1 03811613N0
1000 / 5 40 10 VA 5P20 ARM9T/N1 03811615N0
1250 / 5 40 ARM9T/N1 03811617N0
1500 / 5 40 15 VA 5P20 ARM9T/N1 03811619N0
ARM6T ARM9T 2000 / 5 40 ARM9T/N1 03811621N0
Dimensions page 23 2500 / 5 40 ARM9T/N1 03811623N0
17
CTs: Current Transformers Order form
36 kV primary conductor support CT -
double secondary
18
CTs: Current Transformers Order form
17.5 - 24 - 36 kV - slip-over CT
single and double secondary
DE58014
ARO1b ARO2
Dimensions page 23
19
CTs: Current Transformers Order form
0.72 kV closed core CT -
single and double secondary
ARC2 ARC3
Dimensions page 23
ARC2
DE58016
ARC3
Dimensions page 23
20
CTs: Current Transformers Dimensions
AD12
DE52378
DE52459
AD13
DE52379
DE58052EN
L
102
P1
P2
4 holes
Ø 11
Secondary terminal
and M5 screw type
earthing connector
AD21
DE52380
DE52461
AD22
DE52420
DE52462
ARJD
DE52420
DE52464
AD23
DE52381
DE52463
21
CTs: Current Transformers Dimensions (cont.)
ARJP1
DE52387
DE52468
ARJP2
DE52388
DE52470
ARJM2
DE52386
DE52465
ARJH
DE52385
DE52469
ARJP3
DE52389
DE58045EN
Optional
plastic cover
on secondary
290
260
4 locations
Secondary terminal Ø 11
and M6 screw type
earthing connector
ARJA1
DE52384
DE58046EN
Optional
plastic cover
on secondary
260 40
4 locations
Secondary terminal Ø 11
158 and M6 screw type
333 earthing connector 198
22
CTs: Current Transformers Dimensions (cont.)
ARM6T
DE52390
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ARM9T
DE52391
DE52472
ARO1b
DE52392
DE58049EN
248
ARO2
DE52393
DE52471
ARC2
DE52444
DE52473
ARC3
DE52445
DE52475
23
LPCT: Electronic current Selection guide
transformers Technical description
LPCT’s (Low Power Current Transformers) LPCT low power current transformers
meet IEC standard IEC 60044-8. LPCT’s are specific current sensors with a direct voltage output of the “Low Power
Current Transformers” type, in conformity with standard IEC 60044-8.
These are CT’s with a direct voltage output LPCT’s provide metering and protection functions.
which has the advantage of having a very They are defined by:
wide range of applications, simplifying b the rated primary current
selection. b the extended primary current
b the accuracy limit primary current or the accuracy limit factor.
These have a linear response over a large current range and do not start to saturate
DE58034
24
LPCT: Electronic current Order form
transformers
Primary current Secondary Accuracy Accuracy Short-time Rated Secondary Internal Type Reference Qty
rated extended voltage class limit thermal insulation connector diameter
(A) (A) (mV) factor current (kV) (mm)
FLP (kA - 1 s)
100 1250 22.5 0.5 – 5P 500 50 17.5 RJ45 - 8 pts CLP1 62623
100 1250 22.5 0.5 – 5P 400 40 24 RJ45 - 8 pts CLP2 51238696F0
100 2500 22.5 0.5 – 5P 400 40 24 RJ45 - 8 pts CLP3 AAA10474
100 2500 22.5 0.5 – 5P 400 40 0.72 RJ45 - 8 pts 160 TLP160 AAA10094
100 2500 22.5 0.5 – 5P 400 40 0.72 RJ45 - 8 pts 190 TLP190 AAA10095
25
LPCT: Electronic current Dimensions
transformers
CLP1
DE52394
DE52373EN
M8 x 12
90
20
80
Shielded cable L = 6,5 m
8-pin RJ45 connector
CLP2
DE52395
DE52374EN
88.5
Shielded
plug RJ45 8 pts
Shielded
96.5 cable
L = 6.5 m
M8 x 12
Tightening
torque 20 Nm
CLP3
DE52396
DE52375EN
88.5
8.5 Shielded
plug RJ45 8 pts
Shielded
96.5 cable
L = 6.5 m
M8 x 12
Tightening
torque 20 Nm
TLP160
PE56703
DE52376EN
6.5
2.5
Shielded cable L = 6.5 m
Shielded plug RJ45 8 pts
TLP190
DE52397
DE52377EN
6.5
2.5
Shielded cable L = 6.5 m
Shielded plug RJ45 8 pts
26
VTs: Voltage Transformers Selection guide
Technical description
Connection of a VT
27
VTs: Voltage Transformers Selection guide
Technical description (cont.)
Accuracy class
Defines the error limits guaranteed relative to the transformation ratio and the phase
shift under specified conditions of power and voltage.
Voltage error ε (%)
Error that the transformer introduces into the voltage measurement when
the transformation ratio is different from the rated value.
Phase shift or phase error (ψ in minutes)
Phase difference between primary and secondary voltages, in angle minutes.
Rated voltage factor KT
This is the factor, a multiple of the rated primary voltage, which determines the
maximum voltage which the transformer must meet the specified temperature rise
and accuracy recommendations. The maximum operating voltage depends on
the network neutral system and the earthing conditions of the primary winding.
Table of voltage factors KT
Voltage Rated duration Connection mode of Network neutral
factor the primary winding system
1.2 Continuous Between phases Any
Continuous Between the star- Any
connected transformer
neutral point and earth
1.2 Continuous Between phase and earth Directly earthed
1.5 30 s
1.2 Continuous Between phase and earth Earthed via a limiting
1.9 30 s resistor with automatic
earthing fault elimination
1.2 Continuous Between phase and earth Insulated neutral without
1.9 8h automatic earthing fault
elimination
1.2 Continuous Between phase and earth Earthed via a limiting
resistance with automatic
earthing fault elimination
VT operating characteristics
Operation of a VT is more simple than that of a CT because the secondary voltage is
virtually independent of the load, due to it being connected through a high impedance
(virtually used in an open circuit).
Therefore, the secondary must not be short circuited. Under these conditions
an excessively high current will damage the transformer.
28
VTs: Voltage Transformers Selection guide
Technical description (cont.)
VT connections
Several metering connection arrangements are possible (fig. opposite)
b star-connection of 3 transformers: requires 1 isolated MV terminal for each
transformer
b connecting to 2 transformers, so-called V-connection: requires 2 isolated MV
terminals per transformer.
DE58035
Star-connected VT and example of transformation ratio
DE58036
Vrsd = 3 • V0 = V1 + V2 + V3
DE58038
29
VTs: Voltage Transformers Selection guide
Technical description (cont.)
Example:
Metering voltage transformer 20 000 / 110 , 50 VA, cl. 0.5
3 3
b rated primary voltage 20000 V/3, rated secondary 110 V/3
b accuracy power 50 VA
b accuracy class 0.5. The table of limit error values gives, under the specified
conditions for the accuracy class:
v a primary voltage 80% to 120% of the rated voltage (16 kV to 24 kV)
v a load of between 25% and 100% of the accuracy power, i.e. between 12.5 VA
and 50 VA with an inductive power factor of 0.8, the metering errors will be y ± 0.5%
for voltage and y ± 20 min for phase shift.
Example:
Protection voltage transformer 20 000 / 110 , 100 VA, 3P, KT = 1.9 8h
3 3
b rated primary voltage 20000 V/3, rated secondary 110 V/3
b accuracy power 100 VA
b accuracy class 3P. The table of limit values shows that for:
v a primary voltage of 5% of the rated voltage at KT times the rated voltage, i.e.
20000 x 5% = 1000 V at 20000 x 1.9 = 38000 V
v a load of between 25% and 100% of the accuracy power, in other words of between
25 VA and 100 VA with a power factor of 0.8, the metering error will be y ± 3% in voltage
and y ± 120 min in phase shift.
30
VTs: Voltage Transformers Selection guide
Technical description (cont.)
Connecting a VT
VT with a double (or triple) secondary
A VT can have one or two secondaries (figure opposite), and more rarely three
secondaries for the appropriate applications (protection and/or metering).
Identifying terminals
A VT is connected across the terminals identified according to the IEC:
b A for phase and N for earth on the MV side
b a and n on the corresponding secondary side. In the case of a double output,
the first output is shown by 1a and 1n, the second by 2a and 2n.
DE52440
DE52441
Single secondary Double secondary
31
VTs: Voltage Transformers Order form
DIN standard phase-earth VT
DE58018
VDF12 VDF21
Dimensions page 39
32
VTs: Voltage Transformers Order form
DIN standard phase-phase VT
VDC11
Dimensions page 39
33
VTs: Voltage Transformers Order form
Phase-earth VT
DE58021
DE58022
DE58022
DE58023
34
VTs: Voltage Transformers Order form
Phase-earth VT (cont.)
35
VTs: Voltage Transformers Order form
Phase-earth VT with fuse-holder
DE58025
VRS3 VRS2B
Dimensions page 41
36
VTs: Voltage Transformers Order form
Installation structure for phase-earth VT
with fuse-holder
Technical description
The mobile installation structure, ready to be assembled for phase-earth voltage
transformers with fuse-holders comprises the following components:
b movement selector for the internal part
b movement control arm
b movement selector for the external plastic cover
b torsion spring selector
b self-adhesive VT mimic diagram
b control panel
b 12 contact entrelec unit
b contact rod
b self-adhesive VT indicator mimic diagram.
37
VTs: Voltage Transformers Order form
Phase-phase VT
DE58027
DE58028
38
VTs: Voltage Transformers Dimensions
DIN standard VT
VDF12
PE56700
DE58000EN
DIN 40430
225 102
4 holes
Secondary terminal Ø 11
190 150 and M5 screw type
earthing connector
VDF21
DE52401
DE52480
VDC11
DE52446
DE52483
VDC21
DE52398
DE52484
39
VTs: Voltage Transformers Dimensions
Phase-earth VT
VRFR
DE52406
DE52482
VRQ1
DE52407
DE52481
VRQ2
DE52408
DE52485
VRQ3
DE52409
DE52486
VRF3
DE52422
DE52493
40
VTs: Voltage Transformers Dimensions
Phase-earth VT with fuse-holder
Phase-phase VT
VRS3
DE52410
DE52487
VRS2B
DE52530
DE58050EN
Secondary terminal
and M5 screw type
earthing connector
Tightening torque 5 Nm
M4 x 8
M6 x 8
Tightening
torque
10 Nm
VRCR
DE52405
DE52491
VRC1
DE52402
DE52488
VRC2
DE52403
DE52489
VRL3
PE56704
DE58047EN
380 325
320
300 4 holes Ø 11
Optional
Secondary terminal 390 plastic cover 225 248
and M6 screw type on secondary
earthing connector
30
41
Notes
42
Notes
43
Notes
44