Medium Voltage Distribution

Catalogue | 2012

Outdoor instrument
transformers
Current transformers
Voltage transformers

Make the most of your energy

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 Outdoor instrument General contents
transformers

Outdoor instrument
5
transformers

Outdoor current transformers

11
(CTs)

Outdoor voltage transformers

21
(VTs)

Outdoor current and voltage

31
transformers (CTs and VTs)

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 Outdoor instrument Contents
transformers

Presentation 6

Protection for outdoor use 8

Applications and type 9

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 Outdoor instrument Presentation
transformers

The range of Schneider Electric, outdoor Conformity with standards

instrument transformers has been designed All Schneider Electric instrument transformers are in conformity with IEC standards,
for 7.2 kV to 40.5 kV voltage and rated sections 2099 - 2134, and recommendations 60044-1/IEC 60044-2.
Transformers in conformity with specific country standards can also be supplied
currents from 5 to 2500 A. In order to comply
(IEEE C57.13, NBR6855, NBR6856…).
with higher short circuit levels in the systems,
the current transformers have been Main features
designed to withstand 60 kA x 1 second The working parts (windings and magnetic cores) are entirely enclosed in an epoxy
short circuit currents. resin bloc casting, whose twofold function is to:
b guarantee electric insulation inside the device
b the highest strength.
All Schneider Electric instrument transformers The external surface of device is covered with silicon, whose function is to:
are in conformity with IEC standards. b insulation outside the device
b the highest strength.
Current transformers can be in accordance
Product quality over time is guarantee not only by thirty years experience in the
with the accuracy classes “TPS-TPX-TPY- field of resin insulated instrument transformer manufacturing but also by the use of
TPZ” defined by IEC 60044-6 standard silica filled epoxy resin which gives:
refering to transformer behaviour during b high dielectric strength including at high temperatures (18 kV/mm at 180°C for
transient short circuit conditions. 20,000 hours)
b insulation class B according to IEC 44-1 provisions
b extremely good ageing behaviour both to heat mass ageing according to IEC 216
(over 20 years at 120°C) and to surface ageing obtained in salty mist
b lack of emissions of any harmful substances in case of fire, in conformity with IEC
standards IEC 60020-37, IEC 60020-22 and ASTM D 3286
b extremely effective behaviour in tropical climates
b high mechanical strength, even at high service temperatures:
Epoxy resin glass transition temperature ≥ 105°C.

Accurate production process resulting in:

b no blisters or blowholes in the resin thanks to vacuum casting
b low constant partial discharge figure also thanks to the high quality of the other
insulating materials used
b high strength and very good electric conductivity in primary and secondary
terminals even at the temperatures reached during a short circuit, thanks to
mechanical connections
b process parameters remaining unchanged over time thanks to computer control
used to manage and monitor the whole production line.

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 Outdoor instrument Presentation
transformers

Quality is the result of scheduling and Certified quality system

monitoring at each stage, from initial design Schneider Electric’s quality guarantee is certified in documents that are available
through to production and testing, and right on request:
b documents explaining the company’s quality policy
through to final delivery and after sales
b a schedule for each stage of each product’s execution
service. b the continuous assessment of indicators checking all possible quality faults during
This is expressed in terms of execution the production process
in conformity with the quality certification. b a set of technical/quality documents providing proof of what has happened
throughout the production and testing processes so as to guarantee the required
This procedure allows us to supply
quality level.
a product that has all of the specified The production process applies standardized methods for Quality Assurance and
characteristics and also to provide the Control.
customer with a production and execution Quality Control plans ensure that the defined procedures are applied to the product,
from testing through to delivery of equipment used in production right through to final
schedule that guarantees product quality.
production.
The initial phases of product design and industrialization are also subject to Quality
Certification procedures.

The Schneider Electric quality system is certified by the CSQ

The CSQ (independent certification organization for quality management systems)
has certified Schneider Electric’s quality to be in conformity with IEC standard -
EN 29001 (ISO 9001), which require a company to implement a comprehensive
quality assurance system covering all aspects from product definition through to
after sales service.

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 Outdoor instrument Protection for outdoor use
transformers

The silicon material used on Schneider The design of Schneider Electric outdoor instruments transformers was studied
Electric outdoor transformers is manufactured in order to:
b perform the required behaviours on highest pollution level (level IV as described
by world known companies. in document IEC815)
The use of silicon for outdoor electrical b perform the required behaviours for ageing, by application of silicon on the sand
equipment is a process well known in High blasted surface of the resin.
Voltage Industry to prevent flashover and
The secondary connections are protected by an enclosure specially designed for
arcing, especially in severely contaminated electrical equipments, in compliance with all major standards (UL, CSA, CE, Lloyds,
envronments. BV, FI). The materials used is polycarbonate which ensure the resistance to outdoor
The experience obtained after more than conditions.
25 years of intensive use shows its efficiency The protection level, according with IEC529 is IP44 standard or higher level on request.
and reliability, on glass and epoxy isolators. PE50724

Many additional tests were performed

in Schneider’s laboratories in order to verify
all the properties needed for this use
(dielectric strength-in volume and
superficial, adhesion,ageing, ...).
The tests made show that an epoxy resin
covered with silicon age less quickly than
the same geometry made with
cycloaliphatic resins.
The superficial breakdown strength is also
higher with silicon than with resin.
In case of flashover (i.e. by overvoltage),
the silicon has the unique property of
maintaining hydrophobicity.
Other materials have to be changed.
Moreover, the silicon maintains its
hydrophobicity during the lifetime of the
transformer, as other polymeric materials
which have hydrophobic properties to loose
these properties after a relatively short time.

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 Outdoor instrument Applications and type
transformers

Protection or metering devices have to Metering transformer applications

receive data on electrical values (current or In MV electrical distribution, the high current and voltage values mean that they
cannot be used directly by metering or protection units.
voltage) from the equipment to be protected. Instrument transformers are necessary to provide values that can be used by these
For technical, economic and safety reasons, devices which can be:
this data cannot be obtained directly on the b analogue devices, directly using the supplied signal
equipment’s MV power supply; we have to b digital processing units with a microprocessor, after analogue/digital conversion of
the input signal.
use intermediary sensors:
b current transformers

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.

Example of metering transformer application in a protection system

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.
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.

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 Outdoor current transformers Contents
(CTs)

Selection guide 12
Technical description 12

Current transformers 18
7.2 to 24 kV - Type OAM3/N1 - OAM3/N2 18
7.2 to 40.5 kV - Type OAM7/N1 - OAM7/N2 - OAM7/N3 19

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 Outdoor current transformers Selection guide
(CTs) Technical description

Current transformers (CTs) meet standard Current transformers

IEC 60044-1. Current transformers have two basic functions:
b adapting the MV current value at the primary to the characteristics of the metering
Their function is to supply the secondary or protection devices by supplying a secondary current with a reduced, but proportional
circuit with a current that is proportional to current value
that of the MV circuit on which they are b isolating power circuits from the metering and/or protection circuit.
installed.
The primary is series-mounted on the MV Composition and types
network and subject to the same A current transformer comprises a primary circuit and a secondary circuit connected
overcurrents as the latter and withstands via a magnetic core and an insulating coating system in epoxy-silica covered with
the MV voltage. silicon, in the case of Schneider Electric transformers.
The secondary generally has one of its
terminals connected to earth. Characteristics
The secondary must never be in an open These are defined in standard IEC 60044-1.
circuit (short-circuit it if not loaded). Insulation
Characterized by the rated voltage:
b of the insulation, which is that of the installation (e.g.: 24 kV)
b of the power frequency withstand 1 min (e.g.: 50 kV)
b of the impulse withstand (e.g.: 125 kV).
Rated frequency
50 or 60 Hz.
Rated primary current (Ipn)
Rms value of the maximum continuous primary current. Usual values are 25, 50, 75,
100, 200, 400, 600, 1000, 1200, 1600, 2000, 2500 A.
Rated secondary current (Isn)
This is equal to 1 A or 5 A.
Rated transformation ratio
Kn = I rated primary / I rated secondary (e.g.: 100 A / 5 A).
Short-time thermal current Ith - 1 second
This characterizes the thermal withstand under short circuit conditions for 1 second.
It is expressed in kA or in a multiple of the rated primary current (e.g.: 80 x Ipn)
for 1 second.
The value for a duration that is different to 1 second is given by:
I’th = Ith/ t.
For example 16 kA - 1 s is equivalent for t = 2 s to I’th = 16 /2 = 11.3 kA.

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 Outdoor current transformers Selection guide
(CTs) Technical description

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 at 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 value 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.
Characteristics of voltage transformer
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 - 1000 -
1200 - 1600 - 2000 - 2500
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

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 Outdoor current transformers Selection guide
(CTs) Technical description

The choice of CT is decisive in order for CT operation

the overall metering or protection system Importance of CT selection
to work properly. The operating accuracy of metering or protection devices depends directly on the CT
accuracy.
Operating principle
A CT often has a load that is quite resistive (Rc + its wiring), as shown in the schematic
diagram below.

DE58031EN

Schematic diagram for a current transformer

I1: primary current
I2 = Kn I1: secondary current for a perfect CT
Is: secondary current actually flowing through the circuit
Im: magnetizing current
E: induced electromotive force
Vo: output voltage
Lm: magnetization inductance (saturable) equivalent to the CT
Rtc: resistance at the CT secondary
Rfil: resistance of the connection wiring
Rc: load resistance

Current I2 is a perfect image of the primary current I1 in the transformation ratio.

However, the actual output current (Is) is subject to an error due to the magnetization
current (Im).
I 2 = I s + I m if the CT was perfect, we would have Im = 0 and Is = I2.

A CT has a unique magnetization curve (for a given temperature and frequency).

With the transformation ratio, this characterizes its operation.
This magnetization curve (voltage Vo, magnetizing current function Im) can be divided
into 3 zones:
1 - non-saturated zone: Im is low and the voltage Vo (and therefore Is) increases
virtually proportionately to the primary current.
2 - intermediary zone: there is no real break in the curve and it is difficult to situate
a precise point corresponding to the saturation voltage.
3 - saturated zone: the curve becomes virtually horizontal; the error in transformation
ratio is high, the secondary current is distorted by saturation.
DE58032EN

Magnetization curve (excitation) for a CT.

Output voltage as a function of the magnetizing current.
Vs = f (Im)

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.

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 Outdoor current transformers Selection guide
(CTs) Technical description

CT’s for metering must have the right CT for metering

accuracy for the rated current. Accuracy class
They are characterized by their accuracy A metering CT is designed to send an image as accurated as possible of currents
below 120% of the rated primary.
class (generally 0.5 or 1) as well as a safety
IEC standard 60044-1 determines the maximum error in the accuracy class
factor Fs. for the phase and for the module according to the indicated operating range
(see “error limits” table opposite).
Example: 400/5 A, 15 VA, cl 0.5, FS 10 These accuracy values must be guaranteed by the manufacturer for a secondary
load of between 25 and 100% of the accuracy power.
The choice of accuracy class is related to the application (table opposite).
Primary current Safety
factor The usual accuracy class is 0.5 there are metering classes of 0.2S and 0.5S
Secondary current
Accuracy power
specifically for metering applications.
Accuracy
(see explanation in the example) class Safety factor: Fs
In order to protect the metering device connected to the CT from high currents
on the MV side, instrument transformers must have early saturation characteristics.
Accuracy class according to application The limit primary current (Ipl) is defined for which the current error in the secondary
Application Class is equal to 10%. The standard then defines the Safety Factor FS.
Laboratory measurement 0.1 - 0.2 Ip l
Accurate metering (calibration devices) FLP = (preferred value: 10)
Ip n
Industrial metering 0.5 - 1
Billing metering 0.2 - 0.5 - 0.2S - 0.5S This is the multiple of the rated primary current from which the error becomes greater
than 10% for a load equal to the accuracy power.
Switchboard indicators statistical 0.5 - 1
metering Example of a metering CT
Metering CT 400/5 A, 15 VA, cl. 0.5, FS 10
b rated primary current 400 A
Error limits according to the accuracy class b rated secondary current 5 A
Accuracy % rated Current error Phase shift b rated transformation ratio 400/5 A
class primary ±% error ± min b accuracy power 15 VA
current b accuracy class 0.5.
For S For S The table or error limits given for class 0.5 for a primary current:
0.2 / 0.2S 1 (0.2S alone) 0.75 30 b between 100% and 120% of the rated current (here 400 A to 480 A), a current error
5 0.75 0.35 30 15
± 0.5% and the phase shift error of ± 30 min.
b at 20% (here 80 A) the error imposed by the standard is less than or equal to
20 0.35 0.2 15 10
0.75%
100 0.2 0.2 10 10
b between 20% and 100% of the rated current the standard does not give the
120 0.2 0.2 10 10 metering point and the maximum error is between 0.5 and 0.75%, with a normally
0.5 / 0.5S 1 (0.5S alone) 1.5 90 permitted linear variation between these two points
5 1.5 0.75 90 45 b safety factor FS = 10
20 0.75 0.5 45 30 For a primary current greater than 10 times the rated current, in other words here
100 0.5 0.5 30 30 4000 A, we will have a metering error > 10% if the load is equal to the accuracy load;
120 0.5 0.5 30 30 for a load less than this we can still be in the linear part of the magnetization curve.
1 5 3 180
20 1.5 90
100 1 90
120 1 90

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 Outdoor current transformers Selection guide
(CTs) Technical description

CT’s for protection must have suitable CT for protection

accuracy for fault currents. They are Accuracy class
characterized by their accuracy class A protection CT is designed to send an image as reliable as possible of the fault
current (overload or short circuit). The accuracy and the power are suited to these
(generally 5P) and the accuracy limit factor
currents and different from those for metering applications.
ALF. IEC standard 60044-1 determines the maximum error for each accuracy class
in the phase and in the module according to the indicated operating range.
Example: 400/5 A, 15 VA, 5P10 Error limits according to the accuracy class
Accuracy class Combined error for Current error Phase shift error
Primary current Accuracy limit the accuracy limit between lpn and for the rated
Secondary current factor ( ALF) current 2lpn current
Accuracy power Accuracy 5P 5% ± 1% ± 60 min
(see explanation in the example) class
10P 10% ± 3% No limit

For example for class 5P the maximum error is y ± 5% at the accuracy limit current
and y ± 1% at the rated current.
Standardized classes are 5P and 10P. The choice depends on the application.
The accuracy class is always followed by the accuracy limit factor.
Accuracy class according to application
Application Class
Zero sequence protection differential protection 5P
Impedance relay amperemetric protection 5P - 10P

Accuracy limit factor: ALF

A protection CT must saturate at sufficiently high currents to enable sufficient
accuracy in the measurements of fault currents by the protection device whose
operating threshold can be very high.
We define the limit primary current (Ipl) for which current errors and phase shift
errors in the secondary do not exceed values in the table opposite.
The standard then defines the accuracy limit factor ALF.
Ip l
ALF = (standardized values: 5 - 10 - 15 - 20 - 30)
Ip n
In practice this corresponds to the linearity limit (saturation curve) of the CT.
Example
Protection CT: 400/5 A, 15 VA, 5P10.
b rated primary current 400 A
b rated secondary current 5 A
b rated transformation ratio 400/5 A
b accuracy power 15 VA
b accuracy class 5P.
Under a load corresponding to the accuracy power of 15 VA, the error limit table
gives an error y ± 1% and ± 60 min at Ipn (400 A).
b accuracy limit factor 10.
At a load corresponding to the accuracy power, the error y ± 5% for a value
of the primary current less than 10 x 400 = 4000 A.

Calculating the power (VA)

Indicative metering consumptions
Device Max. consumption
in VA (per circuit)
Ammeter Electromagnetic 3
Electronic 1
Transducer Self-powered 3
External powered 1
Meter Induction 2
Electronic 1
Wattmeter, varmeter 1
Indicative protection consumption
Device Max. consumption
in VA (per circuit)
Static over-current relay 0.2 to 1
Electromagnetic over-current relay 1 to 8
Indicative secondary cabling consumption
Cables (mm2) Consumption (VA/m)
1A 5A
2.5 0.008 0.2
4 0.005 0.13
6 0.003 0.09
10 0.002 0.05

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 Outdoor current transformers Selection guide
(CTs) Technical description

Selection criteria
1 - Define the primary current Ipn
Use the standard values prescribed by IEC regulations:
10, 12.5, 15, 20, 25, 30, 40, 50, 60, 75 A and their decimal multiples.
2 - Define the short circuit current for 1 second Ith
The short circuit current generally refers to 1 second. Should this current be known
for different time values “t”, calculate the value for 1 second by applying the following
formula:
Ith (for 1 sec.) = Ith x t
e.g.: 25 kA for 3 sec. = 25 x 3 = 43.3 kA for 1 sec.
3 - Calculate the “K” coefficient
This value will be the access key to the various tables
lth x 1 sec.
K=
lpn
e.g.: Ipn = 100 A, Ith = 12.5 kA x 1 sec. => K = 12500/100 =125
4 - Position on the table
Enter the “K” column and position on the line corresponding to the K value
immediately above the calculated value.
e.g.: calculated K = 125 = K line =150
5 - Check feasibility
A current transformer is feasible with the specifications indicated in the columns
marked with .

Remarks:
For protection secondaries the following formula is guaranteed:
ALF x VA = constant K
e.g.: 10 VA / 5 P10 = 10 x 10 = 100
5 VA / 5 P20 = 5 x 20 = 100
WARNING: this equation is only guaranteed during the CTs selection phase.

Terminal markings
DE52792

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 Outdoor current transformers Current transformers
(CTs) 7.2 to 24 kV
Type OAM3/N1 - OAM3/N2

Single and double primary ratio

PE58461

Characteristics
b Standard reference IEC 60044-1
b Rated highest voltage: 7.2 - 12 - 17.5 - 24 kV
b Rated continous thermal current 1.2 x Ipn
b Frequency 50 or 60 Hz
b Rated secondary current standard 5 or 1A
b For primary current < 800 A Double primary ratio through primary coupling
b For primary current > 800 A Double primary ratio through secondary reconnection
b Value “K=Ith/Ipn” must be fixed in comparison with the smaller rated primary
current ratio
b Creepage distance > 700 mm
b Weight 25 kg.

Selection table
No. of secondaries per CT 1 2
Standard types OAM3/N1 OAM3/N2
1st measure secondary
Cl 0.5 Fs = 10
VA
Alternatively 5 7.5 10 15 20 20 30 30 30 30 30
"K" lpn Measure second Protection 2nd protection
k = lth/lpn Rated primary current (A) second secondary
Cl 05 Cl 5P Cl 5P
lth max 50 kA Fa = 10 ALF = 10 ALF = 10
for 1 s VA VA VA
SR DR 7.5 10 15 20 30 50 5 7.5 10 15 20 30 50 5 5 5 7.5 5 10 10 15 20 30 50

100 10 - 800 10-20 - 400-800

150 10 - 300 10-20 - 300-600
200 10 - 300 10-20 - 300-600
250 10 - 200 10-20 - 200-400
300 10 - 150 10-20 - 150-300
400 10 - 100 10-20 - 100-200
500 10 - 50 10-20 - 100-200

1000
1200
1250
500-1000
600-1200
For other characteristics, please consult us.

Dimensions
4 holes
DE58040EN

M12 x 23

341
302
333
294

270

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 Outdoor current transformers Current transformers
(CTs) 7.2 to 40.5 kV
Type OAM7/N1 - OAM7/N2 - OAM7/N3

Single and double primary ratio

PE50725

Characteristics
b Standard reference IEC 60044-1
b Rated highest voltage: 7.2 - 12 - 17.5 - 24 - 36 - 40.5 kV
b Rated continous thermal current 1.2 x Ipn
b Frequency 50 or 60 Hz
b Rated secondary current standard 5 or 1 A
b For primary current < 800 A Double primary ratio through primary coupling
b For primary current > 800 A Double primary ratio through secondary reconnection
b Value “K=Ith/Ipn” must be fixed in comparison with the smaller rated primary
current ratio
b Creepage distance > 1100 mm
b Weight 35 kg.

Selection table
No. of secondaries per CT 1 2 3
Standard types OAM7/N1 OAM7/N2 OAM7/N3
1st measure
secondary
Class 0.5
Fs = 10
VA
5 10 15 20 30
1st measure secondary 2nd protection
secondary
Class 0.5 Class 5P
FS = 10 ALF = 10
VA VA
Alternatively 5 7.5 10 15 20 20 30 30 30 30 30 5 5 7.5 10 15
"K" lpn Measure second Protection second 2nd protection secondary 3rd protection
k = lth/lpn Rated primary current (A) secondary
Class 0.5 Class 5P Class 5P Class 5P
lth max 50 kA Fa = 10 ALF = 10 ALF = 10 ALF = 10
for 1 s VA VA VA VA
SR DR 7.5 10 15 20 30 50 5 7.5 10 15 20 30 50 5 5 5 7.5 5 10 10 15 20 30 50 5 5 7.5 10 15
100 10 - 800 10-20 - 400-800
150 10 - 300 10-20 - 300-600
200 10 - 300 10-20 - 300-600
250 10 - 200 10-20 - 200-400
300 10 - 150 10-20 - 150-300
400 10 - 100 10-20 - 100-200
500 10 - 50 10-20 - 100-200

1000
1200
1250
2000
2500
500-1000
600-1200
750-1500
1000-2000
For other characteristics, please consult us.

Dimensions
DE58041EN

4 holes 8 holes
M12 x 23 M12 x 23

432 393
424
385

270

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 Outdoor voltage transformers Contents
(VTs)

Selection guide 22
Technical description 22

Voltage transformers 27
Phase-earth 7.2 to 24 kV - Type OVF2n/S1 - OVF2n/S2 - OVF2n/S3 27
Phase-earth 36 kV - Type OVF3n/S1 - OVF3n/S2 - OVF3n/S3 28
Phase-phase 7.2 to 24 kV - Type OVC2/S1 - OVC2/S2 29
Phase-phase 36 kV - Type OVC3/S1 - OVC3/S2 30

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 Outdoor voltage transformers Selection guide
(VTs) Technical description

Voltage transformers (VT) meet standards Voltage transformers (VT)

IEC 60044-2. Voltage transformers have two key functions:
b adapting the value of MV voltage on the primary to the characteristics of metering
Their function is to supply a voltage or protection devices by supplying a secondary voltage that is proportional and lower
proportional to the MV circuit that they are b isolating power circuits from the metering and/or protection circuit.
installed on to the secondary.
The primary, which is parallel mounted on Composition and type
These comprise a primary winding, a magnetic core, one or several secondary
the MV network between phases of from windings, with everything encapsulated in an insulating resin covered with silicon.
phase to earth, is subject to the same There are two types, according to how they are connected:
overvoltages as the latter. The secondary b phase/phase: primary connected between two phases
supplies a voltage that is virtually constant, b phase/earth: primary connected between a phase and the earth.
whatever the load. Characteristics
The secondary must never be placed These are defined by standard IEC60044-2.
in short circuit. Insulation
Characterized by the rated voltages:
b insulation voltage, which will be that of the installation (e.g.: 24 kV)
DE52477

b power frequency withstand 1 min (e.g.: 50 kV)

b impulse withstand (e.g.: 125 kV)
Rated frequency
50 or 60 Hz.
Simplified schematic diagram of a voltage transformer
Rated primary voltage (Upn)
IS: secondary current
Us: secondary voltage According to their design, voltage transformers are connected:
Zc: load impedance. b either between phase and earth and in this case Upn = U/3 (e.g.: 20/3)
b or between phases and in this case Upn = U.
Rated secondary voltage (Usn)
This is equal to 100 or 110 V for phase/phase voltage transformers. For single phase,
phase/earth transformers, the secondary voltage must be divided by 3 (e.g.: 100/3).
Accuracy power Pn
Apparent power (VA) that the VT can supply the secondary for the rated secondary
voltage for which the accuracy is guaranteed (accuracy load).
Standardized values 30, 50, 100 VA (IEC).
DE52478

Connection of a VT

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 Outdoor voltage transformers Selection guide
(VTs) Technical description

Characteristics (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 factor Rated duration Connection mode Network neutral
1.2 Continuous Between phases Any
Continuous Between the Any
star-connected
transformer neutral
point and earth
1.2 Continuous Between phase and DIrectly earthed
earth
1.5 30 s
1.2 Continuous Between phase and Earthed via a limiting
1.9 30 s earth resistor with automatic
earthing fault
elimination
1.2 Continuous Between phase and Insulated neutral
1.9 8h earth without automatic
earthing fault
elimination
1.2 Continuous Between phase and Earthed via a limiting
earth resistance with
automatic earthing
fault elimination

Table of voltage transformer characteristics

Characteristics Rated values
Insulating voltage (kV) 7.2 12 17.5 24 36
Insulation level:
b power frequency withstand (kV) (1) 1 min 20 28 38 50 70
b ligthning impulse withstand (kV - peak) 60 75 95 125 170
Frequency (Hz) 50 - 60
Frequency voltage U1n (kV) 3 - 3.3 - 5 - 5.5 - 6 - 6.6 - 10 - 11 - 13.8 - 15 -
divided by 3 if single phase) 20 - 22 - 30 - 33
Secondary voltage U2n (V) 100 - 110 or 100/3 - 110/3
Accuracy power (A) 30 - 50 - 100
(1) When there is a major difference between the highest voltage for the equipment (Um) and
the rated primary voltage, the power frequency must be limited to five times the rated voltage.

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.

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 Outdoor voltage transformers Selection guide
(VTs) Technical description

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

V- connected VT and example of transformation ratio

Residual voltage metering

The residual voltage. which characterizes the voltage of the neutral point relative
to earth, is equal to the vectorial sum of the three phase-earth voltages.
The residual voltage is equal to 3 times the zero-sequence voltage V0.
DE52356

Vrsd = 3 • V0 = V1 + V2 + V3

Please note, it is impossible to measure a residual voltage with

phase/phase VT’s.
The appearance of this voltage signifies the existence of an earthing fault.
It is obtained by measurement or by calculation:
b measuring by three voltage transformers whose primary circuits are star-connected
and whose secondary circuits are open-delta connected, supplying the residual
voltage 1
b calculation by the relay based on three voltage transformers whose primary
and secondary circuits are star-connected 2 .
DE58037

DE58038

1 Direct measurement of the residual voltage 2 Calculation of the residual voltage

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 Outdoor voltage transformers Selection guide
(VTs) Technical description

Voltage transformer for metering

Accuracy class
These devices are intended to send an image as accurately as possible of the rated
primary voltage between 80 and 120% of the latter.
The accuracy class determines the permissible error in the phase and in the module
in this range for the accuracy load.
It is valid for all loads of between 25 and 100% of the rated accuracy power with
an inductive power factor of 0.8.
The table below gives the usual classes according to application.
Application Class
Accurate laboratory metering applications (calibration devices) 0.2
Billing metering industrial measurements 0.2
Statistical switchboard metering indicators 0.5 - 1

b Class 0.5 corresponds to an error y ± 0.5% for the rated primary voltage,
with the accuracy load over the secondary.
b Class 1 corresponds to an error y ± 1% in the same conditions.
For a given accuracy class, voltage and phase-shift errors must not exceed
the values indicated in the table opposite.
Error limits according to the accuracy class
Accuracy class Voltage error Phase-shift error
(ratio) ± % ± mm
0.2 0.2 10
0.5 0.5 20
1 1.0 40

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.

Voltage transformer for protection

Accuracy class
These devices are intended to send an image that is as accurate as possible
of the voltage in the case of a fault (voltage drop or overvoltage).
They must have the right accuracy and power for the fault voltages and therefore
different from those used for instrument transformers.
In practice, the accuracy class 3P is used for all applications and the error limits
for voltage and phase given in the table below.
These are guaranteed for all loads of between 25 and 100% of the accuracy power
with an inductive power factor of 0.8.
Error limits for each accuracy class
Accuracy Voltage (± %) between Phase shift error (minutes)
class between
5% Upn 2% Upn 5% Upn 2% Upn
and KT and KT and KT and KT
3P 3 6 120 240
6P 6 12 240 280
KT: over-voltage coefficient.
Upn: rated primary voltage.

Example:
Protection voltage transformer 20 000 / 110 , 100 VA, 3P, KT = 1.9 8 h
3 3
b the 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.

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 Outdoor voltage transformers Selection guide
(VTs) Technical description

Selection criteria Terminal markings

1 - Define the primary voltage Upn

DE52794
According to the installation voltage (U) and the type
of transformer connection:
b between phase and ground (Upn = U/3)
b between phase and phase (Upn = U)
VT accuracy is always guaranteed to be between
0.8 Upn and 1.2 Upn. Use this information to choose
standard voltage values.
2 - Define the rated insulation level
The rated insulation level should be that immediately
above the primary voltage level.
Note: the industrial power frequency test according
to IEC standards should be carried out by applying
the formula:
5 x Upn with a maximum value given by the
corresponding insulation value.
3 - Define the secondary voltage Usn
The standard values are:
b 100 and 110 divided by 3, for instrument and
protection Y-connected windings
b 100 and 110 divided by 3, for residual voltage open
delta connection.
4 - Define the frequency
Values are either 50 or 60 Hz.
5 - Voltage factor
It is the factor by which the primary voltage Upn
should be multiplied in order to determine
the maximum insulation voltage for the Um device:
b 1.9 for 8 hours, for insulated pole voltage
transformers (phase-ground)
b 1.2 permanent, for insulated pole voltage
transformers (phase-phase).
6 - Position on the table
Enter the column corresponding to the number of
secondaries and the type of (actual or relative)
performance simultaneity.
7 - Check feasibility
The feasible characteristics are identified by
the columns with boxes marked:

Reference voltage for insulation Calculating the power (VA)

Max. reference Single Two (insulated) Indicative metering consumption
voltage for (grounded) pole Device Max consumption in VA
insulation pole (per circuit)
7.2 kV 3:3 - 3.3:3 - 3 - 3.3 - 6 - 6.6 kV Voltmeter Electromagnetic 5
6:3 - 6.6:3 kV Electronic 1
12 kV 6:3 - 6.6:3 - 6 - 6.6 - 10 - 11 kV Transducer Self-powered 5
10:3 - 11:3 kV
External power 2
17.5 kV 10:3 - 11:3 10 - 11 - 15 kV
- 15:3 kV Meter Induction 5
24 kV 15:3 - 20:3 15 - 20 - 22 - 24 kV Electronic 4
- 22:3 - 24:3 kV Wattmeter, varmeter 5
36 kV 25:3 - 30:3 25 - 30 - 33 - 36 kV
- 33:3 - 36:3 kV Indicative protection consumption
Device Consumption in VA
(per circuit)
Static overvoltage relay 0.2 to 1
Electromagnetic overvoltage relay 1 to 9

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 Outdoor voltage transformers Voltage transformers
(VTs) Phase-earth 7.2 to 24 kV
Type OVF2n/S1 - OVF2n/S2 - OVF2n/S3

Description
PE50727

Voltage transformer for phase-ground connection.

Characteristics
b Standard reference: IEC 60044-2
b Standard primary voltage Upn: 3 - 3.3 - 5 - 5.5 - 6 - 6.6 - 10 - 11 - 13.8 - 15 - 20-
22:3 kV
b Rated insulation level: 7.2 - 12 - 17.5 - 24 kV
b Rated secondary voltage Usn: 100:3 - 100:3 - 110:3 - 110:3 V
b Frequency: 50 or 60 Hz
b Rated voltage factor: 1.9 for 8 hours
b Thermal burden: 300 VA
b Creepage distance > 700 mm
b Weight 35 kg.

Table of options
No. of secondaries for VT 1 2 3
Standard type OVF2n/S1 OVF2n/S2 OVF2n/S3
Application Measuring or protection 1st measure 1st measure or protection 1st 2nd measure or
2nd protection or measure 2nd residual voltage protection
3rd residual voltage
Standard secondary voltage (V) 100:3 or 110:3 100:3 - 100:3 100:3 - 100:3 100:3 or 110:3 and
or 110:3 - 110:3 or 110:3 - 110:3 100:3 or 110:3
Operation - Separate Separate Simultaneous separate
3rd secondary Accuracy class - - - 3P
Output - - - 75 50 100
2nd secondary Accuracy class - 0.5 or 1 3P 0.5 or 1
Output - 15 20 30 30 50 75 50 50 75 50 75 100 30 50 75
1st secondary Accuracy class 0.2 0.5 0.2 0.5 0.2 0.5 0.5
Output 30 40 50 50 75 100 15 20 30 30 50 75 25 30 50 50 75 100 30 50 75
For other characteristics, please consult us.

Dimensions
4 holes 14 x 25 375
DE58042EN

4 holes Ø13 345

320

321 312
280 220 185

49

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 Outdoor voltage transformers Voltage transformers
(VTs) Phase-earth 36 kV
Type OVF3n/S1 - OVF3n/S2 - OVF3n/S3

Description
PE50728

Voltage transformer for phase-ground connection.

Characteristics
b Standard reference IEC 60044-2
b Standard primary voltage Upn: 30 - 33 - 35:3 kV
b Rated insulation level: 36 kV
b Rated secondary voltage Usn: 100:3 100:3 110:3 110:3 V
b Frequency 50 or 60 Hz
b Rated voltage factor: 1.9 for 8 hours
b Thermal burden: 450 VA
b Creepage distance > 1100 mm
b Weight 45 kg.

Table of options
No. of secondaries for VT 1 2 3
Standard type OVF3n/S1 OVF3n/S2 OVF3n/S3
Application Measuring or protection 1st measure 1st measure or protection 1st 2nd measure or
2nd protection or measure 2nd residual voltage protection
3rd residual voltage
Standard secondary voltage (V) 100:3 or 110:3 100:3 - 100:3 100:3 - 100:3 100:3 or 110:3 and
or 110:3 - 110:3 or 110:3 - 110:3 100:3 or 110:3
Operation - Simultaneous Separate Simultaneous separate
3rd secondary Accuracy class - - - 3P
Output - - - 75 50 100
2nd secondary Accuracy class - 0.5 or 1 3P 0.5 or 1
Output - 15 20 30 30 50 75 50 50 75 50 75 100 30 50 75
1st secondary Accuracy class 0.2 0.5 0.2 0.5 0.2 0.5 0.5
Output 30 40 50 75 100 150 15 20 30 30 50 75 25 40 50 50 75 100 30 50 75
For other characteristics, please consult us.

Dimensions
447 375
DE58043EN

4 holes 14 x 25 345
4 holes Ø13
320

403 393 280 220 185

25 max.

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 Outdoor voltage transformers Voltage transformers
(VTs) Phase-phase 7.2 to 24 kV
Type OVC2/S1 - OVC2/S2

Description
PE58462

Voltage transformer for phase-phase connection.

Characteristics
b Standard reference IEC 60044-2
b Standard primary voltage Upn: 3 - 3.3 - 6 - 6.6 - 10 - 11 - 15 - 20 - 22 - 24 kV
b Rated insulation level: 7.2 - 12 - 17.5 - 24 kV
b Rated secondary voltage Usn: 100 -100 or 110 -110 V
b Frequency 50 or 60 Hz
b Rated voltage factor: 1.2 ill.
b Thermal burden:
v OVC2/S1 = 500 VA
v OVC2/S2 = 250 ± 250 VA
b Creepage distance phase-ground > 700 mm
b Creepage distance phase-phase > 1400 mm
b Weight 33 kg.

Table of options
No. of secondaries for VT 1 2
Standard type OVC2/S1 OVC2/S2
Application Measuring or protection 1 for measure or
protection (1st sec.)
1 for protection (2nd sec.)
Standard secondary voltage (V) 100 or 110 100 - 100 or 110 - 110
Operation - Simultaneous
2nd secondary Accuracy class - 0.5 or 1 0.5 or 1
Output - 15 25 30 50 100
1st secondary Accuracy class 0.2 0.5 0.2 0.5
Output 25 50 50 75 100 15 25 30 50 100
Feasibility
For other characteristics, please consult us.

Dimensions
DE58044EN

375
4 holes 14 x 25 345
4 holes Ø13 320

475 280 220 185

436
109 53

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 Outdoor voltage transformers Voltage transformers
(VTs) Phase-phase 36 kV
Type OVC3/S1 - OVC3/S2

Description
PE50730

Voltage transformer for phase-phase connection.

Characteristics
b Standard reference IEC 60044-2
b Standard primary voltage Upn: 30 - 33 - 35 kV
b Rated insulation level: 36 kV
b Rated secondary voltage Usn: 100-100 or 110-110 V
b Frequency: 50 or 60 Hz
b Rated voltage factor: 1.2 ill.
b Thermal burden:
v OVC3/S1 500 VA
v OVC3/S2 250 ± 250 VA
b Creepage distance phase-ground > 900 mm
b Creepage distance phase-phase > 1560 mm
b Weight 43 kg.

Table of options
No. of secondaries for VT 1 2
Standard type OVC3/S1 OVC3/S2
Application Measuring or protection 1 for measure or
protection (1st sec.)
1 for protection (2nd sec.)
Standard secondary voltage (V) 100 or 110 100 - 110 or 110 - 110
Operation - Simultaneous
2nd secondary Accuracy class - 0.5 or 1 0.5 or 1
Output - 15 20 30 50 100
1st secondary Accuracy class 0.2 0.5 0.2 0.5
Output 25 50 50 75 100 15 20 30 50 100
Feasibility
For other characteristics, please consult us.

Dimensions
DE52799

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 Outdoor current and voltage Contents
transformers (CTs and VTs)

Ordering informations 32

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 Outdoor current and voltage Ordering informations
transformers (CTs and VTs) Current and voltage transformers

Order form Tick the appropriate box X and fill in these the needed value
: boxes for double primary voltage

Common characteristics
Type Quantity

Standard IEC ANSI AS

Frequency 50 Hz 60 Hz

Highest voltage for equipment (kV) 7.2 12 17.5 24 36

Number of secondaries 1 2 3

Rating plate language French English Spanish

CT’s specifications
Primary
Rated short time current (kA) (kA)

Rated primary current 1st rated (A) 2nd rated (A) 3rd rated (A)

Secondary
1st secondary 2nd secondary 3rd secondary

Protection Measure Protection Measure Protection Measure

Rated secondary current (A) (A) (A)

Rated output (VA) (VA) (VA)

Accuracy class

Security factor (FS) / accuracy limit factor (ALF) (FS / ALF) (FS / ALF) (FS / ALF)

VT’s specifications
Primary
Phase type Phase / ground Phase / phase

Rated primary voltage 1st rated (kV) 2nd rated (kV) 3rd rated (kV)

Secondary
1st secondary 2nd secondary 3rd secondary

Protection Measure Protection Measure Protection Measure

Rated secondary voltage (V) (V) (V)

Rated output (VA) (VA) (VA)

Accuracy class

Simultaneous operation

Separate operation

Options accessories
Routine test French English Spanish

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 Notes

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 Notes

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 ART47229 © Schneider Electric Industries SAS - All rights reserved

Schneider Electric Industries SAS

335, rue Joseph Monier As standards, specifications and designs change from time
CS 30323 to time, please ask for confirmation of the information given
F - 92506 Rueil Malmaison Cedex (France) in this publication.
10-31-1247
Tel.: +33 (0)1 41 29 70 00
RCS Nanterre 954 503 439 Design: Schneider Electric Industries SAS
Capital social 896 313 776 € Photos: Schneider Electric Industries SAS This document has been
www.schneider-electric.com Printed: Altavia Connexion - Made in France printed on recycled paper

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