Resistive Capacitive Voltage Transformers
For Power Quality Applications
Version 03 2012
Introduction:
Power quality has become a major concern for both, electricity providers and their
customers. Today‘s electrical equipment is far more sensitive than the electrical
devices of the past. Power disturbances results in customer dissatisfaction, load and
revenue losses.
To measure and determine the origin of the disturbances, an true and reliable image
of the voltage on the HV line is needed.
The Trench RC Voltage Transformers (Fig. 1) provides this image because of their
exceptional characteristics:
• Accurate over the range from DC up to more than 10 kHz!
• Bandwidth up to 2 MHz!
• Excellent transient characteristics.
• Available for voltage levels from 24kV up to 765kV.
Measurements at rated frequency:
RC Voltage Transformers cover all IEC and ANSI metering requirements: class 0.2
or lower.
RC Voltage Transformers can also be used for protection purposes, according IEC or
ANSI standards.
Harmonics measurements:
Conventional Voltage Transformers give a poor image of the harmonics on high
voltage networks (Fig. 2):
CVTs are tuned to resonate at system frequency: 50 or 60 Hz. The accuracy is
obtained on a narrow frequency band. The lowest frequency resonance appears at
around a few hundred Hz, therefore CVTs cannot be used for harmonic
measurements.
Inductive IVTs cannot be used for harmonic measurements in HV networks because
harmonic frequency resonances between winding inductances and stray
capacitances can cause large ratio and phase errors. The higher the voltage, the
lower the frequency resonances.
RC Voltage Transformers are linear from DC up to more than 10 kHz:
Harmonics can be measured with an accuracy better than 1% and a phase deviation
better than 1° over this frequency range.
Fig. 1: Electrical scheme of RC Voltage Transformers
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Fig. 2: Comparison of different 420 kV Voltage Transformers
Construction:
Trench has a long experience with capacitive dividers and capacitors for different
applications: CVTs and coupling capacitors for HV AC networks, dividers for DC
applications or test labs, energy storage capacitors or grading capacitors.
Our RCVTs are designed based on this long experience, assuring good performance
over the temperature range within the lifetime of the Voltage Transformer.
The resistors connected in parallel to the capacitors windings have been selected
after several tests to guarantee an extremely low resistance variation with time and
electrical stress and temperature .
The insulation system is made of oil / paper-polypropylene or of SF6 / polypropylene.
The insulators are made of porcelain or composite insulators.
Other features:
As RCVTs do not have any saturable cores, they cannot get into ferro-resonance.
The RCVTs are not affected by the discharge of the line: no risk for the unit.
Trapped charges:
RCVTs are not affected by the trapped charges phenomena, unlike CVTs and
capacitive dividers (please refer to IEC 60044-7, Annex B).
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Electrical and Mechanical Data:
Type
Highest
Rated
voltage for
power
equipment frequency
Um (kV) test voltage
Up (kV)
SIL
USIL (kV)
BIL
UBIL (kV)
Minimum
sparking
distance
(mm)
Standard
creepage
distance
(mm)
(1)
Net weight
(kg)
(2)
Height
(mm)
RCVT 72.5
72
140
-
325
630
1813
130
900
RCVT 123
123
230
-
550
1000
3075
165
1270
RCVT 145
145
275
-
650
1200
3625
190
1470
RCVT 170
170
325
-
750
1400
4250
210
1670
RCVT 245
245
460
-
1050
2000
6125
255
2440
RCVT 300
300
460
850
1050
2000
7500
260
2440
RCVT 362
362
570
950
1175
2400
9050
310
2880
RCVT 420
420
630
1050
1425
3200
10600
405
3720
RCVT 525
525
680
1175
1550
3800
13750
450
4255
(1): other values available on request
(2): for oil / paper-polypropylene insulated units with porcelain insulator
Please contact us for more information:
Trench France SAS
16, rue du Général Cassagnou
B.P. 80070
F-68302 Saint Louis Cedex, France
Phone + 33 3 89 70 23 23
Fax
+ 33 3 89 67 26 63
E-Mail sales@trench-tsf.com
Product Manager RCVT:
Christian Weber
Phone + 33 3 89 70 35 94
E-Mail weber@trench-group.com
Version 03 2012
www.trenchgroup.com