Resistive Capacitive Voltage Divider ROF

Resistive capacitive voltage dividers type ROF (RC divider) are used in high-voltage networks within the 72.5-550 kV range. They divide the primary voltage into a standardised, equivalent secondary voltage for meters, measuring and protection devices.

RC divider

The active part of the RC divider consists of capacitive and parallel connected resistive dividing elements. The length of the active part extends along the entire insulator length, which results in linear voltage distribution. Both elements are calibrated to each other and provide accurate transient voltage signals from the high-voltage side to the low-voltage side. The RC divider enables very high frequency bandwidth; even direct voltages (DC) can be measured.

As the active part of the RC divider is hermetically sealed, an expansion bellow in the head section compensates volume changes of the oil due to temperature variations. The operating pressure will be visualised by monitoring unit.

For voltage levels of 300 kV and higher, field distortions are avoided by using a corona ring around the head of the divider.

The secondary elements, like adjustment and overvoltage protection components, are located in the terminal box together with the equivalent burden replications. The cover plate of the terminal box can be opened laterally. The connecting sockets for the measuring cables are located on the bottom side of the terminal box.

The connection of the secondary output voltage can either be implemented by analogue via a shielded measuring cable or optionally digital using a fibre optic cable. The RC dividers are factory calibrated and will be delivered with specified measuring cable.

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Features

  • Ferroresonance-free and no saturation effects
  • Secondary output can be operated under short-circuit or no-load conditions
  • AC and DC accuracy class ±0.1% @fR
  • Measurement of harmonics possible up to 1 MHz
  • Transient signals can be measured
  • Accuracy with harmonics up to 10 kHz of ±0.2

Highlights

Linear voltage distribution

  • The optimised arrangement of the resistive and capacitive elements across the entire insulator length results in excellent voltage distribution.
  • The RC divider shows a perfect performance under transient voltage stresses and under high pollution conditions.
  • The linear voltage distribution prevents the occurrence of external partial discharges.

High accuracy at frequencies up to 10kHz

  • The specially developed design of the active part with resistive and capacitive elements guarantees high measurement accuracy and stability up to the 200th harmonic of the rated system frequency.
  • At the same time, high accuracy and stability in voltage variation (linearity) is achieved, starting from lower voltages up to the overvoltage factor.

Simple measurement cable connection

  • The terminal box has connecting sockets on the bottom side. The measuring Cable can be easily connected without any opening of the terminal box.
  • In case additional measuring cable (transmission cable) is needed, the cable can be plugged into the next free available terminal socket. To do this, the prepared burden adaption must be switched off in the terminal box. The divider is still calibrated and ready for operation.

Specifications and Downloads

Technical Specifications

Dimensions

RC divider

Type ROF

 

72

123

145

170

245

362

420

550
Standard   IEC / IEEE
Highest voltage for equipment kV 72.5 123 145 170 245 362 420 550
Rated power-frequency withstand voltage kV 140 230 275 325 460 510 630 680
Rated lightning impulse withstand voltage kV 325 550 650 750 1050 1175 1425 1550
Frequency Hz 16.7 / 50 / 60
Accuracy class   0.1; 0.2; 0.5; 1.0; 3.0
Expanded frequency band Hz 15 - 10000
Burden   R or R//C
Burden range   ≥ 100 kΩ
Rated voltage factors   1.5 - 30 sec / 1.9 - 30 sec / 1.9 - 8 h

Type ROF

 

 

72

123

145

170

245

362

420

550
Height of unit* A mm 1306 1606 1806 2006 2606 3371 3771 4571
Height to primary terminal* B mm 1186 1486 1686 1886 2486 3491 3891 4691
Depth of unit including terminal box

C

mm

 725 725 725 725 725 725 851 851
Depth of unit base

D

mm

 500 500 500 500 500 500 650 650
Width of unit base

E

mm

 500 500 500 500 500 500 700 700
Distance between screw holes at base

F

mm

 450 450 450 450 450 450 600 600
Min. creepage distance*

 

mm

 1340 1340 1950 3080 3900 4394 8250 10230
Approximate weight*

 

kg

 220 220 230 285 295 300 830 800

 

*with standard composite silicone insulator, creepage distance 25 mm/kV

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