Application of DC shunt in high voltage DC transmission system

Author： GOZ Electric Time：2014-05-04 09:31:12 Read：13

In order to ensure that the high-voltage DC transmission system has reliable regulation and protection functions, there must first be available and reliable system data, so a complete measurement system should be set up at the converter station. Although the traditional DC measurement system has mature manufacturing technology and rich operating experience, the measured signal is susceptible to interference, the measurement accuracy is not high, and the measurement range is limited. Therefore, in actual engineering applications, photoelectric current transformers and voltage transformers are used, which can better meet the requirements of ultra-high voltage DC transmission projects.

DC shunt

1 Overview

The biggest advantages of photoelectric DC shunts compared to traditional electromagnetic transformers are: the diameter of the ground insulation pillar is small and the electronic circuit is simpler. This has significant advantages in reducing flashover faults and electromagnetic interference, and can reduce the cost. However, the response speed of photoelectric shunts is currently not as fast as that of traditional electromagnetic current transformers.

2 Working principle

A DC shunt is connected in series in the high-voltage DC circuit, the current value flowing through the shunt is measured, and then the current is converted into a digital quantity, which is transmitted through optical fiber and used as electrical isolation to transmit the digital quantity to the corresponding control or protection.

  The high-voltage primary part and the low-voltage secondary part are connected by two optical fibers. One optical fiber transmits data, and the other optical fiber transmits the energy emitted by the laser diode of the low-voltage power supply to the high-voltage primary part. After passing through the power converter, it serves as the electronic circuit of the high-voltage primary part. power supply. The structural block diagram of the photoelectric DC voltage divider measurement device mainly consists of: signal acquisition unit, photoelectric conversion module, optical fiber loop and optical receiving module. The following mainly introduces the hybrid optical fiber DC current measurement system.

basic structure:

1) Tubular box

The entire integrated optical DC measurement system, including the detector (shunt, Rogowski coil) and sensor head, is housed in a tubular box. The system is equipped with corona rings to control the electromagnetic field in the box and synthetic insulator armature. There is also a sun shield to prevent sunlight from overheating the measuring system. Note that the diverter of the tubular box is only fixed with soft copper strips, and the diverter must not be dragged to prevent it from sliding out of the box and damaging the copper strips.

As shown, a DC shunt works as follows:

1) Signal acquisition unit. It is a Rogowski coil that samples the current value in the DC loop. This section is located in the high voltage section of the device.

2) Photoelectric conversion module. Realize the analog-to-digital conversion of the measured signal and the transmission of data. The electronic components in the photoelectric conversion module are

A separate power supply is provided through optical fiber from the optical power source located in the control protection panel cabinet. This part is also located in the high voltage part of the unit.

3) Optical fiber loop. There are two signal transmission optical fibers that transmit data and energy respectively.

4) Optical receiving module. This part is located in the control protection panel cabinet and is used to receive digital signals transmitted by optical fiber and send them to the corresponding control and protection device through the inspection and control of the processor chip in the module.

  in conclusion

1) The DC shunt adopts optical measurement principles and closed-loop control technology to avoid electromagnetic interference and improve the reliability, measurement accuracy and range of DC current measurement;

2) The DC shunt uses optical materials to isolate primary and secondary equipment, which effectively reduces insulation costs and improves the reliability of equipment operation.