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Journal International Association on Electricity Generation, Transmission and Distribution
Year : 2022, Volume : 35, Issue : 1
First page : ( 3) Last page : ( 7)
Print ISSN : 2250-012X. Online ISSN : 2229-4449.

Case Study – Improving Reliability of Circuit Breaker by using Controlled Switching and Removing Pre Insertion Resistor (PIR)

Khanna Jivesh1, Singh Amandeep1, Kumar Rakesh1, Tyagi R.K.1

1Power Grid Corporation of India Limited, India

Online Published on 13 May, 2022.

Abstract

Over-voltages are produced during routine switching operations and unscheduled opening operations aimed at interrupting a short-circuit current in power systems. Switching On/Off of Transmission Lines by Circuit Breaker operation leads to generation of Switching Over-Voltages due to sudden change in configuration of electrical Transmission network. Over-Voltages during the closing operation are entirely random and may depend on the CB pole mechanical scatter and point of closing in the source voltage wave. Limiting these Switching Over-Voltages are extremely crucial especially in Transmission network with rated voltage of 400kV or above as Switching Impulse Withstand Voltage level in these High Voltage network may between 2.0 – 3.0 p.u. or even more. The switching over-voltages are more pronounced during the operation of long transmission lines due to the high capacitance of the very long lines.

In order to mitigate Switching Over-Voltages during Line Switching, most common technique is to provide Pre Insertion Resistors (PIRs) in Circuit Breakers. However, addition of this extra component i.e Pre Insertion Resistors impacts the overall reliability of Circuit Breakers due to problem arising in linkages/levers and subsequent stucking of Pre Insertion Resistors, SF6 Leakage through Pre Insertion Resistors joints etc. These issues associated with Pre Insertion Resistors have led to development of an alternative method that can be used for mitigating Switching Over-Voltages i.e. Controlled Switching of Transmission Lines using Controlled Switching Device (CSD). In this method, Mechanical Closing/Opening of Circuit Breakers are controlled to an optimal instant by introduction of a suitable time delay through an electronic device called as Controlled Switching Device (CSD). Benefits of Controlled Switching in Transmission Lines are more pronounced incase of re-closing than normal closing as trapped charges presence during re-closing may lead to very high switching over-voltages. In addition to Controlled Closing/Re-Closing, Controlled Opening of Transmission Line reduces the probability of forced outages of Circuit Breaker due to electrical failures as Controlled Opening eliminates risk of re-strikes.

Implementation of Controlled Switching technique for Transmission Line must take into account configuration of Transmission Line:

  • Uncompensated Transmission Line

  • Shunt Compensated Transmission Line

In this paper, a 400kV (340 km long) Transmission Line provided with shunt compensation was switched through both techniques i.e. Circuit Breaker with Pre Insertion Resistors & Controlled Switching Device and In-rush current & Over-Voltages observed during switching were measured. Results for both cases (switching with Pre Insertion Resistors & through CSD) are presented in this paper.

All the retro-fitments made in substation connecting aforesaid 400kV Line like Installation of Controlled Switching Device (CSD) to switch Line from one end, Installation of sensors to provide feedback of Line side Voltage to CSD etc are discussed in the paper. In addition to this, philosophy considered in Controlled Switching of Line to mitigate Switch Over-Voltages and Inrush current has also been highlighted in this paper. The long term objective of this exercise is to compare switching over voltages generated in long transmission using CSD & PIR.

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Keywords

CSD, PIR, CB.

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