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A case study on Capacitive Voltage Transformer (CVT) behaviour on multiple earthing of CVT secondary circuit in a 400 kV Transmission line.

Published: 21 April 2022 Publication History

Abstract

The neutral point of secondary circuits of Instrument transformers e.g., Capacitive Voltage Transformer and Current Transformer (CVT & CT) must be earthed, IEEE emphasises that the secondary of instrument transformer must be grounded to protect the connected equipment and to ensure safety of working personnel. It recommends grounding of all in-service secondary circuits at the first point of its application (for CVT, typically a relay or meter) to counter the rise in electrostatic potential in secondary circuit due to stray capacitance. On the contrary, if the secondary neutral point of CVT has multiple earthing, the output voltage is not a replication of primary voltage during fault. This leads to mal-operation or non-operation of protection relays. As no discrepancy in secondary voltages is sensed by relays during normal operation, hence multiple earthing remains unnoticed and thereby compromising the integrity of relay operation. In this case study the behaviour of CVT having multiple neutral earthing has been illustrated, based on the site experience along with disturbance records and relay data. This paper, based on field data and vectorial mathematical analytics establishes the causes of distortions in the CVT secondary voltages due to multiple earthing on its neutral, causing maloperation of protection/relay. Study conclusively brings out correlation between CVT secondary magnitude, phase angle and harmonic generation and suggests formulation of a suitable algorithm/logic in Intelligent electronics device (IEDs)/relay for automatic identification of problem. There is a global trend of automation in the Power system to improve reliability and security. Automatic identification of multiple earthing as illustrated in this paper is a step toward the assimilation of automation in the power system that helps in timely rectification of faults that otherwise cause maloperations or outage of important elements.

References

[1]
IEEE C57.13.3-2014, IEEE Guide for grounding of instrument transformer secondary circuit and cases,
[2]
IS 4146 – Application guide for a voltage transformer
[3]
Helmut Ungrad, Wilibald Winkler, Andrzej Wiszniewski-Protection Techniques in Electrical Energy systems (Marcel Dekker Inc, New York).
[4]
IS 3156 (Part III) – Protective voltage transformer
[5]
IEEE 367-2012, IEEE Recommended Practice for determining the electrical power station ground potential rise and induced voltage from a power fault, 2012

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EEET 2021: 2021 4th International Conference on Electronics and Electrical Engineering Technology
December 2021
290 pages
ISBN:9781450385169
DOI:10.1145/3508297
Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from [email protected]

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Association for Computing Machinery

New York, NY, United States

Publication History

Published: 21 April 2022

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Author Tags

  1. CVT
  2. Ground potential rise
  3. Harmonics
  4. Multiple earthing
  5. Phase shift
  6. Relay under reach
  7. zero sequence

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