Brief Travel Around Transient Recovery Voltage

The Transient Phenomenon

Imagine a fault occurs in the transmission line. In this way, the relay sends a signal to open the circuit breaker. At this moment,?the arc extinction occurs when the current reaches zero.?The system responds with the formation of a voltage between the circuit breaker terminals, known as Transient Recovery Voltage, TRV.?

"Transient Recovery Voltage is a voltage difference measurement between each circuit breaker contact and ground."

Follows TRV curves, [1]:

TRV values depend on the system impedance seen from the breaker terminals, the rated system voltage, the load, the fault type, location, and grounding. During TRV studies, the period of interest in the analysis is around 1 to 2 ms.

The Important Keywords: TRV and RRRV

Two parameters are important in the TRV analysis: TRV Peak Values and Rate of Rise of Recovery Voltage (RRRV). Both must be evaluated in the TRV study. The figure below shows these main parameters [2].

The steps that characterize the fault interruption?are:

1st Step: In the first moments of the current interruption (circuit breaker contacts very close to each other), cooling of the interior of the circuit breaker chamber must be faster than the RRRV. If this doesn't happen, you may have a re-strike.

2nd Step: When the circuit breaker contacts are very open, the temperatures inside the chamber are already lower, and there is no longer the risk of thermal re-ignition. TRV peak values cannot be greater than the dielectric withstand.

Verification circuit breaker withstands, consists of comparing the TRV waves obtained from the simulation with the normalized envelope curve, which can be described by two or four parameters. The objective is to verify the overcoming of two characteristics: the Rate of Rise of Recovery Voltage (RRRV - kV/μs) and the TRV peak value (kV).

The standard currently used in TRV studies in Brazil is IEC 62271-100:2021 - High-voltage switchgear and controlgear - Part 100: Alternating-current circuit-breakers.

Electric Power System faults (TRV Analysis)

In the study of TRV it is important to evaluate some fault conditions applied in the electrical power system. The following conditions must be considered in these studies: A. Terminal fault (bus), B. Terminal (line) fault, C. Kilometric fault.

These fault conditions TRV helps engineers to identify the worsts system conditions imposed by the TRV. In the development of the TRV study, TRV peak values and RRRV must be observed and compared to the normalized values, to conclude if the circuit breaker specify is appropriate to the electric power system.

That's all folks!

Transient Recovery Voltage (TRV) is one of the most interesting transient phenomena that occur in the electrical power system. It's indispensable to understand the basic definitions of these transient. That is essential, to help analyze simulation results obtained in simulations.

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About the Author:?Electrical engineer from the Federal University of Itajubá. He has a master's degree in electrical engineering, with an emphasis on electrical power systems. Member of the International Council on Large Electric Systems, Cigre. He has experience in studies of electromagnetic transients in electrical power systems using software (ATPDraw, MATLAB). Teacher and researcher, he loves to teach and share his job's experiences. He is currently an electrical engineer at ProNext Engenharia.?

References

[1] Smeets, R. P., & Belda, N. A. (2021). High‐voltage direct current fault current interruption: A technology review. High Voltage, 6(2), 171-192.

[2] Manitoba-HVDC Research Centre. "Webinar Transient Recovery Voltage (TRV) Study. - PSCAD"

[3] ONS, Diretrizes para a Elabora??o de Projetos Básicos para Empreendimentos de Transmiss?o – Estudos Elétricos, Especifica??o das Instala??es, de Equipamentos e de Linhas de Transmiss?o. Operador Nacional do Sistema Elétrico , 2013.