HIGH VOLTAGE PRODUCTS
Shunt reactor switching
High voltage circuit-breakers
Hitachi's circuit-breakers are well suited for
switching of shunt reactors and are type
tested for this switching duty according to
IEC 62271-110. Nevertheless, to reduce
stress on both the reactor and the circuitbreaker, safeguard their long service life and
minimize the probability of re-ignitions,
Hitachi highly recommends point-onwave switching of reactor circuit-breakers.
1. Introduction
Shunt reactors are used for reactive power management in power
systems. They are installed at substation level for reactive power
control and voltage regulation on main bus, and for reactive power
compensation on long transmission lines or cables. Sometimes
they are also connected on the tertiary winding of power transformers for the same purposes.
This paper explains the reactor switching duty for circuit-breaker
and the advantages of applying point-on-wave (POW) switching
for this application.
Recommendations are based on:
● IEC, IEEE, CIGRE standard and technical reports
● Technical aspects of reactor switching duty
2. Reactor switching duty for circuit-breakers
De-energization of a shunt reactor leads to voltage transients with
very short rise time and frequency in the range of several kHz.
Such transients are due to interaction between the inductance of
the reactor and the stray capacitance on the reactor side, post the
current interruption, and are generally not harmful [1].
Generally, the latest generation of circuit-breakers have very low
value chopping currents, thus the inductive current in each pole is
interrupted in the vicinity of a natural current zero. Moreover, this
may vary based on the specification and design of the reactor and
may create higher chopping current. Consequently, the transient
recovery voltage (TRV) across the contact gap will vary in magni-
2/4
HITACHI ENERGY | GENERAL TECHNICAL INFORMATION| SHUNT REACTOR SWITCHING
tude but it will have very short rise time and frequency in range of
several kHz. The fast-rising transients can lead to a breakdown of
the contact gap and, hence, reappearance of the current through
arcing as shown in Fig. 1. This happens in a very short time, less
than a quarter cycle post current interruption, and it is known as a
“re-ignition”. The re-ignition will lead to steep voltage transient with
high magnitude and frequency in the range of kilohertz, known as
“re-ignition overvoltage”, which may affect the dielectric integrity and
electrical lifetime of the circuit-breaker and/or the reactor [2], [3].
Dielectric strength
of circuit-breaker
(UDS)
Current
Steep voltage across
contact gap (UCB)
UCB > UDS
Re-ignition resulting into
another current loop
Source voltage
Fig. 1: Example of circuit-breaker re-ignition during reactor de-energization
3. Type testing and results
IEC standards [4], [5] define the type testing procedures for circuitbreakers intended for reactor switching duty. This test is mainly to
obtain the corresponding circuit-breaker characteristic parameters
such as chopping current and voltage withstand capability. With the
test circuit used, the results are most relevant for the specific nominal current magnitude and transient recovery voltage (TRV) shape
applied to the circuit-breaker.
For every installation, the TRV shape as well as the chopping current will differ based on the design, connection configuration and
specification of the reactor. It will also be impacted by the stray capacitances at site. Consequently, the stresses on the circuit-breaker
and the reactor will be different from that imposed during the type
testing. Therefore, it is challenging to anticipate the impact of these
variations on expected life cycle duration of the breaker or the reactor. To minimize this impact, IEC, IEEE and CIGRE study committees recommend application of point-on-wave (POW) switching [1],
[2], [3]. Alternatively, other methods such as surge arresters can be
used to suppress the TRV peak [6]. Nevertheless, the preferred solution needs to be evaluated for each installation [7].
for reducing the probability of re-ignitions and consequently re-ignition over-voltages by ensuring sufficient gap between arcing contacts at the time of current interruption when the TRV appears. This
is achieved by separating the arcing contacts well before the natural
current zero where the arc is expected to be quenched. The time
difference between contact separation and current interruption is
known as "arcing time”.
The range of arcing times that will minimize the probability of re-ignitions is known as "re-ignition free window" and is shown in Fig. 2
[1], [5]. It shall be derived for individual phases based on the circuitbreaker characteristics obtained from the type test, considering the
reactor specification and its connection configuration. This is well
explained in IEC and IEEE guidelines [2], [3].
An additional benefit of point-on-wave switching is minimizing the
asymmetry of inrush currents during reactor energization. With that,
the probability of protection mal-operation will be reduced. The mechanical and dielectric characteristics of the circuit-breaker as specified in [8] also need to be furnished for successful application of
point- on-wave switching.
4. Point-on-Wave switching of reactor breakers
Point-on-wave switching (controlled switching) is the technique of
controlling circuit-breaker operations to occur at a specified point on
the reference voltage in each phase. For reactor breakers, it is used
2GHV065591 en B Released Public (Original document) | Shunt reactor switching High voltage circuit-breakers
HITACHI ENERGY | GENERAL TECHNICAL INFORMATION | SHUNT REACTOR SWITCHING
Re-ignition free window
Dielectric strength
of circuit-breaker
TRV
Current
Source voltage
Minimum arcing time for
specific reactor configuration
Fig. 2: Re-ignition free window for point-on-wave controlled de-energizaiton of shunt reactor
5. References
[1] CIGRE TB 757: Guidelines and best practices for the commissioning and operation of controlled switching projects.
[2] IEC/TR 62271-306: High-voltage switchgear and controlgear Part 306: Guide to IEC 62271-100, IEC 62271-1 and other IEC standards related to alternating current circuit-breakers.
[3] IEEE Std C37.015™: IEEE Guide for the Application of Shunt
Reactor Switching.
[4] IEC 62271-100: High-voltage switchgear and controlgear - Part
100: Alternating-current circuit-breakers.
[5] IEC 62271-110: High-voltage switchgear and controlgear - Part
110: Inductive load switching.
[6] CIGRE TB 546: Protection, Monitoring and Control of Shunt Reactors.
[7] CIGRE Green Book: Switching Equipment. Springer, 2019.
[8] IEC/TR 62271-302: High-voltage switchgear and controlgear Part 302: Alternating current circuit-breakers with intentionally nonsimultaneous pole operation.
2GHV065591 en B Released Public (Original document) | Shunt reactor switching High voltage circuit-breakers
3/4
FACEBOOK.COM/HASHTAG/HITACHIENERGY
INSTAGRAM.COM/HITACHIENERGY
TWITTER.COM/HITACHIENERGY
YOUTUBE.COM/C/HITACHIENERGY
Hitachi Energy Switzerland AG
High Voltage Products
Brown Boveri Strasse 5
8050 Zurich / Switzerland
Hotline 24 hours service: hitachienergy.com/contact-us
e-mail: contact-us@hitachienergy.com
hitachienergy.com
ABB is a registered trademark of ABB Asea Brown Boveri Ltd.
Manufactured by/for a Hitachi Energy company.
© Hitachi Energy 2021 . All rights reserved.
Specifications subject to change without notice.
2GHV065591 en B Released Public (Original document) | Shunt reactor switching High voltage circuit-breakers
LINKEDIN.COM/COMPANY/HITACHIENERGY