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A Revolution in Circuit Breaker Operating Mechanism Technology 1
9 May, 2001
A Revolution in Circuit Breaker Operating Mechanism Technology
Michael A. Lane
ABB Switchgear AB
Ludvika, Sweden
Richard Thomas
ABB Switchgear AB
Ludvika, Sweden
Abstract: A brief review of current operating mechanism
technology, its benefits and limitations. Introduction of a new
type of operating mechanism (drive), for circuit breakers
rated 72.5 kV and above, using one moving part and fully
electronic control.
Keywords: operating mechanism, circuit breaker.
1 INTRODUCTION
Development of transmission circuit breakers is most often
described in terms of the evolution of interrupter
technologies and the insulating mediums they employ. The
1950s to 1970s were dominated by oil minimum and air-
blast designs. During the 1970s, SF
6
technology began to
supersede oil minimum and air-blast technologies. SF
6
gas
interrupters continued a trend of providing higher ratings per
interrupter and thus simplifying the primary system
construction of circuit breakers.
In the last twenty-five years, substantial progress has been
made in increasing reliability and reducing maintenance
requirements of SF
6
circuit breakers. The most successful
approaches in these respects have focussed on modular
designs reducing the number of components in the interrupter
(see also [1]). The majority of circuit breakers rated above
72.5 kV delivered today incorporate simple, reliable SF
6
interrupters.
In contrast to the major performance leaps made in
interrupter technologies, circuit breaker operating mechanism
(drive) designs have seen less dramatic development in core
functional performance during the past fifty years. Of course
there have been major differences in type of operating
principles applied (e.g. pneumatic, hydraulic and spring).
While there may appear to be a wide range of operating
principles for circuit breaker drives, they all share a common
basis in being highly mechanical designs and essentially all
performing the same core function of closing and opening the
circuit breaker.
Statistically seen, most major and minor circuit breaker
failures can be traced to the operating mechanism [2].
Modular designs, extended endurance testing and field
experience have all contributed to raising the performance
level circuit breaker drives. Nevertheless, ever-increasing
demands for power system availability require that equipment
availability be continually improved.
Currently, there is more focus on increasing the functionality
of power system apparatus to improve electrical power
quality and facilitate better system asset management.
Conventional mechanical drives are inherently limited in
their functional flexibility.
In order to transcend the limitations of conventional,
mechanically driven operating mechanisms, it is necessary to
look towards new solutions. Today, a new operating
mechanism technology, Motor Drive, has emerged. The new
technology, based on an electrical system design, exceeds the
benefits offered with conventional operating mechanisms
while at the same time overcoming previous limitations,
particularly with respect to significantly enhanced
functionality.
This paper briefly discusses the benefits and limitations of
conventional operating mechanisms and introduces the design
of operating mechanisms of tomorrow, Motor Drive.
2 CURRENT TECHNOLOGY
As outlined above, circuit breaker drives in use today are of
conventional, mechanical designs using spring, hydraulic or
pneumatic technology.
While a range of mechanical drive solutions exists,
essentially all designs address the same basic core functions
required for the operation of the circuit breaker. Five (5)
major core drive functions can be identified in regard to
comparing both the conventional, mechanical and new
electrical design solutions:
1.

Energy Transmission
2.

Energy Release
3.

Energy Storage / Buffering
4.

Energy Charging
5.

Control & Signaling.
The first four functions relate to the need to provide some
form of operating energy to move the circuit breaker
contacts. The variety of conventional drive designs largely
arises from different methods of addressing these first four
functions. As the circuit breaker forms an essential and
integral part of the overall power system control, there must
also be a reliable means of communication between the drive
and substation control and protection system.
The total system must be highly reliable in order to support
the core reliability of the circuit breaker.
2.1 Energy Transmission
This function relates to the means by which operating energy
is transmitted from the drive to the circuit breaker contact
system. The type of circuit breaker application (e.g. single or
three pole operation, live tank or dead tank interrupter
construction) can influence the method of transmission.
In general, energy transmission uses some form of
mechanical linkage system, coupled to the moving contacts
by way of an operating insulator. The design of such a system
is influenced by many factors, not the least of which is
definition of the required contact travel for the interrupter.
In respect to contact travel, mechanical design systems can be
inherently limited by their fixed dimensional nature. Once 2
9 May, 2001
implemented, a mechanical linkage system offers limited
flexibility in adapting to different stroke or speed
requirements of the interrupter. And, once contact travel is
initiated, it must be completed with conventional drives.
The way in which energy is transmitted in conventional
drives also tends towards mechanical impacts. That applies to
both the moving parts of the operating mechanism itself and
to impacts on the foundation. High impacts on moving
components of the operating mechanism cause wear over
time, high operating noise and also are directly linked to the
need for dampers on opening and/or closing operations.
2.2 Energy Release
This function is typically achieved in conventional drives by
means of latches or valves driven by electrical coils. Reliable
energy release is essential to correct circuit breaker function.
The essential nature of the circuit breaker tripping function
has given rise to a common convention of using two
redundant trip coils. Trip circuit supervision is another
indication of the importance placed on reliability of this
function.
2.3 Energy Storage / Buffering
This function has been a prime source of difference between
the variety of conventional, mechanical drives. The
mechanical nature of conventional drives has also been in
part driven by the historical desire to have a non-electrical
means of providing the energy to operate a high voltage
circuit breaker. This desire can arise from a perceived
concern of the problem of attempting to restore the high
voltage system during a total power outage.
The mechanical solution was also driven by the high
operating energies and short operating times required for
transmission circuit breakers, both of which necessitated use
of mechanical operating systems in line with available
technologies.
Today all major manufacturers can provide circuit breaker
with spring operating mechanisms in large part due to the
higher reliability and performance demonstrated by spring
storage systems.
An important consideration in energy storage design is
meeting the requirement for a high voltage circuit breaker to
operate a rapid auto-reclosing sequence. IEC [3] specifies a
minimum O-0.3s-CO-3min-CO sequence, while ANSI [4]
tends towards CO-15s-CO. The dimensioning of the energy
storage is also governed by the energy deemed necessary per
operation.
2.4 Energy Charging
The method of recharging the stored operating energy is
directly dependent on the type of energy storage.
Conventional drives use electric motors to drive the energy
charging system, either to directly tension springs or to drive
pumps for pneumatic or hydraulic systems. While the
operating times of these motors are relatively short, typically
10-20 seconds during each charging cycle, they tend to have
relatively high starting and running currents, ranging from 10
to as high as 90 amps per circuit breaker. These high
transient loads place considerable stress on substation
auxiliary supply systems (AC or DC) and are a major factor
in dimensioning of auxiliary supply circuitry within the
substation.
2.5 Control & Signaling
The control and signaling interface to transmission circuit
breakers has generally developed more consistently and
independently from the specific mechanical types of
conventional drives. This is in part due to the desire for
utilities to have consistency within the substation control and
protection system, irrespective of the type of circuit breaker
used in the substation. Also, a limited number of standard
control interface functions are used; trip and close coils,
energy charging, breaker status indication, dielectric
monitoring.
The independent development of substation automation from
primary high voltage equipment has also seen substation
automation much more rapidly adopt new