SCIENCE CHINA
Technological Sciences
• RESEARCH PAPER •
January 2011 Vol.54 No.1: 116–125
doi: 10.1007/s11431-010-4154-6
Hydraulic operating mechanisms for high voltage circuit breakers:
Progress evolution and future trends
LIU Wei1, XU Bing1*, YANG HuaYong1, ZHAO HongFei2 & WU JunHui2
1
State Key Laboratory of Fluid Power Transmission and Control, Zhejiang University, Hangzhou 310027, China;
2
Henan Pinggao Electric Co., Ltd, Pingdingshan 467001, China
Received April 26, 2010; accepted September 13, 2010
High voltage circuit breakers are the most important protection and control apparatus in power system. As a core part of circuit
breakers, the operating mechanisms have a trend to be hydraulic-style in high voltage power grid. Compared with other hydraulic systems, the hydraulic operating mechanisms have the characteristics of high hydraulic pressure, high speed, high
power and long-term waiting etc., and it is because of the characteristics that the hydraulic operating mechanisms become difficult to be developed and have been arousing significant study interest from more and more researchers as well as their promising applications. Therefore, it is significant to summarize the hydraulic operating mechanisms on their development, characteristics, and key technologies etc. In this review, the evolution process and recent studies of hydraulic operating mechanisms
at home and abroad are viewed. The review then focuses on the characteristics and key technologies of hydraulic operating
mechanisms, especially on time and velocity characteristics, high-speed cylinder cushioning, fast response and great flow rate
control valve, temperature compensation, system monitoring and fault diagnosis, intelligent operation, energy storage module,
etc. In the end, the future trends of this field are presented.
hydraulic operating mechanism, high voltage circuit breaker, control valve, opening and closing motion, cushioning
Citation:
1
Liu W, Xu B, Yang H Y, et al. Hydraulic operating mechanisms for high voltage circuit breakers: Progress evolution and future trends. Sci China
Tech Sci, 2011, 54: 116−125, doi: 10.1007/s11431-010-4154-6
Introduction
With the development of society and the expansion on scale
of power grids, the safe operation becomes more and more
important for electric power system. Therefore, there is
higher demand for the performance of high voltage circuit
breakers that play an important role in protection and control in electric power system. As the normal opening and
closing motion of the circuit breakers depends on the operating mechanism, its working capability and quality are
very important for the performance and reliability of high
voltage circuit breakers. As a key part of circuit breakers,
*Corresponding author (email: bxu@zju.edu.cn)
© Science China Press and Springer-Verlag Berlin Heidelberg 2011
the operating mechanisms have kinds of types, such as
spring mechanisms, magnetic mechanisms, pneumatic
mechanisms, motor drive mechanisms. Compared with
other mechanisms, the hydraulic operating mechanisms are
widely used in the field of higher-level voltage circuit
breakers based on their advantages of less component quantity, higher reliability, much more stable output performance and larger power.
With the rapid development of economy and increasing
demand for power, the focus of State Grid is on the project
of transmitting power from the west to the east, exchanging
power between the north and the south, and connecting
grids in the whole China. A strategy is proposed to improve
the rank of power transmission voltage and strengthen the
transmission and transformation of 750 kV power grid in
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Liu W, et al.
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northwest China to build a stronger power grid. Meanwhile,
the technologies concerning 1100 kV ultrahigh voltage are
becoming the focus in the field of transmission and transformation in China. All of these provide good opportunities
for the development of power transmission and distribution
of secondary equipment industry, especially for circuit
breakers and hydraulic operating mechanisms. It is clear that
enhancing the performance of hydraulic operating mechanisms for circuit breakers is extremely urgent. Therefore, the
review has guiding significance to accelerate the development of hydraulic operating mechanisms technology in China
through the overview of technology evolvement and characteristics of hydraulic operating mechanisms at home and
abroad.
2 Development of hydraulic operating mechanisms
The development of hydraulic operating mechanisms can be
traced back to operating mechanisms of 420 kV gas circuit
breakers manufactured by Dalle in France before World
War II, which is shown in Figure 1. Although it is limited to
the role of signal transmission [1–3], it is the first time that
a hydraulic drive was applied to high voltage circuit
breaker.
Until the 1950s, the first hydraulic operating mechanism
was invented by Perri to be used in monopole high voltage
circuit breakers of 230 kV, as shown in Figure 2. The conventional free tripping device, bladder accumulator and
single stage spool valve were used, and the response time of
the spool valve was about 0.9 alternating current cycles
[3–5].
In the 1960s, the ETNA company provided Dalle company in France with a variety of hydraulic operating mechanisms for circuit breakers, e.g. series OP, of which the
OP2B and OP2A are the instantaneous-pressure type and
the rest are constant-pressure type. Moreover, hydraulic
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operating mechanisms were applied to FA-type SF6 circuit
breakers of MG company in France [4–7].
From the mid 1960s, with the development of the SF6
circuit breakers of single-pressure puffer, the requirement
for operation power became much higher. In order to increase the capacity and shorten the opening time, hydraulic
operating mechanisms were developed in Japan, such as the
SHF series of high voltage circuit breakers, OH-type of
hydraulic operating mechanisms manufactured by Mitsubishi Company [6, 7]. Hydraulic mechanisms were also used
instead of pneumatic mechanisms in Kawasaki Company.
Therefore, single-pressure puffer type SF6 circuit breakers
were developed in the field of higher-level voltage power
grid.
As the schematic diagram shown in Figure 3, hydraulic
mechanisms for the puffer circuit breakers were developed
by Toshiba Company in the 1980s using three-stage valve
and double-acting single piston rod cylinder in the mechanisms. Closing valve spool and opening valve spool were
separately put on the second stage valve seat, which made
the oil-drain channel more smooth and manufacture more
easily. Closing operation must be carried out after the
Figure 2 A hydraulic mechanism invented by Perri.
Figure 1 Schematic diagram of oil-air control system.
Figure 3
A hydraulic operating mechanism of Toshiba in the1980s.
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completion of opening operation due to the self-locking
valve. The notable feature of the hydraulic mechanisms,
which reduces the pipeline and increases reliability, is high
integration of three-stage valves.
BBC Company developed the hydraulic mechanisms for
ELK-type of circuit breakers in 1974, whose schematic diagram could be described in Figure 4. The three-stage valve,
double first stage opening valves to enhance reliability, and
the accumulator with a balance piston structure were used in
the mechanisms.
An anti-slow opening operation subunit, which was controlled by a pressure switch, was located in the contact directly but not in the valve block. It is an important characteristic that the hydraulic mechanism is of high integration
of all cylinders, valves, accumulator and tank.
ABB developed a unique style of AHMA and HMB-type
hydraulic spring mechanisms in the 1980s. Until now, ABB
is also committed to improving the hydraulic spring mechanisms and developing new generation products.
In recent years, a new generation of HMB-4/8 type of
hydraulic spring mechanisms was developed, as shown in
Figure 5. The hydraulic spring operating mechanisms fulfill
Figure 4 A hydraulic mechanism of BBC’s ELK circuit breaker.
Figure 5 A hydraulic operating mechanism of Type HMB-4/8.
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all demands placed on a modern high voltage circuit breaker
with the advantages of mechanical energy storage, longterm stability, temperature independence of the energy
storage device, wear-free cylinder-piston unit for power
transmission, integrated and wear-free hydraulic damping,
no pipe unions in the hydraulic system, no oil leakage etc.
They make full use of advantages of high adaptability to
different power mechanisms and various advantages of disc
spring energy storage for creating the maintenance-free
conditions. At present, the mechanism, which is not only
equipped for ABB products but also for some products in
China, occupies a large market share.
From the early 1960s, Shanghai Huatong Switch Factory
developed the first domestic hydraulic mechanism of CY1type of bi-directional instantaneous pressure. Because of
many leakages due to complicated structure and manufacturing difficulty for high-voltage insulated pipe, CY1-type
of hydraulic mechanisms withdrew from the market gradually. Thereafter, hydraulic mechanisms of instantaneous
pressure type CY2 with non-storage module and constant
pressure type CY3 to type CY6 have been developed successively. As shown in Figure 6, it is a sketch map of the
hydraulic mechanisms of type CY3. It could be observed
that there are hybrid drive with hydraulic and linkage rod,
less components and simple structure with opening and
closing valves, but the potential danger action of “slow
opening motion” seriously affected the reliability of the
system [8–11].
Further development of high-level voltage hydraulic operating mechanisms has been achieved in China in the last
few years. As shown in Figure 7, it is a hydraulic operating
mechanism for a 220 kV circuit breaker developed by Pingao Electric Co. Ltd. Its operating performance has
achieved the same level of foreign products with simple
structure of control valves, improved system integration and
good reliability compared with the previous products.
To improve the technology of high voltage apparatus and
meet the demand of electric power industry with the forward development of economy, high voltage switchgear
companies imported advanced technology of circuit breakers from MG, Mitsubishi, Hitachi, Toshiba, ABB etc. With
the assimilation of the imported technology, the manufac-
Figure 6 A hydraulic operating mechanism of CY3 type.
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Figure 7 A hydraulic operating mechanism of a 220 kV circuit breaker. 1,
Oil tank; 2, motor; 3, oil switch; 4, work cylinder; 5, auxiliary switch; 6,
pressure meter; 7, accumulator; 8, signal cylinder; 9, control valve; 10,
opening solenoid; 11, closing solenoid.
turing engineering of hydraulic operating mechanisms for
circuit breakers would be developed and improved to a
great extent.
According to the development of worldwide high voltage
circuit breakers, hydraulic operating mechanisms have been
applied widely due to their advantages of high output power,
fast response, high compatibility of load characteristic and
high reliability [2], and the process of development could be
summarized as follows:
(1) As the previous hydraulic operating mechanisms followed the hydraulic principle of machine tool, later hydraulic and mechanical hybrid drives were adopted during
opening and closing motion. Thereafter, hydraulic mechanisms of instantaneous-pressure type, which were shown in
Figure 8(a), were developed, but they gradually withdrew
from the market due to complex structure, low response etc.
Hydraulic mechanisms of constant-pressure type with simple structure are popularized at home and abroad nowadays,
which are shown in Figure 8(b).
(2) The present structures of three typical hydraulic
Figure 8 Schematic diagrams of hydraulic operating mechanisms. (a)
Instantaneous-pressure type; (b) constant-pressure type.
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operating mechanisms are shown in Figure 9. Hydraulic
operating mechanisms are progressing in the process of
“simple-complex-simple” structure.
From the structures of pipe connection between valve
and valve, valve and cylinder, the hydraulic operating
mechanisms were developed to that of the integrated valve
block previously. Lastly, with the simplification of the
structure of interrupter and mechanisms, the full integration
of valves, cylinders and accumulators is developed and
widely applied to hydraulic operating mechanisms.
(3) Original bladder accumulators were replaced by piston accumulators in storage module entirely. Disc springs
are applied to hydraulic spring mechanisms only produced
by ABB that induce the advantages of long-term stability,
temperature independence and no gas leakage.
(4) The principle of hydraulic operating mechanisms of
constant-pressure type is followed, as shown in Figure 10.
Two-stage valves are used in the mechanisms under the
rank of 220 kV circuit breakers, as shown in Figure 10(a).
As shown in Figures 10(b) and 10(c), three-stage valves are
Figure 9 Structures of hydraulic operating mechanisms. (a) Hydraulic
spring type; (b) horizontal arrangement; (c) vertical arrangement.
Figure 10 Schematic diagrams of hydraulic operating mechanisms. 1, Oil
tank; 2, filter; 3, motor; 4, pump; 5, check valve; 6, accumulator; 7, relief
valve; 8, 8.1, 8.2, cylinders; 9.1, 9.2, 10, 10.1, 10.2, 11, 11.1, 11.2 main valves.
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used in the mechanisms over the rank of 550 kV circuit
breakers. However, compared with Figure 10(b), two thirdvalves for opening and closing are adopted in Figure 10(c).
Though all the systems used the differential cylinder, there
is little difference in control valve and its layout. As shown
in Figure 10(d), auxiliary cylinders are added in 1000 kV
circuit breakers to meet the large power demand during
opening and closing motion.
(5) Figure 11 shows three basic structures of the main
valve, and it can be seen that 2-position 3-way valves are
mainly used in hydraulic operating mechanisms. Switch of
opening and closing motion is realized through pressure
relief and charge of control chamber. The main valve is
conical sealing valve to maintain opening or closing position. Figures 11(a) and 11(b) are spool valve throttling area
and Figure 11(c) is poppet valve throttling area.
3
Figure 11
Structures of the main valve.
Key technologies and the status & trends
3.1 Matching characteristics of time & velocity during
opening and closing motion
Opening & closing time and velocity, which vary with different types of circuit breakers, are important characteristic
parameters to evaluate the performance of hydraulic mechanisms for circuit breakers. It is very beneficial to prolonging
circuit breaker’s lifetime and enforcing performance of
breaking abnormal currents that shorten opening time and
increase opening velocity. The required opening time is
about one alternating current cycle. The comparisons of
simulation and experiment results about displacement characteristics of a hydraulic mechanism for a 550 kV high voltage circuit breaker are described in Figures 12 and 13 during
opening and closing motion.
It can be obtained that the simulation results are in accordance with the experiment results. Opening and closing time
corresponding to opening point and closing point separately,
as well as opening and closing velocity of the average velocity in 10 ms are the key technical parameters of hydraulic
mechanisms performance evaluation [7, 12–16].
As shown in Figure 14, owing to the coupling relationship between hydraulic operating mechanisms and interrupters, the opening and closing velocity should be improved and the opening and closing time should be reduced
to achieve a good interrupter performance. However, high
opening and closing velocity will challenge great energy
cushioning and then affect the reliability of the system.
Analysis of coupling relationship between hydraulic operating mechanisms and interrupters, and optimization of
velocity and time characteristics during opening and closing motion are the core design technologies of hydraulic
mechanisms.
At present, the study on opening and closing characteristics of SF6 high voltage circuit breakers is more concentrated on the electric field and gas flow field distribution in
Figure 12
Displacement of hydraulic cylinder (opening motion).
Figure 13
Displacement of hydraulic cylinder (closing motion).
Figure 14 Coupling relationship between hydraulic operating mechanisms and interrupter.
interrupter with given output pressure and velocity of mechanisms or in the performance of hydraulic mechanisms with
given constant load. However, the research is less considering the coupling relationship between hydraulic operating
mechanisms and interrupter.
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Liverpool University and Menoufiya University have
done a lot of research on gas pressure characteristics in
interrupters with a given constant hydraulic force [17]. In
the 1990s, Ding from Zhejiang University, China studied
the characteristics of velocity and time influenced by
structural parameters of hydraulic mechanisms during
opening and closing motion with the assumed load force of
interrupter [4].
With emphasis on the internal gas pressure properties
and flow-controlled studies in the interrupter chamber
[18–20], Wang from Shenyang University of Technology,
China established co-simulation model of a 252 kV circuit
breaker hydraulic mechanism and the interrupter. However,
it is difficult to make the detailed analysis on the characteristics of valves, cylinders and pipeline due to too much simplified model of the hydraulic mechanism.
Xu from Zhejiang University established integrated
simulation model with a hydraulic system, linkage and nonelectrical load interrupter. Static and dynamic characteristics of hydraulic components have been verified experimentally and analyzed in detail. It focused on opening &
closing time and velocity influenced by various structure
parameters [12–16].
3.2
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Figure 15 Structure of cushion piston (opening motion). 1, Cylinder; 2,
cushion piston; 3, sidestep-shape plunger; 4, cushion cover.
High-speed cylinder cushioning
The maximal cylinder velocity of hydraulic operating
mechanisms is normally up to 10 m/s. Efficient cushioning
with about 2–3 times as high as the system pressure is quite
necessary to reduce the rate of travel of a cylinder before
the piston strikes the end cover and to improve reliability
and working life of the system. Reducing the velocity of
piston at the end of its travel lowers the stresses on the cylinder while reducing vibration in the structure of mechanisms [21–23].
With integrated hydraulic end position, structures of inside-cylinder cushioning are almost adopted in circuit
breakers due to their simple structure, small size and nonaddition on any flow control valves and other components.
Sidestep-shape plunger structure produced by ABB is used
in hydraulic spring mechanisms. With 2.5 times as high as
the system pressure, the peak value of the damping pressure
near the hydraulic end position is up to 1400 bar during
operation. As shown in Figure 15, it is a sidestep-shape
plunger with 7 steps for a domestic mechanism of a 550 kV
circuit breaker. Under the condition of the peak pressure
being 2.1 times as high as the system pressure, the comparisons of simulation and experiment results about pressure in cushion chamber during opening motion are shown
in Figure 16 [15, 16].
The terminal velocity needs to be as low as possible
while reducing the peak pressure for efficient cushioning.
As shown in Figure 17, cushioning structure should be optimized [15, 16] when the impact is large with a terminal
velocity up to 1 m/s.
Figure 16
Figure 17
Pressure in cushion chamber (opening motion).
Pressure and velocity-displacement characteristics.
It is of great importance to control the peak pressure and
the terminal velocity for cushioning design. The method for
simulation and optimized design is mostly adopted based on
high cost and long cycle via abundant experiments. As a
result of the complicated and changeful flow field in the
process of cushioning, how to build a precision model, especially to determine and build a model at the throttling
state of a turning point, is a difficult research for cushioning
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technology.
Ding from Zhejiang University has carried out an investigation on different inside-cylinder cushioning structures, such
as the column-shape, taper-shape, parabola-shape, sidestepshape plunger pistons, especially on modeling and analyzing
with the principle of equal flow at different throttling stages of
a turning point [4]. However, Wu et al. pointed out that the
Reynolds number can be used for determining throttling
stages of a turning point for modeling [15].
In an Integrated Project financed by the European Commission, Roquet Company performed simulations on cushioning Bond-graph and carried out many experimental cushioning tests in 3 different types of cushioning, such as
piston grooves, metallic ring, conic cushioning. Cylinders
were tested in the cushioning testing bench with monitoring
the displacement, speed and pressure within both chambers.
Cantelli from Roquet Company, Spain investigated that the
cushioning could be improved by adding a second metallic
ring, and varying the number of grooves and its depth, as
well as the geometry and the piston length etc. [24].
In cooperation with the Politecnico University in Turin,
Atos carried out a significant research on the design and the
optimization of the technical constructive geometries, related to the inside components of its cylinders and the introduction of new materials along with the specific treatments. The work was to enable the improvement in the
softness of cushioning and lengthen working life of cylinders in heavy-duty applications. The new developed cushions have shown better progressing in the pressure “flowing” to the cushioning chamber during the cushion initiation
phase with granting a greater constancy in such action all
along its length. At the same time, external cushioning
method and innovative structural design are important research fields.
3.3
Fast response and great flow rate control valve
Fast response and 2-position 3-way valves with great flow
rate are almost used in hydraulic operating mechanisms, of
which switch time is about 8–10 ms and instantaneous flow
rate needs to be up to 2000 L/min. One of the key technologies for hydraulic operating mechanisms is to improve the
response performance and flow passage capacity [25–28].
By now, there are no applications of this kind of products
in China. Therefore, domestic hydraulic mechanism manufacturers mainly import this kind of products from hydraulic
companies such as Bucher and Hawe. Reducing influence
of flow force, optimizing the matching relationship of pressure and flow between each stage valve, and improving the
response performance of electromagnetic actuator are important to the study of control valves.
The response time is a primary characteristic for the circuit breaker control. Usually, on/off solenoids are used for
their activation. The displacement characteristics of each
stage valve and cylinder are shown in Figure 18. As one of
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Figure 18
Displacement of valves and cylinder (opening motion).
the important components influencing the response characteristic of valve [12–14], the response time of solenoid is
about 6 ms. Developing a new type actuator is an important
study aspect on further study of high-speed on/off solenoid.
The use of piezoelectric system is an alternative way to
improve the response time. The piezoelectric actuator has a
great potential to be applied to hydraulic operating mechanisms for its advantages of fast response (up to GHz) and
high output force (kN), and it has been applied to control
valves of hydraulic operating mechanisms produced by
ETNA industry, which shortened response time to 1 ms or
even less [28]. Though the application of piezoelectric actuator is widely studied, it is still a great challenge because
its performance stability is greatly affected by temperature,
especially when the hydraulic mechanisms work in hard
environment with large temperature variation.
3.4 Performance stability and temperature compensation
Stability quality is greatly affected by the ambient temperature that is usually from −50°C to +50°C in hydraulic operating mechanisms. Heating device is usually applied to keep
temperature in a certain range at present, but the study in the
aspects of relationships between velocity and temperature,
temperature control range and compensated method has
been seldom reported.
Little research has been conducted in cryogenic tests investigation due to its high cost. The intention of the research
at IFAS in cooperation with ABB is the accomplishment of
cryogenic tests. It will be determined whether the drives are
capable of performing reliable switching operations in extreme climatic conditions. Function tests and endurance
switching operations at temperatures down to −35°C were
performed. Thereby, the performance of the drive changed
with temperature was observed [12].
Zhejiang University has been involved in studying the
velocity characteristic influenced by temperature-induced
variations in the viscosity of the hydraulic fluid. The heating
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range of the compensation for the change of such characteristic with temperature has been put forward, as shown in
Figure 19 [12–14]. Xi’an Jiaotong University has studied
the opening velocity influenced by ambient temperature, as
shown in Figure 20, and presented a compensation method
of regulating throttling orifice in hydraulic circuit [23, 29].
To confirm that proper opening and closing performance
is maintained at extreme temperatures, the circuit breaker
produced by Mitsubishi was placed in a large environment
controlled testing room and operated at temperature from
−30°C to +60°C. The study showed that the change in
opening time was negligible. The delay time of the contact
separation in the opening operation of the resistance interrupter remained within the stable range of 32–33 ms, confirming that the hydraulic delay circuitry was sufficiently
immune to temperature-induced variations in the viscosity
of the hydraulic fluid of this produce [30].
3.5
System monitoring and fault diagnosis
The reliability of circuit breakers is an important characteristic to evaluate the performance of the electric system, so it
is necessary to carry out monitoring and fault diagnosis on
line.
The system monitoring and fault diagnosis of hydraulic
operating mechanisms have been studied abundantly at
home and abroad. Based on the improved generalized Radial Basis Function Neural Network, Wang from Xi’an
Jiaotong University has researched on parallel processing
Figure 19
Figure 20
Oil viscosity influence on opening velocity.
Ambient temperature influence on opening velocity.
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and expert system to realize fault type recognition and a fast
approach of fault diagnosis for circuit breakers [31]. Ren
from Tianjin University studied on on-line monitoring and
diagnosis for operating pressure, current signal and vibration
signal of circuit breakers using wavelet analysis [31, 32].
Bartosz et al. from Darmstadt University have carried out
research on leakage model and leakage detection methods
of hydraulic mechanisms [32, 33]. Moreover, running online monitoring and fault diagnosis has become a research
focus to improve the reliability of the system with application of fieldbus and communication network technology in
circuit breakers.
By now, on-line monitoring technology for circuit breakers is incomplete. The most research has been made on
electromechanical devices but scarcely on development of
devices with on-line monitoring and auto diagnosis function
for high failure rate hydraulic system.
However, the study aspects of on-line monitoring and
fault diagnosis on leakage, pump motion, characteristic of
opening and closing motion, pressure characteristic of control valve etc. are significant for the reliability of hydraulic
operating mechanisms and intelligent circuit breakers.
3.6
Intelligent operation of hydraulic mechanisms
Circuit breakers are currently designed according to single
no-load opening characteristic, i.e. its no-load opening
characteristics are the same in despite of any working condition. However, with very low severity failure rate in practical terms, the majorities of operations are under normal
condition, such as power grids overhaul, power control running, and load shedding. Breaking can be realized under all
these situations, so the working life and reliability of circuit
breakers are improved largely [34–37].
As shown in Figure 21, to realize the intelligent control
of operating mechanism, information collected from power
grids was processed by controller and sent out as different
breaking signals to control hydraulic operating mechanisms.
Therefore, there was a guarantee that the circuit breakers
work with prearranged velocity characteristic and that the
displacement and velocity of contact are adjustable.
The focus of intelligent hydraulic mechanisms is the development of electric operated hydraulic systems and
Figure 21
Intelligent control of operating mechanisms.
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running safety of proportional and servo system under the
harsh conditions. The operation processing of hydraulic
operating mechanisms would hold only 20 ms from the beginning action of the opening solenoid to contact breaking.
Ordinary valves cannot meet the demand to a great extent.
Therefore, two methods are employed. The first one is to
make continuous regulation by high frequency proportional
valve or servo-valve, and the second one is to make discrete
regulation by high-speed on/off valve and throttle valve.
Wu from Xi’an Jiaotong University has investigated intelligent operation by high speed on/off valves [36–38]. On the
other hand, it is difficult to develop intelligent control units
with strong robustness. The intelligent control unit needs to
carry out monitoring on line and opening & closing operations reliably. This unit can identify automatically the
working states of circuit breakers, adjust automatically the
hydraulic operating mechanism to meet its breaking characteristic expected, record and display the working states of
the circuit breaker, communicate remotely to the center
computer and so on [39]. Although there are no related applications, the developments of hydraulic operating mechanisms and controller to suit for intelligent operation are important study aspects and can meet the demand of intelligent
power grids.
3.7
Energy storage module
Piston accumulators are widely applied in hydraulic operating mechanisms. The performances of consistency and stability of hydraulic operating mechanisms are affected by
accumulator pressure changed with the ambient temperature.
Hydraulic spring mechanisms with disc spring overcome
the effects of environmental temperature.
In addition, compared with spring operating mechanisms
and N2 accumulator hydraulic mechanisms, disc spring for a
smooth force-displacement characteristic also contributes to
opening and closing operation, as shown in Figure 22.
Burn-in tests for disc spring of HMB-4/8 have been carried
out in the Institute of Mechanics of Materials, Darmstadt
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University of Technology with research on fatigue failure
and spring force. In recent years, domestic hydraulic spring
mechanisms are being developed to have a clear difference
from the ABB products. Temperature compensation for N2
storage stability, high quality material of disc spring and its
manufacture technology, and new storage module are all
important study aspects in the future.
4
The domestic products of hydraulic operating mechanisms
for circuit breakers, which are mainly under the rank of 220
kV, was based on the technologies from ETNA, MG, Mitsubishi, Hitachi, Toshiba, ABB etc. Characteristics are
shown as follows throughout the development of domestic
hydraulic operating mechanisms:
(1) In terms of performance, domestic hydraulic operating mechanisms for circuit breakers under the rank of 220
kV perform well in velocity and time during opening and
closing motion. However, the reliability of electric power
system is affected by its complicated structure, high fault
rate, and stability, which needs to be improved.
(2) In terms of market share, compared with spring hydraulic operating mechanisms produced by ABB, whose
market share is comparatively large in China, domestic hydraulic operating mechanisms under the rank of 220 kV
account for the majority of shares in state grid. However,
the main control valves of high power hydraulic operating
mechanisms over the rank of 550 kV, which cannot be produced in China, are totally imported.
(3) In terms of corporation, the intellectual property of
high power hydraulic operating mechanisms is controlled
by several major foreign companies, such as ABB, Alstom,
Hyosung, Siemens, Toshiba, Hitachi, and Mitsubishi. Pinggao Electric Co. Ltd. and XD Switchgear Electric CO. Ltd.
etc. are the few influential manufacturers in China and do
not have complete intellectual property on important hydraulic elements.
5
Figure 22
Output force characteristics of different mechanisms.
Development status and gaps in China
Conclusions
This review has introduced the technique of hydraulic operating mechanisms and has demonstrated their great important role due to many advantages. In recent years, there has
been a resurgence of interest in the technique, driven by the
demand for society. The focus has been on solving the
technology difficulties to improve its performance. As to its
status quo and trend of the development, there could be
some points as follows:
(1) The basic structure and principle of constant highpressure hydraulic system remain the same in the development of hydraulic operating mechanisms. The technologies
of high speed, high pressure, high integration and high reli-
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ability will be improved in the future continuously.
(2) With the development of related technologies, such as
electronic, computer, material, manufacture, and the study
on hydraulic operating mechanisms and interdisciplinary
applications, the reliability and intelligence technology of
hydraulic operating mechanisms will be recognized and
popularized.
(3) China lags behind many other industrialized countries
in terms of its technology of hydraulic operating mechanisms for circuit breakers. However, high demand will play
a positive role in promoting the development of hydraulic
operating mechanisms.
This work was supported by the National High Technology Research and
Development Program of China (Grant No. 2007AA041803), Doctoral.
Programs Foundation of Ministry of Education of China (Grant No.
20090101110041) and Program for New Century Excellent Talents in
University.
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