21, rue d’Artois, F-75008 Paris
http://www.cigre.org
Session 1998
13-113
© CIGRÉ
INNOVATIVE SWITCHING DEVICES FOR MEDIUM AND HIGH VOLTAGE NETWORKS
APPLICATION OF SENSOR-TECHNOLOGY, FIELD- AND SERVICE EXPERIENCES
V. REES* , F.J. KÖRBER
M. TIPPMANN, H. WOLTERS
ABB Calor Emag
VEW Energie AG
P. KIRCHESCH
AEG Energietechnik GmbH
(Germany)
Summary
1
The report describes several applications of novel
technologies for high- and medium voltage switching
devices, demonstrating the progress of development in
the primary and the secondary equipment for medium
and high voltage substations.
After introduction of SF6 as insulation and arc
quenchig gas remarkable progress has been reached in
development and optimisation of high voltage switching equipment regarding compactness and increased
reliability of circuit breakers and complete substations.
As a first example the configuration of an intelligent
high voltage circuit breaker equipped with an integrated digital system is described. Experience during
installation and commissioning and the results of the
long term recording of the service period in the field
are reported, especially focusing on the influence of
climatic conditions on the digital auxiliary equipment
for the open air installation.
As a further example an integrated switching package
is described, which is equipped with similar digital
auxiliary technique and sensors as mentioned above.
Additionally, for the primary high voltage components
it was possible to integrate important primary functions as circuit breaker, disconnector, earthing switch
and measuring transformers into a metal enclosed
compact compartment. In case of retrofit of existing
air-insulated switchgear (AIS) the device can be easily
integrated into the existing substation
Finally a medium voltage circuit breaker with vacuum
interrupter and wear free magnetic operating mechanism incorporating touchless position sensors is presented.
Keywords
Switchgear, Control, Sensors, Field Experiences
Introduction
In medium voltage circuit breakers the vacuum interrupter together with small low-energy drives has
shown its excellent service behaviour for many years.
As examples for improved primary technology can be
mentioned:
• Application of self-blast interrupter technology for
HV circuit breakers in order to reduce operating
mechanism energy by about 80% compared with
puffer breakers of the same electrical ratings and
therefore to increase mechanical reliability.
• Development of very compact and enviromentalfriendly gasinsulated switchgear (GIS) by utilising
powerful computer-aided design tools and the excellent insulating behaviour of SF6-gas.
Comparable innovations recently have been introduced
in the secondary technology of high and medium voltage equipment substituting conventional mechanical
auxiliary switches, relays and parallel copper wiring.
These integrated digital control and supervision systems in high- and medium voltage switching equipment are providing modern powerful tools for improving both economy and availability. Major improvements in auxiliary circuits are achieved by re-
_______________________________________________________________________________________
* ABB Calor Emag Schaltanlagen AG, P.O. Box 901220, 63421 HANAU
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placing the conventional parallel wired auxiliary
equipment by a digital system using sensors incorporated in high voltage switchgear with the additional
feature of self-supervision of the secondary system,
which is not possible for conventional technique.
The progress in secondary technology is supported by
the fact, that powerful and reliable digital processor
units are available today.
Table 1 summarises a result of the second international inquiry on the reliability of high-voltage single
pressure SF6 circuit breakers performed by CIGRE
Working Group 13.06 /1/. It shows, that 29% of the
major failures are caused by malfunction of the conventional control and auxiliary systems. The figures
for minor failures are similar.
Subassembly or component
Components at service voltage
Control and auxiliary circuits
Operating mechanism
Others
Distribution of major failures
21%
29%
43%
7%
Table 1: Distribution of major failures
Considering the above figures, application of reliable
sensors and actuators for control and supervision can
contribute to the reliability and availability of the
complete system. Furthermore simplification of operating mechanism and application of advanced supervision systems to monitor the mechanical functions are
important items.
Some examples for innovative solutions for high and
medium voltage applications concerning advanced
primary and secondary technologies are described in
this report.
2.
The Intelligent Life Tank Breaker
2.1
Switchgear Concept
The secondary switchgear systems are designed as part
of a system having decentralised intelligence. In such
a system the sensor information is processed directly
by a microcomputer located in the switching device
itself. This concept has the following advantages:
• The present structure of the secondary systems is
retained. This means that by using suitable interfaces it is possible to gradually introduce new devices – not only primary switchgear but also devices on the bay control level.
• Intelligent primary devices permit independent
collection of operating data and are not dependent
on the design of substation control systems.
The system executes all monitoring and control functions. This means that conventional control systems
are no longer necessary. This concept also has definite
advantages for early fault detection and diagnosis.
Transfer of the control functions to a microcomputer
system makes it possible for the first time to achieve
economic and continuous self-monitoring of secondary
systems.
Besides these functions, the system also assumes the
function of communication with higher-level control
systems. The switching device therefore has serial
fiber-optic communication capabilities.
2.1.1
Sensors
Transfer of the control functions to the microcomputer
system means that special demands are imposed on the
secondary systems of primary devices, compared with
higher levels. Examples are the expanded temperature
range, device vibrations, and especially the proximity
to high voltage. Of central importance are the connections between the microcomputer system and the sensor peripherals. In this case electromagnetic compatibility can be maintained by fibre optics with a high
degree of reliability. Optical fibres are free from electromagnetic interference and ensure electrical isolation
of computer and sensors. The sensors are built into the
switchgear. Optical fibres connect them to the microcomputer. Innovative fibre-optic sensors were developed to implement this concept. The sensors function
on the reflection light barrier principle and therefore
provide digital optical signals. Digital signals are less
sensitive to interference factors such as the tolerances
of electro-optical components. They can also be directly processed by microcomputers. In addition,
fibre-optic sensors are wear-free. They also do not
need a voltage supply since they operate passively.
• The high voltage switchgear will remain autonomous, even in the future. The devices can execute
functions independently and do not depend on
higher levels of the station's secondary systems.
In the example cited, sensors are used to
• Device-specific information is processed in the
switchgear close to the process itself, i.e., where all
the process know-how is immediately available.
• monitor the latches of the operating mechanism.
• monitor the contact-movement,
• monitor the spring energy,
• monitor the SF6 density,
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2.1.2
Interface
Like conventional switchgear, intelligent switchgear
can be connected to station control systems by parallel
wiring. In this case the connection is via a conventional interface. Computer-controlled, passive electronic relays in the control circuits of the trip coils
then take over the job of enabling breaker trip coils.
The functions of auxiliary switches are simulated by
relays. Command sensors receive electrical commands
from breaker coils. The information from these sensors
is required to carry out control functions – an example
is the anti-pumping system. In addition, the electrical
operating times can be measured. Significant benefits
of intelligent switchgear such as early fault detection
and the resulting early warning signals are retained,
even with conventional connection systems. Switchgear of this type can later be connected serially to
digital control systems. It is therefore protected against
obsolescence. Fig. 1 shows an intelligent circuit
breaker in the 123 kV system of a large German utility
that has been connected in this manner.
perature and humidity conditions in the mechanism
housing, among other things.
2.2
Incorporation of an Intelligent Breaker in
a Total System
An intelligent circuit breaker has been installed as part
of a 110 kV transformer-station. The new building of
the substation – conceived as an H-circuit in a cable
design – serves as the main facility for the local municipal system and went into operation in 1996. The
station design includes three circuit breakers installed
on support frames so that free access to all areas of the
facility is permitted. The circuit breakers are assigned
to the two transformers and the coupler unit according
to Fig. 2.
Fig. 2: Top view of the station
The intelligent circuit breaker, which has been developed to allow for optimised maintenance planning, is
installed in the coupler bay Fig. 3.
Fig. 1: Intelligent breaker in a 110 kV substation
The breaker in this case is permanently connected via
fibre optics to a personal computer (PC) in the control
room, which displays the breaker status. From here the
operator also has access to the breaker condition data.
In addition, all events such as switching operations,
movement curves, etc., are stored together with a date
and time stamp.
A second PC stores the measurement results from
additional sensors that are built into the breaker and
are designed to provide information about the tem-
The coupler bay is integrated into an important busbar
run and is therefore operated primarily with a closed
circuit breaker. The protective device for the busbar
run acts on the intelligent circuit breaker. The built-in
sensor system is controlled by conventional control
systems and switchgear interlocking, which means
that it receives operating commands and issues both
status signals and alarm and fault signals to the control room and the system control centre. After it has
proved successful in the field this breaker type will be
used when needed to supplement previous breaker
types both in substations with conventional control
systems and those with modern control systems involving serial interfaces.
2.3
Field- and Service Experience
Plans for utilising an intelligent circuit breaker
focused on two main goals:
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• Proof of long-time operation over a period of several years.
• Measurement of environmental conditions at the
breaker in order to guarantee that the design and
testing of the microcomputer system will be consistent with environmental effects.
Final inspection in the factory test bay involved not
only the normal tests required by standards but also
testing of the additional functions of the intelligent
circuit breaker. In addition, calibration and functional
checking of all pressure, temperature and humidity
sensors was carried out. During commissioning there
was another functional check of all measuring points.
The measured data were evaluated over a period of
five months (Jan.-May 1997). Temperatures ranging
from -10.5°C to +24.5°C were measured on the circuit
breaker. The temperature sensor inside the microcomputer housing indicated an excess temperature of from
+2 K to +18 K relative to the ambient temperature.
Fig. 4: PCs for data acquisition
to PC
Fig. 3: Single line diagram of the station
In order to achieve the second goal the mechanism
housing was equipped with three measuring points for
temperature measurement and one for humidity measurement. In addition there are three other temperature
measuring points on the breaker so that the ambient
temperature can be detected at different locations.
Communication for transmitting the climatic data is
via measuring leads run directly to the control room.
There the measurement signals are converted to digital
values by an A/D converter (data shuttle), and the
characteristic curve of the thermocouples is linearised.
These data are then transmitted via a parallel interface
to a PC where they can be displayed at any time. These
data are recorded and stored in permanent form. Every
three months the data are read out and evaluated.
The two PCs in Fig. 4 (one for condition or status
data acquisition and the other for climatic data acquisition), together with the data shuttle, are protected
against short power failures by an uninterruptible
power system (UPS).
The components in the mechanism cabinet followed
the fluctuations in outside temperature with a corresponding time delay. The atmospheric humidity measured in the mechanism housing was between 11 %
(min) and 41 % (max). The operating mechanism is
equipped with an anti-condensation heater as standard
equipment.
During type testing proof of functional reliability at
ambient temperatures ranging from -40oC to +70oC
has been demonstrated. The routine burn-in test that
was provided for also represents a much higher load
than occurs in the case cited. The burn-in test involves
four different temperature cycles of over six hours each
at temperatures ranging from +20°C to +55°C. The
test takes a total of 144 hours.
The goal of obtaining specification values for design
and testing from the measured operating data has now
been fully achieved.
3.
Progress in gasinsulated switching devices
3.1
Plug and switch system (PASS)
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The design of SF6-insulated switchgear made a remarkable progress regarding optimisation of dimensions, especially in the subtransmission range of GIS
up to 170 kV /2/. Considering the good experiences
with fully metal enclosed technique, new solutions for
air insulated substations are developed recently. Fig. 5
shows as one example an integrated and intelligent
bay module for voltages up to 170 kV. This module
can be connected easily to the rest of the substation via
the SF6/air bushings by wire to the station busbar.
In the operating mechanism of all switching devices
the conventional mechanically driven auxiliary
switches and the relays for switching the coil- and
motor currents are substituted by novel sensors and
actuators. Each mechanism is equipped with a digital
control switchgear unit with the following main functions:
• Power semiconductors for switching the coil- and
motor currents.
• Central processor unit (CPU) for processing the
information about the actual status of the switching
device.
• Digital and analogue in- and outputs for switching
position, gas density and energy storage (in case of
circuit breaker operating mechanism).
• Interfaces to the optical bay process bus and to the
protection relays.
In order to detect the actual position of the contacts of
a switching device all operating mechanism are
equipped with touchless inductive proximity sensors,
which are well proven from other industrial applications under severe enviromental conditions for many
years. The advantages compared with mechanical
driven conventional auxiliary switches are:
• No mechanical wear
• Exact indication of the end-position of the switching device.
Fig. 5: PASS up to 170 kV
The shown concept comprises all functions needed in
a substation bay and includes a 3phase common enclosed circuit breaker, disconnector and earthing
switch on the line exit and integrated voltage and
current transducers. The operating mechanism for the
included switching devices and the according secondary control technology are integrated in a common
control cubicle. At both sides modern silicone compound bushings are part of the concept. Especially for
retrofit of existing substations, where short replacement times with minimum disturbance of the service
of the substation is important, such compact and factory tested solutions are useful.
The actual stored energy of the circuit breaker drive,
in this case a hydraulic spring drive, where the energy
is stored in a spring package, is monitored by an inductive rotating sensor, measuring the spring displacement continuously.
All status information of the switchbay is collected in
a digital bay controller according to Fig. 6.
For higher voltages similar concepts, preferably single
phase enclosed, are available /3/.
3.2
Sensors and Electronic Secondary Control
Technology
For the unconventional secondary technology of HV
switchgear the following approach regarding sensor
and control technology is made.
Fig. 6: Bay controller
On a large liquid display the bay controller shows the
single-line diagram of the according bay. It offers local
control operation and it is the connection between the
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digital switchgear units on the bay level and the substation interbay bus. .
Additionally the sensor- and computer based secondary system is the presupposition for on-line monitoring of the main functions of the switchgear using suitable software modules. Furthermore a very important
function is included in the innovative secondary technology. Whereas in conventional technology a malfunction of e.g. a relay is only recognised during operation of a switching device (failure of an element
exactly when it is needed), a self supervision feature is
implemented in the novel secondary system. Every
second a test-impulse for a duration of one microsecond is set over the whole system, Therefore defect
elements are detected immediately also when no
switching operation is performed.
4.
Medium voltage circuit breaker
At medium voltage technology, also much effort has
been spent in further improvements in primary technology, looking for new opportunities to simplify the
design and to further contribute to the excellent behaviour in service.
As a last example Fig.7 shows a vacuum circuit
breaker with magnetic operating mechanism.
The characteristics of the actuator´s magnetic circuit
are designed in such a way, that the armature operates
directly via a lever shaft the moving contact of the
vacuum interrupter. This method contributes to very
high electrical endurance, as mechanical wear is unknown. The energy is stored in a capacitor, which is
recharged by the electric power supply only within a
few second after an autoreclosing cycle. The release of
operating energy, the operating motion and the energy
storage are fully controlled by an electronic controller,
which is also a very suitable interface to digital modern control and protection systems..
It is evident, that the control system of this circuit
breaker concept is working without any mechanically
driven auxiliary contacts and makes use of touchless
inductive proximity sensors to detect the end positions.
5.
Conclusion
Innovative technology in primary and secondary technology in high- and medium voltage will become more
and more common in the future. These developments
are driven by the possibilities offered by modern sensors and powerful processor technology. As a result,
higher functionality, integrated supervision functions
and higher reliability and availability can be foreseen.
Application of sensors and processor technology on
life tank circuit breakers has shown excellent service
behaviour at different climatic outdoor conditions.
Retrofit and renovation of existing substations is becoming increasingly frequent, requiring short replacement time with minimum service interruption.
Integrated bay modules as PASS offer flexibility and
short replacement times in order to enable to reduce
costly redundancy.
From the experiences gained in service, further improvement steps in primary and secondary technology
are foreseen in the future.
6.
References
/1/
CIGRE Working Group 13.06:
A summary of the final results and
conclusions of the second international inquiry on the reliability of high-voltage circuit
breakers
CIGRE Report 13-202, Paris 1994
V. Rees, M. Schumacher:
Innovative Gas-Insulated Switchgear (GIS)
with modern Control and Sensor Technology
IEEE Substation Seminar, July 1997
IEEE Section Mexico, Acapulco
K. Hakansson:
Issues in power systems
1997 CIGRE Regional Meeting South East
Asia and Western Pacific, Melbourne
Fig. 7: Vacuum circuit breaker with magnetic drive
/2/
All operating mechanism functions are integrated in
the magnetic actuator (basically numbers 3 to 6 in Fig.
7). The actuator is a bi-stable magnet system, in which
switchover of the armature to the relevant limit position is effected by the magnetic field of two electrically
excited coils. In both end positions the armature is
held by the fields of a permanent magnet.
/3/
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