Design Objectives of New Digital Control and Monitoring of High Voltage Circuit Breakers J. P. Dupraz, Member, IEEE, A. Schiemann and G. F. Montillet, Member, IEEE
Abstract—This paper describes the monitoring devices that were developed to integrate electronic systems for control and monitoring of the main functions of circuit breakers with respect to three main objectives: First, they must improve the overall reliability, availability and dependability of high voltage substations, transmission system and electrical distribution networks where the circuit breakers with monitoring are installed, as for example in a strategic location in a network. Second, the monitoring and control system must offer a minimum set of connections and simplicity of operability and self-maintenance to the user, and insure interoperability with other type of equipment installed in the substation. Third, the monitoring equipment has to be designed to be flexible enough to reply to the galaxy of user requirements of the world. The result is to make the use of a high voltage circuit breaker less expensive during its life by less regular maintenance, in a “New World” of electrical power deregulation, and competition.
II. HISTORY [1] [2] The authors have experienced, back in 1992 their first control and monitoring of a 550 kV circuit breaker type at the Grizzly substation in the USA, and then later on, the application to several 550 kV type FX32D circuit breakers at Hanmer substation in Canada. These monitoring and control systems included several microcontroller systems each powered by 8 bit microprocessor chips running at 12 MHz. Lately we have installed more modern monitoring in Australia in late 1999 and 2000.
Index Terms-- Availability, Circuit breaker, Control, Maintenance, Monitoring, Operability, Reliability.
I
I. INTRODUCTION
NTERNATIONAL standards such as IEC and ANSI/IEEE do not require today that the circuit breakers be monitored continuously by additional means other than the one required by the manufacturer (and user special purposes requirements) for proper operation of the circuit breaker. This is traditionally limited to analog SF6 gauges or hydraulic pressure switches for SF6 breakers with hydraulic mechanism. New expectations based on the increase of availability of circuit breakers and new hopes to decrease and sometimes not to perform any scheduled maintenance (mainly to reduce direct and indirect expenses) have led many users to field test, and to install various monitoring devices today from diverse manufacturers. The monitoring devices and the controls of circuit breakers proposed – and satisfying all the above conditions – are presented for circuit breakers rated 52 kV and up to 800 kV, with SF6 gas used for insulation and interruption of the arc. First we will describe rapidly the progress made since 1990 and then the technical characteristics of the various components that are available today. Support on the above work was by ALSTOM. J. P. Dupraz is with ALSTOM Research Center in Villeurbanne, 69611France. (e-mail:
[email protected]). A. Schiemann is with ALSTOM Energietechnik GmbH, in Kassel, D-34123 Germany. (e-mail:
[email protected]). G. F. Montillet, is with ALSTOM Power Transmission, in Charleroi, PA 15022 USA (e-mail:
[email protected]).
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Fig. 1. Installation of 345 kV circuit breakers with digital monitoring.
Particular features of these monitoring devices: - An electronic densimeter based on the state equation of the SF6 gas as developed by Beattie and Bridgeman and proven as the most reliable formula available at the time and today in its gaseous and liquid phase by the 1992 experiment of Thuries[3]. The temperature range is from –40°C to +80°C where the temperature and pressure sensors were directly in the SF6 gas, located at the foot of the column of the live tank circuit breaker. -
A set of pole position sensors with an optical sensors.
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An electrical wear monitoring to be used autonomously where the intensity of current passing though the pole at interruption is measured.
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All of the above was controlled by optical fibers and with a gateway towards a remote control PC located in the control building and a man-machine interface for setting and control of the main parameters of the circuit breaker:
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alarms, pressure switch levels, maximum wear and intermediate wear, thresholds, etc. At that time, the electromagnetic compatibility tests were very important due to the fact it was new electronic material included in the substations. Development tests and prototype testing were performed extensively. Already, the industry was made aware of induced transients in all types of switchgear with the introduction of Gas Insulated Substations in the 1960’s and the operation of disconnecting switches. We observed the influence of rapid transients generated by switching equipment in the 550 kV stations, that could induce parasite currents in the numerous wires in the control cubicles, in the trip coils, in the microprocessors, in the optoelectronic receivers, in the random access memories, etc. Claddings and other shielding were the solutions. Fig.3. CBWatch-1 and CBWatch-2 analyzing results.
1) The CBWatch-1 capabilities. •
It calculates the SF6 density by the Beattie and Bridgeman algorithm, which is the physical law closest to experimental results.
•
It inhibits false alarms in the event of gas liquefaction, and indicates liquefaction. It calculates SF6 leakage rates in order to give advance warning of alarm and lockout threshold levels.
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It operates within the ambient SF6 temperature range of –50°C to +60° C when heaters are included around the tank of circuit breakers within a dead tank design.
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It has a direct digital communication between the sensor and the main board, with LCD display locally, uses a proprietary algorithm, and has programmable time span alarms.
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The system uses the standard MODBUS protocol to communicate with other digital devices as an option.
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The system performs continuously a self-diagnostic check.
•
It can monitor also the gas mix (SF6/N2 for example) through time and indicate when the gas mix is not within the required ratio.
Fig.2. Tests and observations on cladding and shielding.
III. THE CBWATCH FAMILY The CBWatch family of monitoring was a simplified version of the first monitoring used in the early days. A. THE CBWATCH-1 The CBWatch-1 was our first attempt to apply simple components of the SF6 monitoring device and to use it on a circuit breaker. The idea was to locate it as a large relay or as an annunciator in a control cubicle. The characteristics of the CBWatch-1 are quite impressive, because it measures directly the temperature and the pressure of the gas in the tank, and sends the information digitally to the control board. The digital sensor selected is from Keller- Switzerland, which supplies many precision components to the aeronautic industry, as for the F15 Fighter plane. The board can be connected to a PC as various functions can be set and trends can be analyzed.
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2) Technical data The set is very light: only 3.5 lbs. and it can have a power supply from 48 V to 250 VDC as per standard power DC supplies available in substations. The power consumption is only 15 VA and can measure the density of the gas from 0 to 144 psi or 0 to 1000 kPa. The accuracy is of + or – 0.725 psi within the above range of densities.
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B. THE CBWATCH-2 The CBWatch-2 is more sophisticated than the CBWatch1. It continuously monitors nearly all the circuit breaker conditions. It signals in real time any malfunction and requests maintenance services. This modular monitoring device was designed with optional functions to be tailored to utilities. 1) SF6 Monitoring. The system has the same functions as the CBWatch-1 for SF6. 2) Mechanical operation. The CBWatch-2 monitors the close and open operating times, allows the use of conventional auxiliary switches, static auxiliary switches or primary contact travel sensors. It is quite sophisticated in that it monitors primary contact separation speed, buffering and over travel. It also detects deterioration in mechanical performance (such as friction, corrosion, breakage, spring fatigue and buffer defects). Finally, it monitors auxiliary switches (52a, 52b) timing.
Fig. 4. Density monitor for mix SF6/Nitrogen.
The system allows a correct definition of the composition in % of the gas in the mix at all times. Temperature range is from –40°C to + 60°C, which satisfies all requirements for ambient from –55°C to +60°C because of heating the tanks of the dead tank circuit breaker. There is an interface communication with external computer with an optical RS-232 connector, and the output relays are isolated to 1 kV AC with an isolation of ground of 4 kV AC. 3) Optional requirements For use of the optional remote interface and for the optional online setting of the main parameters, the user needs to connect a PC Windows in any flavor: 95, 98, NT or 2000 from the RS232 port. The suggested silica fiber converter is the BlackBox No. ME570A-FST made in Pittsburgh, PA. A hard disk free space of 10 MB is required, (which is very small) divided in 2 MB for the software and 18 MB to store the data. Single phase monitoring or three phase monitoring are available. SF6 mixtures as SF6/N2 monitoring density and % of type of gas systems are also available. Connection by Internet is also an option.
current
travel
Fig. 6. Travel sensor with travel and current curves recorded by CBWatch-2.
3) Spring operated mechanism The device monitors recharging motor operating time, and it detects motor or motor limit switch defect. 4) Hydraulic Operated mechanism. As an alternate to spring operated mechanism, we provided for a hydraulic mechanism. Here the monitoring is a little more extensive, since we have to monitor pump motor operating time to detect internal and external leakage. Moreover due to storage of energy for the typical 5 CO in nitrogen accumulators, we detect the nitrogen loss and the threshold pressures on the hydraulic system. 5) Switching operations. This is the concept of the contact electrical wear in which we monitor the current during interrupting operation, estimate the primary contact wear by ∑ the arc duration.
Fig. 5. CBWatch-2 installed in a cubicle.
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ƒi2dt., and monitor
6) Auxiliary and control circuits. The CBWatch-2 monitors operating coil continuity, the auxiliary supply voltage, and the heater integrity. 7) Sensors required for different options. The standard board can perform all the standard functions described above, but we need sensors to send the information to the board. There are as many thinking approaches as there are clients, so the sensors are optional. We have sensors for pressure and temperature of the SF6, the sensors for the trip and closing coils, the auxiliary contacts, and the primary contact travels. To measure the current we need to add auxiliary current transformers, and according to the mechanism – spring or hydraulic, various sensors are added to perform the duties described above. To monitor the auxiliary and control circuits we add temperature sensors and coil supervision relays.
Fig. 8. Interface as viewed on a portable: checking the recorded events as saved by the CBWatch-2
C. THE COILWATCH From the CBWatch family, the last born is the COILWatch that is now a small micro relay manufactured in large volume that monitor the tripping and closing coils continuously.
8) Communication The CBWatch-2 is supplied with two-communication interfaces: • One RS232 interface to connect a portable computer • One MODBUS RS485 interface to integrate the CBWatch-2 in a control and monitoring type SCADA system.
Fig. 9. The COILWatch.
IV. SWITCHGEAR INTELLIGENT CONTROL UNIT (SICU) As it was described above, the CBWatch family is a monitoring system only. The next logical step is to design an integrated control and monitoring system, taking all the advantages from the monitoring-system described above and having additional features due to the control-system.
Fig. 7. CBWatch-2 connection to portable computer by RS232
In addition, we can connect a regular MODEM to the RS485 interface, and the CBWatch-2 can be connected to any network or can be called using normal telephone lines. A powerful tool software for the Man-Machine CBWatch-2 interface allows use of the following functions: − Connection to the CBWatch-2 via a connection RS232, or a connection RS485, or a MODEM, − Setting of the parameters of the CBWatch-2, access to the alarms, measures, and saved archives. − Connection via the Internet is now an option.
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This design will reduce the wiring within the substation dramatically if a serial connection between circuit breaker and control-level is used. The wiring for this "serial connected" circuit breakers consists of: - a power-supply, - the serial connection via fiber-optics - and a redundant connection for protection-tripoperation, if required. The German Unit of the Switchgear Group has been developing such a system – called SICU 3 – for the last 5 years. The first circuit breakers were installed in 1997. Meanwhile more than 80 circuit breakers are in service worldwide with the SICU system.
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Coils
C O NTRO L
Positions
Locking and orders
Protection Control
COM M UN ICATIO N
M aintenance
Condition m onitoring Parameters settings and m onitoring report
Locking, positions and internal orders
CON DITIO N M ON ITO RIN G
Sensors
Fig. 10. SICU-3 installed on a live tank
The serial communication is based on IEC-protocol 608705-101. Consequently we will now gather all various experiences together and develop the new ALSTOM Control and Monitoring System SICU 4. It is based on the monitoring part of CBWatch-2 and the experience of the control-system of the SICU-3. SICU 4 will be the advanced system of the future, able to work together with different control systems via different protocols. The first port (monitoring & control) will communicate with the protocols: MODBUS (PC, Modem), IEC 60870-5-101 and others, e.g. Ethernet for communications according to UCA2, IEC 61850 and Internet. Therefore SICU 4 will be part of the "complete electronic substation" of the future. SICU 4 is not developed for circuit breakers only (SICU 4 C), but also for disconnecting switches and grounding switches (SICU 4 D/E) and the complete electronic substation. A bay unit – SICU (SICU 4 G) - will be able to monitor and control a standard bay. This unit can been used for GIS, AIS - compact substations and reduced sized AIS substations also. The general layout of SICU 4 is shown in Fig.10. The main modules are: • the condition monitoring module • the control module and • the communication module. The monitoring module is the same as for CB-Watch 2 and is described in section III -B.
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Fig. 11. Simplified block diagram of the SICU 4.
The control module gets trip-orders directly in the conventional way via copper wires and as serial commands from the communication module. Based on information from the monitoring module (e.g. SF6 lockout), the trip-order is locked to the trip-coils. In parallel, SICU 4 has an "purely" conventional back-up-trip-channel, which will stay active in case of a major fault of the electronic unit. The last locking condition (circuit breaker locked / unlocked) of this back-uptrip will have been taken into account, even if the electronic unit is switched off completely. The communication module has a second output (monitoring & service) based on MODBUS protocol to send all monitoring information to a higher level. Also this port is used for local communication (PC) or remote communication via modem. This port is used for purely monitoring functions and service (set fingerprint, change limits etc.) The controls direct the different command-paths, which can be performed with SICU 4. All commands can be performed for single-phase or threephase systems: • remote opening and closing orders, • local opening- and closing orders via a local/remote switch, • protection 1 opening orders, • protection 2 opening orders (as back up path, if the power supply is missing). The SICU checks with different interlocking functions to determine whether the system should operate or not. For example: monitoring information is used to lock the circuit breaker in case of loss of SF6. Anti-pumping interlocking allows different modes and is programmable, for example close-priority or open-priority.
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Locking conditions can be set due to client wishes and can be changed later on site, if necessary.
functions on substation equipment were described in Chapter IV. The final purpose is to increase the availability, and ultimately, the overall reliability of any electrical system, to decrease the maintenance cost, and make the user more cost competitive, in a “New World” of electrical power deregulation, and competition. VI. REFERENCES [1] [2] [3]
[4]
Fig.12. SICU-3 in spring mechanism control cubicle.
[5]
V. CONCLUSION New developments in monitoring and control go hand to hand with the objective to decrease the total cost of purchase and operation/maintenance of a circuit breaker during its life. First, we have described rapidly the achievements and progress made since the early 1990 in monitoring and control at the 345 kV and the 550 kV level, and then the various simplifications of the technical solutions proposed today. The monitoring devices here are geared for circuit breakers rated 72 kV and up to 800 kV, with SF6 gas (or SF6 mixed with another gas) used for insulation and interruption of the arc. The operating mechanisms of the circuit breakers could be spring or hydraulic. The second point is that all the electronic equipment added for monitoring and control decreases the cost of operation and maintenance during the life time of the circuit breaker. It includes direct cost and indirect costs for the utilities and users since status of the wear and health of a circuit breaker is known at all time. We can note that the latest publication on the subject is the IEEE C37.10.1.2001 “Guide for Selection of Monitoring for Circuit Breakers”. An economic evaluation form to help the user is proposed in this Guide. The monitoring and control systems proposed also reply to all technical criteria and objectives described in the abstract. This is very important, because it is the technological answer to the passage from regular and sometimes high "scheduled maintenance" cost, to "no-scheduled based maintenance", or in other words, to only "on-demand maintenance." As indicated, all monitoring and control systems described in this paper are requesting remotely maintenance of the monitored functions of the circuit breaker. The new generation of SICU-4 with digital monitoring and control of a whole substation, embedding all the new
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[6] [7] [8]
R. Jeanjean, M. Landry, D. Demissy “Electronic System for Controlling and Monitoring the Mechanical and Electrical Integrity of HCV Circuit Breakers” IEEE Winter Power Meeting 1991 E.Thuries, G.Ebersohl, J.P.Dupraz, O.Chetay. J.P. Moncorge. “Introduction of Digital Electronics in Switchgear Auxiliary circuits and Improvement of Reliability “ CIGRE paper 23/13-09 1994 Session. E. Thuries, A. Girodet, M.Collet . “Evolution of SF6 Pressure at Constant Volume versus Temperature Between Liquefaction Point and +20°C. Experiment of Thuries”, Paper 94WM011-7-PWRD IEEE Winter Power Engineering Society, January 30, 1994 E.Thuries, H. Lefort, G.Ebersohl, J.P.Dupraz, C. Baudart, O.Chetay, T.Jung, J.P. Moncorge .:. “Digital Control and Condition Monitoring: Integration and Application” Paper 13/109, CIGRE 1998 Turning Data Into Knowledge at the Substation: The value and Implications of on-line Condition Monitoring of Substation Power Equipment, Substations Committee, 1998 IEEE Winter Meeting New York, N.Y. Panel Session IEEE Guide for Selection of Monitoring for Circuit Breakers. C37.10.12001 “High Voltage Switchgear and Control gear - The use of electronic and associated technologies in auxiliary equipment of switchgear and control gear.” IEC Technical Report : TR 62063 C. Baudart, O.Chetay, J. P. Dupraz, D. Gebhardt, D. Hirst, P. Kirchesch, “Electronic Control of Circuit Breakers” CIGRE paper 13-206 2000 Session.
VII. BIOGRAPHIES Jean-Pierre Dupraz was born in Chambéry, France on June 18, 1952. He graduated from “Ecole Nationale Supérieure de l’Electronique et Applications ” (ENSEA Paris) in 1975 in Electronic Engineering and in 1978 obtained a DESS in management from IAE-Paris. After working three years on several projects, he joined ALSTOM in 1978, working on several projects including electronic and optical instrument transformers. In 1988, he joined ALSTOM Switchgear Research Center (ARC ) in Villeurbanne, where he is the head of electronic research. He obtained several patents in the field of switchgear monitoring and electronic current and voltage measurement. He is a member of IEEE, HighVoltage Subcommittee, of several IEC working groups (TC 17WG 20, TC 38WG23 and TC 57WG12). Since 1998, he is a Senior Member of the French Société des Electriciens et Electroniciens. Author of many technical papers, he provides courses on EMC. Andreas Schiemann was born in Norderney, Germany on Jan. 25, 1954. He graduated from the Brunswik Technical University, Germany in High Voltage Technology. He joined AEG-factory in high voltage circuit breakers in Kassel , Germany in 1978. There he worked 5 years in development-department. In 1984 he became the head of the development department for AIS-High Voltage Circuit Breakers. Since 1996 he is within ALSTOM after the merger between AEG and GECALSTHOM and now responsible for the development of ALSTOM-AIS-Highvoltage circuit breakers up to 170 kV Georges F. Montillet was born in Nice, France on December 8, 1944. He graduated from the Polytechnic Institute of Grenoble (ENSI) in 1968 in Power Electrical Engineering, moved to the US in 1969 and in 1974 obtained a MBA in Finance/Operational research from Stern Business School, NYU-New York. He worked for two years in a consulting engineers firm in New York, and joined Cogenel, now ALSTOM, New York, in 1971. He is now V.P. Power Transmission - T&D Sector in ALSTOM. He is a member of IEEE since 1970, and a member of the High Voltage Switchgear Committee, High Voltage Circuit Breaker Subcommittee and various others Subcommittees.
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