AU640451B2

AU640451B2 - Control scheme for the adaptive protection and the control of feeder circuit breakers on an electric railway

Info

Publication number: AU640451B2
Application number: AU71311/91A
Authority: AU
Inventors: Anthony Joseph Griffin
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-02-23
Filing date: 1991-02-22
Publication date: 1993-08-26
Anticipated expiration: 2011-02-22
Also published as: AU7131191A

Description

640451 Our Ref: 354680

AUSTRALIA

Patents Act COMPLETE SPECIFICATION FORM

(ORIGINAL)

Application Number: Lodged: Complete Specification Lodged: Accepted: Published: 0 0 Priority: Related Art: 0 0 Applicant(s): Anthony Joseph Griffin 13 Bungalow Road PEAKHURST NSW 2210

AUSTRALIA

Address for Service: oa ARTHUR S. CAVE CO.

Patent Trade Mark Attorneys Level 10, 10 Barrack Street SYDNEY NSW 2000 Complete specification for the invention entitled "Control scheme for the adaptive protection and the control of feeder circuit breakers on an electric railway".

The following statement is a full description of this invention, including the best method of performing it known to me:- 1 5020 S0350a/AMD CONTROL SCHEME FOR THE ADAPTIVE PROTECTION AND THE CONTROL OF FEEDER CIRCUIT BREAKERS ON AN ELECTRIC RAILWAY The present invention relates to a protection device, and in particular, to a protection device which controls the adaptive protection operation of the circuit breakers of a feeder. The present invention is particularly applicable to electric railways.

In the past, control schemes for the adaptive protection of feeder circuit breakers on electric railways have had a number of disadvantages.

0 For instance, the substation battery has been required to S be transmitted on a pilot cable, resulting in problems with remote earth potentials.

00 Also, the control schemes have relied on the integrity of the pilot cables to maintain supply to the electric railway, rendering the reliability of the supply unreasonably 0000: 0 susceptible to interference.

00 0 On present day d.c. traction systems, most feeders, .00. except in the direction of a terminus, are double-ended, and circuit breakers are provided at the two ends of the double-ended feeder, and are closed except when a fault .0 occurs. The whole of the d.c. traction system is operated in parallel, with all substations being paralleled via the overhead wiring.

On present day a.c. traction systems, the currect practice is for each substation to only feed radially to open mid points between the substations, i.e. the substations are not paralleled.

2 0350a/AMD To detect faults on these prior art traction systems, the following methods are known to be used.

On d.c. traction systems the overcurrent trip device on almost all of the circuit breakers in commercial service is an integral part of the magnetic circuit which holds the circuit breaker closed. Fault conditions are detected by magnetic fluxes opposing. At come critical magnitude of load or fault current, the magnetic force is not sufficient to overcome the forces developed by the opening springs, and the circuit breaker opens quickly. The fault detection is not done by an *@fee: add-on device.

0:000: Circuit breakers for a.c. traction systems follow conventional high voltage a.c. practice and are equipped with a 9:000: trip coil which must be energised to mechanically trip the circuit breaker.

There are a number of known ways to electrically change the magnitude of the fault current required to trip the circuit breaker while it is closed, in service, and carrying load S current. These prior art methods include: on magnetically held circuit breakers the flux in the holding coil can be varied by varying the holding coil current; a coil intended only for testing the trip setting can be excited to bias the trip setting; add-on external tripping relays can be enabled to cause the circuit breaker to trip when the load current exceeds the setting of the add-on relay, and before the load current has reached the trip setting determined by the integral tripping device; 3 0350a/AMD local (push-button) and supervisory remote control is these days normal in virtually all power system and traction substations for the deliberate opening and closing of circuit breakers; add-on tripping devices are not universally used but are common on traction system feeder circuit breakers. Typical of these devices is the "Delta I" relay which operates on the magnitude of the rate of rise and/or magnitude of a step increase of feeder current to open the holding coil circuit and therefore open the circuit breaker. More than one add-on tripping device may be installed with each circuit-breaker.

The present invention seeks to obviate the disadvantages of these prior art adaptive protection apparatus and methods, by eliminating the necessity to transmit the station battery on the pilot cables whilst enabling the desirable galvanic isolation bet ,en substation earth potentials and the remote earths of the communication system.

The present invention also seeks to provide a control scheme whereby, during periods of communications failure, the control scheme causes the local protection to revert to a fail-safe condition to maintain supply to the feeder, such that, for instance in railway applications, the trains can continue running with restriction.

In one broad form, the present invention provides a control system for the adaptive protection and control of a feeder network, comprising: a circuit breaker provided at each end of at least one feeder; control means, to operate its respective circuit breaker -4- S0350a/AMD when a fault is detected; fault detecting means to detect a fault on the feeder and provide a signal indicative of the presence of said fault to said control means; central processing means interconnecting said control means with control means of adjacent circuit breakers, adapted to control the operation of each control means, in response to operator inputs and/or inputs derived from each control means.

Preferably, the control system is embodied wherein each control means is provided with an adaptive trip setting.

Preferably also, the control system is embodied wherein a fail-safe command is utilised to activate each circuit breaker.

Also preferably, the control system utilises a fail-safe command having at least two signals adapted to concurrently change state for activation of the circuit breaker.

Preferably, communications between the control means and the central processing means is via a conventional telephone S circuit, and appropriate modems.

eoee• Also preferably, binary signals are utilised in the communications.

The protection device of the present invention will be understood to be preferably adapted to electric railways.

In a further broad form, the present invention provides a method of protecting and controlling the operation of circuit breakers on at least one feeder, comprising the steps of: "."detecting local faults and providing a signal indicative of the presence of said fault to a respective control means; operating a local circuit breaker by operator inputs and/or inputs derived from said control means; indicating the activation of said circuit breaker to a 5 0350a/AMD central processing means which interconnects each control means; and, supplying signals from said central processing means to adjacent control means to operate their respective circuit breakers.

Preferably, said operating step is performed by, comparing the fault or load current or voltage with the trip setting provided within said circuit breaker.

The present invention will become more fully understood from the following detailed description of a preferred embodiment thereof, in connection with the accompanying drawings, wherein: Fig. 1 illustrates the arrangement of the basic components of the protection system in accordance with the present invention; Fig. 2 illustrates the interconnection of the protection system between stations; Fig. 3 illustrates a distributed control system, showing a first arrangement of the present invention; and, Fig. 4 illustrates an alternative arrangement showing a centralised control processor.

As shown in Fig. i, a feeder 1 is provided with a circuit oe breaker 2. The operation of the circuit breaker 2 is enabled by control means 3 which is adapted to transmit a trip command signal 4 upon detection of a fault on the feeder i. A fault may, for instance, be a high or low current or voltage identifi.ed on the feeder i, indicated to the control means 3 via signals 5 and 12. The control means 3 is provided with a 6 0350a/AMD trip setting means 6 which, once set manually with the circuit breaker 2 out of service, is fixed. The control means 3 is also provided with local manual and remote trip command 7 to open and close the circuit breaker 2. In addition, the control means 3 is adapted to receive external commands 8 and 13 to modify the magnitude of the load or fault current required to open the circuit breaker 2 upon information received from a central processing unit which interconnects the control means and its associated circuit breaker with the control means of adjacent circuit breakers. Therefore, if a circuit breaker at eog...

S another location on the feeder opens, then the circuit breaker oo o S 2 opens if the load or fault current exceeds the trip setting determined by the combination of the control signals being Sreceived by the trip logic unit 3. Fig. 1 is also shown having an input 13 to the control means 3 to measure the feeder voltage at one or more locations along the feeder 1. Data is Salso provided from the circuit breaker 2 to the central processing means 9 to activate other circuit breakers at a eg remote location, if the circuit breaker 2 changes state from

C

open to closed or closed to open.

It will be appreciated that the magnitude of load or S. fault current required to open the circuit breaker is adjustable by: An operator modifying signal 6, when the circuit-breaker is out of service. This setting is pre-set and is usually mechanical. Usually, the operator must physically manipulate the circuit breaker mechanism to make the adjustment.

7 0350a/AMD An operator physically manipulating the circuit breaker control equipment with the ciruuit breaker out of service to pre-set the effects of signals 8 and 13 on the magnitude of the trip setting.

An operator physically manipulating the control equipment of the add-on fault detecting device 15 to pre-set the magnitude or characteristics of the load or fault current required to command the trip logic unit 3 to issue the trip command 4 to the circuit breaker.

Once the adjustments are pre-set the effects of signals -eoeo S 6, 8, 13 and 15 on any given circuit breaker are pre-determined. However, the pre-set adjustments differ between the substations and the circuit-breakers on the electric railway power system. In most cases, the pre-set adjustment provided by above are inherently dependent on the feeder voltage 12. The characteristics of the add-on ~fault detecting device 15 may be feeder-voltage dependent.

.In the future, operator-commanded reductions of trip settings by remote control may enhance system operation during times of maintenance and equipment failure.

Fig. 2 illustrates the interconnection between go. substations, like numerals identifying like features to those S described in Fig. 1. Also shown in Fig. 2 are modems 10 and the communication circuit 11 which enables communications between the various substations.

As therefore shown in Figs. 1 and 2, a circuit breaker 2 is provided at each end of the feeder section with an associated fault detecting and tripping device 3. On d.c.

0350a/AMD electric railways, one of the fault detecting devices 15 which forms part of the tripping device 3 is usually an integral part of the circuit breaker, whilst on a.c. electric railways, the fault detecting device 3 is usually a separate relay which acts on a trip coil of the circuit breaker. More than one add-on trip detecting hence 15 may be installed on the circuit breaker of both a.c. and d.c. electric traction systems.

The control means 3 is adapted to electrically command a change in the trip setting of each of the circuit breakers 2, whilst the circuit breakers 2 are in service and carrying fault see**: 0 current. This control is best arranged as a fail-safe command, 00.0 S whereby, in the absence of a command signal, the trip setting

O

S

reverts to the lower or lowest of the possible settings. In o e 6 •this way, a deliberate command signal is therefore required to raise the trip setting. In most applications, it is anticipated that there will only be two settings, that is, a "low" and a "high" setting.

The communications link 11 is therefore adapted to transmit information related to the detection of the state

S.

S (open or close) of the local circuit breaker to the remote circuit breakers and/or to a central processor. It is also

S.

adapted to transmit information related to the voltage (high, low, or a numeric value) at selected locations along the feeder, where the transducers 14 are installed, to the remote circuit breakers and/or a central processor.

The communications link 11 is also adapted to transmit data over conventional (public) telephone type circuits which may or may not be a dedicated pair, and the characteristics of 9 0350a/AMD which are relatively independent of the communications technology used for voice-frequency communications.

The communications link 11 is also adapted to transmit signals to the receiving end or at the central processor to select the trip setting of the circuit breaker. If the conversion is done at a central processor, it may be necessary to retransmit some or all of the selection command signals to the circuit breakers.

The system is preferably implemented whereby receivers at each circuit breaker, in the absence of a valid signal from the eeloa S transmitters, give no command signal to increase the trip o o S setting of the circuit breaker, and therefore cause the circuit 0* 00 go 0 breaker to trip at the lowest of it pre-set settings.

o soa: The means of communicating the state of the circuit breakers and the voltages include, but are not confined to, discrete voice-frequency transmitter-receiver pairs, or serial-parallel transmitter-receiver pairs, modems, and similar 0* 0 devices which may or may not be designed to work over the public telephone network.

To achieve the desirable fail-safe characteristic, it is preferable to transmit more than one signal for each changeable 00 device monitored, so that a change of state of the monitored S device causes more than one signal to change state. As an example, the opening or closing of a circuit breaker needs to be detected by a set of changeover contacts. One signal will change from a binary "one" to a "zero", while the other change from a binary "zero" to a "one". A valid change of state is therefore detected by the change in both of the related 10 0350a/AMD signals. Any other combination is to be recognised by the control scheme as an invalid combination which causes the low setting of the fault detecting device(s) to be selected on either one circuit breaker, selected circuit breakers, or, on all circuit breakers, depending on the specifics of the installation.

For d.c. electric railways, not all circuit breakers can have adaptive protection in a fail-safe manner. Most of the circuit breakers used on dc electric railways are polarised and magnetically held. The tripping of the circuit breaker is 000* 0 S achieved by the main circuit current setting up a magnetic flux oo o s e which opposes the holding ccil flux. The trip setting can be :4.10. S* *0 Schanged either by switching a preset current into the "test o o S coil" (which has been provided by the manufacturer to verify the trip setting of the circuit breaker), or by causing a preset reduction in the holding coil current. At reduced to*: holding coil current, there is less holding flux to oppose the 0 main circuit current. By both methods, that interaction of the main circuit current and the holding coil flux which causes the *0 0 circuit breaker to trip can be made to occur with less curre,," in the main circuit.

to For ac electric railways, the most practical method of changing the trip setting is considered to be the installation of two or more protection relays, each relay being set to a predefined pickup (and if necessary, time). To change the trip setting of the circuit breaker, the trip setting command signal can be arranged to short circuit the current coil(s) of the 11 0350a/AMD lower-set relays. When there is no command signal, the lowest-set relay is the first to operate and trip the circuit breaker. Whilst a valid adaptive protectio, command signal is being received, the lowest-set relay which is not short-circuited causes the circuit breaker to trip when the load or fault current exceeds the setting of the relay.

Figs. 3 and 4 illustrate two optional arrangements of the protection device and method for operating same in accordance with the present invention, Fig. 3 illustrating a distributed system, and Fig. 4 illustrating a centralised control system.

Figures 3 and 4, for simplicity, do not show the voltage transducers 14 and the add-on tripping device It will be appreciated by the persons skilled in the art

U

that numerous variations and modifications are envisaged to the protection device and method as hereinbefore described. Such variations and modifications should however be considered to fall within the scope of the invention as hereinbefore

U

described and hereinafter claimed.

0e c 12

Claims

2. A control system as claimed in claim 1 wherein each control means is provided with an adaptive trip setting.
3. A control system as claimed in claims 1 or 2 wherein a fail-safe comaiand is utilised to change the trip setting and hence the magnitude of the fault or load current or voltage required to operate each circuit breaker.
4. A control system as claimed in claim 3, wherein said fail-safe command utilises at least two signals adapted to concurrently change state for operation of said circuit breaker. A control system as claimed in any one of claims 1 to 4, wherein communication between said control means and said central processing means is via a conventional telephone circuit and appropriate modems.
6. A control system as claimed in any one of claims 1 to wherein binary signals are utilised. 13 0350a/AMD
7. A control system as claimed in any one of claims 1 to 6, adapted for use in an electric railway.
8. A control system, substantially as herein described with reference to the accompanying drawings.
9. A method of protecting and controlling the operation of circuit breakers on at least one feeder, comprising the steps of: detecting local faults and providing a signal indicative of the presence of said fault to a respective control means; operating a local circuit breaker by operator inputs and/or inputs derived from said control means; indicating the activation of said circuit breaker to a central processing means which interconnects each control means; and, supplying signals from said central processing means to adjacent control means to operate their respective circuit breakers. A method of protecting and controlling the operation of circuit breakers on at least one feeder, as claimed in claim 9 Swherein said operating step is performed by comparing the fault or load current or voltage with the trip setting provided within said circuit breaker.
11. A method of protecting and controlling the operation of oe circuit breakers on at least one feeder, as claimed in claim wherein said trip setting is operator adjustable.
12. A method of protecting and controlling the operation of circuit breakers in at least one feeder as claimed in any one of claims 9 to 11, when applied to electric railways. 14 0350a/AMD
13. A method of protecting and controlling the operation of circuit breakers on at least one feeder, substantially as herein described in relation to the accompanying drawings. DATED this llth day of September, 1992. ANTHONY JOSEPH GRIFFIN By His Patent Attorneys ARTHUR S. CAVE CO. r o r 15