AU607497B2

AU607497B2 - Alternating current traction system voltage regulator

Info

Publication number: AU607497B2
Application number: AU16659/88A
Authority: AU
Inventors: Anthony Joseph Griffin
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-05-25
Filing date: 1988-05-24
Publication date: 1991-03-07
Anticipated expiration: 2008-05-24
Also published as: AU1665988A

Description

607497

AUSTRALIA

PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Application Number: Lodged: This do"nTrrnt contains the amendments made under Section 49 and is correct for printing 00 c 0 0 C 0 0 0 o 00 00 0 0000 Complete Specification Lodged: Accepted: Published: Priority: Related Art: TO BE COMPLETED BY APPLICANT ooiName of Applicant: Address of Applicant: 4 C 0 00 C 0 a o0 ®Actual Inventor: ,'Address for Service: 000 0 0000 0( 0 0 oooo 0 0 3 0 (0 o Anthony Joseph GRIFFIN 13 Bunglow Road Peakhurst NSW 2210

AUSTRALIA

Anthony Joseph GRIFFIN ARTHUR S. CAVE CO.

Patent Trade Mark Attorneys Level Barrack Street SYDNEY N.S.W. 2000

AUSTRALIA

614- Complete Specification for the invention entitled: Alternating Current Traction System Voltge Regulator.

The following statement is a full description of this invention including the best method of performing it known to me:- 1 ASC 49 l ALTERNATING CURRENT TRACTION SYSTEM VOLTAGE REGULATOR The present invention relates to an alternating current traction system voltage regulation device, and in particular, to such a device, when utilised in application to the regulation of feeder voltage and current for electrically powered trains.

Previously, mechanically-switched capacitors have occasionally been applied to ac traction systems. The reasons o o for not applying capacitors and more widespread scale is not o0 O clear but it is believed to be due to a combination of the 0000oo O o°o0 following circumstances.

oooooo A desire for simplicity: simple systems do not contain high voltage capacitors; o o The rapid voltage fluctuations on an ac traction system o° would require the capacitors to be switched in and out o o frequently; The electro mechanical voltage sensing devices and switches are relatively slow compared with electronic switches, 0000 00.. hence the voltage may fall too low or rise too high before the 00 0 0 0 1 capacitor is connected or disconnected from the system; Commericially available capacitors have a reputation of being relatively unreliable; The impact of installing capacitors on ac traction systems (which have relatively high harmonic currents) is not widely or thoroughly understood; The major cause of high voltage capacitor failure is over voltage. AC traction systems are rich in harmonic currents and 2 1245E AMD/0298a therefore readily generate over voltages in capacitors; The frequent switching of mechanically switched capacitors causes wear on the switches which increases the maintenance requirements and hence costs; and The train loads are varying in location, magnitudes, and harmonic generation. Engineering analysis of the system is therefore time consuming, expensive, and not always conclusive.

No thyristor (SCR) switched capacitors are known to have been installed at fixed location on any AC traction system, 0oo0 whether at the source substation or at other fixed points along 0 0 00oo o 00 the AC traction system, but 3 phase static VAR compensators oe o o 0 0 have been applied at transformer primary voltage primarily for 0 0 0000 other purposes (minimisation of negative sequence voltage 00 00 0 .0o. regulation as a lower priority).

0 00oo00oo 0 0 In one broad form, the present invention provides an AC traction system regulation device when used for the regulation 0000 of single phase traction systems, said device comprising: 0000 *ooo a monitoring means to continuously monitor the line 00 oo 0 voltage of a feeder; o00000oooo S0° a control means adapted to supply a control signal in 0 o o response to the magnitude of said line voltage monitored by 0400 o0 0° said monitoring means; IC a switching means controlled by said control means; andr a capacitive device adapted to selectively provide capacitive reactance to said feeder, wherein, said capacitive device is selectively electrically connected to said feeder by said switching means.

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AMD/0298a Preferably, the ifvention as hereinabove described is used for the regulation of single phase electric railways.

Preferably, said switching means is a Silicon Controlled Rectifier (SCR) or thyristor being a high speed switching means.

CO

C O r O 00 S 0 0O 0 00 00 0 00 0 000 00 0000 0 0

OO

00 0 0000 0 oo 0 0

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0 0a a 0000 0000 oC o oO c 3a Said control means preferably operates said switching means by the comparison of said magnitude of said line voltage to predetermined adjustable upper and lower turn-on and turi-off voltages.

The present invention will become more fully understood from the following detailed description thereof, in connection with the accompanying drawings, in which: Fig. 1 shows a schematic diagram of the alternating current traction system, in accordance with the present invention; a Fig. 2 illustrates a block diagram of one simple embodiment of the regulator device; Fig. 3 shows various alternative embodiments of the

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regulator device; Fig. 4 illustrates the provision of a plurality of regulating devices in use with a single feeder; and Fig. 5 shows a modified control device of the regulator tn device of the present invention.

In Fig. i, is illustrated in schematic form, an alternating current traction system voltage regulator in accordance with the present invention. The AC traction system comprises one or more feeders i, extending from a substation 2, each feeder 1 supplying loads 3 in the form of electrically powered trains. The loads 3 are therefore moving in time, and the size of the loads are fluctuating in magnitude. Since the transformer in the substation 2 and the feeder 1 each possess electrical resistance and inductive reactance, the instantaneous load current and instantaneous load voltage are 4 1245E C C 0 0 IC

CC

0 C C C C 0 C Q 0 00 C C 0c C) o c 0 oo 0 00e 00 0 00C 0C'00i S. U 0 0 0 0 not normally in phase. Therefore the load current, the resistance, and the inductive reactance of the feeder interact to cause a voltage drop between the substation 2 and the load 3. It is generally known that a capacitor is a device which, when connected to an alternating current voltage circuit generates reactive power in the alternating current system.

The capacitor, by virtue of its property of generating reactive power when connected to an AC traction system is able to counteract such a voltage drop.

The AC traction voltage regulator system of the present invention is therefore designed to generate a controlled amount of reactive power in close proximity to the fluctuating and moving train loads 3, to both minimise the reactive power losses and to raise the voltage by counteracting the effects of the resistive and inductive reactance voltage drops. That is, the system of Fig. 1 is designed to maintain a substantially constant voltage at the point where a regulator 4, being a capacitive type device, is installed in the AC traction system.

In Fig. 2, is shown a block diagram of one simple embodiment of the regulator system in accordance with the present invention.

A capacitor 5 chosen to give a degree of compensation for the inductive load, line and supply reactance is adapted to be switched by a fast bi-directional switch 6 each switch being driven by a control system 7 which responds to the fundamental-frequency voltage, measured by a voltage measuring device 8 connected to the system feeder 1. The AC traction system voltage may, for example, be controlled to operate 5 1245E before the under voltage relay on each train drops out (on a falling voltage) or before the capacitor itself and the equipment at the load is damaged by over voltage (on a rising voltage).

The control system 7 should respond only to the fundamental frequency voltage as any harmonics and spikes which exist on an AC traction system feeder 1 would otherwise cause instability in the controller 7 and the resulting switching of the capacitors 5 would have an undesirable effect on the AC o0 traction system. The switch 6 should also be fast acting so 000 0 o o that the rms AC voltage is below a low-set value for the 0 0 shortest possible time when the AC traction system voltage is 0o, 0 falling, and so that the rms AC voltage exceeds a high-set 0 0 value for the shortest possible time when the AC traction system voltage is rising.

Because of the limitations in the physical properties of C o 0 commercially available capacitors, the fast-acting switch should be closed at a time when the instantaneous AC traction system voltage is the same as the instantaneous capacitor .oo voltage.

0o 0o Pairs of Silicon Controlled Rectifiers (SCR) or thyristors connected in reverse parallel (or in smaller sizer, triacs), being fast-acting, commercially available devices at an economical price, are considered to be the most suitable devices for the fast-acting switch which satisfy the above mentioned requirements, but that does not prevent other devices having similar properties from being used.

Because an AC traction system is usually rich in harmonic 6 1245E currents, and those harmonic currents can cause destructive overvoltages on the capacitors, it is preferable an harmonic filter is provided at each voltage regulator installation.

Since an harmonic filter consists of a shunt connected capacitor in series with other devices, the capacitor used for the traction system voltage regulation may with the addition of series and/or shunt connected devices function as an harmonic filter and a voltage regulator. Subject to detail design each .oc0 branch of the voltage regulator may be arranged to function as o o o 0 o S harmonic filter or only the branch(es) which are first o 00 connected to the AC traction system may function as an harmonic filter.

o 0 In Fig. 3, is shown various embodiments of the present invention in which transformer 9 or inductor 10 is provided in 0°0 the voltage regulation system 4, to enable the system 4 to meet design performance criteria and to enable the ratings of o 0 0 commercially available components to be matched to the system 0 ,0 0 voltage and the performance criteria.

It is intended that the controllers, high speed switches o. and capacitors described below be installed at fixed locations beside an AC electrified railway each installation consisting of one or more controllers, high speed switches and capacitors.

In order to generate sufficient reactive power, but at the same time cause only small step changes in the AC traction system voltage, it is necessary to install one or more controllers, switches and capacitors at a location Fig. 3d and 3e. As the AC traction system voltage tends to fall, the controller(s) close successive high speed switches to connect 7 1245E capacitors to the AC traction system. As the AC traction system voltage tends to rise, the controller(s) open successive high speed switches to disconnect capacitors from the AC traction system.

If the high speed switch closes at the time that the instantaneous AC traction system voltage is equal to the capacitor voltage, the instantaneous capacitor current is comparable to the rated capacitor current. If the switch is Sclosed at some other time, the capacitor current may for a S short time exceed the rated current of the capacitor and the SCR and either the capacitor or the SCR may be damaged. To ssro soften the turn on of the SCR and the capacitor, a reactor as shown in Fig. 3(c) and other devices may, subject to detailed design for a specific installation be connected in series with Sthe capacitor and switch. The inclusion of a series reactor, o a unless it is part of an harmonic filter, is not preferred as a o. reactor absorbs reactive power, counteracting the action of the capacitor. A transformer, as shown in Fig. 3(a) and 3(b) also has inductive reactance and can serve the same purposes as a reactor. In a commercial application a transformer may be specified for economic reasons.

In Figs. 4(a) and are shown two alternative embodiments of the present invention, wherein a plurality of alternating current traction system voltage regulators are provided along the feeder. In Fig. the regulators are totally separate entities, each comprising all the components as shown in Figs. 1 and 2. The regulator devices 4 are spaced along the feeder 1 in spaced apart relationship, as required to -8- 1245E maintain regulation of the line voltage and current. In Fig.

each of the capacitors 10 is separately switched into the regulation system as required by means of switches 11. The switches 11 are each controlled by a common controller 12.

The controller device may be a device which turns on the switch when the AC traction system voltage falls to pre-set level, and turns off the switch when the AC traction system voltage rises to a pre-set level. However, the control device response may be modified by an external signal as shown in Figs. 5(a) and 5(b) such as a command to reduce the maximum demand of the AC traction system, or by an external signal from Sa master controller regulating a number of control devices and which may be acting to simultaneously optimise the operating conditions at several locations in an AC traction system. The reduction in the maximum demand of the AC traction system may, for example, in some cases be achieved by a reduction of the AC C traction system voltage.

While particular embodiments of this inventio. have been described, it will be evident to those skilled in the art that oooo 0 000 0 ooa the present invention may be embodied in other specific forms o 0 0 0 0 0o 0 00a without departing from the essential characteristics thereof.

The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

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Claims

1. An AC traction system regulation device when used for the regulation of single phase traction systems, said device comprising: a monitoring means to continuously monitor the line voltage of a feeder; a control means adapted to supply a control signal in response to the magnitude of said line voltage monitored by said monitoring means; a switching means controlled by said control means; and, a capacitive device adapted to selectively provide capacitive reactance to said feeder, wherein, said capacitive device is selectively electrically connected to said feeder by B said switching means.

2. An AC traction system regulation device as claimed in claim 1, when used for the regulation of single phase electric railways.

3. An AC traction system regulation device as claimed in claims 1 or 2, wherein said switching means is a Silicon Controlled Rectifier (SCR). S

4. An AC traction system regulation device as claimed in any one of claims 1 to 3, wherein said control means operates said switching means by the comparison of said magnitude of said line voltage to predetermined adjustable upper and lower turn-on and turn-off voltages.

An AC traction system regulation device as claimed in any one of claims 1 to 4, further comprising a transformer means, electrically connected between said capacitive device and said 10 __od AMD/0298a feeder.

6. An AC traction system regulation device as claimed in any one of claims 1 to 5, further comprising a harmonic filter to filter any unwanted harmonic currents or spikes existing on the AC traction system.

7. An AC traction system regulation device as claimed in claim 6, wherein said harmonic filter is a shunt connected capacitor.

8. An AC traction system regulation device as claimed in claim 6, wherein a transformer or inductor or other components S are in series and/or parallel connection between said S, capacitive device and said feeder. o?

9. An AC traction system regulation device as claimed in any one of claims 1 to 8, wherein said capacitive device consists of a plurality of capacitors and said switching means consists of a plurality of switches, wherein each of said capacitors is selectively connected to said feeder by a respective one of said switches, each of said switches being controlled by said control means. °U00

10. An AC traction system, comprising a plurality of AC 00*.4,0. Straction system regulation devices as claimed in any one of o claims 1 to 9. o 11. An AC traction system regulation device, substantially as herein described with reference to the accompanying drawings. DATED this 23rd day of October, 1990. ANTHONY JOSEPH GRIFFIN By His Patent Attorneys ARTHUR S. CAVE CO.

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