AU629379B2 - Method for synchronising the transmitters of a plurality of transmission stations of a telecontrol transmission system - Google Patents

Abstract

In ripple-control transmitting installations, which consist of a ripple-control centre and a plurality of decentralised substations, each substation containing a ripple-control transmitter which supplies a ripple-control message into a current supply network, it is intended that the ripple-control message be supplied synchronously by the individual transmitters. The invention proposes a method for transmitting a data message from the ripple-control centre to the substations and for synchronised generation of a ripple-control message in the substations which corresponds to the data message. In this method, the data message is transmitted in the multi-point traffic from the ripple-control centre to the substations, acknowledgement of receipt of the data message is asked for and, if necessary, the data message is transmitted repeatedly. In the substations, receipt of a data message initiates the start of a delay period after which the ripple-control message is transmitted provided no countermand message, transmitted by the ripple-control centre, occurs before the delay period has elapsed. <IMAGE>

Description

629379 COMMONWEALTH OF AUSTRALIA Patents Act 1952 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number Lodged Complete Specification Lodged Accepted Published Priority 22 AUGUST 1989 Related Art Name of Applicant 0 Address of Applicant :ASEA BROWN BOVERI AKTIENG-

ESELLSCHAFT

:KALLSTADTER STRASSE 1, D-6800 MANNHEIM 31

GERMANY

:JOACHIM DOBBERSTEIN, Dr. BERTHOLD BUNTEN, MANFRED HERR, F.B. RICE CO., Patent Attorneys 28A Montague Street BALMAIN NSW 2041 Actual Inventor(s) Address for Service

I

4 Complete Specification for the invention entitled: "METHOD FOR SYNCHRONISING THE TRANSMITTERS OF A PLURALITY OF TRANSMISSION STATIONS OF A TELECONTROL TRANSMISSION

SYSTEM"

The following statement is a full description of this invention including the best method of performing it known to us/mte- 1A- Method for synchronisin the transmitters of a plurality of transmission stations of a telecontrol transmission system The invention relates to a method for transmitting data telegrams from a telecontrol central station to a plurality of substations each having a telecontrol transmitter, and for controlling the telecontrol transmitters to achieve a pulse-synchronised transmission of an audiofrequency telecontrol telegram.

io°. Telecontrol systems are used for controlling loads in o power supply systems. A telecontrol system consists of a Scentral telecontrol transmission system and a large S* 15 number of receivers. Telecontrol transmission systems superimpose audio-frequency control signals, termed telecontrol telegrams, on the system voltage. The telecontrol telegrams are inserted in the medium-voltage or high-voltage system. From there the telecontrol telegrams proceed into the low-voltage system, in which the receivo ers are installed. The switching instructions transmitted with the telecontrol telegram are evaluated in the receivers and are output to the equipment connected.

A telecontrol transmission system can consist of one telecontrol central station and a plurality of substations, the substations containing in each'case one Stelecontrol transmitter which inserts the telecontrol telegram into the medium-voltage or high-voltage system S3o with a typical output of 100 kVA, for example. The telecontrol telegram can be generated here decentrally in the substations. A telecontrol command which is to be transmitted as telecontrol telegram is defined in the telecontrol central station according to aspects of load .3 management and is first transmitted as data telegram from i I 2 the telecontrol central station to the substations.

The audio-frequency pulses of a telecontrol telegram superimposed on the power supply system must be inserted synchronously by all transmitters in order to achieve the required voltage level in the case of meshed operation or when different subnetworks are interconnected. The voltage level is obtained from the sum of the partial currents of the individual transmitters multiplied by the resistance of the system load. If one or more substations have not received the data telegram of the telecontrol central station correctly, and hence do not transmit a telecontrol telegram, the level required for the reliable activation of the telecontrol receivers is not reached.

For the above reasons, it is necessary to ensure a secure *t transmission of data telegrams from the telecontrol central station to the substations and a suitable control of the telecontrol transmitters in the substations in do order to guarantee the desired pulse-synchronised transmission operation.

This state of affairs is described in the ABB Publication No. DSN 107688 D of March 1988 with the title "Rundsteuerzentrale Ricontic RLZ 400 Neue Fdhigkeiten und Strukturen (Telecontrol Central Station Recontic RLZ 400 New Capabilities and Structures), in particular on page 6 under "Neue gesicherte Datenibertragung" (New Secure Data Transmission). A known arrangement and a 3 method for transmitting the data telegrams in multi-point traffic mode (broadcast) with high speed and in a secure manner from the telecontrol central station to the substations is also disclosed there. In the reverse direction, there is in each case a point-to-point connection between the substations and the central station. It is thus also possible to transmit data telegrams to the substations for test purposes, and to acknowledge the correct reception of data telegrams without generating a telecontrol telegram.

3 Although telecontrol systems do not need to function with absolute reliability, since no security-relevant switching actions are controlled with telecontrol commands, as a high a level of reliability as 'possible, however, should be achieved in view of the considerable economic significance of fault-free load planning. In order to achieve that all substations receive the data telegram correctly with a high degree of probability even in the case of brief transmission faults, with the known method the data telegram is always transmitted twice in succession. This is shown in Figure 5 of the aforesaid publication and described in the associated text. The two data telegrams are transmitted in succession by a process *o0. computer, capable of real-time operation, at a time 0 15 interval which must be complied with exactly. The recep- 0 o* tion of the first and of the second data telegram trig- 0 0 o gers, in accordance with the t.ime interval between the 0, data telegrams, different delay times, following the o 0" expiry of which the audio-frequency telecontrol telegram iO is transmitted even if only one of the data telegrams was received correctly.

Starting from this known method for data transmission from a telecontrol central station to substations, the invention is based on tha nbjrm n developing the method further in such a way that no real-time capability of a controlling computer is necessary for carrying out the method, and thus a conventional personal computer, for example, can be employed.

This obectis achieved by the variants of a method for transmitting data telegrams from ctelecontol cenr station to a plurality of substations ttd-n First variant: Method For transmitting data telegrams from a telecontrol 4V central station to a plurality of substations each 4 II.t t 1t q 4 9 containing a telecontrol transmitter, and for controlling the telecontrol transmitters to achieve a pulse-synchronised transmission of an audio-frequency telecontrol telegram, a) a first data telegram being transmitted first of all from the telecontrol central system in multi-point traffic mode to ,all substations, and triggering hebsethe beginning of a delay period, after the expiry of which the telecontrol telegram is transmitted, with the following further steps: b) after transmission of the first data telegram the telecontrol central station asks the substations to confirm the correct reception of the first data telegram (yes); if all substations confirm the reception, there is no further reaction from the telecontrol central station and the telecontrol telegram is transmitted after the delay period has expired; Q0 c) if at least one of these substations does not report confirmation of the reception of the first data telegram the following further procedure is executed: cl) the telecontrol central station transmits a cancellation telegram already before the delay period has expired, whereupon the running of the delay period is cancelled in the substations where the delay period is running, c2) the telecontrol central station transmits a :0o second data telegram which triggers the beginning of the delay period again, c3) the telecontrol central station asks the substations to confirm the correct reception of the second data telegram and omits further 3S reactions if it receives confirmation (yes) from all substations, so that the telecontrol telegram is transmitted after the delay period has expired; d) if at least one of the substations does not report

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1: 1 5 4*4a 'Ir o a 4k confirmation of the reception of the second data telegram the telecontrol central station again transmits a cancellation telegram, whereupon the running of the delay period is.cancelled again in the substations, and hence the telecontrol telegram is not transmitted.

In a second variant of the method below, the reception of a cancellation telegram from the telecontrol central station is also interrogated: Method for transmitting data telegrams from a telecontrol cental station to a plurality of substations each containing a telecontrol transmitter, and 15 for controlling the telecontrol transmitters to achieve a pulse-synchronised transmission of an audio-frequency telecontrol telegram, A) a data telegram being transmitted first of all from the telecontrol central station in multi-point j0 traffic mode. t. all substations, and triggering the beginning of a delay period, after the expiry of which the telecontrol telegram is transmitted, with the following further steps: B) after transmission of a data telegram the telecontrol central station asks the substations to confirm the correct reception of the data telegram; if all substations confirm data telegram reception (yes), there is no further reaction from the telecontrol central station and the telecontrol telegram is transmitted after the delay period has expired; C) if at least one of the substations does not report confirmation of the reception of the data telegram the following further procedure is executed: Cl) the telecontrol central station transmits a cancellation telegram already before the delay period has expired, whereupon the running of the delay period is cancelled in the substations where the delay period is running, i i i1- 6- C2) the telecontrol central station asks the substations to confirm the correct reception of the cancellation telegram, D) if all substations confirm the reception of the cancellation telegram (yes), the central station checks whether a predetermined period of time has been reached, if the predetermined period of time has not yet been reached the transmission attempt is repeated by transmission of a data tele- [0 gram (step A) and of the interrogation step B; if the predetermined period of time has been reached (yes), the transmission attempt is aborted; E) if at least one of the substations does not report ots, confirmation of the reception of the cancellation Sof, telegram (result "no" in step C2), the telecontrol so central station checks whether the delay period has expired; if the delay period has expired (yes), the transmission attempt is aborted, if the delay period has not yet expired steps C and B are repeat- Q0 ed, that is to say transmission of a cancellation telegram is repeated.

According to an advantageous embodiment for the two method variants, a fault message is provided after each 96 unsuccessful abortion of the transmission attempt.

An ~s advantage of the invention is that a conventional personal computer which does not have the capability of a real-time computer can be employed, and it is ao also unnecessary for said personal computer to be provided with this capability by means of a downstream interface device. This is made possible by the fact that the method requires no fixed time intervals between data telegrams transmitted repeatedly. It is only necessary ZS for the time interval between a faulty first transmission of a data telegram and the reception of a cancellation telegram to be shorter than the delay period. During this delay period, therefore, it is necessary for interrogation with respect to the correct reception of a data 7 telegram, the transmission of a cancellation telegram, the interrogation with respect to the'reception of the cancellation telegram and, if necessary, a repeated transmission of the cancellation telegram to take place.

In addition, the time intervals between double or multiple transmissions of the data telegrams may vary for each telecontrol telegram transmission operation, that is to say in the case of transmission at different times of LO the day.

The delay period required can be estimated from the following example. If the transmission takes place at a rate of 200 Bd and a data telegram has 100 bits, the transmission of one data telegram takes 500 ms. If telegrams shortened to 50 bits are used for interrogation and response telegrams, and if it is assumed that substations must be interrogated in succession, 5 seconds are necessary for this. The total time for determining a SO fault-free transmission is thus 5.5 s. If a cancellation telegram becomes necessary in the case of faulty transmission, and if its reception is likewise interrogated, then a further 5.5 s are required, i.e. a total of 11 s.

If it is assumed that the cancellation of the telegram was also faulty, and a further cancellation telegram is to arrive in the substation before the delay period expires, then a delay period of 12 s would be suitable.

With higher baud rates or fewer stations, the delay period necessary is correspondingly shortened.

3o SThe method is described below with reference to the drawing, in which Figs. la to Ic show the method as a flow chart and Fig. 2 represents diagrammatic examples of possible method procedures.

The function chart according to Fig. la illustrates the method procedure in the telecontrol central station in accordance with the first method variant, and next to it the corresponding procedure in the substations in Fig.

-8- ~ttr r rii n o r rr r ri r, n t

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lb. The procedure in the substations illustrated in Fig. lb also applies to the second variant, the function procedure of which is shown in the central station in Fig. ic.

S

If the transmission of a telecontrol telegram is initiated in the telecontrol central station, a first transmission of the data telegram to the substations takes place first of all (step A in Fig. la).

[0 In the substations, the reception of a data telegram triggers the switching-on of the telecontrol transmitter.

This means that capacitors are charged in the transmitter and the transmitter is placed in a state of readiness.

15 The transmitter is switched off after each cancellation of the data telegram and after each transmission of the telecontrol telegram.

In addition, the reception of a data telegram triggers Qo in the substations the start of a delay time, after the expiry of which a corresponding telecontrol telegram is generated on the basis of the data telegram, and is transmitted by the telecontrol transmitter.

After the data telegram has been transmitted to the substations, the telecontrol central station asks the substations in succession in an interrogation cycle (step B in Fig. la) whether the data telegram was received. If all substations report a reception confirmation (yes), ;0 then a further reaction of the telecontrol central station is omitted and the substations generate the telecontrol telegram and transmit it after the delay period has expired.

This fault-free procedure is illustrated in Fig. 2 as example In example the data telegram is received at time 1, and the telecontrol telegram is generated and transmitted at time 6 after the delay period to has expired.

t i;;i i -9- If, on the other hand, the interrogation of the telecontrol central station results in at least one of the substations not confirming reception (no) of the data telegram (compare first branch point in the flow chart of S the central station in Fig. 1A), then the telecontrol central station transmits a first cancellation telegram (step cl) which causes the running delay period to be cancelled in the substations (compare first branch point in the flow chart of the substation in Fig. ib). Follow- LO ing this, the data telegram is transmitted a second time (step c2 in Fig. la), whereupon the delay period commences again in the substation. This is again followed by the telecontrol central station interrogating (step c3 in Fig. la) with respect to the reception of the second transmission of the data telegram, and the further procedure is as described above for the first transmission of the data telegram, i.e. either no further reac- I tion of the central station or transmission of a cancel- Sf lation telegram (step d in Fig. la) to terminate an o unsuccessful transmission attempt. The unsuccessful transmission attempt can be reported as a fault.

Fig. 2 shows as second example b) a previously described faulty transmission of a first data telegram at time i, a cancellation telegram which leads to the cancellation of the running of the delay period being transmitted at a time 2. The delay period thus shortened to the period to* does not trigger any transmission of the telecontrol Stelegram. The second data telegram arrives at a time 3.

In the example b) illustrated, it is assumed that this second data telegram is received correctly by all substations, so that no cancellation is issued and the generation and transmission of the telecontrol telegram can take place at time 6.

Fig. 2 illustrates as example c) a case where a second data telegram is transmitted at a time 3, said data telegram being cancelled after an interrogation and a lack of confirmation at time 4. The reception of the 10 a 4 4 ft cancellation telegram is confirmed correctly, so that a data telegram is transmitted a third time at time which data telegram is confirmed as correctly received in all stations. After expiry of delay period the telecontrol telegram is then finally generated and transmitted at time 6.

Time periods tl to t 3 which in each case lie between the transmission of data telegrams are indicated in the examples b) and c) illustrated in Fig. 2. With respect to the suitability of computers, it is important that the time periods tj, t 2 and t 3 may be different, and may also be different from the period t 0 t5 Fig. lb shows the function sequence in the telecontrol central station in the case of the second method variant.

The steps A (transmission of a data telegram), B (interrogation of the substation) and C1 (transmission of a cancellation telegram) corresponding [sic] to the steps Qo a to cl in Fig. la. In the second variant, however, an interrogation cycle C2) is added, in which the reception of the cancellation telegram is interrogated. If the reception is confirmed (yes), then in a step D it is checked whether a predetermined period of time has expired. For operational reasons, this period of timne is provided for limiting the transmission attempts. If the time period has not yet expired the step A and the following steps are repeated. If the period of time has expired (yes), the transmission attempt is aborted.

S0 If the reception of the cancellation telegram is not confirmed (no) in the interrogation cycle C2 of a substation, then it is checked in a step E whether a repetition of the transmission of the cancellation telegram is sensible. This is the case as long as a delay period which has been activated in the substations has not yet expired. If the delay period has expired, the attempt to prevent the transmission of a telecontrol telegram is aborted. Otherwise, the steps C1 and C2 are repeated.

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Claims (3)

1. Method for transmitting data telegrams' from a telecontrol central station to a plurality of substations each containing a telecontrol transmitter, and for controlling the telecontrol transmitters to achieve a pulse-synchronised transmission of an audio-frequency telecontrol telegram, a) a first data telegram being transmitted first of all from the telecontrol central station in multi-point traffic mode t 41ll substations, and triggering -te=Es the beginning of a delay period, after the elapse of which the telecontrol telegram is trans- mitted, characterized by the following further steps: b) after transmission of the first data telegram the telecontrol central station asks the substations to confirm the correct reception of the first data telegram (yes); if all substations confirm the reception, there is no further reaction from the telecontrol central station and the telecontrol telegram is transmitted after the delay period has expired; c) if at least one of these substations does not report confirmation of the reception of the first data telegram the following further procedure is executed: cl) the telecontrol central station transmits a cancellation telegram already before the delay period has expired, whereupon the running of the delay period is cancelled in the substa- tions where the delay period is running, c2) the telecontrol central station transmits a second data telegram which triggers the beginn- ing.of the delay period again, c3) the telecontrol central station asks the substations to confirm the correct reception of the second data telegram and omits further I I II A.) 0L I;L reactions if it receives a confirmation (yes) from all substations, so that the telecontrol telegram is transmitted after the delay period has expired; d) if at least one of the substations does not report confirmation of the reception of the second data telegram the telecontrol central station again transmits a cancellation telegram, whereupon the running of the delay period is cancelled again in the substations, and hence the telecontrol telegram is not transmitted.

2. Method for transmitting data telegrams from a telecontrol cental station to a plurality of substations each containing a telecontrol transmitter, and for controlling the telecontrol transmitters to achieve a pulse-synchronised transmission of an audio-frequency telecontrol telegram, A) a data telegram being transmitted first of all from the telecontrol central station in multi-point traffic mode to ,all substations, and triggering -thm the beginning of a delay period, after the elapse of which the telecontrol telegram is trans- mitted, characterized by the following further steps: B) after the transmission of a data telegram the telecontrol central station asks the substations to confirm the correct reception of the data telegram; if all substations confirm data telegram reception (yes), there is no further reaction from the tele- control central station and the telecontrol telegram is transmitted after the delay period has expired; C) if at least one of the substations does not report confirmation of the reception of the data telegram the following further procedure is executed: Cl) the telecontrol central station transmits a cancellation telegram already before the delay period has expired, whereupon the running of H: 13 G rt rt U8 i' t the delay period is cancelled in the substa- tions where the delay period is running, C2) the telecontrol central station asks the substations to confirm the correct reception of the cancellation telegram, D) if all substations confirm (yes) the reception of the cancellation telegram, the central station checks whether a predetermined period of time has elapsed yet, if the predetermined period of time has not yet elapsed the transmission attempt is repeated by transmission of a data telegram (step A) and of the interrogation step B; if the predeter- mined period of time has elapsed (yes), the trans- mission attempt is aborted; E) if at least one of the substations does not report confirmation of the reception of the cancellation telegram (result "no" in step C2), the telecontrol central station checks whether the delay period has expired; if the delay period has expired (yes), the transmission attempt is aborted, if the delay period has not yet expired steps C and D are repeat- ed, that is to say transmission of a cancellation telegram is repeated.

3. Method acording to Claim 1 or 2, characterized in that a fault message is issued in the telecontrol central station afer unsuccessful transmission of a second or further data telegram. DATED THE 6th DAY OF AUGUST 1990 9 I ASEA BROWN BOVERI AKTIENGESELLSCHAFT. PATENT ATTORNEYS FOR THE APPLICANT F.B. RICE CO. i 1~ U