GB2188800A

GB2188800A - Method of controlling parallel operation of tapped transformers in master-follower relationship

Info

Publication number: GB2188800A
Application number: GB08707946A
Authority: GB
Inventors: Kurt Kugler
Original assignee: Maschinenfabrik Reinhausen Gebrueder Scheubeck GmbH and Co KG
Current assignee: Maschinenfabrik Reinhausen Gebrueder Scheubeck GmbH and Co KG
Priority date: 1986-04-05
Filing date: 1987-04-02
Publication date: 1987-10-07
Anticipated expiration: 2007-04-02
Also published as: JPS6339425A; JP2635583B2; GB8707946D0; DE3611415A1; FR2596928A1; SE8701189D0; GB2188800B; FR2596928B1; SE8701189L; SE468494B; DE3611415C2

Abstract

A method of controlling parallel operation of tapped transformers in master-follower relationship is able to control transformers with unequal voltage taps. The data of all possible voltage taps of each transformer is deposited as a characteristic value and as voltage range in coding units (A1) and one of the transformers is assigned a master function through individual connection to an automatic regulating system (C1). The characteristic value of the instantaneous tap setting of the master transformer is fed to a data bus (B) which is connected by means of a respective switch (S2) with a comparison unit (A2) of each follower transformer. It is ascertained in the comparison unit of each follower transformer whether the characteristic value of the voltage tap of the master transformer agrees, in terms of voltage range, with the voltage tap present at the follower transformer. If this is not the case, the motor drive (MA) of the <IMAGE>

Description

SPECIFICATION Method of controlling parallel operation of tapped transformers in master-follower relationship The present invention relates to a method of controlling parallel operation of tapped transformers in master-follower relationship and to apparatus for carrying out the method.

A method for the parallel control of tapped transformers can be carried out readily insofar as transformers with identical performance specifications are in use. In that case it is sufficient in principle simply to ensure that the transformers assume the same tap setting. However, difficulties arise when transformers with different tap windings are to be operated in parallel running. It is then necessary to ensure, for parallel operation, that the difference between the open-circuit voltages has a minimum value.

There is thus a need for a simple and reliable method for control of the parallel running of two or more tapped transformers, especially transformers with unequal voltage taps.

According to a first aspect of the present invention there is provided a method of controlling parallel operation of tapped transformers in master-follower relationship, the method comprising the steps of assigning master status to a selectable one of the transformers by controlling the selected transformer from voltage regulating means and assigning follower status to the or each other transformer, detecting the instantaneous tap setting of each transformer and assigning to the detected setting a first code value respective to that setting and a second code value respective to the voltage range of that setting, comparing the first code value for the mastertransformerwith the second code value forthe or each followertransformer, and changing the tap setting of the or any follower transformer if the associated second code value represents a voltage range outside that respective to the compared first code value.

According to a second aspect of the invention there is provided apparatus for carrying outthe method of the first aspect of the invention, the apparatus comprising a plurality of tapped transformers operable in parallel and in master-follower relationship, voltage regulating means connectible to tap changing drive means of a selectable one of the transformers thereby to assign master status to that transformer and follower status to the or each other transformer, respective detecting and coding means to detect the instantaneous tap setting of each transformer and to assign to the detected setting a first code value respective to that setting and a second code value respective to the voltage range of that setting, and respective comparison means to compare the first code value for the master transformer with the second code value for the or each follower transformer and to cause the respective tap changing drive means to change the tap setting of the or any follower transformer if the associated second code value represents a voltage range outside that respective to the compared first code value.

Such a method and apparatus may enable simple adaptation of the open-circuit voltages of the transformers to be operated in parallel: In this case, each of the transformers concerned can enter into the master function or exercise the follower function at any time. This can be achieved through corresponding setting of the switching means, which preferably are electronic switches but can, of course, be constructed as purely mechanically acting switches. The method can be performed with presentation of the data to be transmitted as digital values or in analog form, for example as impressed measurement current, -in the milli-amp region.

An example of the method and an embodiment of the apparatus will now be more particularly described with reference to the accompanying drawings, in which: Fig. lisa schematic block diagram of apparatus embodying the invention; Fig. 2 is a table showing the switch settings for individual switch members of the apparatus; and Fig. 3 is a coding table for several tapped transformers of the apparatus.

Referring now to the drawings, there is shown in Fig. 1 apparatus comprising a plurality of tapped transformers (only one of which is illustrated) each having a tap switch OTL and motor drive MA for the tap switch. Each transformer is drivable individually by a drive control Cl, for example from a voltage regulator. The transformers are drivable in masterfollower relationship in which only a selectable one of the transformers is connected to the drive control Cl.The nature of the transformer drive is determined by switch settings, i.e. as is evident from Figs. 1 and 2, switches S0 and S1 are closed and switches S2 and S3 open for a master function of the selected transformer, while for the follower function the switches S2 and S3 are closed and the switches S0 and S1 open.

From this, there results the following functional course: The motor drive MA of the tap switch OTL of the master transformer receives a command for a tap change by way of the drive control Cl, the closed switch S0 and a further drive control C2. The motor drive MA of the tap switch of the master transformer reports the found setting by way of C3 to a coding unit Al. The associated code value is fed by way of the switch S1 to a data bus B, which leads to the other transformers which operate in follower function.

In the case of follower operation, the following course results when the switches S2 and S3 are closed and the switches S0 and S1 are open: The tap setting present at the follower transformer is again reported from the associated motor drive MA of the tap switch OTL by way of C3 of the associated coding unit Al. The voltage range corresponding to this tap is reported by way of C4 to a comparison unit A2. The code value, which is present on the data bus B, of the voltage tap setting of the master transformer is fed by way of the closed switch S2 into this comparison unit A2.If it is ascertained in the comparison unit that this characteristic value lies outside the voltage range of the voltage tap present at the follower transformer, then the motor drive of the tap switch of the follower transformer receives a corresponding command for setting change by way of the closed switch S3 and the drive control C2. This command continues until a voltage range, which covers the characteristic value of the master transformer, has been found at the follower transformer.

Fig. 3 clarifies these relationships. Shown in a first scale is the open-circuit voltage UL, the coded values of which are shown again, for example as 8bit values, atthe extreme right in the scale. The characteristic values and the voltage ranges of a first transformer with taps 1 to 6 are fixed in the scale Tr 1, those of a second transformer with taps -3 to +3 in the scale Tr 2 and those of a third transformer with taps 1 to 5 in the scale Tr 3. It will now be assumed that the first transformer Tr 1 runs in master function and stands at tap 2, while the second, follower transformer Tr 2 stands at tap -2 and the third, follower transformer Tr 3 at tap 1.The characteristic value (UL = 5.8) respective to the tap 2 of the first transformer Tr 1 agrees with the characteristic value of the tap -2 of the second transformerTr 2 and thus lies in the voltage range of this tap, i.e. the transformer Tr 2 already has the correct position. The situation is different in the case of the third transformer Tr 3, since the characteristic value (UL = 5.8) of the master transformer lies outside the voltage range of the tap 1 of the follower transformerTr 3. Thus, this transformer, as previously described, receives a command for a setting change. It must assume tap 2 as is evident from Fig. 3. It is also evident that the range for the parallel running of the three transformers in this exampleextendsfrom UL = 5.7 to UL = 6.2, which are the lowest and the highest characteristic value of the master transformer.

The apparatus shown in Fig. 1 can also be used at any time for individual regulation. The previously described master-followerfunctions are excluded by opening the switches S1, S2 and S3, and the driving of each transformer takes place solely by way of the drive control C1 and the closed switch SO.

Claims

1.A A method of controlling parallel operation of tapped transformers in master-follower relationship, the method comprising the steps of assigning master status to a selectable one of the transformers by controlling the selected transformer from voltage regulating means and assigning follower status to the or each other transformer, detecting the instantaneous tap setting of each transformer and assigning to the detected setting a first code value respective to that setting and a second code value respective to the voltage range of that setting, comparing the first code value for the master transformer with the second code valueforthe or each follower transformer, and changing the tap setting of the or any follower transformer if the associated second code value represents a voltage range outside that respective to the compared first code value.

2. A method as claimed in claim 1, wherein the step of detecting comprises determining the setting of tap changing drive means of each transformer.

3. A method as claimed in either claim 1 or claim 2, wherein the step of comparing comprises feeding the first code value for the master transformer to a data bus common to all the transformers and then from the bus to comparison means of the or each follower transformer.

4. A method as claimed in claim 1 and substantially as herein before described with reference to the accompanying drawings.

5. Apparatus for carrying out the method claimed in claim 1, comprising a plurality of tapped transformers operable in parallel and in master-follower relationship, voltage regulating means connectible to tap changing drive means of a selectable one of the transformers thereby to assign master status to that transformer and follower status to the or each other transformer, respective detecting and coding means to detect the instantaneous tap setting of each transformer and to assign to the detected setting a first code value respective to that setting and a second code value respective to the voltage range of that setting, and respective comparison means to compare the first code value for the master transformer with the second code value for the or each follower transformer and to cause the respective tap changing drive means to change the tap setting of the or any follower transformer if the associated second code value represents a voltage range outside that respective to the compared first code value.

6. Apparatus as claimed in claim 5, each detecting means being arranged to determine the setting of the tap changing drive means of the associated transformer.

7. Apparatus as claimed in either claim 5 or claim 6, comprising a data bus common to all the transformers, first switching means operable to allow feed to the bus of only the first code value for the master transformer, second switching means operable to allow feed of said first code value from the bus to the comparison means of only the or each follower transformer, and third switching means operable to allow feed of a drive control signal from the comparison means to the tap changing drive means of only the or each follower transformer.

8. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.