CONTROLLER AND METHOD FOR CONTROLLING ELECTRICAL SUPERGRID TRANSFORMER VOLTAGE

Abstract: A controller for controlling the tap positions of a group of on-load tap changing transformer (2, 2') has a respective tap position controller (14, 34, 14', 34') associated with each transformer (2, 2') each of which is arranged to be able to control its associated transformer in response to a measurement value dependent on the voltage at the transformer (2, 2'). A group sequence controller (16) is able to selectively disable the tap position controllers (14, 34, 14', 34') and output its own tap changing signals to adjust the spread of tap positions of the transformers as desired. Methods of use of such a controller are also disclosed. The invention finds primary application with the control of the high voltage supergrid transformer sections of National Power distribution systems.

Description: CONTROLLER AND METHOD FOR CONTROLLING ELECTRICAL SUPERGRID TRANSFORMER VOLTAGE This invention relates to a controller and method for controlling the tap positions of a group of on-load tap changing transformers whose outputs are connected to a respective- common busbar. The principal, but not exclusive, application of the present invention is to the control of the UK high voltage supergrid transformers section of the national power distribution system (132 kV and 66 kV) or other non-UK equivalents. In a typical sub-station each supergrid transformer is capable of being connected to, or disconnected from, a busbar. The busbar associated with each transformer can be connected to, or disconnected from, each other. In multiple transformer substations it is possible to have a number of busbars connected together to form a Main and Reserve distribution systems. The busbar voltage is maintained at a particular value within a predetermined range and can implement desired network operating modes including, for example, reactive power compensation. A known way of controlling the output voltage from a transformer is to use a regulating transformer with selectable tap positions from the secondary windings. The tap position can be changed by means of a motor which moves the tap point. A transformer tap position controller continuously monitors the transformer and generates appropriate signals to cause the motor to move to maintain the output voltage within desired limits. The voltage deadband (gap) within which the output voltage is to be maintained is usually expressed as a percentage of the desired voltage, the voltage deadband (gap) being equally disposed about the desired value. The tap changer controller will not act if the voltage is within the deadband (gap) . The control of multiple transformers in a group has, to date, been a totally manual operation in which the transformer tap positions operator manipulated to obtain equal or different positions to meet the network requirements such as reactive power compensation, precautions against load disturbances, and so on. This is a labour intensive, time consuming task which can be difficult to perform where the transformer controllers are distant from each other or under rapidly changing supply or load conditions. According to a first aspect of the present invention a controller for controlling the tap positions of a group of tap changing transformers whose outputs are connected to a respective common busbar, the controller comprises: a plurality of transformer tap position controllers each of which is associated with a respective transformer of the group of transformers and is arranged to generate tap changing signals whereby the tap position of the associated transformer may be adjusted in dependence on whether a measurement value dependant on the voltage at the output respective transformer lies within a predetermined range of values and including means for putting the tap controller on hold or override; and a group sequence controller coupled to the transformer tap position controllers and arranged to monitor the respective tap positions, and to be able to put selected transformer tap position controllers on hold and to output tap changing signals to override said outputs from the selected tap changer controllers, as necessary, to directly adjust the spread of the tap positions of the transformers so as to fall within a predetermined limit. According to a further aspect of the present invention, a method of controlling a controller according to the first aspect of the present invention comprises: a) measuring the voltage at each transformer; b) calculating the average value of the voltages at each transformer at any given time; c) holding the tap positions of all but one transformer (the allocated transformer) of the group; and d) adjusting the tap position of the allocated transformer until the average voltage lies within a selected band of voltages. According to a further aspect of the present invention, a method of controlling a controller according to the first aspect of the present invention comprises adjusting, at intervals, the spread of the tap positions to less than or equal to a predetermined limit. The present invention provides a controller and methods which includes a group sequence controller and transformer tap position controllers which can together provide co-ordinated tap changes to maintain a predetermined output busbar voltage by automatic action of the transformer tap position controllers overridden, at intervals, by transformer tap position control signals from the group sequence controller. In a preferred embodiment of the present invention the controller includes a plurality of motor controllers each associated with a respective transformer and arranged to generate control signals to control the movement of the motor of the transformer in response to receipt of respective tap changing signals. The motor controllers generate electrical signals suitable for direct control of the tap position motors of the respective transformers on receiving tap changing signals from the respective controller. Such motor controllers can provide a convenient means for providing the required replacement of the tap changing signals from the transformer tap position controllers by signals from the group sequence controller when the transformer tap position controllers need to have their instructions overridden in order to allow the tap positions of the transformers to be adjusted to lie within a predetermined range of values. The transformer tap position controllers are conveniently arranged to receive a measurement value related to the output voltages of the transformers in the group and to automatically generate a tap changing signal if the measurement value lies outside a predetermined range of values for a predetermined length of time. In practice all but one of the group of transformers will have the transformer tap position controllers disabled by the group sequence controller so that the respective transformers remain in the position they have already attained unless overridden by tap changing signals generated by the group sequence controller. The transformer associated with the transformer tap position controller which continues to provide automatic regulation of the tap position is the one used to provide regulation of the output of the group of transformers. This controller associated with the transformer that is allocated by this control system shall be referred to from here on as the "allocated transformer" . In a preferred embodiment the voltage at the output of each of the transformers in the group is independently measured and the group sequence controller includes means for determining the average of these voltages and it is this average voltage that is used by the transformer tap position controllers to regulate the tap position of the respective transformers. The average voltage is continuously recalculated and provided to the transformer tap position controllers to provide appropriate feedback for the control loop. The transformers conveniently will have means associated with them indicating to the group sequence controller the tap positions of each of the transformers. This information is then utilised by the group sequence controller to override, when necessary, the automatic control of the transformers to adjust the tap positions of the group of transformers within predetermined bounds. That is, a allocated transformer has its transformer tap position controlled according to the average of the transformer outputs and at intervals the group sequence controller, as necessary, adjusts the tap positions of the transformers before returning once again to the automatic control of the allocated transformer to provide the regulated output of the transformer group. An embodiment of the present invention will now be described, by way of example only, with reference to the accompany drawings of which: Figure 1 is a schematic diagram of a control system incorporating a controller according to the present invention; Figure 2 is a schematic diagram of a transformer tap position controller; Figure 3 is a control schematic for a typical control system according to the present invention for controlling a group of transformers; and Figure 4 is a schematic diagram showing an overview of software suitable for automatic voltage control of the present invention. Referring to Figure 1, there is shown an overview of a controller according to the present invention illustrated, for clarity, with a single transformer of a group of transformers each having an output voltage measurement (VT) the value of which depends on the tap position of the transformer. The tap position is adjusted by means of a motor (not shown) controlled via "UP" and "DOWN" control lines 4 from a servo drive 6. The servo drive 6 can be controlled either manually or via the controller of the present invention according to the setting of a transfer switch 8, shown, for convenience, external to a manual drive controller 10 in which it is actually housed. In the position of the transfer switch as shown in Figure 1 the servo drive 6 is connected to the controller. When the transfer switch is switched to the alternative position the servo drive 6 is connected to the local manual drive unit 10 and is operated in the usual manner. A status feedback line 12 coupled between the manual drive and the controller indicates the status of the transfer switch to the controller 1. The controller 1 includes a transformer tap position controller 14 having "UP DRIVE" and "DOWN DRIVE" outputs 16 connected to the transfer switch 8 for connection when desired to the servo drive 6. The transformer tap position controller 14 is coupled to a group sequence controller 16 which provides overall coordination to the transformer tap position controller 14 and any other transformer tap position controller of the transformer group. Referring now to Figure 2 , there is shown schematically the control algorithm for a transformer tap position controller 14. The heart of the design for the transformer tap position controller is a gap action position algorithm which is dedicated to each transformer whether in single or multiple groups. This algorithm provides continuous surveillance of the voltage on the transformer busbar and initiates corrective action directly the bus voltage moves outside a pre-configurable deadband gap that is equally disposed about a target voltage. The output of the control algorithm is an initially delayed series of pulses of uniform shape directed to the transformer tap positioning servo drive 6 (see Figure 1). The transformer tap position controller of Figure 2 uses software control blocks, in particular I/A series standard blocks available from The Foxboro Company. In this case the gap action tap position algorithm is implemented using a differential GAP controller block 18 (DGAP) and a proportional time control block 20 (PTC). The DGAP block 18 and PTC block 20 receive the same measurement value. The measurement value may be the actual voltage on the busbar or an average voltage over all the transformers as calculated by the group sequence controller 16. The GAP settings and set points are identical for both the DGAP block 18 and PTC block 20. The DGAP block 18 is configured to manipulate a pair of 20 to 100 second delay timers 22 and 24. The PTC block 20 produces an UP or a DOWN pulse train depending on the direction of the deviation outside of the GAP. The measurement value is continuously compared with the desired target voltage as the set point within both the DGAP and PTC blocks. If the measurement is within the deadband then there is no output from the transformer tap position controller. If, however, the measurement value is outside the deadband then corrective action is initiated. In this case both the DGAP block 18 and PTC block 20 produce an output. The DGAP block 18 produces one of two Boolean outputs, one to timer 22 if an increase in tap position is required and the other to timer 14 if a decrease is required. The PTC block 20 produces two pulse trains, one to drive the tap position servo drive 6 up and the other to drive the tap change servo drive 6 down. The pulse duration is adjustable from 0 to 10 seconds. The DGAP block 18 starts the appropriate initial "delay on" timer. The output of this controller gates the pulse train from the PTC controller via one of the AND gates 26 and 28 dependent on whether time 22 or timer 24 has been initiated. The AND gate allows the pulse train from PTC block 20 through after the pre-defined delay as determined by the timer 22 or 24. The timer 22 or 24 as set by the DGAP block 18 is not reset until the measurement value returns to a value that is within the preset deadband. If the measurement value returns to a value within the deadband gap during the initial delay period of 20 to 100 seconds then no correction is applied to the transformer 2 associated with the transformer tap position controller since no pulses will have been allowed through the appropriate gate 26 or 28. If the measured value is still in the same direction and outside the deadband gap after the timer 22 or 24 has timed out, the first pulse of the pulse train of the PTC block 20 is sent to the servo drive 6 to change the tap position of the transformer 2 by one tap position. The change in tap position of the transformer will alter the output voltage VT of the transformer which will be reflected in the measurement value supplied to the blocks DGAP 18 and PTC 20 whether the measured value is the output voltage VT of the transformer or the average voltage of the output of the transformer group. If the measurement continues to remain outside the deadband gap for a time in excess of the period that has been set for the pulse train from the PTC block 20, say 10 seconds, a second pulse is sent to the servo drive 6 to provide for a further movement of the tap position of the transformer 2. If the measurement value returns to a value within the deadband gap within the 10 second period of the pulse train, then the output from the PTC 20 is stopped since no further pulses need to be generated. The tap position of the transformer 2 is then the last value to which it was driven under control of this algorithm. The pulse output from either of the AND gates 26 and 28 is passed via a respective one shot logic gate 30 or 32 to produce a reshaped pulse train of uniform width to be applied to the servo drive 6. The transformer tap position controller also includes a MOVLV block 34 also obtainable from The Foxboro Company which has a manual switch input 35. When a manual switch input 35 is present it overrides any inputs from the one shot blocks 30 and 32. This means that control of the servo drive can be transferred either by an operator via an appropriate console or, as will be explained, which inputs control signals onto input line 35 or, as will be explained in detail below, by a group sequence controller outputting tap UP/DOWN tap change signals to adjust the tap positions of the transformers as required. The DGAP block 18 and PTC block 20 are each configured to have their operation suspended when in receipt of a HOLD signal from the group sequence controller 16 as indicated on line 36 of Figure 2. Referring now to Figure 3 there is shown a control schematic of two transformers of a 4 transformer group. Only two transformers (36 and 38) are shown in Figure 3, the other two are indicated schematically as boxes 40 and 42. The transformer and control system 36 comprises the group sequence controller 16 and transformer tap position controller as shown in Figure 1 with the same components given the same reference numerals. The following additional aspects shown in Figure 3 are as follows. A volt transducer 42 measures the voltage output from tap changing transformer 2 as supplied to a busbar 44. The actual measured voltage obtained from the volt transducer 42 is made available to the group sequence controller 16 as indicated by the line 46. The current output from transformer 2 is measured by ammeter 48 which is made available to the group sequence controller 16 as indicated by line 50. The group circulating MVAr is measured by a transducer 52 the value of which is also made available to the group sequence controller 16 as indicated by the line 54. The transformer system 38 is exactly as that of transformer system 36 with like components indicated by the same reference numerals primed. The group sequence controller 16 is arranged to be able to calculate the average voltage of the transformers in the group 36, 38, 40, 42 and selectively control the transformer tap position controllers to control the output voltage of the respective transformers based on the calculated average voltage or the actual output voltage as schematically indicated by switch 56 controlled as indicated by line 58. The group sequence controller 16 is a continuously running sequence program that acts as an executive over the individual transformer tap position controllers. In the course of its processing it provides a capability of receiving commands from high levels of the power systems operations associated with the transformer group, checking for the selected group configurations determined by the operator or other external sequences, receiving measurements for specific aggregate computations of reactive power and forming control connections to lower level control blocks including the GATPCs of the transformer tap position controllers. The group sequence controller manipulates the transformer tap position controllers and via HOLD instructions or via tap position signals transmitted to the auto/manual block 34. Interconnections to other control blocks on external sequences are provided through the normal block pointers of the control processor algorithms. An operator is also able to see from the console the status and process steps of the controller and intervene with manual control if and when desired. Two transformer tap position control methods are envisaged, primarily, with the present invention to meet operational requirements. After letting the master controller of the allocated transformer 2 correct for busbar voltage deviations, the group sequence controller 16 reviews the overall pattern of the tap positions in the selected group and adjusts for one of two mode tap patterns. In the first patterning method, "Pattern", the allocated transformer 2 is controlled by sequentially overriding each controller and tapping the associated transformer in the appropriate direction. A computation of tapping differentials between transformers is used to direct the action. In the second patterning method, "Equalize", all the transformers in a group are controlled to be at equal tap positions. The group sequence controller 16 computes the average tap position (rounded up to the nearest integer) as a target and once again sequentially overrides each controller and adjusts the tap positions to align them. The Pattern and Equalize modes of operation will now be described in more detail. Referring to Appendix 1, the pseudo-code for applying the Pattern mode of operation for groups of three and four transformers is listed. A bit pattern is generated for the particular group of transformers. For example, the group of transformers numbered 1, 3 and 4 from a total of four transformers 1 to 4 gives a pattern of 1011. If there are three transformers in the group, the difference between the tap positions of the allocated transformer and each of the remaining transformers is obtained. If the tap position of the allocated transformer is smaller than any of the other transformers, its tap position is increased until it equals the larger of the tap positions of the other two transformers. In the pseudo-code, TRl_MAST=l if the 1st transformer is the allocated (master) transformer, and so on. The minima, SIGMAMIN_l-2 and SIGMAMIN_l-3, of the differences in tap positions of the allocated transformer and each of the other two transformers, respectively, are made non- negative by increasing the tap of position of the allocated transformer as indicated by the subroutine "SUB «TAP»" of Appendix 1. If there are four transformers in the group, the average tap positions of middle and end bus transformers, NOME.AVG and INME.AVG, respectively, are calculated and the difference between the two obtained. That is, a tap position differential calculation is made between the middle two transformers and the end two transformers to determine whether the tap positions of the middle transformers are higher than those of the end transformers, and if this is not the case, the lower tap position of the two middle transformers is increased progressively and the higher tap position of the two end transformers is decreased progressively until the tap positions of the middle transformers are higher than the tap positions of the end transformers. The pseudo code of Appendix 1 lists the control sequence which is effected if the middle transformers are transformers number 1 and 2. There are further control sequences, not listed, for other arrangements of four transformers with the indices of the parameters changed accordingly. Referring now to Appendix 2, the pseudo-code to apply the Equalize mode of operation for three or four transformers is listed. The average tap position, rounded up to the nearest integer, POSN-AVG, is determined and the tap positions of each transformer driven up or down to move each tap position towards the average value. In each of the two control sequences just described the priority is to maintain the output voltage at the desired value with the coordination of tap positions to keep their spread values within desired limits carried out at intervals during the automatic control of the allocated transformer. An alternate preferred embodiment of the control system utilises a modified Sequencer program. This alternative method is based on considering a group of transformers as consisting of multiple pairs and where necessary, as in the case of an odd numbers of transformers, the remainder as single transformers. The Sequencer activates/deactivates the tap position controllers as in the previous embodiment, but on a pair by pair basis uniformly across the group, and not in a Master/Follower methodology. The alternative method of operation of the Sequencer comprises: a) receiving the measurements of voltage from each transformer; b) calculating the average value of the voltage for the group of transformers at any given time; c) arranging the transformer groups in as many pairs as possible to suit a typical busbar arrangement; and d) selecting a transformer pair and allocating one of the pair to be tapped initially based on the following criteria: i) the transformer being a tertiary transformer, and ii) the transformer being nearest to an end busbar. The method of tap change is to: a) restrict tap change movement to only one pair at a time; b) allow only one tap position change at a time for any transformer; c) alternate the movement within the pair by holding and releasing the automatic mode of the tap change controller for each transformer in turn; d) when one pair is activated arranging for all others (pairs or singles) in the group to be on hold; and e) sequentially repeat the above cycle for the next pair. There are three types of tap change movement or operation. 1. From a given initial tap position pattern all taps are driven, while maintaining the tap pattern, either to a higher or a lower position to satisfy an average voltage target. 2. From a given initial tap position all pairs have their taps driven apart by one or more taps to provide absorption/compensation of reactive power (MVar) target. 3. From a given initial tap position derived from the action of the preceding paragraph where all pairs of transformers have their taps apart, all pairs are now driven to reduce the tap spread to within one tap or less of each other in order to remove MVar compensation. The sub-station Super Grid Transformer (SGT) tap position control methods are envisaged to meet the following operational requirements: 1. To control the busbar voltage on the secondary winding of the SGTs. 2. To absorb excess grid reactive power (MVar) by creating a tap spread pattern also called 'Stagger'. 3. To remove the tap stagger and align the tap pattern to within one tap of each other. This operation is called 'Equalise'. In operation 1 the pairs are sequentially controlled by alternating the Hold and Auto functions of the tap position controllers to satisfy the voltage target. The Sequencer manipulates the controller modes by Boolean variables applied to the Hold input of the controller. In operation 2 each pair within the group is tapped apart, one tap position at a time alternately, to force the tap position controller to produce a spread of taps. The Sequencer effects this by 'overriding' the controller and driving the first of the pair (selected by the criteria defined in d(i) and d(ii) above) upward one tap position and the second of the pair downward one tap position. This operation is repeated for each pair in the group, but excludes any single transformer that might form part of the grouping. When more than one group is involved the up/down drive is applied to the next group of transformers. On completion of all groups the drive reverts to the first group and initiates another tap position change et seq. These cycles are repeated as many times as necessary to achieve a spread that is equal on all pairs that meets the required 'stagger'. In operation 3 each pair within the group is tapped in a method that reverses the Stagger operation defined in 2 above to produce an "Equalised" tap position pattern. This has the effect of removing the reactive power compensation Further aspects of the alternate method consists of the sequence control modes. The Sequencer comprises a suite of configured modules of sequences and sub-sequences arranged as shown in figure 4. The diagram illustrates the structure of the hierarchy of tasks comprising the following: 1. A program called GROUPS that identifies the groups within a sub-station via the connect/disconnect status contacts on the busbar selectors. 2. An executive control sequence called GRP_MODE attached to sub-modules of Individual Mode sub-sequences which in turn are connected to the controllers of the identified group. The executive runs continuously and activates appropriate control modes. e.g. Control (voltage). Stagger, Equalise, Single etc. of the group. These control modes are governed by the related subsequences which perform the tasks using the pair by pair method, described earlier. Appendix 3 is a listing of the pseudo code for this alternative method of control. As noted above, the above control systems are designed using a block firmware structure within an industry standard (non-customised) advanced Distributed Control System (DCS) . The block structures cover all the functionality of computational, logic, sequence, and continuous control within the same hardware. These arrangements are in achieving high robustness, security and availability. The arrangement of control blocks can be modified such that the MOVLV are replaced by two GDEV blocks which give much better facilities for the control action. APPENDIX I SUB-SEQUENCE «PATTERN» {Tap position Pattern invoked when Tap Stagger is ON & a group of 3* s & 4' s} {Read Transformers/Controllers group BIT-PATTERN_1 selection} {Check for groups of 3' s AND 4' s> IF SUM OF BITS 1+2+3+4 >2 THEN {Identify End-Bus Transformer or use the selected Master Transformer} {For group of 3* s> IF SUM OF BITS 1+2+3+4 =3 THEN IF TR1_MAST=1 THEN LET SIGMA_1 = (P0SN_1*BIT1) - (POSN_2*BIT2) LET SIGMA_2 - (P0SN_1*BIT1) - (POSN_3*BIT3) LET SIGMA_3 - (POSN_l*BITl) - (POSN_4*BIT4) CALL SUB «TAP» IF TR2_MAST=1 THEN LET SIGMA_1 = (POSN_2*BIT2) - (P0SN_1*BIT1) LET SIGMA_2 » (POSN_2*BIT2) - (POSN_3*BIT3) LET SIGMA_3 = (POSN_2*BIT2) - (POSN_4*BIT4) CALL SUB «TAP» IF TR3_MAST=1 THEN LET SIGMA_1 = (POSN_3*BIT3) - (P0SN_1*BIT1) LET SIGMA_2 - (POSN_3*BIT3) - (POSN_2*BIT2) LET SIGMA_3 - (POSN_3*BIT3) - (POSN_4*BIT4) CALL SUB «TAP» IF TR4_MAST»1 THEN LET SIGMA_1 - (POSN_4*BIT4) - (POSN_3*BIT3) LET SIGMA_2 ■ (POSN_4*BIT4) - (POSN_2*BIT2) LET SIGMA_3 = (POSN_4*BIT4) - (P0SN_1*BIT1) CALL SUB «TAP» SUB «TAP» LET SIGMAMIN_l-2 = SIGMA_1 < SIGMA_2 LET SIGMAMIN_l-3 = SIGMA_1 < SIGMA_3 WHILE SIGMAMIN_l-2 = < -1 DO GOTO «PATN-MANUAL» {TRJLNSF_1 } « PATN-MANUAL 1» {TRANSF_1 } {Transfer controller to Manual } SET CONTROLLER MOVLV_l. [MANSW] : ■ 1 {Pulse Output to move UP} SET CONTROLLER MOVLV_l. [MANOPN] := 1 ENDWHILE WHILE SIGMAMIN_l-3 ■ < -1 DO GOTO «PATN-MANUAL» {TRANSF_1 } « PATN-MANUAL 1» {TRANSF_1 } {Transfer controller to Manual} SET CONTROLLER MOVLV_l. [MANSW] : - 1 {Pulse Output to move UP} SET CONTROLLER MOVLV_l. [MANOPN] 1 ENDWHILE WAIT UNTIL [TAP CNG PROG] TIME GOTO «AUTO» «AUTO» {Transfer controller back to Auto} SET CONTROLLER MOVLV_l.[MANSW] : ■ 0 ENDIF {For σroup of 4' s> {Reading the group bit pattern BIT_#1 thru BIT_#n} IF SUM OF BITS 1+2+3+4 -4 THEN {Reading the Middle/End Busbar Pattern MEBIT_#1 THRU _#4} {Inverting the busbar Bit Pattern} LET INMEBIT_1 = NOT MEBIT_1 (ETC ) {Calculating the avg tap posn. of mid bus transformers} LET NOME_AVG = ( (POSN_l * MEBIT_1) + (POSN_2 * MEBIT_2) + (P0SN_3 * MEBIT_3) + (POSN_4 * MEBIT_4) ) / 2 {Calculating the avg tap posn. of end bus transformers} LET INME_AVG - ( (POSN_l * INMEBIT_1) + (POSN_2 * INMEBIT_2) + (P0SN_3 * INMEBIT_3) + (POSN_4 * INMEBIT_4)) / 2 {Calculating the difference of sums} LET SIGMA_AVG - N0ME_AVG - INME_AVG {Testing for stagger} IF SIGMA_AVG < 1 THEN {Identifying the mid busbar transformers & tapping the lowest Up & identifying the end bus transformers & tapping the highest Down} {For mid bus transformers 1 &2 end bus 3 & 4> IF MEBIT_1 AND MEBIT_2 •» 1 THEN IF POSN_l - POSN_2 < ■ 0 THEN {Tap UP transformer #1} {Transfer controller to Manual} SET CONTROLLER M0VLV_1. [MANSW] : = 1 {Pulse Output to Open} SET CONTROLLER MOVLV_l. [MANOPN] : ■ 1 WAIT UNTIL [TAP CHNGE PROGRESS] AFTER TIME GOTO «AUTO» «AUTO» {Tranβfer controller back to Auto} SET CONTROLLER MOVLV_l. [MANSW] : » 0 {Else Tap up transformer #2} ELSE SET CONTROLLER MOVLV_2.[MANSW] : » 1 {Pulse Output to Open} SET CONTROLLER MOVLV_2. [MANOPN) : = 1 WAIT UNTIL [TAP CHNGE PROGRESS] AFTER TIME GOTO «AUTO» «AUTO» {Transfer controller back to Auto} SET CONTROLLER MOVLV_2.[MANSW] : - 0 ENDIF IF POSN_3 - POSN_4 > - 0 THEN {Tap Down transformer #3} {Transfer controller to Manual} SET CONTROLLER MOVLV_3.[MANSW] : ■ 1 {Pulse Output to Close} SET CONTROLLER MOVLV_3. [MANCLS] : = 1 WAIT UNTIL [TAP CHNGE PROGRESS] AFTER TIME GOTO «AUTO» «AUTO» {Transfer controller back to Auto} SET CONTROLLER MOVLV_3. [MANSW] : » 0 {Else Tap Down transformer #4} ELSE SET CONTROLLER MOVLV_4.[MANSW] : = 1 {Pulse Output to Close} SET CONTROLLER MOVLV_4. [MANCLS] : = 1 WAIT UNTIL [TAP CHNGE PROGRESS] AFTER TIME GOTO «AUTO» «AUTO» {Transfer controller back to Auto} SET CONTROLLER MOVLV_4. [MANSW] : - 0 ENDIF APPENDIX II SUB-SEQUENCE «EQUALIZE» {Tap position Equalization invoked when Tap Stagger is OFF & a group of 3' s & 4' s} {Read Transformers/ Controllers group BIT-PATTERN_1 selection} IF SUM OF BITS 1+2+3+4 > 2 THEN {Read Tap Position feedback & calculate Mean Tap Number for the group - Average Position (round up to Nearest Integer) } LET P0SN_AVG * ROUND ( ( (P0SN_1*BIT1) + (POSN_2*BIT2) + (P0SN_3*BIT3) +(P0SN_4*BIT4) ) / (BITl +BIT2+BIT3+BIT4) ) IF TR1_PATN_BIT1:= 1 THEN IF POSN_AVG <> POSN_l THEN {Transfer controller to Manual} SET CONTROLLER MOVLV_l. [MANSW]:« 1 IF POSN_AVG < POSN_l THEN {Pulse Output to Close} SET CONTROLLER MOVLV_l. [MANCLS] :■ 1 ENDIF IF POSN AVG > POSN 1 THEN {Pulse Output to Open} SET CONTROLLER MOVLV_l. [MANOPN] :» 1 ENDIF WAIT UNTIL [TAP CHNGE PROGRESS] AFTER TIME GOTO «AUTO» «AUTO» {Transfer controller back to Auto} SET CONTROLLER MOVLV_l. [MANSW] : - 0 ENDIF ENDIF IF TR2_PATN_BIT2: « 1 THEN IF POSN_AVG <> POSN_2 THEN {Transfer controller to Manual} SET CONTROLLER MOVLV_2.[MANSW]:= 1 IF POSN_AVG < POSN_2 THEN {Pulse Output to Close} SET CONTROLLER MOVLV_2. [MANCLS] := 1 ENDIF IF POSN_AVG > POSN_2 THEN {Pulse Output to Open} SET CONTROLLER MOVLV_2.[MANOPN]:= 1 ENDIF WAIT UNTIL [TAP CHNGE PROGRESS] AFTER TIME GOTO «AUTO» «AUTO» {Transfer controller back to Auto} SET CONTROLLER MOVLV_2.[MANS ] : - 0 ENDIF ENDIF IF TR3_PATN_BIT3:- 1 THEN IF POSN_AVG <> POSN_3 THEN {Transfer controller to Manual} SET CONTROLLER MOVLV_3. [MANSW] := 1 IF POSN_AVG < POSN_3 THEN {Pulse Output to Close} SET CONTROLLER MOVLV_3. [MANCLS] :■ 1 ENDIF IF POSN_AVG > POSN_3 THEN {Pulse Output to Open} SET CONTROLLER MOVLV_3. [MANOPN] :- 1 ENDIF WAIT UNTIL [TAP CHNGE PROGRESS] AFTER TIME GOTO «AUTO» «AUTO» {Transfer controller back to Auto} SET CONTROLLER MOVLV_3.[MANSW] : = 0 ENDIF IF TR4 PATN BIT4:= 1 THEN IF P0SN_AVG <> P0SN_4 THEN {Transfer controller to Manual} SET CONTROLLER M0VLV_4.[MANSW]:= 1 IF POSN_AVG < POSN_4 THEN {Pulse Output to Close} SET CONTROLLER MOVLV_4. [MANCLS] := 1 ENDIF IF POSN_AVG > POSN_4 THEN {Pulse Output to Open} SET CONTROLLER M0VLV_4. [MANOPN] := 1 ENDIF WAIT UNTIL [TAP CHNGE PROGRESS] AFTER TIME GOTO «AUTO» «AUTO» {Transfer controller back to Auto} SET CONTROLLER MOVLV_4.[MANSW] : = 0 ENDIF ENDIF ENDIF END SUB-SEQUENCE «EQUALIZE» APPENOIX III SUB-SEQUENCE < <GRP_CTRL> > {Reading group structure via CPLBUS_a,b,c,d. Three typical cases are defined below: Case "a"as typical of 4, Caβe"ab" as typical of 2, Case"ad" as typical of 2 , to give a total of 8 cases.} {Case "a" \ IF CPLBUS_a -1 AND CPLBUS_b - _c - _d « 0 THEN REPEAT CALL VTAP(a) UNTIL VOLT >< GAP ENDIF {Case 'ab" \ IF CPLBUS_a - _b - 1 AND CPLBUS_c - _d = 0 THEN {case of Mains I and II} IF SUM (PAT_aBIT's) «■ SUM (PAT_bBIT's) » 2 THEN {case of 2 + 2 transformers} REPEAT {repeat cyclic sequence} CALL VTAP(a) IF VOLT >< GAP THEN EXITLOOP CALL VTAP(b) UNTIL VOLT >< GAP ENDIF IF SUM (PAT_aBIT's) ■ 2 AND SUM (PAT_bBIT * s) ■ 1 THEN {case of 2 + 1 transformers} REPEAT {repeat cyclic sequence} CALL VTAP(a) IF VOLT >< GAP THEN EXITLOOP CALL VTAP(b) UNTIL VOLT >< GAP ENDIF IF SUM (PAT_aBIT's) ■ 1 AND SUM (PAT_bBIT's) = 2 THEN {case of 1 + 2 transformers} REPEAT {repeat cyclic sequence} CALL VTAP(a) IF VOLT >< GAP THEN EXITLOOP CALL VTAP(b) UNTIL VOLT >< GAP ENDIF IF SUM (PAT_aBIT' s) ■ 1 AND SUM (PAT_bBIT' s) = 1 THEN {case of 1 + 1 transformers} REPEAT {repeat cyclic sequence} CALL VTAP(a) IF VOLT >< GAP THEN EXITLOOP CALL VTAP(b) UNTIL VOLT >< GAP ENDIF ENDIF {Case "ad'\ IF CPLBUS_a - _d ■ 1 AND CPLBUS_b = _c = 0 THEN {case of Main I and Reserve 1} IF SUM (PAT_aBIT' s) > 1 THEN REPEAT CALL VTAP(a) IF VOLT >< GAP THEN EXITLOOP CALL VTAP(d) UNTIL VOLT >< GAP ENDIF ENDIF SUB VTAP( ) {Tapping transformer upward} IF VOLT < (SET - GAP/2) THEN «TA 2» IF PAT[ ]BIT[2] - 1 THEN SET TCA[ ][2] [HOLD] = 0 AND TCA[ ][1] [HOLD] = 1 IF POSN[2] - 19 THEN SENDMSG ( ) GOTO «TAP1» ENDIF IF VOLT >< GAP THEN EXIT ENDIF WAIT UNTIL TCIP[2] - 0 AFTER TIME GOTO «TAP1» ENDIF «TAP1» IF PAT[ ]BIT[1] - 1 THEN SET TCA[ ][2] [HOLD] = 1 AND TCA[ ][1] [HOLD] - 0 IF POSN[l] ■ 19 THEN SENDMSG ( ) GOTO «END_TAPUP» ENDIF WAIT UNTIL TCIP[1] = 0 AFTER TIME GOTO «END_TAPUP» ENDIF ENDIF «END_TAPUP» {Tapping transformer downward} IF VOLT > (SET - GAP/2) THEN «TAP1» IF PAT[ ]BIT[1] - 1 THEN SET TCA[ ][2] [HOLD] * 1 AND TCA[ ][1] [HOLD] - 0 IF POSN[l] » 19 THEN SENDMSG ( ) GOTO «TAP2» ENDIF IF VOLT >< GAP THEN EXIT ENDIF WAIT UNTIL TCIP[1] * 0 AFTER TIME GOTO «END_TAPDWN» ENDIF «TAP2» IF PAT[ ]BIT[2] = 1 THEN SET TCA[ ][2] [HOLD] - 0 AND TCA[ ][1] [HOLD] = 1 IF POSN[2] = 19 THEN SENDMSG ( ) GOTO «END TAPDWN» ENDIF WAIT UNTIL TCIP[2] » 0 AFTER TIME GOTO «END_TAPDWN» ENDIF ENDIF «END_TAPDWN» ENDSUB VTAP ★*★*******★★*★•*•_**•>•★******#★*★***-tr*************************- END SUB-SEQUENCE «GROUP_CTRL» SUB-SEQUENCE «STAGGER» {Reading group structure via CPLBUS_a,b,c,d. Three typical cases are defined below: Case "a"as typical of 4, Case"ab" as typical of 2, Case"ad" as typical of 2, to give a total of 8 cases. Read SET STAGGER from a calculation elsewhere. SETSTAGGER =-*4 require tap stagger converted in terms of tap spread (tap position max minus tap psition min} ***♦******„ „•»★**#********★★*****★* AUTOMATIC VOLTAGE CONTROL SEQUENCES &**: 1 SUB-SEQUENCE~«STAGGER» (Reading group strva rr vie CPIm.USjs.bAd. Three typical cases are defined below: Case * "a "as typical ofJ. Case "ab~ as typical of 2. Cast "ad' as typical of 2. to give a total ofS cases. Road SET STAGGER from a calculation elsewhere. SEISTΛGGΣR - require tap stagger converted in terms of 5 tap spread (tap position ma: minus tap psttton min) /Case -a-* {The case of a single pair on isolated busbar) EF CF BUS a -l AND CPLBUS b- c- d-O THEN 0 IF PATtalBITTi] - I AND PATtøBmil - I THEN SET TCA{_ ][1] [MANSW] - 1 AND TCA(a][II [MANSW] - 1 (Pvmng GDEV on Manual) REPE (Action to tap the transformers in a cyclic manner cne tap each at a tone} 5 CAl STAPMft) UNTIL SPREAD - SETSTAGGER (zl TAP) SET TC a ][2] [MANSW] - 0 AND TCA(al[l] [MANSW] - 0 {Putting GD&'back in Auto) ENDIF 0 ENDIF /Case -__ -.t IF CP__-US_a - _b • 1 AND (_PLBUS_c - _d -0 THEN (case of Mains I and II) IF SUM " (PAT__BΓΓJ) - SUM (PATJ_BΓΓ J) - 2 THEN ( ase o : - 2 transformers; 5 SET CA(a ][2] [MANSW] - I AND TCAtøP ] [MANSW] - l SETTCAI- IP] [MANSW] » l AND - __Mb][l] [MANSW] - 1 REPEAT {repeat cv Jic sequence) CA L STAPMfo) IF SPREAD - SETSTAGGER (zl TAP) THEN 0 EXITLOOP CA L STAPEfb) UNTIL SPREAD - SETSTAGGER (±1 TAP) SET TCA(a IP] [MANSW] - 0 AND TCA[a)[l] [MANSW] « 0 SET T -jb ][2] [MANSW] - 0 AND TCA[b][I] [MANSW] = 0 3- E DIF IF SUM (PAT iBlT J) - - AND SUM (PAT -HIT * i) « I THEN {case of 2 - I transformers) SET CAla 1(2] [MANSW] - 1 AND TCA(a][lI IMANSW] - 1 REPEAT (repeat cyclic sequence) CALL. STAPM(a) ■ W UNTIL SPREAD » SETSTAGGER f *1 TAP) SET TCΛ(a IP] [MANSW] - 0 AND TCΛ(a][I] [M NSW] = 0 ENDIF IF SUM (PAT iBITs) - I AND SUM (PATJbBTTs) - 1 THEN {cast of! -- 2 transformers' SET TCAP P] [MANSW] - l AND T___(b][l] [MANSW] - I *5 REPEAT {repeat cvciic seaueπce) CAL STAPE/b) UNTIL SPREAD - SETSTAGGER fctl TAP) SET TCArøp] [MANSW] » 0 AND TCA[b][l] [MANSW! - 0 ENDIF 30 IF SUM (PAT aBTTi) - I AND SUM (PAT.bBITs) - 1 THEM {case of I - I transformers) SET f CA(a ]PI [MANSW] - 1 AND TCA(a](l] [MANSW] - I SETTCAfb 1(2] [MANSW] - l AND TCA(b][l] [MANSW] - 1 REPEAT {repeat cycu ' c sequence) 55 CALL STAPE(a) ENDIF Rev 1 AUTOMATIC VOLTAGE CONTROL SEQUENCES EFPATtalBrrm-l * * CALL STAPMO) ^SPREAD - SET-TAGGER (±1 TAP) THEN EXΠLOOP ENDIF IFPA-TDIBΓΠU-I " "^ CALLSTAPM(b) ENDIF _^ τ IFPATDIBΓΓUI-I THEN CALL STAPE ) ENDIF ENDIF ENDIF AUTOMiπC VOLTAGE CONTROL SEQUENCES Rev. i {Case "ad") IF CPLBUS.a - _d - I AND CPLBUS.b - _c - 0 THEN (cau of Main I and Reserve 1} IF SUM ( AT__B-T's) > I THEN SET TCA[a ][2] [MANSW] - I AND TCA(_][1] [MANSW] - 1 REPEAT CALL STAPM(a) UNTIL SPREAD - _ki _i AGGER (±1 TAP) SET TCA[Λ ][2] [MANSW) - 0 AND TCA[a][l] [MANSW] - 0 ENDIF IF SUM (PAT_dB_T * -) > I THEN SET TCA[d][2] [MANSW1 = I AND TCA[d][l] [MANSW] - I REPEAT CALL STAPM(d) UNTIL SPREAD - SETSTAGGER (±1 TAP) SET TCA[d][2] [MANSW] = 0 AND TCA[ ][l] [MANSW] = 0 ENDIF IF SUM (PAT__Bl s) - < I OR SUM (PAT dBTTs) -< I THEN SET TCA{a 1[2] [MANSW] - l 5 TCA[a][l] [MANSW] - I SET TCA[d 1[2J [MANSW] = 1 AND TCA[d][l] [MANSW] - I REPEAT DF PAT[a]B-TP] - I THEN CALL STAPM(a) ENDIF IF SPREAD - SETSTAGGER (±1 TAP) THEN EXITLOOP ENDIF CALL STAPMtø) ENDIF _F PAT[d}BITT2] = l THEN CALL STAPE d) ENDIF UNTIL SPREAD - SETSTAGGER (±1 TAP) SET TCA(a ][2] [MANSW] -0 AND TCA[a][l] [MANSW" = 0 SET TCA(d][2] [MANSW] - 0 AND TCA(d][l] [MANSW] - 0 ENDIF SUB STAPM( ) {Tapping transformer pair apart} «TAP2» {The middle transformer} IF PAT[ ]BIT[2]»1 THEN SET TCA[ ][2] [MANOPN] = 1 {moving tap position upwards} IF POSN[2] - 19 THEN SENDMSG ( ) GOTO «IDLE» ENDIF IF SPREAD=SETSTAGGER (± TAP) THEN EXIT ENDIF WAIT UNTIL TCIP[2] - 0 AFTER TIME GOTO «IDLE» «IDLE» SET TCA[ ][2] [MANOPN] - 0 «TAP1» {The end transformer} ENDIF «TAP1» IF PAT[ ]BIT[1]»1 THEN SET TCA[ ][1] [MANCLS] = 1 IF POSN[l] = 1 THEN SENDMSG ( ) GOTO «IDLEC» ENDIF WAIT UNTIL TCIP[1] - 0 AFTER TIME GOTO «IDLEC» «IDLEC» SET TCA[ ][1] [MANCLS] ■ 0 ENDIF ENDSUB STAPM ****»***w******w*************^ SUB STAPE( ) {Tapping transformer pair apart} «TAP1» IF PAT[ ] BIT[1]=1 THEN SET TCA[ ][1] [MANOPN] ■ 1 IF POSN[l] ■ 19 THEN SENDMSG ( ) GOTO «IDLE» ENDIF IF SPREAD =SETSTAGGER (±TAP) THEN EXIT ENDIF WAIT UNTIL TCIP[1] = 0 AFTER TIME GOTO «IDLE» «IDLE» SET TCA[ j[l] [MANOPN] = 0 ENDIF «TAP2» IF PAT[ ]BIT[2]=1 THEN SET TCA[ ][2] [MANCLS] - 1 IF POSN[2] - 1 THEN SENDMSG ( ) GOTO «IDLEC» ENDIF WAIT UNTIL TCIP[2] = 0 AFTER TIME GOTO «IDLEC» «IDLEC» SET TCA[ ][2] [MANCLS] - 0 ENDIF ENDSUB STAPE END SUB-SEQUENCE «STAGGER»

Claims: CLAIMS : 1. A controller for controlling the tap positions of a group of tap changing transformers whose outputs are connected to a respective common busbar, the controller comprising: a plurality of transformer tap position controllers each of which is associated with a respective transformer of the group of transformers and is arranged to generate tap changing signals whereby the tap position of the associated transformer may be adjusted in dependence on whether a measurement value dependant on the voltage at the output respective transformer lies within a predetermined range of values and including means for putting the tap controller on hold or override; and a group sequence controller coupled to the transformer tap position controllers and arranged to monitor the respective tap positions, and to be able to put selected transformer tap position controllers on hold and to output tap changing signals to override said outputs from the selected tap changer controllers, as necessary, to directly adjust the spread of the tap positions of the transformers so as to fall within a predetermined limit. 2. A controller as claimed in claim 1 including a plurality of motor controllers each associated with a respective transformer and arranged to generate control signals to control the movement of a tap position motor of the respective transformer in response to receipt of tap changing signals. 3. A controller as claimed in claim 2 in which each motor controller is arranged to receive tap changing signals generated by the group sequence controller and is arranged to ignore tap changing signals from the transformer tap position controller associated with the motor controller when in receipt of tap changing signals from the group sequence controller. 4. A controller as claimed in any preceding claim in which each transformer tap position controller is arranged to receive a measurement value related to the output voltages of the transformers and to generate a tap changing signal if the measurement value lies outside a predetermined range of values for a predetermined length of time. 5. A controller as claimed in any preceding claim, the group sequence controller including means for determining the average voltage of the values of the voltages at each transformer the average voltage comprising the measurement value. 6. A controller as claimed in claim 5 in which the group sequence controller includes means for supplying to each transformer tap position controller either the average voltage or the measured voltage of a transformer as the measurement value. 7. A method of controlling a controller as claimed in any one of claims 1 to 6 comprising: a) measuring the voltage at each transformer; b) calculating the average value of the voltages at each transformer at any given time; c) holding the tap positions of all but one transformer (the allocated transformer) of the group; and d) adjusting the tap position of the allocated transformer until the average voltage lies within a selected band of voltages. 8. A method of controlling a controller as claimed in any one of claims 1 to 6 comprising: adjusting, at intervals, the spread of the tap positions to less than or equal to a predetermined limit. 9. A method as claimed in claim 8 in which the predetermined limit is 1. 10. A method as claimed in either one of claims 8 and 9 in which there are three transformers in the group and the tap position of an allocated transformer is increased, if necessary, to be at least equal to the higher of the tap positions of the other two transformers. 11. A method as claimed in either one of claims 8 and 9 in which there are four transformers in the group and a tap position differential calculation is made between the middle two transformers and the end two transformers to determine whether the tap positions of the middle transformers are higher than those of the end transformers, and if this is not the case, the lower tap position of the two middle transformers is increased progressively and the higher tap position of the two end transformers is decreased progressively until the tap positions of the middle transformers are higher than the tap positions of the end transformers. 12. A method as claimed in any one of claims 8 to 10 in which, at intervals, the average of the tap positions of the controllers rounded up to the nearest integer is determined and the tap positions are adjusted to equal the average tap position. 13. A method as claimed in claim 7 comprising: a) receiving the measurements of voltage from each transformer; b) calculating the average value of the voltage for the group of transformers at any given time; c) arranging the transformer groups in as many pairs as possible to suit a typical busbar arrangement; and d) selecting a transformer pair and allocating one of the pair to be tapped initially based on the following criteria: i) the transformer being a tertiary transformer, and ii) the transformer being nearest to an end busbar. 14. A method as claimed in claim 13 in which the method of tap change is to a) restrict tap change movement to only one pair at a time; b) allow only one tap position change at a time for any transformer; c) alternate the movement within the pair by holding and releasing the automatic mode of the tap change controller for each transformer in turn; d) when one pair is activated arranging for all others (pairs or singles) in the group to be on hold; and e) sequentially repeat the above cycle for the next pair. 15. A method as claimed in either one of claims 13 and 14 in which from a given initial tap position pattern all taps are driven, while maintaining the tap pattern, either to a higher or a lower position to satisfy an average voltage target. 16. A method as claimed in either one of claims 13 and 14 in which from a given initial tap position all pairs have their taps driven apart by one or more taps to provide absorption/compensation of reactive power (MVar) target. 17. A method as claimed in claim 16 in which after all pairs of transformers have their taps driven apart, all pairs are subsequently driven to reduce the tap spread to within one tap or less of each other in order to remove MVar compensation

Inventors: DE SA DOUGLAS, MAALOUF SALIM IBRAHIM, DE SA, DOUGLAS, MAALOUF, SALIM, IBRAHIM
Applicants: DOUGLAS DE SA, FOXBORO CO, MAALOUF SALIM IBRAHIM, DE SA, DOUGLAS, MAALOUF, SALIM, IBRAHIM, THE FOXBORO COMPANY
Application year: 1996
Main classification: G05F1
IPC codes: G05F1