GB1592951A

GB1592951A - Electrical regulators

Info

Publication number: GB1592951A
Application number: GB4523576A
Authority: GB
Original assignee: Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1976-10-30
Filing date: 1976-10-30
Publication date: 1981-07-15
Also published as: DE2700755A1

Description

(54) IMPROVEMENTS IN OR RELATING TO ELECTRICAL REGULATORS (71) We, THE MARCONI COMPANY LIMITED, a British Company, of Marconi House, New St. Chelmsford, Essex CMi 1PL, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to electrical regulators and in particular voltage regulators.

One object of the invention is to provide an improved voltage regulator which is satisfactory both as regards the degree and speed of regulation.

According to this invention an electric regulator is provided having a stepwise multi-tapped transformer between its input and its output, means responsive to changes in the input or output voltage or current of said regulator for selecting an appropriate tap of said transformer to tend to restore the output voltage or current of the regulator to that value required and means which inhibits the selection of another tap unless the change in the input or output voltage or current, whether upward or downward, is greater by a predetermined extent than that which would cause to be crossed a threshold appropriate to the selection of that other tap.

This invention further provides a voltage or current regulator of the type having a step-wise multi-tapped transformer between its input and its output, and means, responsive to changes in the regulator's input ot output, for selecting an appropriate transformer tap, so as to tend to restore the regulator's output to the required value, wherein: the means responsive to regulator input or output changes comprises an input detector whose output is fed to a store in the form of a latch circuit the output of which is fed in turn to a decoding circuit which controls the selection of the appropriate tap in dependence thereon; and there is provided means for inhibiting the selection of another tap unless the change in the regulator's input is of a predetermined extent, which means acts by inhibiting change in the stored contents of the latch circuit.

Preferably the regulator is a voltage regulator, the input detector is a peak-to-peak voltage detector, the multi-tapped transformer is an auto-transformer, whose multiple taps are provided solely on the input side thereof, and the means which inhibits tap selection comprises a comparator circuit connected to compare the output of the detector with the output of the latch circuit.

Conveniently the predetermined extent is at least that which would be compensated for by the step change in transformation effect obtained by switching from one tap to the next, but it may be equivalent to the interval of the taps of the transformer.

Preferably the input detector output is in analogue form, the latch circuit is a digital device, and the former is connected to the latter via an analogue-to-digital converter.

Preferably at the regulator's input there is provided an overload trip circuit breaker of the type which is subject to a short time delay before tripping which delay reduces with increase of overload current.

Preferably again a crowbar circuit is provided between the input of the regulator and the transformer to protect the regulator from excessive input voltages, the crowbar circuit also being arranged to be tripped by a temperature sensitive device in response to undue increase in the temperature of the transformer.

Preferably again a relay is provided between the input of the regulator and the transformer, which relay is controlled by a voltage sensor which monitors the voltage of the low voltage power supply for the logic circuits whereby if that voltage falls below the minimum required for correct logic circuit functioning the relay is opened.

Preferably again the relay is subject to a time delay before closing following "switch-on", so as to provide time for the logic circuits to stabilise.

Preferably again a protective crowbar circuit is provided between the transformer and the output of the regulator.

The invention is illustrated in and further described with reference to the drawing accompanying the provisional specification which is a block schematic circuit diagram of one voltage regulator in accordance with the present invention.

Referring to the drawing two input terminals 1 and 2 are provided to receive an alternating current waveform the voltage of which is to be regulated before application to two output terminals 3 and 4.

Input terminal 1 is connected to a circuit breaker 5 of the short delay, series trip type.

In this particular example an Airpax 209-2-1-61F-3-9-30 is used, which is capable of passing 30 amperes r.m.s. continuously but which will trip after a short delay if this rating is exceeded. As the overload current increases so the trip delay decreases.

The output of circuit breaker 5 is connected both to the primary winding of a transformer 6 and to a crowbar circuit 7 of the triac type which is provided to protect the regulator from voltages exceeding 150% of the input voltage. The triac crowbar circuit acts with a delay of the order of microseconds and resets at the zero crossing of the input waveform. A transient voltage suppressor (not shown) such as a metal oxide varistor, is provided in practice for protection against extremely short transients.

Output from input crowbar circuit 7 is connected to the input of a solid state relay 8 (standard logic type D 2240) which is subject to a short time delay after switch-on to enable the logic control circuits (to be described later) to settle down or stabilise.

Thereafter relay 8 is controlled by a low voltage sensor 9 provided to monitor the voltage of the low voltage power supply, represented by the block 10, of the logic circuits. If sensor 9 detects that the voltage of the low voltage power supply is below the minimum required for correct functioning, relay 8 is opened (rendered non-conductive) at the next zero crossing to avoid incorrect logic states.

The output of relay 8 is connected in parallel to ten relays 11 to 20 the outputs of which are connected to different taps upon an auto-transformer 21. In this particular example the taps are at 6.25% intervals.

Thus the output voltage appearing at the output connection 22 of the autotransformer 21 will depend upon which one of the relays 11 to 20 is closed (i.e. conductive).

A further crowbar protection circuit 23 is provided between output connection 22 and output terminal 3 to provide added protection. Input terminal 2 and output terminal 4 are both connected together.

A temperature sensor, represented by the block 24 is incorporated within the winding of the auto-transformer 21 in order to detect undue increase in temperature. Temperature sensor 24 is connected to input crowbar circuit 7 to trip the same if such undue temperature increase is detected.

So far the current supply part of the voltage regulator has been described. The logic control part of the regulator will now be described, that is to say the part of the regulator which controls the relays 11 to 20 and thus the regulation of the output voltage.

As has already been mentioned, the output of circuit breaker 5 is connected to the primary winding of a transformer 6. The secondary winding of transformer 6 is connected to a peak-to-peak input voltage detector and store shown within dashed line block 25.

Store 25 is of known form and consists of two recitifers 26 and 27 in series with each other. The secondary winding of transformer 6 is connected between the junction of rectifiers 26 and 27 and the junction of capacitors 28 and 29. The free ends of rectifier 26 and capacitor 28 are joined via a resistor 30, whilst the free ends of rectifier 27 and capacitor 29 are joined via a similar resistor 31. The junction of capacitor 29 and resistor 31 is connected to the earth return, whilst the junction of capacitor 28 and resistor 30 provide output to a buffer circuit 32.

Upon each cycle of the a.c. input, the store 25 rectifies and stores the peak-to-peak input voltage and provides this as a reference (until updated upon the next cycle) to buffer circuit 32.

The output of buffer circuit 32 is applied across a potentiometer chain of three resistors 33, 34, 35 of which the middle resistor 34 is adjustably tapped to provide an input to an eight bit analogue-to-digital converter 36. The adjustable tap of resistor 34 is set to provide a given input voltage (e.g. 5 volts) to the analogue-to-digital converter 36 for a given supply voltage (e.g. 115 volts) at the output of the circuit breaker 5.

Analogue-to-digital converter 36 is a standard logic circuit type ADC 590-8 and provides a digital output of 10000000 for 5 volts input: The output of analogue-to-digital converter 36 is connected to the input of an eight bit latch circuit 37 (standard logic circuit type SN 74100) the output of which is connected to a decoding circuit 38. Decoding circuit 38 is arranged to close the appropriate one of the relays 11 to 20 in dependence upon the number stored in latch circuit 37.

For the stored number 10000000, relay 16 is closed in this particular example.

A comparator circuit 39 is connected between the input and output of the latch circuit 37 to compare the output of analogue-to-digital circuit 36 with the output of latch circuit 37. Comparator circuit 37 is arranged to inhibit change in the number stored by latch circuit 37 unless a difference greater than 6.25% occurs, which corresponds to the intervals of the taps on auto-transformer 21. This is equivalent to a digital difference of 00001000. Thus if the peak-to-peak voltage at the terminals 1 and 2 changes by more than 6.25%, a tap is changed on auto-transformer 21 by closing a different one of the relays 11 to 20 in order to tend to restore the output voltage at output connection 22 to that required.

WHAT WE CLAIM IS: 1. An electric regulator having a stepwise multi-tapped transformer between its input and its output, means responsive to changes in the input or output voltage or current of said regulator for selecting an appropriate tap of said transformer to tend to restore the output voltage or current of the regulator to that value required and means which inhibits the selection of another tap unless the change in the input or output voltage or current, whether upward or downward, is greater by a predetermined extent than that which would cause to be crossed a threshold appropriate to the selection of that other tap.

2. A voltage or current regulator as claimed in claim 1 and of the type having a step-wise multi-tapped transformer between its input and its output, and means, responsive to changes in the regulator's input or output, for selecting an appropriate transformer tap, so as to tend to restore the regulator's output to the required value, wherein: the means responsive to regulator input or output changes comprises an input detec-.

tor whose output is fed to a store in the form of a latch circuit the output of which is fed in turn to a decoding circuit which controls the selection of the appropriate tap in dependence thereon; and there is provided means for inhibiting the selection of another tap unless the change in the regulator's input is of a predetermined extent, which means acts by inhibiting change in the stored contents of the latch circuit.

3. A regulator as claimed in claim 2, wherein the regulator is a voltage regulator, and the input detector is a peak-to-peak voltage detector.

4. A regulator as claimed in any of the preceding claims, wherein the multi-tapped transformer is an atuo-transformer.

5. A regulator as claimed in claim 4, wherein the multiple taps of the autotransformer are provided solely on the input side thereof.

6. A regulator as claimed in claim 2 or in claim 2 and any of claims 3 to 5, wherein the means which inhibits tap selection comprises a comparator circuit connected to compare the output of the detector with the output of the latch circuit.

7. A regulator as claimed in any of the preceding claims, wherein the predetermined extent is at least that which would be compensated for by the step change in transformation effect obtained by switching from one tap to the next.

8. A regulator as claimed in claim 7, wherein the predetermined extent is equivalent to the interval of the taps of the transformer.

9. A regulator as claimed in claim 2 or in claim 2 and any of claims 3 to 8, wherein the input detector output is in analogue form, the latch circuit is a digital device, and the former is connected to the latter via an analogue-to-digital converter.

10. A regulator as claimed in any of the preceding claims, wherein at the regulator's input there is provided an overload trip circuit breaker of the type which is subject to a short time delay before tripping, which delay reduces with increase of overload current.

11. A regulator as claimed in any of the preceding claims, wherein a crowbar circuit is provided between the input of the regulator and the transformer to protect the regulator from excessive input voltages, the crowbar circuit also being arranged to be tripped by a temperature sensitive device in response to undue increase in the temperature of the transformer.

12. A regulator as claimed in any of the preceding claims, wherein a relay is pro vic!ecI between the input of the regulator and the transformer, which relay is controlled by a voltage sensor which monitors the voltage of the low voltage power supply for the logic circuits whereby if that voltage falls below the minimum required for correct logic circuit functioning the relay is opened.

13. A regulator as claimed in claim 12, wherein the relay is subject to a time delay before closing following "switch-on", so as to provide time for the logic circuits to stabilise.

14. A regulator as claimed in any of the preceding claims, wherein a protective crowbar circuit is provided between the transformer and the output of the regulator.

15. A voltage regulator as claimed in any of the preceding claims and substantially as hereinbefore described with reference to the drawing accompanying the Provisional Specification.

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**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. difference greater than 6.25% occurs, which corresponds to the intervals of the taps on auto-transformer 21. This is equivalent to a digital difference of 00001000. Thus if the peak-to-peak voltage at the terminals 1 and 2 changes by more than 6.25%, a tap is changed on auto-transformer 21 by closing a different one of the relays 11 to 20 in order to tend to restore the output voltage at output connection 22 to that required. WHAT WE CLAIM IS:

1. An electric regulator having a stepwise multi-tapped transformer between its input and its output, means responsive to changes in the input or output voltage or current of said regulator for selecting an appropriate tap of said transformer to tend to restore the output voltage or current of the regulator to that value required and means which inhibits the selection of another tap unless the change in the input or output voltage or current, whether upward or downward, is greater by a predetermined extent than that which would cause to be crossed a threshold appropriate to the selection of that other tap.

TE r TE A I T