GB2279516A - Electricity supply control systems - Google Patents

Abstract

An electricity supply control system including a contactor 28, in particular a prepayment electricity meter 12 or a radio teleswitch, is provided with a circuit 30 for detecting the presence of the elecricity supply down-circuit of the contactor. If the supply is detected at a time when the contactor is supposed to be open, indicating for example that the contactor has welded shut or been bypassed, the circuit sends several pairs of control signals to the contactor, each pair tending to close the contactor and immediately re-open it, since such pairs of signals have been found effective in breaking the weld if the contactor has indeed welded shut. Additionally, a signal indicative of the detection of the supply when the contactor is supposed to be open is stored, in case it is indicative of an attempt to defraud the system. <IMAGE>

Description

ELECTRICITY SUPPLY CONTROL SYSTEMS This invention relates to electricity supply control systems, and is more particularly concerned with electricity supply control systems employing a contactor to selectively control the supply of the electricity.

Several types of electricity supply control system employing a contactor are in use in the United Kingdom at the present time for controlling domestic electricity supplies. For example, there are systems providing timed off-peak supplies, where a dedicated electricity supply is made available, eg for off-peak heating purposes, only at certain times of day, under the control of either a quartzcontrolled timer or a radio teleswitch (a device which receives digital control signals modulated onto the BBC's Radio Four radio broadcast signal on 198kHz) forming part of the system. Additionally, there are prepayment systems, where the supply of electricity is controlled by a prepayment unit which accepts tokens, typically in the form of electronic keys or magnetic cards, containing data which is representative, directly or indirectly, of an amount of electricity paid for in advance.

In use, the contactor in such a system is sometimes required to switch a current of up to 100 amps. However, the contactor is also required to be physically small, so as to fit easily within a normal-sized electricity meter. As a result of this, such contactors can occasionally become welded shut, and therefore fail to open when commanded to do so. It is an object of the present invention to alleviate this problem.

According to the present invention, therefore, there is provided an electricity supply control system including a contactor for controlling the supply of the electricity and a control circuit coupled to the contactor and arranged to control it in dependence upon desired control criteria, wherein said control circuit includes means for detecting the presence of the electricity supply down-circuit of the contactor, and means responsive to such detection at a time when the contactor is supposed to be open to send at least one opening command to the contactor.

Preferably, said opening command takes the form of at least one pair of control signals which tend to close the contactor and substantially immediately re-open it.

Advantageously, several such pairs of control signals are sent to the contactor, in reponse to each such detection.

The detection means preferably comprises a capacitor arranged to be charged to a given DC voltage by the electricity supply down-circuit of the contactor. The given voltage may be determined by a resistor or a zener diode.

The system may be or include an off-peak electricity supply control system, in which case the control circuit may include or be controlled by timing means and/or a radio receiver adapted to receive broadcast timing and/or control signals. Alternatively, the system may be a prepayment system which co-operates with a token having a memory containing data representative of the amount of the prepayment, in which case the control circuit may include a memory circuit, preferably a non-volatile memory circuit, for storing a signal indicative of such detection, and means for writing said signal into the memory of the token the next time the token is used to enter prepayment data into the system.

The invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a simplified block diagram of a prepayment electricity metering system in accordance with the present invention; and Figure 2 is a circuit diagram of a detection circuit forming part of the system of Figure 1.

The prepayment electricity metering system shown in the drawings is intended for installation in an electricity consumer's premises, and is closely based on the system described in our United Kingdom Patent No. 2 191 622 (which was in turn a development of the system described in our United Kingdom Patent No 2 153 573).

Thus the system comprises a key 10, known as a customer key, containing a non-volatile memory such as an EEPROM, and a multi-rate electricity meter 12 having a receptacle 14 for receiving the key 10. The physical form of the key 10 and the receptacle 12 can be as described in our United Kingdom Patent No. 2 191 883.

Associated with the receptacle 14, within the meter 12, is a key interface circuit 16 coupled to a microprocessor 18. The microprocessor 18 is coupled in turn to another non-volatile memory 20 in the form of an EEPROM, to a clock 22, to an LCD display 23, to a power measuring circuit 24 connected in the consumer's electrical power distribution circuit 26 and to a switch unit or contactor 28 also connected in the distribution circuit 26.

The system operates substantially as described in our United Kingdom Patents Nos. 2 153 574 and 2 191 622. In particular, the consumer takes the key 10 to a vending machine, typically located in or near the electricity supplier's premises, and inserts the key 10 into a receptacle, similar to the receptacle 14, in the machine.

The consumer then inserts coins or bank notes into the machine, which, having read the key memory, responds by writing credit data representative of the amount of credit purchased into the key memory, along with tariff data representative of the current electricity supply tariffs and pass number data indicative of how many times the key has been used. The key memory typically already contains identification data uniquely identifying the key, the meter in which it is to be used and the consumer, all of which identification data was entered when the key 10 was first issued to the consumer.

Having charged the key 10 with credit, the consumer returns home and inserts the key into the receptacle 14.

This causes the microprocessor 18 to read the contents of the key memory, to perform checks to see if these contents indicate a valid key as described in United Kingdom Patent No. 2 153 173, and if they do, to write them into the memory 20. The microprocessor 18 also writes the current readings of the meter 12, which are stored in the memory 20, along with the time and date to which the readings relate, into the key memory, substantially as described in United Kingdom Patent No 2 191 622.

Once the microprocessor 18 has accepted the key 10 as valid, and has written the credit data into the memory 20, the contactor 28 closes to permit the supply of electricity. Supply is allowed to continue until an amount of electricity equal in value to the monetary amount represented by the credit data received from the key 10 has been supplied, whereupon credit is exhausted, and the contactor 28 re-opens to discontinue the supply. However, an emergency supply of electricity, either equivalent to a predetermined amount of money or for a predetermined time period, can be obtained by operating a push-button (not shown).

In use, the contactor 28 can be required to switch up to 100 amps. However, it is also fairly compact, being designed to fit within a standard housing of the same size as is used for ordinary domestic credit meters. As a result, it can occasionally happen that the contacts of the contactor 28 weld shut. This welded-shut condition can be detected, in accordance with the present invention, by a detector circuit 30, which is connected between the live and neutral wires, L and N, of the power distribution circuit 26 down-circuit of the contactor 28, and which detects the presence of the supply voltage between the live and neutral wires L and N. The circuit 30 has an output 32 at which it produces an output signal indicative of the detection of the supply voltage, and this output signal is applied to the microprocessor 18.

The detector circuit 30 is shown in more detail in Figure 2, and comprises the series combination of a high value resistor 34, a diode 36 and a capacitor 38 connected between the live and neutral wires L and N of the power distribution circuit 26, with a zener diode 40 connected in parallel with the capacitor. The presence of the supply voltage between the live and netral wires L and N therefore causes the capacitor 38 to charge up to a DC voltage determined by the zener diode 40, typically around 5 volts, which voltage serves as the output of the detector circuit 30.

It will be appreciated that the detection of the supply voltage down-circuit of the contactor 28 at a time when the contactor is supposed to be open is a fairly good (though not conclusive) indication that the contactor has welded shut. In these circumstances, the microprocessor 18 sends a quick succession of pairs of signals to the contactor 28, each pair commanding it to shut and then immediately to re-open (since experiments have shown that such a pair of signals is much more effective at breaking the weld than a simple signal commanding the contactor to open). If the output signal from the detector circuit 30 persists, the microprocessor 18 stores a signal indicative of that fact in the EEPROM 20, which signal is entered in the memory in the key 10 the next time the key is inserted into the receptacle 14. Alternatively, the microprocessor 18 can store a signal indicative of the fact that the detector circuit 30 produced an output signal when the contactor 28 was supposed to be open, which signal is similarly entered in the memory of the key 10. In either case, the next time the key 10 is inserted into a vending machine for the purchase of more credit, the electricity supplier receives an indication that either the contactor 28 in that consumer's meter 12 is prone to welding shut or that consumer is perhaps trying to defraud the meter 12 by bypassing it (which would likely also result in an output from the detector circuit 30).

Many modifications can be made to the described embodiment of the invention.

For example, the zener diode 40 can be replaced by a relatively low value resistor forming a potential divider with the high value resistor 34.

Additionally, the key 10 need not have the physical form of a key, but can instead be constituted for example by a so-called "smart card" or by a magnetic card. Also, although all the elements of Figure 1 (except the key 10) are described as being contained within a single housing, they can if desired be contained in two separate housings, one containing the power measuring circuit 24 and the contactor 28, and the other containing the other elements (except the key 10).

Furthermore, the power measuring circuit can be replaced by a time measuring circuit and the electricity supply can be pre-paid for on a timed basis rather than a metered basis, eg the credit in a key pays for supply of the commodity for a week or a month.

Finally, although the invention has been described for convenience in the context of a prepayment electricity supply control system, it is equally (if not more) applicable to off-peak electricity supply control systems, since the contactor tends to open and close more often (eg twice a day) in these latter systems. In off-peak electricity supply systems, the control circuit typically includes or is controlled by a timing circuit such as a quartz-controlled time switch circuit and/or a radio teleswitch circuit responsive to the digital timing and control signals modulated onto the BBC Radio 4 long wave broadcast transmission at 198 kHz.

Claims (9)

1. An electricity supply control system including a contactor for controlling the supply of the electricity and a control circuit coupled to the contactor and arranged to control it in dependence upon desired control criteria, wherein said control circuit includes means for detecting the presence of the electricity supply down-circuit of the contactor, and means responsive to such detection at a time when the contactor is supposed to be open to send at least one opening command to the contactor.

2. A system as claimed in claim 1, wherein said opening command takes the form of at least one pair of control signals which tend to close the contactor and substantially immediately re-open it.

3. A system as claimed in claim 2, wherein several such pairs of control signals are sent to the contactor, in reponse to each such detection.

4. A system as claimed in any preceding claim, wherein the detection means comprises a capacitor arranged to be charged to a given DC voltage by the electricity supply down-circuit of the contactor.

5. A system as claimed in claim 4, wherein the given voltage is determined by a resistor or a zener diode.

6. A system as claimed in any preceding claim, said system being or including an off-peak electricity supply control system, wherein the control circuit includes or is controlled by timing means and/or a radio receiver adapted to receive broadcast timing and/or control signals.

7. A system as claimed in any one of claims 1 to 5, said system being a prepayment system which co-operates with a token having a memory containing data representative of the amount of the prepayment, wherein the control circuit includes a memory circuit for storing a signal indicative of such detection, and means for writing said signal into the memory of the token the next time the token is used to enter prepayment data into the system.

8. A system as claimed in claim 7, wherein said memory circuit is a non-volatile memory circuit.

9. An electricity supply control system substantially as herein described with reference to the accompanying drawings.