GOVENDER, Desigan (Highveld Technopark, 0157 Centurion, ZA)
| CLAIMS: 1. An electricity meter, which includes a circuit breaker having electrical terminals connectable to electrical cables leading from an electrical source and connectable to electrical cables leading to a load respectively, the circuit breaker operable to open the circuit between the source and the load terminals and to close the circuit between the source and the load; a temperature sensor in thermal communication with the electrical terminals, the temperature sensor operable to measure a temperature at the terminals; a controller connected to the temperature sensor for receiving temperature readings from the temperature sensor and controllably connected to the circuit breaker for opening and closing the circuit breaker, the controller operable to read the temperature from the temperature sensor and to open the circuit breaker when the temperature exceeds predefined temperature parameters. 2. An electricity meter as claimed in claim 1 , in the form of a prepayment electricity meter, with the controller operable to measure electrical energy used and to compare the energy used with an amount of pre-paid electrical energy to determine an energy credit. 3. An electricity meter as claimed in claim 2, in which the controller is operable to close the circuit breaker if the energy credit is positive and to open the circuit breaker if the energy credit reaches a zero amount. 4. An electricity meter as claimed in claim 1 , which is in the form of a single unit. 5. An electricity meter as claimed in claim 1 , which is in the form of two units, one of which contains the controller and the other of which contains the circuit breaker. 6. A method of operating an electricity meter connected in line between an electrical supply and an electrical load, which includes monitoring temperature parameters proximate electrical terminals of an electricity meter; opening a circuit breaker when the temperature parameters exceed certain predefined thresholds. 7. A method as claimed in claim 6, in which the temperature parameters are in the form of any one of absolute temperature values and a temperature gradient. 8. A method as claimed in claim 6, which includes pre-programming a controller, connected to a temperature sensor and controllably connected to a circuit breaker, with temperature parameters. 9. An electricity meter as claimed in claim 1 , substantially as herein described and illustrated. 10. A method as claimed in claim 6, substantially as herein described and illustrated. 11. A new electricity meter and a new method, substantially as herein described. |
This invention relates to electricity meters. In particular, this invention relates to a prepayment electricity meter.
BACKGROUND OF THE INVENTION
A prepayment electricity meter is installed at a user distribution endpoint and connected between a high voltage supply and a load at the user distribution endpoint to control supply of electricity to the load. A controller of the meter is configured to measure electrical energy used and to compare the energy used with an amount of pre-paid electrical energy to determine an energy credit. The controller is controllaby connected to a circuit breaker and operable to close the circuit breaker if the energy credit is positive and to open the circuit breaker if the energy credit reaches a zero amount.
The meter may be in the form of a single unit mounted in or at the user distribution endpoint. Alternatively the meter may be in the form of a split unit, of which one part is installed at the user distribution endpoint and another part is located remote from the user distribution endpoint.
The circuit breaker is connected in line between the electrical energy supply line and the user distribution endpoint load via circuit breaker terminals.
During installation of electrical cables to the circuit breaker terminals, it may happen that electrical cables are not properly fastened to provide low resistance connections between the cables and the circuit breaker terminals. For example, terminal screws may not be properly tightened onto the copper core of the cable. Poor connections are especially problematic in installations where large currents are drawn as they cause heating of circuit breaker terminals and associated cable portions. Accordingly, it is an object of the present invention to provide an electricity meter and associated method with which the applicant believes the aforementioned disadvantages may at least be alleviated.
SUMMARY OF THE INVENTION
According to the invention there is provided an electricity meter which includes a circuit breaker having electrical terminals connectable to electrical cables leading from an electrical source and connectable to electrical cables leading to a load respectively, the circuit breaker operable to open the circuit between the source and the load terminals and to close the circuit between the source and the load; a temperature sensor in thermal communication with the electrical terminals, the temperature sensor operable to measure a temperature at the terminals; a controller connected to the temperature sensor for receiving temperature readings from the temperature sensor and controllably connected to the circuit breaker for opening and closing the circuit breaker, the controller operable to read the temperature from the temperature sensor and to open the circuit breaker when the temperature exceeds predefined temperature parameters.
The electricity meter may be a prepayment electricity meter, with the controller operable to measure electrical energy used and to compare the energy used with an amount of pre-paid electrical energy to determine an energy credit.
The controller being controllably connected to the circuit breaker may be operable to close the circuit breaker if the energy credit is positive and to open the circuit breaker if the energy credit reaches a zero amount. The temperature sensor may include a semiconductor component. The temperature sensor may include an integrated circuit.
The electricity meter may be in the form of a single unit. Alternatively, the electricity meter may be in the form of two units, one of which contains the controller and the other of which contains the circuit breaker.
The invention extends of a method of operating an electricity meter connected in line between an electrical supply and an electrical load, which includes monitoring temperature parameters proximate electrical terminals of an electricity meter; opening a circuit breaker when the temperature parameters exceed certain predefined thresholds.
The temperature parameters may be in the form of any one of absolute temperature values and a temperature gradient.
The method may include pre-programming a controller, connected to a temperature sensor and controllably connected to a circuit breaker, with temperature parameters.
The invention will now be described, by way of example only with reference to the following drawing(s):
DRAWING(S)
In the drawing(s):
Figure 1 shows a schematic block diagram of an electricity meter in accordance with the invention. EMBODIMENT OF THE INVENTION
Figure 1 shows a prepayment electricity meter 10 in accordance with the invention.
The meter 10 includes a housing 12. In the housing there is provided a controller 14, which is connected to a semi-conductor temperature sensor 16, and controllably connected to a communications module 18, a display module 22 and a circuit breaker 24.
An over-heat disconnect flag 20 is implemented on the controller for recording an overheat event.
The meter 10 also includes electrical connection terminals 26.1 and 26.2 for connecting the meter via electrical supply cables 28 to a mains electrical supply 30. The meter 10 also includes electrical connection terminals 32.1 and 32.2 for connecting the meter 10 via cables 34 to a load 36 at a user distribution endpoint 38, such as a domestic dwelling.
In this example the controller 14 is operable to sense the flow of electrical current from the supply 30 to the load 38. By measuring the electrical current, the controller 14 can calculate an energy consumption. The controller 14 is also operable to accept a preloaded energy credit either via the central control station 50 or via a user input. The controller is operable to subtract the measured energy consumption from the energy credit.
In use, the controller 14 is operable to control the circuit breaker 24, to be closed while the energy credit is positive and to be opened when the energy credit reaches a zero amount.
During The cores of the cables 28 and 34 are secured to the terminals by screws 40 cooperating with treaded terminal blocks 42. In use, in event of incorrect installation of the cables 28, 34 into the terminal blocks, for example when the screws 40 are not properly tightened, the electrical contact between the cables 28, 34 and the terminal blocks 26 and 32 may cause a high resistance connection with resultant hot spots on the cables 28, 23 and/or the terminal blocks 26, 32.
The temperature sensor 16 is arranged to monitor the temperature at the terminals 26, 32. The controller 14 is pre programmed with temperature parameters and reads the sensed temperature from the temperature sensor 16. If the temperature parameters exceed certain pre-defined thresholds, such as an absolute temperature threshold or a temperature gradient, the controller 14 opens the circuit breaker 24 to disconnect the load 36 from the supply 30.
Upon the controller 14 sensing the exceeding of the pre-defined thresholds, the over-heat disconnect flag 20 is set and a fault message is send via the communications module 18 to the central control station 50.
It is to be appreciated that the same invention can be employed in various manners on single-phase or multi-phase electricity meters.
The inventor believes that the invention as described and illustrated will reduce the risk associated with the overheating of electricity meters, in particular in harsh environments where electrical installations may be subject to abuse and faulty installation.
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