Abstract: Electronic electricity meter, in which the electrical energy consumed by a load is evaluated using a signal indicative of voltage supplied to the load and a signal indicative of load current. The load current signal is derived from an estimated load current value produced by a current transformer (4). The meter includes a memory (9) storing one or more constants from equations indicative of how current transformer phase and ratio errors vary as primary current varies. An adjusted value for the load current is produced by calculating the phase and/or ratio error using the stored constants and the estimated load current value and correcting the estimated load current value to eliminate the error. Alternatively, the meter includes a memory (9) storing a plurality of values of phase error and/or ratio error for a respective plurality of primary current values of the current transformer of predetermined configuration.

Abstract: An analogue voltage-to-digital voltage converter has a voltage divider with a plurality of stages each providing an output voltage for comparison with the unknown voltage and in addition provides interpolation between the output voltage to improve the accuracy. Interpolation is effected by adding a ramp voltage to the unknown ramping through a magnitude equivalent to the voltage of at least one stage. With one tap on the voltage divider selected, comparison of the unknown plus ramp voltage is effected successively as the voltage ramps. By noting when the combined voltage reaches the level of one of the divider output voltages and by counting the number of comparisons made from the time when the ramp voltage is at a predetermined magnitude and comparing this with the time taken to ramp through one or a plurality of whole divider stages, determination can be made of the magnitude of the unknown voltage to a fraction of a stage.

Abstract: To enable a consumer of electrical energy to effect control of total energy consumption by various individual appliances and loads, each individual load has a control unit, conveniently in a plug top, which responds to pulses broadcast on the power supply wiring in the form of short duration interruptions of the waveform. At each appliance a microprocessor unit counts the number of successive pulses in a predetermined time interval and operates an electronic switch if the received count reaches a predetermined number, which may be different for different loads thereby enabling selective control of the loads. Provision is made for automatic restoration of supply if the overall energy consumption falls. Provision can also be made for automatic resumption of supply after a predetermined time interval.

Abstract: In an a.c. electricity power supply system, to guard against a "blackout", that is to say a cumulative supply failure caused by a fault leading to generating stations being overloaded and having to cease supplying a network, consumers are each provided with means responsive to the supply frequency and operative to reduce or cut out the consumer's load when the supply frequency falls below a predetermined value, which may be different for different consumers.

Abstract: An electrical energy consumption meter for use on a consumer's premises has data processing means responsive to the sensed voltage and current and to data such as tariff rates and clock information, for computing and displaying charges in monetary terms. A data link with the utility enables the utility to make use of this information and to add hire purchase commitments, etc. to the charges for energy consumption and also to enter credits for payments received. The data link may include provision for credit transfer by the consumer. Coin or token prepayment facilities may also be provided.

Abstract: In an electrical power distribution system, a consumer has a control unit comprising a plurality of solid state switches in supply leads to a plurality of separate load circuits, a microprocessor responsive to the magnitude of the total current drawn by the consumer from the supply and arranged to control the various switches so as to limit the total current or power in accordance with a priority program set into the microprocessor. The consumer can thus control the manner of use of the supplied power within a maximum demand limit. This overall maximum demand limit may be predetermined in accordance with an agreed supply tariff or may be remotely controlled by the utility.

Abstract: In a kilowatt-hour meter for measuring electrical energy consumption from an alternating electrical supply, a microprocessor includes a clock signal generator which is synchronized in phase with the incoming supply frequency. Pulse sampling means controlled by the clock generator sample the incoming voltage and current waveforms at a preselected time instant or instants in each cycle and the sampled data is utilized in the microprocessor to determine energy consumption.

Abstract: To detect tampering of a kilowatt-hour meter by the connection of a bypass link across the live connection through the meter, a voltage transformer within the meter unit is coupled to this live connecton so that a small volage is induced in the live connection in opposition to the supply voltage. The induced voltage produces a circulating current in the loop formed by the live connection and the bypass link and the transformer coupling is such that, with a bypass link of negligible resistance, the total current in the live connection is in opposite phase to the applied voltage. By means of a current transformer, a logic unit and a microprocessor, the phase of the current in the live connection within the meter is determined and is indicated by a latched flag indicator and/or transmitted to a distant data processor by a data link.