Electronic watt-hour meter

An electronic watthour meter adapted to be connected in an A. C. electrical power distribution circuit, for producing an output signal related to the energy supplied by an electrical power supplier to an electrical power consumer via said distribution circuit, said distribution circuit consisting of N wires where N is at least 3, the watthour meter comprising:

• (N-1) current sensing means, the nth of which is arranged to produce a respective signal representative of the instantaneous magnitude of the current flowing in the nth wire where n=1 to (N-1);
• (N-1) voltage sensing means, the nth of which is arranged to produce a respective signal representative of the voltage between the Nth wire and the nth wire;
• (N-1) electronic circuits, the nth of which includes at least a respective means for producing a respective signal which varies substantially in accordance with the product of the respective instantaneous magnitudes of the nth current-representative signal and the nth voltage-representative signal;
• means for integrating, over time, said product signal to produce said output signal and for indicating the energy supplied to said electrical power consumer;
• and
• (N-1) power supplies, the nth of which is adapted to be connected between the nth wire and another wire, has at least one power supply point, and is arranged, in use, to generate between said at least one power supply point and the nth a D.C. power supply voltage suitable for operating the nth electronic circuit whereby said nth D.C. power supply electrically floats at the elevated voltage of the nth wire, the nth electronic circuit being connected to receive and be rendered operative by said power supply voltage.

An electronic watthour meter adapted to be connected in an electrical power distribution circuit, for producing an output signal related to the energy supplied by an electrical power supplier to an electrical power consumer via said distribution circuit, said distribution circuit consisting of first, second and third wires of which the first and second wires carry, with respect to the third wire, substantially equal alternating voltages having a phase difference therebetween of substantially 180.degree., the watthour meter comprising:

• first and second current sensing means for producing respective signals each representative of the current flowing in a respective one of the first and second wires;
• means for combining the current-representative signals to produce a signal representative of the sum of the respective currents flowing in the first and second wires;
• voltage sensing means for producing a signal representative of the voltage between any two of the wires;
• an electronic circuit connected to receive the current-sum-representative signal and the voltage-representative signal, said electronic circuit including at least means for producing a signal representative of the product of said current-sum-and voltage-representative signals;
• means for integrating, over time, said product signal to produce said output signal and for indicating the energy supplied to said electrical power consumer;
• and
• a power supply adapted to be connected between the first wire and either of the second and third wires, said power supply having at least one power supply point and being arranged, in use, to generate between said at least one power supply point and the first wire a D.C. power supply voltage suitable for operating said electronic circuit whereby said D.C. power supply electrically floats at the elevated voltage of the live first wire, said electronic circuit being connected to receive and be rendered operative by said power supply voltage;
• said first and second current sensing means respectively comprising first and second shunts, whereby said current-representative signals are voltages, and said combining means comprises an isolating voltage transformer having a primary winding connected to receive the voltage across the second shunt and a secondary winding coupled to the first shunt so as to produce in combination with the first shunt said current-sum-representative signal.

An electronic watthour meter adapted to be connected in a multi-wire A.C. electrical power distribution circuit, for producing an output signal related to the energy supplied by an electrical power supplied to an electrical power consumer via said distribution circuit, said distribution circuit including at least one live wire, the watthour meter including:

• at least one pair of current terminals, for series connection in said live wire;
• current sensing means connected between said pair of current terminals, for producing a signal representative of the current flowing in said live wire;
• voltage sensing means for producing a signal representative of the voltage between said live wire and another wire of the distribution circuit;
• an electronic circuit connected to receive the current-representative signal and the voltage representative signal, said electronic circuit including means for producing said output signal in response to said current-and voltage-representative signals said output signal being indicative of the energy supplied to said electrical power consumer;
• and
• A D.C. power supply for said electronic circuit, wherein the current sensing means comprises a shunt and the voltage sensing means comprises a relatively high value resistance connected between the electronic circuit and a further terminal adapted to be connected to said another wire, and, a substantial part of the electronic circuit is implemented as an integrated circuit on a common substrate and is connected to receive the voltage generated across the shunt via substantially non-inductive circuit paths of relatively low resistance value, and the DC power supply is adapted to be coupled between the live wire with another wire of the distribution circuit and is arranged to produce a D.C. output with respect to the live wire whereby said D.C. poer supply electrically floats at the elevated voltage of the live wire.

An electronic watthour meter designed for service installation in an A.C. utility power line having at least one live wire carrying a voltage typically of at least 100 volts relative to ground or neutral wire and including a shunt for such live wire to develop a low-voltage input signal representing the live-wire current where the respective shunt is connected,

• said watthour meter including a semiconductor based electronic circuit associated with such shunt, including a function circuit responsive to the current input signal from such shunt, for providing an output signal functionally dependent on line power transmitted past the respective shunt connection and indicative of the energy supplied along said power line, the electronic circuit further including all semiconductor components, necessary to derive from the power line any input used by the function circuit, to produce the output signal, a power supply circuit having an output connection to said electronic circuit for supplying D.C. current within circuit operating voltage limits, and means for effecting a connection of said power supply and said electronic circuit to the power line which relates the power supply output to the live wire where the respective shunt is connected, electrically to float said electronic circuit substantially at the live-wire voltage whereby the said semiconductor components of the electronic circuit are effectively protected from signal surges in the power line.