Mcgraw-Edison Company

Cooper Industries, Inc.

James R Hurley

Clyde Gilker

James A Jindrick

Thomas G Dolnik

Naresh K Nohria

Michael Peter Dunk

Norbert J Reis

James A Baranowski

Thomas J Bray

A measuring circuit for obtaining a mean square value of a power distribution line paramter and a process for obtaining a mean square value is disclosed. The measuring circuit and process exploit my discovery that an accurate measurement of the mean square may be closely approximated by sampling the power parameter an odd number of times greater than one during the power parameter cycle. When the power parameter is sampled an odd number of times (N) during its cycle aliasing errors due to the existence of odd harmonics above the Nyquist Frequency are minimized. As a result, the means of the most recent N sample values squared is very nearly equal to the true mean square value which would be produced by a continuous integration of the square of the power parameter during its period divided by the period. By sampling at a relatively low frequency, errors and circuit complexity are reduced, and the speed with which an acceptable mean square value is obtained is increased.

Measuring circuit and method for power distribution equipment

A current measuring apparatus utilizes a known fundamental frequency, e.g., 60 Hz, for measuring current and includes a sensing and measurement pulse generation circuit including a current transformer for developing a low power signal directly related to the line current in a powerline, and a diode bridge with a first Zener diode for sensing when the developed current related signal exceeds a first predetermined positive threshold value and a second Zener diode for sensing when the developed current related signal falls below a second predetermined negative threshold value. Across the bridge is an LED for generating a first measurement signal having a duration related to the time when the developed signal exceeds the positive threshold value and second measurement signal during the time when the current related signal falls below the negative threshold value. The apparatus further includes processing circuitry and optical fibers for transmitting the measurement signals to the processing circuitry which is capable of processing the measurement signals durations (t.sub.1 or t.sub.2) to determine parameters of the developed current related signal thereby to determine the current flowing in the power line.

Current measuring apparatus

The method of the present invention encompasses comparing the instantaneous value of a waveform with at least two reference voltages, -R and +R, when crossing of these voltages occurs and processing this data in a data processor (46) to determine parameters of the waveform such as frequency and amplitude and of fundamental and DC offset. The apparatus of the present invention includes comparators (E.sub.1 and E.sub.2) which senses the voltage crossings and which has outputs (28 and 30) inputted to a latch (36) and to logic circuitry (32). A counter (50) supplies a count to the latch (36) and the output of the latch (36) is coupled to a microprocessor (46). The logic circuitry (32) has an output (34) coupled to the latch and to the microprocessor (46) first for causing, when a crossing occurs, the latch (36) to latch data identifying the particular crossing made and a count of the time it occurred and second to cause the microprocessor (46) to input this latched data and then to reset the logic circuitry.

Method and apparatus for digitally measuring alternating current

A microprocessor based recloser control has a microcomputer for causing trip and close operations of a recloser in response to the conditions of the power distribution lines being protected and operator commands. The microcomputer may be overridden by a mechanical switch in the recloser control. If power to the recloser control is lost, the microprocessor will continue to function with power storage means for a limited duration. Towards the end of that duration, this microcomputer will power down the microprocessor in an orderly manner allowing automatic return to its functions when power is restored. After the microprocessor is no longer functioning, a secondary overcurrent trip circuit is relied upon to cause a trip operation of the recloser for extended durations of power outage. The secondary overcurrent trip circuit can be disabled by the microprocessor. The microcomputer includes means to normalize the input signals from the power distribution lines and multiple redundancy features to prevent undesired operations of the recloser. The recloser control functions in response to the mean square of the currents in the protected power distribution lines, and includes means for protecting its more sensitive components from input signals normally encountered.

Microprocessor based recloser control

The power theft detector circuit (10, 110 and 210) detects when current is being diverted around a line conductor (20 or 220) passing through a meter housing (14 or 214). The circuit (10, 110 or 210) includes a current transformer (12, 112 or 212) coupled to the line conductor (20 or 220) within the meter and defines a primary winding (20 or 220) of the current transformer (12, 112 or 212). A secondary circuit (23, 123 or 224) includes a secondary winding (22, 122 or 226) of the transformer (12, 112 or 212) and sensing circuitry (24, R.sub.m, R.sub.1, and S; 124, R.sub.m, R.sub.1, S and 126; 232, R.sub.m, and 240) for sensing a change in the impedance reflected from the primary circuit into the secondary circuit (23, 123 or 224) when a low impedance jumper (26, 260) is connected in parallel with the line conductor (20 or 220) in the meter thereby to sense a power theft condition.

Power theft detection circuit

The electronic watt-hour meter (10) comprises an electro-optical watt-hour sensor (12) adapted to be coupled to a consumer's connection to a source of electric power for sensing voltage supplied to, and the current drawn by, the consumer's electric load and for producing output signals indicative of a quantity of watt-hours of power utilized by the consumer. In the meter (10) a microprocessor (22) is coupled to the sensor (12) for receiving output signals therefrom and a memory (29) is coupled to the microprocessor (22) for receiving and storing data. A power supply (24) supplies D.C. power to the microprocessor (22) and includes a clock signal generator to supply a 60 Hz. clock signal to the microprocessor (22). Also a visual display (30) is coupled to the microprocessor (22) for providing a readout of the power consumed since the last reading of the solid state watt-hour meter. The electro-optical sensor (12) includes a yoke (14) having a voltage core (62) and at least one current core (66 or 67), an induction disk (16) mounted for rotation in yoke (14), a voltage coil (64) in FIG. 1 on the voltage core (62) and a current loop (68 or 69) on the current core (66 or 67) for causing, when energized, rotation of the induction disk (16). At least one aperture (76) in FIG. 2 is provided in the disk (16). LED's (71 and 72), positioned on one side of the disk (16), are coupled to the microprocessor (22). Photosensors (81 and 82) are positioned on the other side of the disk (16) for receiving light passing therethrough and for generating an output signal which is supplied to a direction sensing and revolution counting circuit (90) in FIG. 2 for sensing the direction of rotation of the disk (16) and for supplying such information to the microprocessor (22). A power supply coil (26) is mounted on the yoke (14) for supplying A.C. voltage to the power supply (24).

Electro-optical sensor for watt-hour meter

A watt-hour meter is disclosed which includes: a microprocessor coupled to a solid-state Hall-Effect sensor; an electrically alterable ROM coupled to the microprocessor; a power supply; a power outage timing means using the discharge characteristic of a capacitor; apparatus for supplying a 60 Hz clock signal to the microprocessor; a readout device coupled to the microprocessor to provide an indication of the power consumed; an output on the microprocessor for controlling a circuit breaker; and a switch for overriding the microprocessor controlled circuit breaker. The microprocessor and the electrically alterable ROM are connected and programmed: to sense the time of day as determined from an initial time of day and setting the 60 Hz clock signal; to sense and compute the power used by the consumer; to automatically open the circuit breaker when power demand on the electric power source is high and/or the cost per kilowatt hour is high; to automatically close the circuit breaker when the power demand on the source of electric power is low and/or the cost per kilowatt power is low; and to allow a consumer to override the microprocessor's control of the circuit breaker.

Solid state watt-hour meter

The power outage timer (36, 136, or 236) forms a part of an electronic watt-hour meter (10) having a microprocessor (22), a real time value memory and a real time clock signal input from a voltage supply (23). The power outage timer (36, 136, or 236) is coupled to the microprocessor (22) for generating a signal when, after a power outage, power is restored, such signal being indicative of the time duration of the power outage and being input to the microprocessor (22) so that the microprocessor (22) can update the real time value in an EAROM (32) to reflect the correct real time.

Power outage timer

The non-linear alternating current transducer includes a current transformer core (14, 50 or 80) comprising a yoke (14, 50 or 80) for receiving a line conductor (20 or 110) and a secondary winding (22 or 86). The yoke (14, 50 or 80) has an air gap (19, 56 or 101-105) configured to provide a non-linear magnetic circuit response for changes in current through the line conductor (20 or 110). The non-linear magnetic circuit response provides a logarithmic voltage output across the secondary winding (22 or 86). The current transformer (12) is used in a control circuit (10) for sensing, monitoring and interrupting current in the line conductor (20 or 110) such that a trip coil is energized to open the circuit whenever current is sensed above a predetermined current. Also, the logarithmic response provides for high gain at low currents and low gain at high currents to that a very uniform percentage-of-reading accuracy is obtained with a meter operating off of the secondary winding.

Non-linear alternating current transducer

A voltage regulating transformer utilizing a microprocessor and a versatile multipurpose set of hardware modules and software modules it is described. A standard tap changing mechanism is driven in response to an analog control signal to change the output voltage of the transformer in response to digitally sampled values of voltage and current which have been transformed from the time domain to the frequency domain through a software program using Fourier transform techniques. The output current is also transformed and digitally processed to determine the power factor and the direction of power flow through the transformer. By inserting the digital values of the line characteristics to the load, line drop compensation is provided for. The difference in voltage across the input and output transformers is transformed to a digital signal and internally processed to provide an indication of the position of the tap changing mechanism without relying upon mechanical devices. The various software and hardware modules are designed so as to be readily utilizable in other electrical distribution controls.

Growing community of inventors

Brookfield, WI, United States of America

James R Hurley