Abstract: The voltage at the test tap of a high voltage bushing is applied to a bushing coupler which includes circuitry to sense and process voltages generated at the test tap and convert the voltages into corresponding data signals. Data signals corresponding to the test tap voltages are then transmitted wirelessly to a bushing monitoring system. The wireless transmission may be, for example, via an optical coupling (e.g., fiber optics) arrangement or an electromagnetic radiation (e.g., RF transmission) arrangement. Thus, the signals from the bushing coupler are wirelessly transmitted to a monitoring system which is not conductively connected to the bushing coupler and the test tap. The bushing coupler includes a power supply which is chargeable from the test tap or wirelessly from the bushing monitoring system which is adapted to receive values of the high voltage applied to the bushing and to calculate changes in the values of selected bushing parameters.

Abstract: A protective system far a power transformer having a neutral line connected to ground where large currents can flow in the neutral line due to electro-magnetic disturbances. The system includes circuitry for: (a) sensing the current level in the neutral line and whether it exceeds a predetermined threshold for a predetermined period; and (b) sensing and processing the harmonic content of the load current and determining the existence of certain relationships of the “even” and “odd” harmonics. Signals, including alarms, indicative of excessive conditions are produced. The system may also include circuitry for sensing the load current level and generating a signal alarm if the load level is above a given value when the harmonics and the DC current have values in excess of certain predetermined values.

Abstract: The voltage at the test tap of a high voltage bushing is applied to a bushing coupler which includes circuitry to sense and process voltages generated at the test tap and convert the voltages into corresponding data signals. Data signals corresponding to the test tap voltages are then transmitted wirelessly to a bushing monitoring system. The wireless transmission may be, for example, via an optical coupling (e.g., fiber optics) arrangement or an electromagnetic radiation (e.g., RF transmission) arrangement. Thus, the signals from the bushing coupler are wirelessly transmitted to a monitoring system which is not conductively connected to the bushing coupler and the test tap. The bushing coupler includes a power supply which is chargeable from the test tap or wirelessly from the bushing monitoring system which is adapted to receive values of the high voltage applied to the bushing and to calculate changes in the values of selected bushing parameters.

Abstract: A protective system far a power transformer having a neutral line connected to ground where large currents can flow in the neutral line due to electro-magnetic disturbances. The system includes circuitry for: (a) sensing the current level in the neutral line and whether it exceeds a predetermined threshold for a predetermined period; and (b) sensing and processing the harmonic content of the load current and determining the existence of certain relationships of the “even” and “odd” harmonics. Signals, including alarms, indicative of excessive conditions are produced. The system may also include circuitry for sensing the load current level and generating a signal alarm if the load level is above a giver) value when the harmonics and the DC current have values in excess of certain predetermined values.

Abstract: The cooling system for a power transformer is activated by sensing and processing the frequency characteristic including the harmonic contents, of the inrush current into the transformer, when the transformer is first energized. The cooling system may include motors operating devices such as oil circulating pumps and fans causing a coolant to flow about the power transformer. The cooling system is deactivated by sensing when the transformer is de-energized and when its temperature is below a predetermined level.

Abstract: A system for cooling a power transformer which generates heat, when driving a load, includes cooling devices, such as fans and pumps, located about the transformer, which are powered for circulating a coolant about the transformer. Each cooling device has a motor which is energized in response to given temperature (heat) conditions. In systems embodying the invention, the currents flowing through the motors of cooling devices are sensed and monitored to determine whether the cooling devices are functioning correctly and to substitute functional cooling devices for those which are malfunctioning. Sensing the currents in the motors enables the early detection of fault conditions in the cooling system. It also enables the monitoring of operating conditions and running time of the cooling devices to aid in the maintenance and operation of the cooling system.

Abstract: The cooling system for a power transformer is activated by sensing and processing the frequency characteristic including the harmonic contents, of the inrush current into the transformer, when the transformer is first energized. The cooling system may include motors operating devices such as oil circulating pumps and fans causing a coolant to flow about the power transformer. The cooling system is deactivated by sensing when the transformer is de-energized and when its temperature is below a predetermined level.

Abstract: A system for cooling a power transformer which generates heat, when driving a load, includes cooling devices located about the transformer which are powered to remove excessive heat from the transformer. The cooling devices may include fans to blow air onto the transformer and pumps for circulating a coolant about the transformer. The cooling devices of interest have a motor (e.g., a fan motor or a pump motor) which is energized in response to given temperature (heat) conditions. In systems embodying the invention, the currents flowing through the motors of cooling devices are sensed and monitored to determine whether the cooling devices are functioning correctly and to substitute functional cooling devices for those which are malfunctioning.

Abstract: A load tap changer (LTC) having a plurality of windings is coupled to one of the primary and secondary windings of a power transformer in order to regulate the output voltage of the power transformer. The LTC includes a plurality of taps physically and electrically connected to the LTC windings and the transformer's output voltage is increased/decreased by moving along the taps a contacting element whose movement is controlled by a rotating shaft driven by a motor. The tap being contacted is determined by sensing the direction and number of shaft rotations and by checking the number of shaft rotations specified to go from a tap to the next tap being contacted. The time for a full rotation of the shaft is also measured. Also, the temperature of the tanks containing the LTC taps and the power transformer is measured for each tap position.

Abstract: A load tap changer (LTC) having a plurality of windings is coupled to one of the primary and secondary of a power transformer in order to regulate the output voltage of the transformer. The LTC includes a plurality of taps physically and electrically connected to and along the windings and a contacting element is selectively moved along the taps to increase or decrease the output voltage of the transformer. The power transformer and the LTC windings are placed in a main tank and the taps are placed in an LTC tank. The temperature in the main tank and the temperature in the LTC tank are monitored by means of first and second temperature probes whose outputs are used to sense the temperature differential (TDIFF) between the main tank and the LTC tank and to determine if the LTC tank temperature exceeds the main tank temperature for a period of time exceeding a specified time period. Also included is circuitry for sensing the rate of change of TDIFF and determining if it exceeds a predetermined value.

Abstract: In systems embodying the invention, a “downed” power line is detected by sensing whether there is an open circuit along the power line and producing an indication that an open circuit condition exists. In response to an indication that an open circuit condition exists, the system compares the nature of the voltage and/or current signals present on the power line at the time an open circuit condition is indicated to exist, with a preprogrammed stored condition which includes typical signals to be expected when a “break” occurs along a power line. When a downed power line is detected, power is then removed from the affected line.

Abstract: A substation for distributing electric power includes protective relays whose trip points are made to be a function of temperature, the protective relays being used to control the opening and closing of circuit breakers for protecting against fault conditions in at least one of the power input and power output portions of the power distribution system. In one embodiment, a temperature probe which is used to sense the temperature at a selected point of the substation supplies the temperature information to a microcontroller which is programmed to set the trip point of selected protective relays as a function of the sensed temperature.

Abstract: The invention is directed to an improved method and apparatus for monitoring the status of an AC electrical transmission line connected between first and second locations. In a disclosed embodiment of the method of the invention, first signal parameter values are generated, for the first location, by time integrating between zero-crossings of an AC signal parameter measured at the first location. Second signal parameter values are generated, for the second location, by time integrating between zero-crossings of the AC signal parameter measured at the second location. The second signal parameter values are transmitted to the first location. In a form of this embodiment, the second signal parameter values transmitted for each of the three phases are transmitted only for time periods between successive zero-crossings beginning with a zero-crossing of one sense (e.g.

Abstract: A wheel is mounted on a rotating shaft and cooperates with at least one pair of inductors fixedly mounted in juxtaposition to the wheel. The wheel has at least one opening formed therein for generating a signal whenever the opening in the wheel is substantially aligned circumferentially with the pair of inductors. An electronic control circuit, responsive to the signal, actuates a remote meter for providing a remote indication of the shaft position. In a preferred embodiment, this improved sensing means is applied to the remote reading of a conventional household electric meter. Two pair of inductors are provided for cooperation with five equiangularly-spaced closed slots formed in the wheel, thereby providing ten signals (or counts) for each complete revolution of the wheel. The wheel is mounted on the shaft of the unit decade dial in the meter.

Abstract: A wheel is mounted on a rotating shaft and cooperates with at least one pair of inductors fixedly mounted in juxtaposition to the wheel. The wheel has at least one opening formed therein for generating a signal whenever the opening in the wheel is substantially aligned circumferentially with the pair of inductors. An electronic control circuit, responsive to the signal, actuates a remote meter for providing a remote indication of the shaft position.In a preferred embodiment, this improved sensing means is applied to the remote reading of a conventional household electric meter. Two pair of inductors are provided for cooperation with five equiangularly-spaced closed slots formed in the wheel, thereby providing ten signals (or counts) for each complete revolution of the wheel. The wheel is mounted on the shaft of the unit decade dial in the meter.

Abstract: An improved pick-up means for the remote monitoring of a rotating shaft, or a wheel mounted on the shaft, utilizes the inductive coupling effect between an aperture formed in an annular conductive member and at least one pair of coils or inductors fixedly mounted radially of the annular member. As applied to the remote monitoring of a standard electric service meter, the annular member comprises a metallic rim on the circumference of a plastic disc mounted on a shaft which is journaled within the top front panel of the meter, concentrically within the unit decade dial. Preferably, three inductors are employed, including first and second inductors and a third common inductor therebetween, thereby forming two pairs of inductors; and the signal is generated in the third common inductor whenever a respective aperture on the rim of the disc circumferentially bridges a respective pair of inductors at a predetermined position of the disc.

Abstract: A safety system for a machine tool is characterized by a capacitively coupled electric field generator (transmitter) and a capacitive receptor antenna. An electrical signal is induced in the capacitive receptor antenna by the action of the electric field. The magnitude of the induced signal is monotonically related to the distance between the electric field generator and the capacitive receptor antenna. When the magnitude of the electrical signal exceeds a predetermined threshold, a machine tool safety indicator is developed.

Abstract: A machine tool safety system includes an electric field generator capacitively coupled to a receptor antenna. A self-test network includes a self-test radiating antenna and a circuit arrangement operative to apply a test signal to the self-test antenna. The test signal may be of sufficient strength to induce in the receptor antenna a first excitation signal having a magnitude greater than a first predetermined threshold to verify that the safety system is operative to detect the entry of the field generator carried on an operator's person into a hazard zone proximal to the machine tool. The test signal may be of sufficient strength to induce a second excitation signal greater than a second threshold to verify that the safety system is operative to detect the entry of the field generator into an arming zone spaced from the hazard zone.

Abstract: A power amplifier includes a plurality of generally identical amplifier elements connected in parallel between input and output transmission lines for phase coherent addition of the signal outputs of each amplifier element. Resistive elements are connected across normally phase identical points on the transmission lines. If the amplifier becomes electrically unbalanced, power is absorbed in the resistive elements, thus protecting the amplifier elements.