S&c Electric Company

Brian P Mugalian

Gregory C Mears

John A Zulaski

Zitao Wang

John Gorecki

A capacitive voltage sensor for estimating voltage on a power line. The sensor includes a dielectric bushing surrounding the line, and an annular conductor formed in the bushing and being capacitively coupled to the line, where a first capacitance is defined between the line and the annular conductor and a second capacitance is defined between the annular conductor and ground. The sensor also includes a capacitance compensation circuit having an amplifier including a first terminal electrical coupled to the annular conductor, and first and second capacitance compensation capacitors electrically coupled to the terminals of the amplifier, where the compensation capacitors are made of different materials having different dielectric constants, and where the materials of the compensation capacitors are selected so as to compensate for changes in the first and second capacitances in response to temperature changes. Also, a thermistor is provided in a resistor compensation circuit to provide resistance compensation.

Capacitive compensated voltage sensor

A phasing and indicator arrangement is provided for switchgear or the like that responds to electrical sources and provides voltage indicator functions, phasing determinations, and self-test features. Phasing provisions are responsive to two or more voltage sensors proximate respective electrical sources to provide an output that represents the phase difference, i.e. time relationship, between the electrical sources as an alternating-current voltage measurable by a voltmeter. The output is relatively independent of the voltage of the electrical sources. The indicator arrangement is operable in a test mode to test the integrity of one or more voltage indicators while clearly identifying that the indicator arrangement is in a test mode. In a preferred arrangement, the indicator arrangement in the self-test mode is powered by a photocell. Further, in the self-test mode, the indicator arrangement generates signals through each voltage sensor and over the complete voltage sensing path, the generated signals being substantially similar to the signals generated by each voltage sensor during normal operation in response to an alternating-current source. In the self-test mode, the phasing arrangement is also tested.

Phasing and indicator arrangements for switchgear or the like

A phasing and indicator arrangement is provided for switchgear or the like that responds to electrical sources and provides voltage indicator functions, phasing determinations, and self-test features. Phasing provisions are responsive to two or more voltage sensors proximate respective electrical sources to provide an output that represents the phase difference, i.e. time relationship, between the electrical sources as an alternatingcurrent voltage measurable by a voltmeter. The output is relatively independent of the voltage of the electrical sources. The indicator arrangement is operable in a test mode to test the integrity of one or more voltage indicators while clearly identifying that the indicator arrangement is in a test mode. In a preferred arrangement, the indicator arrangement in the self-test mode is powered by a photocell. Further, in the self-test mode, the indicator arrangement generates signals through each voltage sensor and over the complete voltage sensing path, the generated signals being substantially similar to the signals generated by each voltage sensor during normal operation in response to an alternating-current source. In the self-test mode, the phasing arrangement is also tested.

An overcurrent protection device is provided for one or more phases of a circuit that generates a control signal dependent upon an adjustable trip level setting after a fault has occurred. The device includes a blocking level detector that blocks the generation of the control signal is the current in any of the phases exceeds either a first predetermined blocking level or the adjustable trip level setting. In a preferred arrangement, before control-signal generation, the device also requires that the current in at least one phase is below a predetermined load level.

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Chicago, IL, United States of America

Brian P Mugalian