Not applicable.
The present invention relates to a high voltage measuring device and, more particularly, to a high voltage detector that can be used for measuring voltages in high voltage AC circuits or systems with improved accuracy.
Voltage detectors are a form of voltmeter that measure voltages without the use of a ground lead. Typically voltage detectors are used for measuring high alternating current (xe2x80x9cACxe2x80x9d) voltages such as those encountered by electrical power utility linemen. To make measurements, voltage detector designers know that they need to determine the magnitude of the alternating current flowing through the voltage detector, and they also know that the magnitude of the alternating current being measured is a function of three things: (1) the internal impedance of the device, which is a known quantity; (2) the external capacitive reactance between the device and electrical ground; and (3) the magnitude of the voltage source being measured, e.g., the voltage carried through a high voltage conductor. To be able to determine the unknown voltage magnitude, the detector designers need to determine or assume a value for the external capacitive reactance. To the best of Applicant""s knowledge, all voltage detectors manufactured today assume a nominal value for the external capacitive reactance, which results in the detector providing a nominal voltage reading based on the capacitive reactance value assumed. However, since external capacitive reactance is a variable that is based on the many conditions under which the detector may be used, e.g., the external capacitive reactance is greatly affected by the height of the detector above ground, this assumed value for external capacitive reactance can cause an accuracy problem, i.e., the voltage measurements taken will be in error whenever the external capacitive reactance is above or below the assumed value.
According to its major aspects and broadly stated, the present invention is a voltage detector that is capable of measuring AC voltages with improved accuracy. To obtain these improvements in accuracy the present invention includes a novel circuit, which can be incorporated into a standard digital type voltage detector. Instead of relying on an assumed, i.e., fixed, external capacitive reactance value, which will lead to AC voltage measurement errors whenever the actual external capacitive reactance differs from the assumed value, this detector is designed to determine the phase angle difference between the applied voltage, e.g., the electrical transmission line voltage being measured, and the resulting current in an alternating current system.
Generally stated, in a purely resistive AC circuit the phase angle difference between the voltage and current waveforms is zero degrees (0xc2x0); in a purely capacitive AC circuit the phase angle difference between the voltage and current waveforms will be ninety degrees (90xc2x0), with the current waveform leading the voltage waveform by this angular amount; and, in a combination resistive-capacitive circuit, the phase angle difference will be in the range between 0xc2x0 and 90xc2x0. By using this phase angle difference concept, i.e, that the phase angle between the voltage and current waveforms is a function of the impedance characteristics of the circuit or system, the present invention is able to determine the actual value of the external capacitive reactance instead of relying on an assumed value for this characteristic and, therefore, is able to provide voltage measurements with improved accuracy by compensating for the variances in the magnitudes of the external capacitive reactance from measurement to measurement.
A major advantage of the present invention is that its design can be used, and/or modified, to measure AC voltages with improved accuracy over a wide range of magnitudes.
Another advantage of the present invention is that the simplicity of design of the novel circuit allows the circuit to be substituted and, therefore, used in a wide variety of meter configurations.
These and other features and their advantages will be apparent to those skilled in the art of from a careful reading of the Detailed Description of a Preferred Embodiments accompanied by the drawings.