System for calibrating a line isolation monitor
US5446682A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Mar 21, 1994 |
| Grant date | Aug 29, 1995 |
| Priority date | — |
| Expiry date | Mar 21, 2014 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01R31/1272
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
A line isolation monitor (LIM) indicates the maximum hazard current of an ungrounded polyphase power distribution system. The LIM is microcontroller based and continuously monitors a fault impedance for each phase of the distribution system. The fault impedance is determined by the LIM by injecting a continuous sine wave measurement current into a ground terminal to generate a measurement voltage across the fault impedance. Using the measurement voltage and current, the LIM calculates the fault impedance and, using this impedance, calculates the hazard current based on the maximum line to ground voltage of the ungrounded system. The LIM has means for self-calibration and self-testing while on-line and during a power-up sequence. These tests compare measured and theoretical values of circuit parameters of voltage and current sensing circuits. During this calibration check, the monitoring circuits of the LIM are removed from the isolated system and known voltage and current signals are injected internally to the monitoring circuits to verify the component parameters. If the calibration parameters are outside tolerances by a first, low level, the LIM annunciates a warning, but will co…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.