H - Electricity – 01 – H
Patent
H - Electricity
01
H
H01H 73/02 (2006.01) G01R 23/10 (2006.01) H02H 3/00 (2006.01)
Patent
CA 2150198
A circuit interrupter with a digital trip unit automatically sets the sampling interval appropriate for the 50 Hz or 60 Hz distribution system to which the interrupter is connected. In order to avoid falsely shifting the interval in response to distorted currents, the trip unit only changes the interval if the number of zero crossings of the current within a fixed number of samples is within two zero crossings of the number of zero crossings for an undistorted current of the other frequency for two consecutive time periods in which the fixed number of samples are taken. Furthermore, changes in the interval are only written into an EEPROM for use on power-up a fixed number of times to preclude disabling the EEPROM. In one embodiment, a 2 pole filter is utilized in the zero crossing counting circuit to eliminate false counts from noise originating in a chopper used in the trip unit power supply. In another embodiment, the zero crossing counting circuit is disabled unless external dc power is available for the trip unit which idles the chopper.
Engel Joseph Charles
Johnson Richard Arthur
Saletta Gary Francis
Shimp Alan Burke
Bereskin & Parr Llp/s.e.n.c.r.l.,s.r.l.
Corporation Eaton
LandOfFree
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