Floating negative automatic grounding switch

Details Floating negative automatic grounding switch Floating negative automatic grounding switch

H - Electricity

02

H

323/6

H02H 3/32 (2006.01) H02H 3/14 (2006.01) H02H 1/00 (2006.01) H02H 3/05 (2006.01) H02H 3/44 (2006.01)

Patent

CA 1307822

FLOATING NEGATIVE AUTOMATIC GROUNDING SWITCH ABSTRACT OF THE DISCLOSURE: In certain DC powered systems, particularly traction power systems such as electrified railways, it is becoming the practise to isolate both the positive and negative busses -- from which the system load derives its power -- from ground. However, the rolling stock (streetcars or train cars) maintains the chassis of the car at the potential of the negative bus; and under certain conditions its potential may float away from ground potential, to the extent that any person standing at ground potential and touching the chassis might receive an electric shock. The present invention provides a circuit having sensing means which determines whether the potential of the negative bus relative to ground has exceeded a predetermined limit, either positive or negative with respect to ground, or whether the rate of change of potential of the negative bus with respect to ground exceeds a predetermined rate; and in either event, the sensing means acts to cause a switch means which is usually a normally open silicon controlled rectifier arranged to face in the appropriate direction, to close and thereby to cause a short circuit between the negative bus and ground. The switch is retained in closed condition until the current through it reduces to substantially zero. In certain circumstances, it may be that it is the positive bus which is monitored. In any event, the circuit acts to ground the monitored bus under abnormal conditions, rather than to lift the monitored bus away from ground potential as would be the usual case. SPE6415

519582

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