GB1254788A - Improvements in or relating to devices for indicating the condition of a switch - Google Patents

Abstract

1,254,788. Protective arrangements. BROWN, BOVERI & CO. Ltd. 24 March, 1969 [26 March, 1968], No. 15273/69. Heading H2K. An arrangement for indicating the on/off condition of a main switch 1 having auxiliary contacts 2, comprises an auxiliary transformer 3 having a primary winding 31 connected in series with impedance 5, 6 across an A.C. supply 4, 20, and a secondary winding 32 connected across the contacts 2. When the switch 1 is closed, the contacts 2 short circuit the winding 32 so that the primary winding 31 has a low impedance and the resulting voltage drop across the impedance, e.g. a resistor 6, provides an output indicating that the switch 1is "on". When the switch 1 is open, the contacts 2 are open, the winding 32 is not short-circuited so that the impedance of the primary winding 31 is high and there is little voltage across the resistor 6. A rectifier 7 may be used instead of the connection 22 so as to provide D.C. output signal. The operation of this arrangement may be checked by a further arrangement comprising an auxiliary transformer 11 with a primary winding III in series with an impedance 12 and a secondary winding 112 connected across further auxiliary contacts 10 which are open when the contacts 2 are closed. Further secondary windings of the two transformers are connected in opposition and in series with a rectifier 13 and resistors 14, 15. As long as one pair of auxiliary contacts 2 or 10 is closed and the other is open, one secondary winding 113 or 33 produces an output so that a signal is available across the resistor 15. Should both pairs of auxiliary contacts 2, 10 be closed, nothing is induced in the secondary windings 33, 113 and should both pairs of contacts 2, 10 be open, the potentials induced in these secondary windings are in opposition, so that in neither case will there be a signal across resistor 15.