Patent GB-1005941-A (GB)
Title: Improvements relating to testing devices for testing protective switches
IPC: G01R31/327
Filed: 1962-09-21
Abstract: 1,005,941. Testing protective switches. SCHUTZAPPARATE-GESELLSCHAFT PARIS & CO. Sept. 21,1962 [Sept. 25,1961], No. 35954/62. Heading G1U. In a device for testing a fault voltage of fault current protective switch there is included at least one variable test resistor and a voltage responsive relay whose operating coil is connected in parallel with the test resistor and which has a contact in series with the test resistor for switching it into circuit to simulate a fault upon commencement of a test and for switching it out of circuit if the simulated fault current or voltage becomes excessive. A piece of equipment M such as a three phase motor is protected by a switch FU-SW which should operate if the voltage of the motor housing rises too much with respect to earth. In order to test whether the protective switch is functioning properly the circuit arrangement of the invention is connected so that terminal K3 is connected to one phase of the power supply, K<SP>2</SP> to the motor casing at Pro and K1 to the neutral of the power supplies. In the arrangement a relay A operates switch contacts a 1 , a 2 , a 3  while a switch P in the relay energising circuit is coupled to the test potentiometers P1 and P2 which are used to simulate fault conditions and is closed when they are set in their initial positions. To carry out a fault voltage test, the switch S2 is set to the position FU and the potentiometer P1 to its initial position. A circuit has already been completed from the conductor R through the lamp L2 to the conductor N to light L2 and now the operation of the relay A upon the closure of the switch P closes contact a 1  to operate the lamp L1, contact a 3  to hold the relay on and contact a 2  to complete a circuit from the lead R through the switches S1 and S2 the variable resistor P1 and back to the connection Pro. By reducing the value of P1 more of the supply voltage is made to appear across the housing resistance Pro, if this has any substantial value, and less across the relay A, which will eventually fall out, thus extinguishing the lamp L1. Before this happens the protecting switch Fu-Sw should have operated if it is working correctly. If this operation cannot be detected audibly, then K3 should be connected to the lead R on the motor side of the switch so that its operation will extinguish the light L2 (as well as L1). For testing a protective switch which operates according to fault-currents the switch S2 is set to the position F1 so that a variable resistor P2 having a graduated winding indicating different release currents may be used. Terminals K4, K5, K6 are provided so that measuring instruments may be inserted. Connection between K4 and K5 with the connection piece D removed enables current flow to be measured, while connection between K5 and K6 with the switch T1 as shown enables the voltage between the phase and protective conductors to be measured, whilst with it in the alternative position the phase-neutral voltage is determined. Provision is made for carrying out tests with a supplementary earth probe,which may be connec - ted to terminal K7 by setting the switch S1 in its alternative position. With a volt meter connected between K5 and K6 and ammeter between K4 and K5 the earthing voltage and earthing current between the protective conductor Pro and the probe may be measured. Operation of the switch T1 enables the protective-neutral conductor voltage to be measured. The apparatus may be used to determine the loop resistance, and may be used with delta networks having no earth conductor by a modification of the described technique.