GB707741A - Improvements relating to the testing of electrical apparatus - Google Patents

Abstract

707,741. Detecting faults. SLANEY, A. H. April 10, 1952 [Jan. 12, 1951], No. 889/51. Class 37 A test plug, for testing high voltage switchgear which is normally operable by relayoperating pilot means from a remote location, is adapted to be engaged in a socket to which main and pilot lines from the relay-operated switch gear are connected, and has test means for connection to the switch gear and relay-operating pilot means adapted for connection to the pilot lead, and includes a manually operated switch. The invention is shown as applied to the testing of the remote control switch gear and trailing cable used in coal mining machinery. A control panel 1, Figs. 1 and 2 has a socket 2 into which is normally fitted a plug 3 on one end of a trailing cable 4, the far end of which has a similar plug for engagement with' the coal-cutting or other machinery. The cable 4 contains three main lines A, B, C, which connect with three-phase supply lines A1, B1, C1, in the control panel, and a pilot line D through which a pilot relay G is controlled. This controls a working relay H which operates in sequence to actuate the contactor F test plug 9, Fig. 3,.has pins 5, 6, 7 for engaging the main line sockets and a pin 8 for engaging the pilot line socket. For testing the control panel the test plug 9 is inserted in the panel socket in place of the trailing cable 4 as shown in Fig. 1, while for testing the cable 4 the test plug is inserted into a socket in a coupler 10, Fig. 2, which has a second socket into which the plug 3 at the far end of the cable 4 is inserted. The test plug 9 comprises a brass casing 11 which is earthed, and within which are neon lamps 12, 13, 14 connected in star to the main pins 5, 6, 7 and observable through windows in the casing. Connected to the pilot pin 8 are a choke 29 and condenser 30 which are connected to contacts 19, 20 on a hand control switch 16. This comprises a rod 23 slidable and rotatable in a sleeve 24 and having on its outer end a hand grip 25 and on its inner end a contact member 21 having a high part 21a and a low part 21b. Normally the member 21 is out of engagement with both contacts 19, 20. On pushing in the rod 23 the high part 21a engages the contact 20 and connects the choke 29 and condenser 30 between the pin 8 and the earthed casing 11. The switch is then rotated so that the contact 19 is also engaged by the contact member 21. The condenser 30 and choke 29 are thus short-circuited, the pilot relay operates, and the working relay is opened. The switch is then turned back to disengage the contact 19 and cause the working relay contacts to reclose. As the pilot relay contacts are also closed the contactor F is switched on. If there is no fault the lamps 12, 13 14, light up; if any lamp does not light a fault exists in the lead to which it is connected. In a modification a resistance and rectifier are substituted for the condenser and choke.