GB1256054A - Improvements in and relating to isolator switches provided with earthing devices - Google Patents

Abstract

1,256,054. Metal clad switchgear. COQ N.V. 26 Jan., 1970 [4 Aug., 1969], No. 3665/70. Heading H1N. [Also in Division H2] In a high voltage, double break, metal clad isolating switch of the kind having two gas tight compartments separated by an insulator 3 which supports two movable contacts whereby each compartment contains a fixed and a movable contact and means are provided to connect the movable contacts to the metal casing in the open position, the two portions 1, 2 of the casing which surround the two compartments are insulated from one another and connect to earth by individual conductors 21, 22 and means is associated with the two conductors for indicating in which chamber an earth fault, if any, exists. In Fig. 1 (not shown), where the isolating and earthing contacts are arranged as disclosed in Specification 1,254,790, the two movable contacts are insulated from one another but connected by an auxiliary switch in all but the fully open position of the contacts; two indicating devices respond independently to fault currents in the two conductors. In Fig. 2 the two movable contacts 30, 31 are permanently connected; a current transformer 36 responds to the current in the connection 32. Two further current transformers 23, 24 respond to the current in the two conductors 21, 22. A single earthing contact 35 is provided. While the contacts 30, 31 are closed a current in connection 32 energizes equally windings 40, 42 of two transformers 37, 38; the secondary windings 43, 44 are also equally energized and a balanced relay 45 remains unoperated. With the contacts 30, 31 open and earthed, if an earth fault occurs between fixed contact 33 and envelope portion 2, fault current flows only in conductor 22 and therefore only winding 47 of relay 45 is energized to operate a first indicating device 51. Similarly an earth fault between fixed contact 34 and envelope portion 1 energizes only winding 46 and a second indicating device 49. If a fault occurs between contacts 31, 34, three windings 40, 41, 42 of the transformers are energized, only secondary 43 giving any output whereby indicator is again operated to indicate a fault in the right hand compartment. In a modification (Fig. 3, not shown) the three current transformers 23, 24, 36 energize respective relays 52, 54, 53 whose several contacts are interconnected to operate the appropriate one of indicators 49, 51.