GB877969A - Improvements in or relating to electric switchgear associated with zoned protection - Google Patents

Abstract

877,969. Protective cut-out arrangements. REYROLLE & CO. Ltd., A. (State Electricity Commission of Victoria). Feb. 7, 1958 [Nov. 15, 1956; Nov. 16, 1956], Nos. 34950/56 and 35076/56. Class 38 (5). In a protective arrangement suitable for outdoor type switchgear, the conductor between a current transformer, which ends a protective zone, and a circuit-breaker, which ends the corresponding sector of the system, is screened from earth by means connected to the main circuit at a point on the side of the current transformer remote from the circuit-breaker. In Figs. 1 and 2 one protection zone has current transformers D<SP>1</SP>, E<SP>2</SP>, and another zone has current transformers F<SP>3</SP>, D<SP>2</SP>. The top casing D<SP>3</SP> of the current transformer unit D and the screen G associated with the conductor C<SP>4</SP> are connected to the main conductor C<SP>1</SP> so that any fault between G and earth, or between the screens G of different phases, operates the protective circuit between current transformers D<SP>1</SP>, E<SP>2</SP> only and circuit-breakers F<SP>1</SP> are not tripped. A current transformer with its screened conductor may be arranged on each side of the circuit-breaker (Fig. 3, not shown) or a transformer arrangement as in Fig. 1 may be used with two circuit-breakers in series (Figs. 4 and 5, not shown). In Fig. 7 the screen is in the form of a shroud M which is connected to the lower casing B<SP>1</SP> of the circuit-breaker and the conductor C<SP>4</SP> is insulated therefrom. A voltage transformer may be connected to the casing B<SP>1</SP> with this arrangement and it will be within the protection zone of the conductor C<SP>1</SP> (Fig. 6, not shown). A screen O between the breaker mechanism and conductors may be connected to the casing B<SP>1</SP> or (Fig. 8, not shown) separately connected to a conductor leading to a point on the main circuit between the current transformers D<SP>1</SP>, D<SP>2</SP>. With the latter arrangement a fault between the screen O and earth will operate the protective equipment of both zones. In Fig. 10 (not shown) the current transformers are mounted between two series circuit-breakers with the shrouds for the conductors on each side, and the lower breaker casings all connected to a point between the two current transformers.