GB422851A - Improvements in or relating to the protection of electric water heating apparatus - Google Patents

Abstract

422,851. Protective cut-out arrangements. REYROLLE & CO., Ltd., A., Hebburn - on - Tyne, and LEYBURN, H., (formerly LEBEN, H.), 212, Wingrove Road, Newcastle-on-Tyne. July 19, 1933, No. 20366. [Class 38 (v)] Polyphase electric water heaters of the kind in which the water is in direct contact with the heating elements, the casing E of the heater constituting an earthed neutral point of the system, are protected against earth faults by means of a directional relay G, Fig. 3, one coil G<1> of which is energized, in accordance with the earth leakage current, from current transformers K<1> ... K<3> in the supply circuit to the heaters, while the other coil G<2> is energized in accordance with the voltage in the circuit. In the arrangement shown, the voltage coil is energized from the open-delta-connected secondary windings M<1> ... M<3> of a potential transformer, whose primary windings L<1> ... L<3> are connected to the supply circuit. Overload protection for the heating apparatus is provided by means of overload trip coils N, N<1>, shunted by fuses N2, N3 and connected in series with the secondaries of the current transformers K', K<3>. In systems in which a power transformer A<1> ... A<3> is connected through two or more sets of feeders C<1> ... C<3> to a number of water heaters, each set of feeders is provided at the power supply end with a directional relay O which acts to cut out the feeder when, owing to an earth fault on the feeder, earth fault current is flowing through the feeder in a direction away from the source of power. In the arrangement shown in Fig. 4, one winding O<1> of the relay O is connected between the star points of the star-connected secondaries of current transformers P<1> ... P<3> in the feeders C<1> ... C', the other winding O<2> being energized from a current transformer Q in the neutral earthing connection A<4> of the power transformer secondary. In a modification, Fig. 5, (not shown), the winding O<2> is energized from the open-delta secondary winding of a potential transformer connected to the feeder.