GB417960A - Improvements in or relating to electric leakage indicators and protection devices for electrically driven vehicles - Google Patents

Abstract

417,960. Protective cut-out systems. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and PHILLIPS, F. C. F., c/o General Electric Co., Stoke, Coventry. May 10, 1933, No. 13621. [Class 38 (v).] A vehicle which is insulated from earth and adapted to derive power from a D.C. overhead conductor or conductor rail, such as a trolley bus with pneumatic tyres, is protected against leakage from the power conductors by arranging for the resistance between live parts and the vehicle, or a portion thereof, to affect the charging or discharging of a condenser, and operation of a control device to depend on the degree to which the condenser is charged or discharged. The control shown is the de-energization at 11 of the holding coil 8 of the breaker 6, and, after a time delay, the closure at 10 of the circuit of a coil which opens a valve 14 to supply compressed air to lower the spring- maintained trolley-poles 2. The maintaining coil 12 of contacts 11, 10 is normally energized from a battery 9 through the anode circuit of valve 17, the grid 19 of which is connected to the cathode 18 and chassis 21 through resistance 20. Slow release relays 39, 40, 41 when energized by a switch 44 act by means of contacts 42 of relay 39 alternatively to energize and de-energize a winding 22. With 22 de-energized, in the position shown, equal condensers 35, 37 and resistances 34, 36 are connected in parallel between the - conductor and an earthed trailer wheel 33 of the bus, the condensers being equally charged. With 22 energized, the contacts 29, 30 and 24, 26 engage whereby 36, 37 are put in series between the - conductor and chassis 21, but temporarily no circuit is made for condenser 35. If therefore a leak such as 43 exists, condenser 37 will be partly discharged and, when contacts 31, 32 separate and 27, 23 close, 34 .. 37 are in series between the grid and cathode and the resultant discharge through resistance 20 sets up a p.d. thereacross and biasses the grid so that the anode current is reduced sufficiently to release contact 11. With a leak from the + conductor the operation is similar, and protection is also effected in the event of failure of the cathode or battery. Instead of an earthing wheel, a counter-E.M.F. may be applied by a battery to the mid-point of a potentiometer connected across the live wires, and the invention is also applicable with pantographs or collecting shoes.