Patent GB-780063-A (GB)
Title: Improvements in protective remote control pilot circuits
Inventor: CHANDLER KENNETH WILLIAM
IPC: H02H7/00
Filed: 1953-05-18
Abstract: 780,063. Protective cut-out arrangements. COAL INDUSTRY (PATENTS), Ltd. Aug. 18, 1954 [May 18, 1953], No. 13921/53. Class 38 (5). In a remote control and protective system suitable for mines wherein a motor 14 (or other device) is connected to the supply 10 over contacts of a contactor X and cable 15, under the control of a two-position switch 13 at the motor, a number of interlocking relays A ... D are provided having contacts which operate to ensure the correct sequence of relay operation in closing the contactor and to ensure opening of the contactor in the event of failure of the supply, open- or short-circuited pilot circuit 16, 17, and in some cases earthing of a power lead to the pilot circuit. The contacts are shown in the positions they occupy when the supply is dead. Relay A has windings a, b polarized by rectifiers so that their effects are additive, relays C, D have copper slugs which cause them to release with a time-delay, and a resistance R1 is adjusted so that relay B will just pick up with a supply voltage of 69 per cent normal. With the switch 13 " off " and rectifiers S4, S9 operative, winding a energizes relay C to close C1 and change C2. If 13 is now moved to " run," B is energized and a de-energized but before it releases, B is energized and makes a maintaining circuit at B1 and also energizes relay D over contacts B2. Relay D makes its holding circuit at D2 (independent of C2) and closes the contactor circuit at D1. When 13 is moved back to " off " position, relay B releases contact B2 and A changes over AI, but the delay of D prevents shorting of the pilot circuit at B2, C2, D2. If the pilot breaks or the supply volts fall unduly, B releases and D opens the contactor X, or if the switch 13 is " off," relay A releases, so that in both cases all relays are de-energized. On restoration of the supply or pilot, switch 13 must be in (or be moved to) the " off " position in order to reclose the contactor as described. With a short-circuit in the pilot, both relays A, B pick up, C, D are (or remain) de-energized and the pilot is locked shorted by contacts B2, C2, D2, current being limited by a resistance R2 to a low value. In order to resume working after repair of the fault, all armatures must be released and starting effected as before described. If a sufficient leakage to the pilot occurs when the motor is running, winding b causes relay A to pick up, the operation then being as with a shorted pilot. Fig. 2 (not shown) illustrates an arrangement employing only one slow-release relay in addition to the starting and running relays, and the contactor circuit has contacts in series and controlled by all the relays. Fig. 3 (not shown) illustrates a further arrangement in which relays A, B have slugs and additional delay-action relays C, D are provided. In Fig. 4 (not shown) relays A, B, C are again timedelayed and have series-connected contacts in the contactor circuit, but a holding contact closed by the contactor shorts the closing-relay contact which opens with a delay.