Patent GB-423305-A (GB)
Title: Improvements in and relating to protective systems for electrical power transformers
IPC: H02M3/34
Filed: 1933-07-31
Abstract: 423,305. Protective cut-out arrangements. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London.- (Assignees of Tritle, J. F.; 507, Seminole Drive, and McNairy, J. W.; 1019, Washington Place, both in Erie, Pennsylvania, U.S.A.) July 31, 1933, No. 21498. Convention date, July 29, 1932. [Class 38 (v)] A protective arrangement for a power transformer 13 in an alternating current railway traction drive comprises a relay provided with an overload operating winding 24, 25 for controlling the energization of the load circuit, represented by motors 16, and current transformers 28, 29 respectively responsive to the current entering and leaving the primary winding 12, the secondary windings of the current transformers being connected in series accumulative relation with the overload winding. A second operating winding 26 on the relay is responsive to the difference between the current entering and leaving the primary winding 12 and serves to protect the apparatus against grounds or short - circuits in the primary winding. The winding 26 also responds to short - circuits on the secondary side of the power transformer, the winding 26 being energized for this purpose from a current transformer 34 connected in a circuit extending from the mid-point 35 of the secondary winding 33 of the transformer 13 to earth through an adjustable resistance 39. In the arrangement shown, the relay is a split-phase shaded-pole induction motor, and, on response, rotates a shaft 21 in a clockwise direction against the action of a spring 50 attached to a cam 53 on the shaft, the cam being so formed that the counter-torque due to the spring remains constant, or decreases slightly, after the relay starts to operate. The motors 16 are started by closing a circuit-breaker 65 provided with an operating coil 71, which is energized from lines 72, 75 by closing a pushbutton 70, and is maintained energized through a hold-on circuit including contacts 63 on a switch-lever 62 normally held in the " on " position by a latch 59. The motors are started up through a controller 17 ; if an excessive load current is taken the relay 19 responds due to the current in the windings 24, 25 and a disc 57 on the shaft 21 rotates to release the latch 59. The switch arm 62 thereupon rotates under the action of a spring 68 to open the hold-on circuit of the coil 71 at the contacts 63. The operating circuit of a contactor 83 controlling the supply of current to auxiliary apparatus, such as blowers, compressors, and heaters, is simultaneously opened at contacts 82 on the switch arm 62, while contacts 81 close to energize a signal light 80 in the cab of the locomotive to indicate that the circuit-breaker has been tripped out by the relay. The switch 63 is reset through the agency of a winding 89 energized by pressing a button 86. As soon as the circuitbreaker 65 opens, the relay is de-energized and returns to its original position, determined by the engagement of a stop 93 on the disc 57 with a detent lever 94 which is held in the position shown, against the action of a spring 95, by a voltage coil 97. If the relay responds to the winding 26, on the occurrence of a fault on the primary or secondary side of the transformer 13, the circuit-breaker 65 is first tripped by the release of the latch 59. The relay is still energized, and the disc 57 continues to rotate until a projection 100 thereon engages a switch lever 102 and closes contacts 104 in the energizing circuit of a switch 106, which thereupon closes to earth the lead-in conductor 110 from the trolley wire 11. As a result of the earthing of the trolley wire, the sub-station circuitbreakers are tripped, thereby de-energizing the line. The disc 57 now rotates in the counter-clockwise direction under the action of the spring 50, and continues to rotate beyond the initial position shown, since the de-energization of the voltage winding 97 has released the detent lever 94. A projection 115 on the disc 57 then engages a switch lever 116 and closes contacts 118 to energize a coil 118<a>, which opens a valve 120 and allows the pantograph 10 to be lowered from the trolley wire by the action of the spring 130. The relay is then latched in this position, with the contacts 118 closed, by the engagement of the detent lever 94 with the end of the switch lever 116. To reset the relay, a lever 135 is rotated manually in a clockwise direction, when a projection 136 on the lever engages the detent lever 94 and returns this to its original position, the disc 57 being simultaneously rotated, by the engagement of the lever with a projection 138 on the disc, until the detent lever 94 snaps on to the projection 93 and holds the disc in its initial position.