Patent GB-470966-A (GB)
Title: Improvements in and relating to protective devices for electrical apparatus and particularly transformers, switchgear and the like, of the oil immersed type
IPC: H02H5/08
Filed: 1936-01-23
Abstract: 470,966. Protective cut-out arrangements. BEAUMONT, J. V., TOMLINSON, A. W., and HACKBRIDGE ELECTRIC CONSTRUCTION CO., Ltd. Jan. 23, 1936, No. 2159. [Class 38 (v)] A protective device for liquid-immersed electrical apparatus has located in a magnetic field and under the influence thereof, means to which motion is imparted when undesired conditions arise in the operation of the apparatus, and which, as the result of such motion, causes or permits operation of a signalling and/ or trip mechanism. The device may be located in the connection between a transformer tank and its conservator, such connection having a baffle 27 of corresponding shape to a conical diaphragm 21, which is normally held by adjustable springs 22 so that an armature 20 is retained at the correct distance from the poles of an H-shaped magnet 5, the winding 6 of which is energized by A.C. at a suitable voltage and frequency, or by interrupted D.C. On the occurrence of a surge or pressure wave in the oil, the armature is displaced towards the core 5, so increasing the impedance of coil 6 and decreasing the current through a series-connected relay which operates a trip circuit. Alternatively, movement of 20 may be adapted to produce the desired result by setting up a currentsurge in coil 6. In order to give an alarm in the event of the liquid-level dropping due to leakage or production of gas, a reed 9 is set in vibration by the coil 6 and when its amplitude increases it strikes a bell-crank 11 which releases an armature 15 which is attracted to core 16 and increases the impedance of the coil 17, thus releasing an alarm-circuit closing contact of a series relay. Fig. 2 shows a circuit-arrangement for changing over automatically from an A.C. source 33 to a D.C. source 43 on failure of the former, the leads 7, 8 to coil 6 being normally connected over leads 28 and a winding 29 to contacts 30 on an armature 31, which is normally retained by a winding 32, energized by source 33, against a suitable bias, so that the contacts 30 engage left-hand contacts 41, 42, so energizing 6 from source 33. When source 33 fails, the bias moves the armature and contacts 30 against the right-hand contacts 41, 42. A further electromagnet 34 is arranged also to be changed over by the contacts 30, and this magnet and magnet 29 act in opposite senses on an armature 35 which is biassed to the position shown, in which it maintains apart contacts 36, 37 in a trip circuit 38, 39. Movement of armature 20 in consequence of an oil-surge or pressurewave, diminishes the field-strength of coil 29 causing armature 35 to close the trip circuit. The alarm circuit 44 is made when coil 48 releases armature 47, this coil being connected by leads 46<1>, 49 to terminals 18, 19. In Fig. 3 (not shown), no alternative D.C. source is provided, and the circuits 7, 8 and 18, 19 are in series with relays which, on fault, release alarm and trip-circuit contacts. In Figs. 4-6 (not shown), the vibratory reed 9 is adapted to actuate a rocking mercury-container switch to close an alarm circuit, the container being reset by means of a press-button energizing a reset solenoid, the plunger of which also opens a valve in the container 1 to allow gas to escape.