Patent GB-320634-A (GB)
Title: Improvements in or relating to the automatic control of electrical apparatus
Filed: 1928-07-16
Abstract: 320,634. General Electric Co., Ltd., Angold, A. E., and Barrell, F. July 16 1928. Running generators in parallel; regulation, automatic.-In a system in which machines are automatically and successively paralleled on a network a single polarized voltage balancing relay may be associated with any one of the machines and simultaneously adjusts the regulating means of all, a single reversible electric motor being coupled to all the field regulating resistances in a rotary converter substation. The relay is associated with a time-delay relay ensuring a time interval after the balancing of voltage before a machine is paralleled. All the machines may be paralleled simultaneously under low network voltage conditions. The voltage balancing relay is preferably of the type described in Specification 272,574, [Class 38 (v), Electric switches &c.]. A single coil 202, 203, Fig. 2, is wound upon an annular core 201 to produce consequent poles, and a permanent magnet 204 is pivoted within the annulus. Spring contact blades 214, 215 are fixed to posts 212, 213 so that they cross and lie normally just free from contact with posts 216, 217. An insulating member 210 coupled to the magnet is arranged with the inner faces of a notch 211 bearing upon the contact springs beyond their crossing, so that the springs centralize the magnet, which experiences a torque in one or other direction, according to the direction of current on the coil, and causes one or other spring to engage its adjacent post. Fig. 1 shows a system for three rotary converters. The means for initiating the automatic starting and synchronizing of the machines may be as described in Specification 261,844. The coil 44 of the voltage balancing relay 42 is adapted to be connected across the open contacts of the d.c. circuit breaker of any machine to be paralleled by means of the contacts 71 of the appropriate unit relay. The relay 42 is designed for a full voltage equal to 25 per cent of the normal network voltage. When a machine has been synchronized a contact 15 on the synchronizing switch energizes, through interlock contact 18 on the d.c. circuit breakers, the appropriate unit relay coil 67 and the coil 44 is connected up bv contacts 71. Reversing contactors 53, 56 operate a polyphase motor 41 driving the coupled field rheostats of the machines, and the contacts of the relay 42 control those contactors. The motorcurrent opens the: contacts 88 of a relay 89 which close after a time interval when the relay 42 has effected a balance between machine and network voltages and the motor circuit is accordingly open. Time delay contacts 76 in the unit relay ensure that the contacts 88 shall have had time to open; when both are closed a contactor 83 proper to the machine is energized and the d.c. circuit breaker is closed. Contact 19 of the circuit breaker renders effective a voltage regulating relay 43 which then controls the contactors 53, 56. The paralleling of subsequent machines occurs immediately upon synchronization since contacts 20 on the circuit breakers short circuit the relay contacts 76, 88. If a machine is being paralleled with network volts too low for a balance the rheostat limit contact 60 opens and relay 89 is deenergized so that the machine will be paralleled at its minimum voltage. A dead bus relay 63 closes contacts 93 when the network volts fall to a low limit and energize contactor 56 to insert all field resistance. The opening of contacts 65 of this dead bus relay on low voltage puts the unit relays out of action; all the machines will be started in sequence and series connected contacts 16 on the synchronizing switches effect their simultaneous paralleling as soon as the last is synchronized. The voltage regulating relay then operates.