Patent GB-239929-A (GB)
Title: Improvements in or relating to electric power distribution systems
IPC: H02P11/00
Filed: 1924-06-17
Abstract: 239,929. Igranic Electric Co., Ltd., (Cutler-Hammer Manufacturing Co.). June 17, 1924. Running generators in parallel. -A distribution system comprises a plurality of rotary transformer units to be connected in parallel between an alternating current supply and a direct current distribution, circuit, means for starting one of the units from the former circuit, and for connecting it to the distribution circuit upon starting thereof, and automatic means adapted when the unit is in operation to start another unit after a given period of time upon given load conditions and after a shorter period of time upon heavier load conditions in the distribution circuit. The distribution circuit DC, containing the automatic reclosing circuitbreaker CB, is fed from the lines L<1> - - L<3> through motor generators MG<1>, MG<2>, each comprising a motor, having an armature A and field F, and generator. having an armature A<1> and series and shunt fields F<1>, F<2>, and each being adapted to be selectively started by automatic starters S<1>, S<2> compfrising starting and running switches 1, 2. Operation of starter. The master switch 10 of either starter is closed by an attendant to energize the coil of switch 11 from the transformer T, the closure of that switch by means of its pole 11<a> connecting the transformer T to the coils of switches 1, 2 and to the coils of relays 13, 15, and to heating coil 12<b>, and by means of pole 11<b> short-circuiting resistance R<1>. The switch 1 then supplies armature A and the relay 15 short-circuits the rheostat 9, while the contacts 1<b> establish a circuit through' timing switch 12 for the coil of relay 13 which closes contacts 13a and maintains the circuit for the relay 13. The motor will run up to speed with its field shorted by contacts 5a through resistance 'R. The generator voltage, owing to exclusion of resistance R<1> and rheostat 9, will rapidly build up under the influence of its shunt field F<2>, and on attaining a certain value the coil of voltage relay 14 will connect the windings of field switches 5, 6 across the generator terminals, and they, in turn, connect the motor field F across the terminals through rheostat R<2> by closing contacts 6<a>, 5<b>, and the opening of contacts 6b deenergizes relay 15, which re-inserts the rheostat 9 in the shunt field F<2>. Subsequent to the response of switches 5, 6, the timing relay 12 is timed to interrupt the circuit of the coil of switch 1, which opens and connects the winding of switch 2 to transformer T through contacts 1<c>, 6<c>, thereby connecting the armature A directly to the lines L<1> - - L<3>, and, by means of contacts 2<b>, the coil 7<a> of circuit-breaker 7 to the generator terminals through overload relay 16 and switch 17. The circuit-breaker 7 in thus closing circuit DC causes the switch 17 to insert the resistance r and to be latched by latch 18 and causes the switch 19 to open. Overload. The relay 16 on overload opens the coil 7<a> and the breaker 7, but, owing to the dashpot 20, the switch 19 does not close the circuit of, and energize, the coil 18a of the latch 18 to close the switch 17 till after a given time, when the resistance r is shorted and, upon the overload relay 16 closing, coil 7<a> is energized to re-close the breaker 7. The two-pole, double-throw, knife switch 25 connects the fields F<2> in parallel across the leading generator, Fig. 1, and switch 26 establishes an equalizing connection between the generators, as later described. Automatic control means between the starters. This includes a two-pole electromagnetic switch 27 controlled by a transfer switch TS and pilot switch PS, both being in the form of movable drums, the former being movable from a central position to extreme positions and the latter in reverse directions by an electromotor 41 having armature a and field f. Operation of automatic control means. Assume the set MG<1> is in operation; on given load conditions relay 46 closes circuit for switch 42 from transformer T to contacts 29 of switch TS, contact 46<b>, coil 42, con tacts 37, 36 of switch PS, contacts 35 35<a>, 35<b> of switch TS, and contacts 6<c> back to T. Switch 62 closes the circuit of motor 41 from generatot MG<1> through contacts 28 of TS, re sistance r<3>, contact 42<b>, armature a, contact 42a, contacts 34, 33 of TS, and back to MG<1>. Resistances r<4>, r<5> are thus connected ir parallel across the armature a, and contacts 42<c> connect the field f across MG<1>. The motor 41 thus moves PS until contact 39 engages 39a and energizes switch 27 from transformer T through contacts 29, coil 27, contacts 39a, 39, 36a, 35, and 6<c>. Closure of switch 27 shunts master switch 10 of starter S<2> by a circuit through con tacts 31, 27a, and 30, thereby establishing a circuit for the starter S<2> which starts up the set MG<2>. Switch 27, after responding, as described, is held closed pending return of switch PS by a circuit extending from the transformer T associated with starter S<1> through coil 27, contacts 27b, 40a 40 and 36<a>. On attainment of sufficient voltage in voltage relay 14 of set MG<2>, the latter energizes the coil of switch 26 through contacts of relay 14, contacts 32, 33, 34<c>, the switch 26 thereby establishing an equalizing connection between the two generators. Also, when the relay 27 closes automatically to start the set MG<2> contact 37<a> moves out of engagement with contact 37 and the switch 42 is de-energized to open the circuit of, and stop, the motor 41. Relay 44 responds at a higher load than that at which relay 46 responds, and in responding excludes the resistance r<4> from the circuit of motor 41, which thus operates at a given speed in a forward direction at a given load and at a higher speed on increased load, whereby switch PS functions to start the second motor generator on a lapse of time which diminishes as the load increases. Falling-off in load. Assuming that, when the idle machine has been put in parallel across the load, as just described, the switch PS is at or near full forward position and the load diminishes so that relay 46 returns to normal position, the switch 43 will be energized by a circuit extending from the transformer of starter S<1> through contacts 29, 46<a>, 45<b>, coil 43, contacts 38<a>, 38, 36<a>, 35, and 6<c>, thereby reversing the connections of motor 41 extending from MG<1>, through contacts 28, resistance r<3>, contact 43a, armature a, resistance r<7>, contacts 43<b>, 34, and 33<c>, and at the same time the contact 43<c> connects the field f across MG<1>. The motor 41 thus operates at a lower speed in the reverse direction to restore switch PS to normal position, thereby separating contacts 38. 38<a>, and opening switch 43 to stop the motor, and if MG<2> is in operation it is stopped by opening switch 27 through the separation of contacts 40, 40<a> leaving the other generator to supply the load. If the set MG<2> is in operation and switch TS is moved to its lower position, the set MG<1> will similarly come into operation under suitable load conditions and relay 45 will be controlled by contacts 7b of breaker 7 of starter S<2>, and, with reday 46, will operate similarly to control switches 42, 43 to operate the motor 41. In these conditions, switches 42, 43 will be energized from the transformer of S<2> and motor 41 from MG<2>, the former circuit being through contacts 29<c>, 35<c>, and 6<c> and the latter through contacts 28<c>, 34<c>. Further, the switch 27 shorts the master switch 10 of starter S<1> through contacts 30<c>, 31<c>, and switch 26 is energized from MG<1> through contacts 32<c>, 33<c>. Overload when one generator is operating and the other is to be connected up. The breaker 7 of the overloaded machine, MG<1> for example, opens and disconnects it from the load circuit, and its contact 7<b> opens the circuit of relay 45, and thereby switch 42 is energized from the transformer of starter S<1> through contacts 29, 46<a>, 45<a>, coil 42, contacts 37<a>, 36<a>, 35, and 6<c>. However if MG<2> is in operation the circuit of switch 42 will be from transformer of starter S<2> through contacts 29<c>, 29, 46<a> 45<a>, coil 42, contacts 37, 36<a>, 35, and 6<c>. Closure of switch 42, as described, drives in a forward direction the motor 41 which causes the switch 27 to close for automatic starting of the idle set. Automatic reclosing circuit-breaker CB, Fig. 4. The closing coil 48 is controlled by an overload relay 49 and switch 50, which is biassed, closed, and held open by a latch 51 controlled by a coil 52 which is in turn controlled by a switch 53 connected to a dash-pot 54. On overload and with the parts as shown, there are two paths for the current between points 55, 56, namely, through resistance r<9>, coil 52, and switch 53, and through resistance r<10> and the load or short-circuit on the system. The coil 52 is of law-resistance and therefore re-closes the breaker as soon as the resistance of the load circuit reaches a safe value. Reclosure is effected as follows. The coil 52 will be energized from points 55, 56 and will trip the latch 51 to close the switch 50 and out out the resistance r<8>. The increased current flowing through the coil 48 from points 55, 56 will close the breaker CB. On voltage failure the coil 48 will be de-energized and the breaker will only close on restoration of voltage after the retarded switch 53 opens. On overload the relay 49 de-energizes coil 48 and the coil 52 only responds after condition return to normal. Interlocks (not shown) are provided so that on tripping of either of the breakers 7, the breaker CB will also open. When either generator set is in operation and its breaker 7 is tripped the other generator will automatically start, and the dashpot 54 of breaker CB is timed to prevent reclosure thereof till the second set has run up to speed and the breaker 7 of the leading genera- 'tor has re-closed,