US1588204A - Transformer - Google Patents

Description

June 8 1926. 1,588,204

H. O. STEPHENS El AL TRANSFORMER Filed Sept. 5, 1925 5 Sheets-Sheet 1 Inventors:

Howard 0.5tephens,

Arthur Palme, by .Thei PAttoPney.

June 8 1926. 1,588,204

H. o. STEPHENS ET AL TRANSFORMER Filed Sept. 5, 1925 3 Sheets-Sheet 2 54 J6 J3 r, 5

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Howard O.5tephens Arth ur- Palme,

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H. O. STEPHENS ET AL I TRANSFORMER Filed Sept. 5

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Inventor-s: Howard O.Stephens Arthur alme,

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Patented June 8, 1926.

UNITED STATES 1,588,204 PATENT OFFICE.

HOWARD O. STEPHENS AND ARTHUR PALME, OF PITTSFTELD, MASSACHUSETTS, AS- SIGNORS TO GENERAL ELECTRIC'GOMPANY, A CORPO RATION OF NEW YORK.

TRANSFORMER.

Application filed September 3, 1925. Serial No. 54,366.

our invention relates to transformers and more particularly to transformers having windings with tap connections whereby the effective number of turns may be varied to change the ratio of transformation. Varying conditions in the circuits connected to a transformer often make it necessary to change the ratio of voltage transformation in the transformer and the general object of the invention is to produce an improved arrangement of transformer and associated control mechanism whereby this result may be attained without interrupting the load current supplied by the transformer.

Other objects and advantages will appear from the following description taken in connection with the accompanying drawings in which Fig. 1 is a view in elevation of a single phase transformer with part of the control mechanism; Fig. 2 is an explanatory detail view of part of the control mechanism; Fig. 3 is a circuit diagram of the control mechanism; Figs. 4 and 5 are detail views of part of the control mecha nism; and Fig. 6 is a circuit diagram show ing the application of the invention to a three-phase transformer;

Like reference characters indicate similar parts in the different figures of the drawings.

The invention will be dcscribed in con nection with the transformer 10 shown in Y Figs. 1 and 2. This transformer is enclosed m a casing 11 adapted to hold a body of insulating oil'in which the transformer is immersed. An expansion chamber 12 com municates with the casing 11 to permit thermal expansion and contraction of the oil and a diaphragm 13 in a. relief pipe 13 is adapted to rupture to relieve pressure in the casing 11 when this pressure becomes excessive.

One of the windings of the transformer 10 is formed in two sections 14 and 15, each section being provided with taps connected to the fixed contacts of switches 16 and 17 respectively. The other winding of the transformer is not shown in the drawing as it forms no part of the invention. One

terminal 18 of the tapped winding is connected to both winding sections 14 and 15.

The other terminal 19 of this winding is connected to the main contacts of two switches or circuit breakers 20 and 21 and 22 and 23 to the movable contacts of the tap I switches 16 and 17. The two winding sections 14 and 15 are similar so that, during normal operation of the transformer, the current between the two terminals 18 and 19 divides into two equal parts, each part flowing through one of the winding sections and its associated tap switch and circuit breaker.

This arrangement of the parallel connected winding sections 14 and 15 with their associated tap switches 16 and 17 and circuit breakers 20 and 21 may be operated by control mechanism which will be described to change the number of effective turns in the winding sections and thus the ratio of voltage transformation without any interrup tion in the load carried by the transformer. To effect this change, the control mechanism causes one of the circuit breakers, circuit breaker 20 for example, to open, thus inter- I rupting the current through the tap switch rent again divides substantially equally between the two winding sections 14 and 15. There is now an unequal number of effective turns and consequent unequal voltage in the two sections 14 and 15. This causes a circulating current in these two winding sections, the two tap switches 16 and 17 and the two circuit breakers 20 and 21 but the reactance of the winding sections prevents this circulating'current from reaching such a value as to be objectionable. The circuit breaker 21 is next opened to interrupt the current in the winding section 15 and its tap switch 17, the tap switch 17 is changed to a position corresponding to that of the tap switch 16, and the circuit breaker 21 is then closed. The number of efiective turns has now been increased or decreased equally in the two winding sections and the steps described may be repeated until the desired increase or decrease in the number of eflective turns in each winding section has been made. 7

The control mechanism is responsive to a single hand wheel 24 fixed to a shaft which carries a. drum contactor 25 and the driving member 26 of a double intermittent gear by means of which the two tap switches 16 and 17 may be operated intermittently and alternately through the two driven members 27 and 28, two sets of gears 29 and 30, and two bevel gear connected shafts 31 and 32. The contactor 25 comprises five contacts 33, 34, 35, 36 and 37 (shown as developed into a plane in Fig. 3), which cooperate with four brushes 38, 39, 40 and 41. The contacts are all conductively connected together and to a source of current 42 through the brush 38. The circuit breaker .20 is pro: vided with a closing coil 43, a tripping coil 44 and two auxiliary contactors 45 and 46. The contactor 45 has two pairs of contacts 47 and 48 and the contactor 46 has two pairs of contacts 49 and 50. The circuit breaker 21 is similarly provided with a closing coil 51, a tripping coil 52, and two contactors 53- and 54, the contactor 53 having two pairs of contacts 55 and 56 and the contactor 54 having two pairs of contacts 57 and 58.

The number of eflective turns in the winding sections 14 and 15 is changed by turning the hand-wheel 24 in the proper direction, one direction effecting an increase and the other direction effecting a decrease and the operation of the control mechanismas the hand-wheel 24 is turned in a clockwise direction will now be described. Rotation of the hand-wheel 24 with the drum contactor 25 through a small angle first moves the contact 35 of the drum contactor under the brush 40 and the contact 37 away from the brush 39. This allows current to flow from the contact 35 through the brush 40, the contacts 49 of circuit breaker 20 and the tripping coil 52 and contacts 55 of the circuit breaker 21, thus causing the circuit breaker 21 to open and interrupt the current through the winding section 15. This opening of the circuit breaker 21 moves its two contactors 53 and 54 to open the contacts 55 and 57 and to close the contacts 56 and 58. Closing the contacts 56 has no effect as the circuit through these contacts is now open between the contact 37 and the brush 39 of the contactor 25. Closing the contacts 58, however, completes a circuit from the source of current 42 through a releasing coil 59 to withdraw a latch 60 from locking engagementwith the gearing 30. The function of the latch 60 is to act through the gearing 30 and shaft 32 to lock the movable contact of the tap switch 1.7 in adjusted posit-ion except at such time as the contact is being shifted by the control mechanism. The driving member 26 of the aeeaaoa double intermittent gear next engages the driven member 28 and rotates it one step, the .driven member 28 acting through the gearing 30 and shaft 32 to shift the movable contact of the tap switch 17 along one step. The contact 34 of the drum contactor 25 then moves under the brush 39 to complete a circuit from the source of current 42 through the coil of a time delay relay 61 and the auxiliary contacts 56 and contactor 53 of the circuit breaker 21. This closes the contacts of the time delay relay 61 which completes a circuit from the source of current 42 through the closing coil 51 of the circuit breaker 21. The purpose of the time delay relay 61- is to keep the circuit through the closing coil 51 of the circuit breaker 21 closed long enough to be sure that the circuit breaker will close properly, thus avoiding the possibility that the contact 34 of the drum contactor 25 might be moved fast enough to leave the brush 39 before the circuit breaker had had time to close.

The closing coils 43 and 51 of the circuit breakers will require a heavier current than that supplied through the contacts and brushes of. the drum contactor 25 and a further advantage of the time delay relays 61 and 64 is that they may be conveniently designed with contacts to carry this heavier current. I

The closing of the circuit breaker 21 connects the winding section 15 back in circuit to carry its share of current. The change inv the number of effective turns in the winding section 15 produces an unbalance between the two winding sections and this causes a circulating current through them which is limited to a safe value bythe reactance of the winding sections.

The hand-wheel 24 has now been turned through half a revolution and this has caused the movable contact of the tap switch 17 to be shifted one step in the desired direction. Rotation of the hand-wheel through the second half of a complete revolution causes the control mechanism to act in a similar manner to shift the movable contact of the tap switch 16 along one step and again balance the two winding sections 14 and 15. The contact 36 controls the tripping coil 44 to open the circuit breaker 20,

the contactor 46 closing the contacts 50 as the circuit breaker 20 opens to send current through a releasing coil 62 to withdraw a latch 63 from looking engagement with the gearing 29. The I11OVlbl contact of the tap switch 16 is then shifted one step to a posi tion corresponding to that of the movable contact of the tap switch 17. The contact 37 of the drum contactor 25 then moves into its original position under the brush 39 to close the circuit through a time delay relay 64 and the closing of the contacts of this relay sends current through the closing coil 3 of the circuit breaker 20. The closing of this circuit ln'eakcr completes the cycle of operations.

The two conductors 22 and 23 are pro long as the currents in the two conductors 22 and 28 and in the winding sections 14 and 15- are equal. \Vhenever the currents in the two winding sections 14 and 15 are unequal, however, the voltages of the two current transformers 65 and 66 will be unequal and this will operate a relay 67 controlling a signal 68. 'lhesignal 68 will thus indicate when either of the circuits through the winding sections 14 and 15 is openand the other winding section is'carrying all the current and it will also indicate when the movable contacts of the two tap switches are not similarly positioned so 'that the two winding sections 14 and 15 are unbalanced.

The auxiliary contacts 49 of the circuit breaker 20 are always open when this circuit breaker is open. These contacts-49 are in circuit with the tripping coil 52 of the other circuit breaker 21 so that the circuit breaker 21 can never be opened while the circuit 20 is opened. The auxiliary contacts 57 of the circuit breaker 21 likewise pre ent opening of the circuit breaker 20 when the circuit breaker 21 is open.- Thus only one circuit breaker can be open at a time and current between the transformer terminals 18 and 19 can never be interrupted.

The tap switches 16 and 17 are locked by the latches 63 and 60 respectively. Each of these latches is controlled by auxiliary contacts on its associated circuit breaker so that neither tap switch connection can be changed unless its associated circuit is open and the corresponding winding section is carrying no current. Thus no arcing can ever occur at the contacts of the tap switches. This is important because the tap switches are located in the same casing and are immersed in the same insulating oil with the transformer so that the tap leads from the winding sections of the transformer to the tap switches are as short as possible and require no insulating bushings through the casing as would be necessary were the tap switches located outside the casing. Arcing at the contacts of the tap switches would seriously alieet the insulating oil in which they and the transformer are immersed but any arcing that may occur must be at. the contacts of the two circuit breakers 20 and 21 which are located outside the casing.

The two tap switches are interlocked by the double intermittent gear so that only one of these switches can be moved at a tlme and so that. they can never be moved more than one step apart.

The signal (58 will indicate any unbalanced condition between the two winding sections 14 and 15. It will indicate not only when the number of efiective turns is not the same in the two winding sections or when the circuit through one of the winding sections is open at the corresponding circuit breaker during a tap changing operation, but it will indicate any accident or failure in the transformer or its connections which unbalances the equal distribution of current between the two winding sections.

It will be obvious that the control mechanism may be operated in either direction through as many cycles as desired within the range of the tap switches and that the operation may be stopped and reversed in direction at any point in a cycle of opera tion.

-The invention has been described and its advantages pointed out as applied in connection with a single phase transformer but it may, of course, be applied to a three-phase transformer as indicated in Fig. 6 where each phase comprises a winding formed in two sections 14 and 15 and connected in parallel between terminals 18 and 19. The two'.

winding sections of each phase are provided with tap switches 16 and 17 and circuit breakers 20 and 21 respectively. The ta switches and the circuit breakers are eac mechanically connected in two groups of three each as shown in Fig. 6 so that adjustment of the three hases is effected simultaneously. Otherwise, the three phase arrangement including the control mechanism may be similar to that already-described in connection witha single phase transformer.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. A transformer comprising a winding formed in two arallel connected sections each provided with taps, a tap switch connected to the taps of each windin section, a circuit breaker in series with eac winding section and its tap switch, means normally locking each ta switch a ainst operation while its circuit reaker is c osed, and means for unlocking each tap switch to permit its tap connection to be changed while its circuit breaker is open.

2. A transformer comprising a winding iormed in two arallel connected sections each provided with taps, a ta switch con- 3. A transformer comprising a winding formed in two parallel connected sections each provided With taps, a tap switch connected to the taps of each winding section, a circuit breaker in series With each Winding section and its tap switch, each circuit breaker being provided with a tripping coil to open it While its tap switch is being operated, and means responsive to the opening of 10 each circuit breaker for opening the tripping coil circuit of the other circuit breaker, whereby neither circuit breaker can be opened unless the other circuit breaker is closed and current through the transformer cannot be interrupted by said circuit breakers.

In Witness whereof, We have hereunto set our hands this 31st day of August 1925. HOWARD O. STEPHENS. ARTHUR PALME.

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