US1764341A - Electrical transforming system - Google Patents

Description

Patented June 17, i930 UNITED STATES PATENT OFFICE m1: A. OTRLINGEB, OI SHARON, PENNSYLVANIA, ASSIGNOB TO WESTINGHOUSE ELEC- TRIO & EANUFACTURJNG COMPANYFA CORPORATION OF PENNSYLVANIA EIZE C'IBJKJAL TRAN SFOBMIN G SYSTEM Application tiled February 11, 1928. Serial No. 253,826.

My invention relates to electrical transforming systems and more particularly to transformers having high voltage ungrounded rimary and secondary win ings.

y invention resides in apparatus for changing the ratio of the voltage transformation between the primary and secondary windings of a high voltage ungrounded transforming system and it is characteristic of my invention that transformers provided with equipment constructed in accordance therewith are efiicient in operation and economical to manufacturel It is further characterist-1c of equipment constructed in accordance with my invention, that it may be mounted within the same tank' as the main transformer unit, thereby providing a complete assembled un t of relatively small size and cost.

Heretofore, transformers have been provided with taps to permit a certain varia- 'tion of ratio between the input and out ut voltages. These taps were usually place 1n the primary winding and were connected to studs mounted on a terminal board. Changesin ratio were effected by moving certain links or jumpers between the studs on the terminal board. This was a slow laborious process and required a disconnection of both the primary and secondary windings of the transformer from the lines.

. Furthermore, the manipulation of the coni Y nections on the terminal board had to be venience, but practically a matter of necessity to provide some means for varyin the voltage delivered from a constant vo tage supply or maintaining a constant delivered voltage with a variable supply. Examples 'of such applications are found in transformers supplying synchronous converters and in electric furnace installations. Also,

transformers with load tap changing equipment have been used to a considerable extent One of the most important applications for tap changing under load equipment is its use with transformers to form an interconnection between two large systems or parts of systems. The function in this case is to control the transfer of wattless powerbetween the two parts. If the voltages of two -system, to be tied together at one point, tend to vary with respect to each other, the wattless transfer would vary in proportion and in many cases would be excessive unless provisions were made to form a flexible tie-in whereby the voltage ratio might be varied to compensate for the difference in voltage between systems. Conversely, if the two system voltages should remain constant, changing the voltage ratio of the interconnecting transformer would permit power factor control of the load transferred.

Tap changing equipment designed in accordance with my invention, is particularly applicable to high voltage ungrounded transformer units and comprises, in general, the combination of a transformer having a primary and a secondary winding of means for changing the voltage ratio of the said two windings comprising a series transformer in circuit relationwith one of said windings, and means for energizing the series transformer comprising a tertiary winding that is inductively related to the primary winding. A tap changing system and a preventive auto transformer are provided for changing the magnitude and direc-,

tion of energization of the series transformer under load. i My invention, however, may be more readily understood if the accompanying drawings are referred to in connection with the following description.

The single figure of the accompanying drawings is a schematic diagram of a single phase transformer having tap changing Itwill be understood, while I have shown.

my invention embodied in a. single phase transformer, that it is not to be thus hmlted but that it is readily applicable to other types, for example, polyphase transformers having their windings connected'in star or in delta.

Referring to the drawings,a tank 1 is shown housing a core 2 of laminated. magnetizable material on which are disposed a primary winding 3, a secondar winding 4 and a tertiary winding 5. Cl he primary winding 3 is energized from any suitable source through conducting leads 6 and 7. The difference of potential between the conducting leads 6 and 7 may be of a high magnitlude, for example, substantially, 132 kilov0 ts. ondary win ing 4 by means of conductin leads 8 and 9. The difference of potentia between the conducting leads 8 and 9 is also of high magnitude for example approximately 120 kilovolts.

It is desirable and it is the object of my invention to provide means for changing the ratio of transformation between the primary winding 3 and the secondary winding 4 while the transforming operation is takin place without disconnecting the circuits 0 either the whole or a portion of either the primary or the secondary winding.

To this end, I provide means for modifying the electromotive force in either the primary or the secondary winding by means of the tertiary windin 5.

Inaccordance wit my invention, I modify the voltage induced in the secondary winding 4 by means of a series transformer 10 that is preferably mounted on and built into the same unit as the main transformer core 2.

The series transformer 10 comprises a laminated magnetizable core 11 on which are disposed a secondary winding 12 and a primary winding 13. The secondar winding4 of the main transformer is divi ed into two substantially equal sections 14 and 15 and the secondary windin 12 on the series transformer 10 is pre erably connected by conducting leads 16 and 17 between the two sections 14 and 15.

The series transformer 10 is energized by the tertiary winding 5 and may be connected therewith in an suitable manner as, for example, throug a preventive auto transformer 18. The preventive auto transformer 18 comprises a magnetizable core 19 having a single winding 20 disposed thereon. The winding 20 is preferably divided into two substantially equal sections 21 and 22. The two sections 21 and 22 are connected at a junction point 23 to one terminal of the sec- Ener ization is taken fromthe sec-' preferably mounted within the casing 1 togather with the senes transformer 10 therey providing a minimum number of auxiliary windings and cores.

The tertiary winding 5 is provided with a plurality of taps 24, 25, 26, 27 and 28. The tap 26 that preferably comprises the midoint' of the tertiary winding 5 is connected by a conductor 29 to the primary winding 13 of the series transformer 10.

A switchin device 30 is mounted'in an auxiliary casing 31 that is preferably secured to the transformer tank 1. This switching device may be of any convenient form and is not to be considered a part of this invention. The switching device 30 has the same number of switches as there are taps on the tertiary winding 5 and comprises, in the example shown, switches 32, 33, 34, 35

and 36. Each of these switches comprises two contactors A and B. Contactors Aand B may be operated to close or to open either by hand or b automatic operation. The contactors A o the switches 32, 33, 34, 35 and 36 are connected by conductors 37, 38, 39, 40 and 41 tothe taps 24, 25, 26, 27 and 28 of the tertiary winding 5.

The middle tap 26 of the tertiary winding 5 is connected through conductor 29-and'the primary winding 13 of the series transformer 10 to the junction 23 of the windings 21 and 22 of the preventive auto transformer 18. One section 22 of the preventive auto transformer 18 is connected to the tertiary in series with the tertiary winding 5. Such impedance drop is almost entirely reactive and therefore its effect on regulation is practically negligible at power factors above 65 per cent.

For normal operation of the transformer, switch 34 of the switching device 30 is closed. To change the taps one step to change the ratio of voltage transformation either switch 33 or 35 is closed. Either operation places both halves of the winding of the auto transformer winding 18 in circuit relation with the primary winding 13 of the series transformer 10 and the glolsition between the taps on the tertiary win g 5.v

By way of explanation, suppose that the switches 34 and 35 are closed. In such case,

the auto transformer 18 is placed directly across the taps 26 and 27 of the tertiary winding 5. The primary winding 13 of the series transformer is connected between the midpoint 23 of the auto-transformer winding 20 and the tap 26 of the tertiary winding 5. The windin 13 is excited by a voltage of a magnitude t at is equivalent to a mid-voltage on the tertiary 5 between taps 26 and 27, connected direc y to the winding 13 and one side of the auto transformer 18.

To change the taps 'zinother step switch- 34 is ,opened and the full vol between taps 26 and 27 of the tertiary 5 is used to excite the winding 13,

Closing the switches controllin the ta s 26 to 28 of the tertia windin 5 c an es t e voltage of the secon ary win 12 in one direction, for example, to increase it, whereas closing the switches contro the ta s 26 to 24 of the tertiar winding 5 c anges tiie voltage of thesecon ary winding 12 in the opposite" direction or in this case operates to decrease it.

When full load current is passed through I one-half of the auto transformer 18 with the other half open, the load current from the tertiar winding 5 becomes the exciting current 0 the auto transformer 18. Under this condition there are no neutralizing ampere turns from the other half, so the transformer becomes a reactor. Air gaps are provided in the core to give low impedance when operating in this manner, which, of course, make the excitin current, when operating as an auto trans ormer across taps higher than it would be otherwise.

The switches of the tap changing device 31 are closed and "opened to change in steps the ratio of transformation of voltage between the windings 3 and 4. To decrease the ratio,

first switch'35 is closed; this is the first step and the voltagejratio is changed accordingly. To decrease the ratio another step the switch 34is opened. For a further change of ratio the switch 36 is closed. Lastly, to change the ratio to a minimum in that direction the switch 35 is opened which places the winding 13 across one-half of tertiary winding 5 with one-half of the auto transformer winding 20 in series circuit relation between them.

Thesequence of operation of the switches in increasing the ratio of transformation is in'the' other direction; that is switch 35' is closed,-36 opened, 34 closed, 35 opened, 33

closed, 34 opened, 32 closed and 33 opened. Each time one of the switches opens or closes the ratio of transformation is changed one step.

A tap changing system constructed in accordance with my invention may be applied directly to the transformer unit by virtue of the fact that no additional separate regulating. units are required. This provides a cheap, efiicient and compact equipment for effecting a change in the voltage ratio be- -tween the windings of a high voltage transset forth both the series and auto transformers may be mounted in the same casing as the mam transformer, thereby reducin the numberof bushings and simplifying t e connections and installation. In the case of tap changing equipment designed to operate on'-.

high voltage ungrounde units in accord- 'ance with my invention the auxiliary exciting winding is built into the same core and the number of auxiliary windings and cores is therefore reduced and the overall efliciency of the apparatus is thereby materially improved.

The tertiary winding described above for exciting the seriestransformer may be used for supplying an additional low voltage cir-' cuit if desired.

Various changes and modifications may be made in my invention without departing from the spirit and scope thereof as set forth I ends thereof, and means comprising a tertiary winding and a series of contactor switches for energizing said lastnamed transformer.

2. In a transformer, the combination with a primary and 'a secondary winding, of means for changing the voltage ratio between said windings while under load comprising a transformer in circuit relation with one of said windings at a point intermediate the ends thereof, and means for energizing said last named transformer comprising a tertiary winding energized by said primary winding.

3. A system-for changing the voltage ratio of a'power transformer under load comprising a series transformer associated with one of the windings of the transformer and connected between substantially equal sections thereof, a tertiar winding energized by the primary windin of the transformer, means for energizing the series transformer by the said tertiary winding, anda series of contactor switches for changing the magnitude and direction'of such energization.

4. A system for changing the voltage ratio of a power transformer under load comprising a series transformer associated with one of the windings of the transformer and connected between sections thereof, a tertiary winding energized by the primary winding of the transformer, means for energizing the series transformer by the said tertiary winding, and means for changing the magnitude and direction of such energization, said last named means comprising an impedance and circuit opening and closing contactors in circuit relation with taps on said tertiary winding.

with

, transformer under 1 including a series transformer for modifying 5. A tap stem for a power changing comprising means the output voltage and having a winding connected between sections of the main transformer winding, means for energizing the said series transformer comprising a tertiary winding in the transformer, and means for changing the magnitude of ener 'zation of the said series transformer incl'u ing a tap changing device associated with said tertiary winding.

In testimony whereof, I have hereunto Subscribed my name this 3rd day of February,

KIRK A. OPLINGER.

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