US1742025A - Electrical system - Google Patents

Description

Dec. 31, 1929. c c To ET AL 1,742,025

ELECTRICAL SYSTEM Filed Aug- 13, 1925 2 Sheets-Sheet l WITNESSES:

7 a Leshe /V, Cr/c/7/0/7 and ATTORNEY Patented Dec. 31, 1929 UNITED STATES PATENT OFFICE LESLIE N. CRICI-ITON AND SHIRLEY I. GOLDSBOROUGH, OF PITTSBURGH, PENNSYL- VANIA, ASSIGNORS TO WESTINGHOUSE ELECTRIC &

A CORPORATION OF PENNSYLVANIA ELECTRICAL SYSTEM Application filed August 13, 1925. Serial No. 49,920.

Our invention relates to electrical systems and particularly to protective systems for high-voltage circuits.

One object of our invention is to eliminate the potential transformer ordinarily employed between a high-voltage transmission circuit and protective relay or other elec tro-responsive device responsive to the voltage of said circuit.

Another object of our invention is to modify the energization of a relay or other I instrument connected to a circuit-in a predetermined manner, such as in proportion to the impedance drop of a portion of the circuit.

A further object of our invention is to provide, in a, system comprising a high-voltage transmission circuit energized through a transformer that is normally traversed by load current, means for so correcting the energization'of a relay connected to the lowvoltage winding of said transformer that said relay will be responsive to the voltage of the-high-voltage circuit irrespective of the impedance drop and resulting voltage phase shift in said transformer.

An important application of the invention is in the energization of protective relays for high-voltage systems. Apparatus of this character may be energized in accordance with the current traversing the circuit or with the voltage obtaining thereon, and watt meters, relays of the impedance type and similar apparatus have both current and voltage windings. No difficulty is encountered in deriving current proportional to the line currents in high-voltage systems but the cost of potential transformers for the transmission voltages in use at the present time is prohibitive. However, high transmission voltages are ordinarily obtained by the use of power transformers which convert the relatively low voltage of the generator to the transmission voltage.

In accordance with our invention, the voltage windings of the protective relays are connected directly or through low-voltage potential transformers to the low-voltage winding of the load transformer. Since there is an impedance drop in the transformer that is proportional to the load current traversng the same, means is provided for correctmg the derived potential in accordance with this impedance drop, in order to energize the relays exactly in accordance with the magnitude and phase-angle characteristics of the potential of the high voltage circuit. The operation of the relays is identical with the usual connection, therefore, and the necessity for special instrument transformers insulated for the high potentials of the transmission circuit is obviated.

Other detailed objects and advantages will appear from the following description of the systems shown on the accompanying drawings.

In the accompanying drawings,

. Figure 1 is a diagrammatic view of tem embodying our invention;

Fig. 2 is a similar view of a system employing both short-circuit and ground relays; and Figs. 3 and 4 are modifications of our inventi on in which three-winding transformers are used.

Referring to Fig. 1, a high-voltage distribution system is shown comprising a generator 1, a transmission circuit 2 and a circuit-interrupter 3 arranged to disconnect the generator from the transmission circuit. An auxiliary source of energy isprovided by a low voltage substation 4 that is connected a systhrough a polyphase transformer 5 to the MA NUFACTURING COMPANY,.

The protective relays 6 may be impedance relays of the type shown in the copending application of L. N. Crichton, Serial N o. 641,- 701, filed May 26, 1923. Each relay comprises .a current winding 7 and a voltage winding 8.

The current windings 7 are connected to current transformers 9 in the transmission circuit 2. On account of the prohibitive cost of high-voltage potential transformers, the voltage windings 8 of the relays are connected to the low-voltage primary winding of the transformer 5. In the system shown, the voltage of the transmission circuit is the same as that of the generator and may be 10,000

or 15,000 volts. The source of power at the substation may be for example, 6600 volts and, accordingly, a material saving isell'ected by connecting the voltage windings of the relays to the 6600 volt source rather than directly to the high-voltage circuit 2.

A potential transformer 10 is connected between the low-voltage primary windings of the transformer 5 and the relays 6. A current transformer 11 is connected in each phase of the low-voltage source 1 and is connected to the primary winding 12 of a second current transformer, the secondary winding 13 of which is shunted by a variable impedance comprising a resistor 14 and a reactor 15. The phase characteristics of the impedance correspond to those of the impedance per phase of the transformer 5. Since the current through the impedance comprising the resistor let and the reactor 15 is proportional to the current traversing the transformer 5, the potential drop across a portion of this impedance is proportional to the potential drop in the transformer 5 under all conditions. The potential drop across the impedance is added to the voltage across the secondary winding of the potential transformer 10 in such a manner that the energization of the voltage windings 8 is corrected for the impedance drop in the transformer 5 and the relays are energized exactly in accordance with the potential on the high-voltage transmission circuit 2. The adjustment of the resistors 14: and reactors 15 may be effected by means of a voltmeter, the required voltages being readily calculated.

In case a short-circuit occurs upon the transmission circuit 2, as indicated at 16, the relays 6 in the short-circuited phases will be operatively energized and, since, the energization of the voltage windings 8 is in accordance with the voltage existing on the transmission circuit, the time of operation of the relay is the same as if the relays were directly connected to said circuit. Accordingly, in a system comprising a plurality of stations, the relays in the respective stations will be selectively operated in accordance with the potential drop in the various portions ofthe system. No potential transformer insulated for the voltage of the transmission circuit 2 is required, the load transformer 5 being employed in connection with the modifying device comprising the transformers 11 and 12 and the. impedances 14: and 15 to derive a.

potential proportional to that obtaining upon the transmission circuit.

In Fig. 2 is shown a modification of the system shown in Fig. 1 embodying both shortcircuit and ground relays. The systemshown may be a high-voltage distribution system. For instance, the generator 1 may generate power at a potential of 13,000 volts and the transmission circuit 2 may be a 90,000 volt transmission line. A transformer 16 is inter- 'posed between the generator 1 and the transmission line: The low-voltage primary windings of the transformer 16 are connected in mesh and the secondary windings in star.

A plurality of short-circuit relays 17 and a plurality of ground relays 18 are provided for controlling the circuit interrupter 3.to disconnect the transmission circuit 2 from the generator upon the occurrence of a fault. The current windings of the relays 17 and 18 are connected to the current transformers 19 in the transmission circuit 2. Since the cost of potential transformers insulated for 90,- 000 volts is prohibitive, the voltage windings of the relays 17 and 18 are connected through a low-voltage potential transformer 20 to the low-voltage primary windings of the transformer 16. In order to correct the energization of the voltage windings of said relays for the impedance drop in the transformer 16, variable impedances 21 are connected in series with the secondary windings of the transformer 20 and the voltage windings of the relays 17 and 18, as in Fig. 1. In order that the relays may be responsive to either grounds or short-circuits upon the transmission line, the current transformers 22, for energizing the impedances 21, are so connected as to be energized in accordance with the currents traversing the primary windings of the transformer 16 instead of the currents traversing the line conductors. With the connections shown, one or more of the relays17 will be operatively energized in the event that a short-circuit occurs on the transmission circuit 2 and one or more of the relays 18 will be energized in the event that one or more of the conductors of said circuit becomes grounded. If the portion of each variable impedance 21 connected incircuit with the relays 17 and 18 corresponds to the equivalent impedance of each phase of the loadtransformer 16, the operation of the relays 17 and 18 will be exactly the same as if they were connected directly to the high-voltage transmission circuit 2.

In Fig. 3 is shown a modification of the system shown in Fig. 2, in which a three-winding transformer 26 is employed between the generator 1 and the transmission circuit 2. The connection of the windings of the polyphase load transformer is immaterial and, by way of example, the transformer 26 is shown as comprising star-connected primary and secondary windings 27 and 28 instead .of the delta-star connection shown inFig. 2.

The tertiary winding 29 of the transformer 26 is connected in delta and is usually a relatively low-voltage winding employed for feeding local circuits in the generating station. For example, the generator 1 may generate a potential of 13,800 volts, the secondary potential of the transformer 26 may be 90,000 volts and the potential of the tertiary winding 29 may be 6600 volts.

A plurality of short-circuit relays 17 and a plurality of ground relays 18 are provided, as in Fig. 2, for the protection of the transmission circuit 2. The current windings of the relays 17 and 18 are connected, as before, to current transformers 19 in the transmission circuit. T he voltage windings of the relays 17'and 18 are connected through a potential transformer to the low-voltage primary winding 27 of the transformer 26. The potential transformer 30 compr ses star-connected primary and secondary windings in order that the phase displacement of the voltage vectors may correspond to those on opposite sides of the power transformer 26.

A series of variable impedances 31 and 32 are connected in series with the voltage windings of the relays 17 and 18 and the potential transformer 30. The three impedances 31 are connected through three insulating transformers 33 to three current transformers 34 associated with the respective primary windings 27 of the transformer 26. The three ixnpcdances 32 are similarly connected through threeinsulating transformers 35 to three current transformers 36 associated with the secondary windings 28 of the transformer 26. Each of the impedances '31 is connected, as shown, between one of the secondary terminals of the potential transformer 30 and one of the variable impedances 32. Thevoltage windings of the relays 17 and 18 are connected between said impedances 32 and other secondary terminals of the potential trans- .t'ormer'SO. I

The vector sum of the two impedances 31 and 32 in corresponding phases represents the equivalent impedance in phase of the transformer 26 between thewindings 27 and 28. This arrangement is necessary because of the fact that the tertiary winding 29 provides, in effect, it second source of energy for the secondary winding 28 when a ground fault occurs on the transmisison circuit. l/Vith the arrangement shown, the relays 17 and 18 are energized exactly in accordance with the potential of the high-voltage transmission cir v cuit 2 and thenecessity for using a high-voltage potential transformer for energizing the relays 17and 18 is obviated.

Various modifications of our invention will occur to those skilled in the art. It may be used in systems having any number of phases and in Fig. 4 is shown a single-phase system embodying the invention. A single-phase generator 40 is connected through a three winc ing transformer 41 to a transmission circuit 42. The transformer 41 comprises primary, secondary and tertiary windings 43, 44 and 45, respectively. The tertiary winding 45 of the transformer 41 may be utilized for supplying energy to a local load, such as in-..

dicated at 46. A circuit interrupter 47 is disposed 1n the transmission clrcuit 42 and is controlled, 1n case a short-circuit occurs on voltage winding 50 in accordance with the impedance drop through the transformer 41, a variable lmpedance 52 1s connected in series therewith. The impedance 52 is connected in l shunt relation to the current transformer 53,

which is connected in turn, to the current transformer 54 in the primary circuit of the transformer 41. The impedance 52 corresponds to the equivalent impedance of the transformer 41 between the windings 45 and 44 and, consequently, the voltage drop across said impedance corresponds to the impedance drop in the said transformer. 'lhercfore the energization of the voltage winding 50 of the relay 48 is exactly in accordance with the potential of the transmission circuit 42, although no potential transformer insulated for the voltage of this circuit is required.

We do not consider that our invention is limited to the precise embodiments shown and described and, accordingly, we do not desire that it be limited in scope except as may be indicated in the appended claims.

We claim as our invention:

1. An electrical system comprising a highvoltage transmission circuit, a low-voltage supply circuit, a transformer connected between said circuits, an electro-reseponsive device connected to said low-voltage circuit to be energized therefrom, and compensating means also connected to the low-voltage circuit for modifying the energization of said device in accordance with aphase characteristic of said high-voltage circuit.

2. An electrical system comprising two associated circuits, a transformer connected between said circuits, an electro-responsive device connected to one of said circuits and means for energizing said device in accordance with a phase characteristic of theother of said circuits which does not appear in the former circuit by reason of the transformer action.

3. An electrical system comprising a transformer supplying a load, an instrument having a potential winding connected there to and energized therefrom and means for modifying the energization of said winding in accordance with the load current traversing said transformer and the voltage unbalance therein.

4. An electrical system comprising a circuit, a transformer having a primary and a secondary winding, said secondary winding being connected to said circuit, an instrument connected to said circuit for energization therefrom and means for modifying the enerwith the in'ipeda-nce drop and voltage phase gization ofsaid instrument in accordance shift in said transformcr.-

An electrical system comprlslng a circuit, a translating device having impedance connected thereto, an instrument connected to'said circuit for energization therefrom, a

current transformer in said circuit, an impedance connected across the terminals of said current transformer and connections between said instrument and said impedance for modifying the operation of said instrument in accordance with the impedance drop.

and voltage phase shift in said translating device. 7

6. An electrical system comprising a highvoltage transmission circuit, a low-voltage circuit, a transformer connected between said circuits, a current transformer in one of said circuits, an impedance connected across the terminals of said current transformer, said impedance corresponding to the equivalent impedance of said first-mentioned transformer, and an instrument connected to said low-voltage circuit and to said impedance and controlled by said impedance in accordance with the voltage unbalance inthe highvolt-age circuit.

7. An electrical system comprising a circuit, a circuit-interrupter therein, a relay connected to be energized from said circuit for controlling said errant-interrupter, a translating device having impedance connected to said circuit and means for modifying the energization of said relay in accordance with the impedance drop and voltage phase shift in said translating device. p

8. An electrical system comprising two circuits, a transformer device connected between said circuits, a relay so connected to one of said circuits as to be operated upon the occurrence of a fault in the other of said circuits and means for modifying the energization of said relay in accordance with the impedance drop in said transformer and in accordance with the phase shift in voltage as effected by the transformer.

9. An electrical system comprising two circuits, a transformer having impedance connected between said circuits, a relay so connected to one of said circuits as to be operated upon the occurrence of a fault in the other of said circuits, a current transformerin one of said circuits,- an impedance connected across the terminals of said current transformer and connections between said relay and said impedance for modifying the operation of said relay in accordance with the impedance drop and voltage shift in said transformer.

10. An electrical system comprising a highvoltage transmission circuit, a low-voltage circuit, atransformer between said circuits, a source of power connected to said lowvoltage circuit, a load connected to said highvoltage circuit, a relay having current and voltage windings, the latter being connected to said low-voltage circuit, meansinclu'd- .ing said connections for operating said relay upon the occurrence of a fault in said highvoltage circuit and means for correcting the "-energization of said voltage winding for the impedance drop and Voltage phase shift in c said transformer. A

11. An electrical system comprising a high-voltage transmission circuit, a transformer normally traversed by a load current, said transformer having a winding connected to said transmission circuit and another winding, a relay so connected to said other winding as to be responsive to faults on said transmission circuit and means for continuously correcting the energization of said re lay for the impedance drop and voltage phase shift in said transformer.

12. An electrical system com-prising a high-voltage transmission circuit, a transformer normally traversed by a load current, said transformer having a winding connected'to said transmission circuit andanother winding, a. relay so connected to said other winding as to be responsive to faults on said transmission circuit, means including an i1npedance connected to said transformer for deriving a potential proportional to the impedance drop and voltage phase shift in said transformer and connections between said relay and said impedance.

13. An electrical system comprising a transformer normally traversed by a load current having a plurality of windings, including high and low-voltage windings, a transmission circuit connected to said high- .voltage winding, a plurality of sources of power for said system, a relay connected to the low-voltage winding of said transformer and means for correcting the energizati'on of said relay for the impedance drop and voltage phase shift in said transformer.-

' 14. An electrical system comprising a transformer having its primary windings connected in mesh and its secondary windings connected in star, current transformers connected to said primary windings within the mesh network, impedanccs connected to said current transformers and relays having voltage windings connected to said impedances.

In testimony whereof, we have hereunto subscribed our names this 3rd day of August,

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