US1617377A - Relay - Google Patents

Description

Feb. 15,1927. 7. 1,617,377 Y L. N. CRICHTON RELAY Filed July 50. 1920 INVENTOR Leslie AZCr/ah 1017 WITNESSES 1 .J X62. MM

' ATTbRNEY Patented Feb. 15, 1927.

' UNITED STATES PATENT OFFICE.

LESLIE N. CBICHTON, F EDGEWOOD PARK, PENNSYLVANIA, ASSIGNOR T0 WESTING- HOUSE ELEC'IRIG & MANUFACTURING VANIA.

Application filed. July 30,

My invention relates to relays and particularly to relays for protecting electrical distributing systems against grounds.

One object of my invention is to provide a relay system for disconnecting a feeder circuit when a ground occurs thereon.

Another object of my invention is to provide a relay, for the above-indicated operation, that shall not be operated by currents .that are produced by third harmonics.

" A further object of my invention is to provide a power-responsive relay, for the above operation, that shall be very sensitive to small values of current, and that shall be 1 simple and reliable in its operation.

Heretofore, relays for protecting electric circuits against grounds have been inserted in the common neutral conductor between current transformers and the overload relays. Such relays, however, have not been satisfactory because they required too much energy to operate, or, required additional current transformers in systems wherein the ratios of the transformers that were employed for the instruments and other relays were too high for the ground relay. Other relays and systems were not adequately pre tective because selective o eration was not obtained when the value 0 the ground ourrent was less than the value of normal load current and the relays were not selective because of the difliculty in obtaining an inverse time element in the operation thereof and because the relay had nodirective element. Such relays were further undesirable since they were responsive to third harmonies in the system to which they were connected.

In view of the above conditions, I provide a power-responsive relay that has its potential winding connected across the terminals of a resistor in the grounded neutral conductor of the system and that has its current winding in circuit with the common neutral conductor between the current transformers and overload relays or instruments. The power-responsive relay is thus sensitive COMPANY, A CORPORATION OF PENNSYL- RELAY.

1920. Serial No. 400,093;

to small currents that may result from leakage to ground because of the co-operation between the two windings, and is unaffected by any currents that may result from third harmonics in the system.

A ground protecting system embodying this relay overcomes the above-mentioned disadvantages since little energy is required and since the relay is selective, in that it has both a directive and an inverse-timeelement characteristic in its operation, and is not responsive to third harmonics in the system.

Figure 1 of the accompanying drawings is a diagrammatic view of a system embodying my invention;

Fig. 2 is a diagrammatic View of the system that is illustrated in Fig. 1, illustrating the distribution of the ground current; and

Fig. 3 is a diagrammatic view of a system including a plurality of feeder circuits. A source 1 of electromotive, force supplies energy to a supply circuit 2 from which energy is transmitted to a distributing circuit 3 through a circuit interrupter 4. The distributing circuit 3 is rovided with a plurality of current trans ormers 5 for energizing a pluralit of overload relays '6 and a ground relay The current winding 8 of the relay 7 isconnected in circuit with the common neutral conductor 9 between the current transformers 5 and the overload relays 6. The potential winding 10 of the relay 7 is connected across the terminals of a limiting resistor 11 that is connected,- by a conductor 12, between ground 13 and the neutral point of a plurality of potential transformers 14 that are connected in Y- relation to the conductors of the supply circuit 2. i

A safety resistor 15 is provided in parallel relation to thewinding 10 of the relay 7 to prevent injury thereto by reason of large potential difierences across the resistor 11.

The interrupter 4 is provided with a tripping magnet 16 that is energized to trip the breaker when therelay 7 operates. The relay 7 is adapted to actuate its contact members 17 to trip the interrupter 4 only when a ground-occurs on a conductor in the distributing circuit 3.

When a ground occurs upon a conductor 18 of the circuit 8 at the point A, a circuit is completed from the source 1 of electromotive force through the conductor 18, the ground, the ground resistor 11, the potential transformers 14 and the conductors of the supply circuit 2 back to the source 1. Potential is now established across the termi nals of the ground resistor that serves to energize the potential winding 10 of the relay -7. The unbalanced current in the conductor 9, that is caused by the traversal of current through the ground circuit, encrgizes the current winding 8 of the relay 7. The two windings of the relay 7 co-operate to effect engagement of the contact members 17 and energize the tripping magnet 16 to trip the interrupter.

A definite distribution of the resulting ground current has been observed in such a system, as is illustrated in Fig. 2. The ground current traverses the ground and the grounded neutral conductor 12 and then divides equally between the three potential transformers. One-third of the ground .current traverses each .conductor of the supply circuit 2 between the points of connection of the potential transformers 14, and of the conductors of the faulty feeder circuit 3, to the supply circuit 2. Beyond the terminals of the feeder circuit 3, onethird of the ground current traverses each of the two normal phase conductors toward the source 1 of electromotive force. The faulty phase conductor between the feeder conductor terminal and the source 1 of electromotive force is traversed by twothirds of the ground current. At the terminal of the faulty feeder conductor, the two-thirds of the ground current combine with the one-third that traverses the circuit 2 between the potential transformer terminal and the faulty feeder conductor terminal.

The effect of the ground current is equivalent to the superposition of a single-phase electromotive force upon the circuit comprising the faulty conductor as one conductor, and the two normal conductors combined as the other conductor, of a circuit. One-third (if the ground current traverses only the faulty conductor, the ground and the potential transformer that is connected to the corresponding conductor in the supply circuit. This third does not traverse the source 1 of electromotive force, but is induced in the primary winding of the transformer connected to the faulty conductor-by the circulating current that has been induced in the secondary windings of the potential transformers by the ground currents traversing the primary windings of the other two transformers.

The secondary windings of the potential transformers 14 may be employed to provide potential for measuring instruments, etc. and need not, therefore, be of special design or construction.

Since the ground current that traverses the current winding 8 of the ground relay 7 is in phase with the current that traverses the grounded neutral conductor 12, the relay 7 may be made so directive and selective as to select and isolate a faulty feeder circuit in an electrical distributing system.

The factors that are required for the operation of the relay 7 are the unbalance effects that are produced both in the currents that traverse the conductors of the feeder circuit 3 and in the effective ground currents that traverse the windings of the potential transformers.

Although a generator 1 is shown, it is obvious that the protective system illustrated is readily applicable to a transformer substation and that modifications may be made in the arrangement of'the current and potential transformers to obtain the effects required to operate the relay without departing from the spirit and scope of the invention as set forth in the appended claims.

I claim as my invention:

1. In a polyphase distributing system, the combination with a plurality of current transformers connected in series with the conductors thereof, and a plurality of potential transformers connected between each conductor and ground through a common current-limiting resistor, of -a relay having two co-operating windings, one of which is responsive to unbalance in the current transformers and the other of which is responsive to a traversal of current in the currentlimiting resistor.

2. In a polyphase distributing system, the combination with a source of energy, a plurality of feeder conductors and an interrupter connected therebetween, of a lurality of current transformers energize from the feeder conductors, a plurality of potential transformers connected from the source of energy to ground through a common current-limiting resistor, means for actuating the interrupter and a relay for energizingthe interrupter actuating means comprising means responsive to an unbalance in the currents traversing the current transformers and means responsive to a current traversing the current-limiting resistor.

3. In a pol hase distributing system, the combination with a plurality of feeder conductors and a plurality of star-connected current transformers energized thereby, of

current transformers that is responsive to an unbalance in the currents that traverse the current transformer but non-responsive .to third harmonics in the system.

4. In a distributing system, the combination with a supply circuit, a plurality of feeder circuits and a plurality of connecting means therebetween, of a plurality of watt relays severally responsive to a ground current in the feeder circuit and to a corresponding current in the supply circuit for selectively isolating the faulty feeder circuit.

In testimony whereof, I have hereunto subscribed my name this 19th day of July,

LESLIE N. CRICHTON.

Images