US1292585A - Protective relay. - Google Patents

Description

L. N. CRICHTON.

PROTECTIVE RELAY.

APPLICATION FILED SEPT. 14. 1914.

Patented Jan. 28, 1919.

mv Y n m M TV. R m r m v T W A W Y 8 B L UNITED STATES PATENT OFFICE.

LESLIE N. CRICHTON, OF SALT LAKE CITY, UTAH, ASSIGNORQ T0 WESTINGHOUSE ELEC' TRIO AND MANUFACTURING COMPANY, A CORPORATION OF' PENNSYLVANIA.

PROTECTIVE REI-AY.

Patented Jan. 28 1919.

Original application filed December 13, 1912, Serial No. 736.603. Divided and this application filed S cptember 14 1914. Serial No. 861,623.

T 0 all whom it may concern:

Be it known that I, LESLIE N. Cnicirrox, a. citizen of the United States. residing in Salt Lake City. in the county of Salt Lake. State of I'tah. have invented a new and useful Protective Relay, f which the following is a Specification.

My invention can be applied to that class of apparatus known as overload relays and reverse current. or reverse-energy relays. In these specifications. I use the term overload relay in order toprevent confusion, because it is the name commonly given to such apparatus, but my invention is intended to be operative only in case of shortcircuit on the electrical system which is to' be protected.

My invention will find its principal a-pplicatioii in sectionalizing electrical transmission and distribution systems consisting of complicated net worts and loops. and is a division of my application. Serial No.

736603. filed December 13, 1912.

At the present time. electrical systems are sectionalized. and disabled apparatus is disconnected by means of overload and reverse current relays which actuate the proper circuit-breakers. Selective action is obtained by means of a definite time limit. or by an inverse time limit. or by a combination of the two. The time limit of the relays must be adjusted beforehand. and in many cases, this cannot be done advantageously because of the changes which occur in the arrange mentof the electrical circuits from time to time, and because the location of short-circuits cannotbe determined in advance. In my invention. the time limit depends on the location of the short-circuit. The fart-her the short-circuit. the greater the time. until a point is reached beyond which a short circuit will not cause the relay to operate.

In the accompanying drawings. in which like parts are similarly designated. Figure 1 shows the principle of the invention. Figs. 2, and 3, show alternative methods of applying the invention to various forms of relays. and Fig. 1 is a curve showing the characteristic operation of one form of the relay.

In Fig. 1 a single phase or direct current transmission line 1 is shown connected to relay and to the circuit-breaker 2. The current on the transmission line passes through the cpil 3, and acts in such a way as to raise the plunger it in the di ect-ion shown by the arrow when the curr t exceeds a predetermined amount. Thevoltage ot' the circuit is'applied to the coil 5 and opposes the action of the coil 3 by pulling down on the core 6 as shown by the arrow. The force with which the coil 5 pulls on the core is regulated by means of the series resistance 17 which can be adjusted to the particular conditions required. The cores -1 and 6 are composed of iron and are fastened to a rod 7, which is made of nonmagnetic material and the cores are spaced a sufiicient distance apart. or a shreld s placed between them so that neither coil exerts any influence on the magnetic field of the other coil. the forces between the two being purely mechanical. A movable contact 8 is fastened to the lower end of the rod 7 and is arranged to make contact with two fixed contact pieces 9. 9 whenever the rod is raEsed. Vhenever the contacts are, closed, a urrent flows from the battery 10 through the. trip coil 11 to trip the circuit-breaker. An air bellows 12 is fastened to the top end of;- the rod 7 and is used as a timelimit to the relay. the time being adjusted by moving the timing screw 13.

The coil 5,- I have named the restraining' coil and it will be seen that with a given current flowing through the relay. the force which acts upon the bellows will depend upon the amount which the restrainin coil retards the action of the current coil. If the short-circuit occurs on the transmission line veryclosto the relay. there will be'no voltage to counteract the pull due to the current coil. and the resultant force on the bellows will'be strong enough to operate the relay quickly. If. on the other 'ha-nd.'tlie shortcircuit is a long way off. the voltage at the relay will be comparatively high and will oppose the action 15f the current coil so that the force acting on the bellows will be decreased with aconsequent increase in the time of operation. If the short-circuit is sufiiciently remote. the pull due to the restraining coil will be greater than that due ,to the current coil. with the result that the relay will not move. The fact that the re straining coil prevents the movement of the Iva relay when the trouble is more than "a short relay protects causes it to require only a small amount of time limit and still be selective. In some cases it is possible that no time limit would be required.

In Fig. 2 is shown a restraining" coil applied to what is known as a reverse-current relay. This relay is similar to the one ust described, except that in addition to the current coil 3, it contains a voltage coil 15 wound with the current coil so that the magnetic effect of the two coils are combined. The object of this arrangement is to make the operation of the relay stronger when power flows in a reverse direction to normal, which is desired under some practical conditions. In Fig. 2 arrow 16 indicates the normal direction of power flow, and the operation of the relay is stronger when power flows in a reverse direction. Except for the differences shown, the operation of the relays in Fig. 1 and Fig. 2 are identical.

Fig. 3 shows a preferred form of overload relay which I consider valuable because its time of operation varies directly as the distance between the relay and the short circuit, the mathematical equation of its operation representing a straight line. The current coil 45, with its core *6, and shadingcoil *7 reacts on the disk l8 in the direction of the arrow. The disk is pivoted on the shaft 49 around which is wound a cord 50.

. On the end of the cord is fastened aplunger 51 which moves inside the cylinder 52, thus forming a dashpot. \Vhen the disk revolves due to the action of the currentcoil,

. the cord is wound on the shaft which raises the plunger. The time required to raise the plunger depends upon the force exerted by the coil, and upon the adjustment of the timing screw 53. A spring 5st is fastened to the under side of the plunger, and the other end is fastened to a core 55. This core is held down by the pull of the restraining'coil 56. When the relay operates and the plunger. 51 is raised,,the spring 5; is stretched, with the result that after a sufficient time, the pull due to the restraining coil is overcome and the contact 8 is forced against the contacts 9, 9. That is, by properly proportioning the spring, any characteristic curve may be obtained. On most electrical systems, the relay shown in Fig. 1 is superior to the one shown in Fig. 3 because of its simplicity, but the latter is necessary in a few, cases.

Fig. 4 is a diagram illustrating. the characteristic curves of, the relays shown in Figs. 1 and 3. The various parts of the relays have been so proportioned that it will not operate when a short-circuit is more than 20 miles from the relay. This adjustment would frequently be used when the relays are connected to a. section of line about 15 nnles long. If, for example, with the relay shown in Fig. 1, ,a short-circuit drawing 400 amperes occurs close to the relay the time of operation will be slightly less than second; whereas if a short-circuit of the same magnitude should occur 15 milesaway, the time of operation would be about 1% seconds. Heavier short-circuit currents will cause the relay to operate faster in both cases. If a short-circuit should occur on any section of line beyond the 15 mile section under discussion the action of the relay would be slow enough to allow the relay in the farther section to operate first. Such a relay can'be used on many electrical networks for disconnecting both bad sections of line and disabled apparatus. On loop systems it will be necessary to use a. reverse-energyrelay having a similar characteristic. With the relay shown in Fig. 3, the characteristic curve may be substantially a straight line as shown, by proper adjustment. of the sprmg and dash pot.

The relays described can be adjusted so that their characteristics will suit any conditions required in practice. and the method of varying the characteristics, and applying them to practical cases is well understood by electrical engineers. It is not necessary that the relay characteristics be mathematically exact.

It will be readily understood that many other modifications than those that have been illustrated and described may be made in the relay without altering its mode of operation or departing from the spirit of the invention and I desire that all such modifications shall be included within its scope.

I claim as my invention:

1. A relay for an electric circuit comprising a movable member actuated in accord-- ance with the current traversing the circuit, a second movable member actuated in accordance with the potential of the circuit. and means for so connecting the movable members that theirrresultant time of operation is directly proportional to the voltage and inversely proportional to the current of the circuit.

'2. A relay device for an electric circuit comprising an independently movable current-responsive device operatively connected to the circuit, a movable voltage-responsive device operatively connectedto the circuit,

and means so operatively connected between the said movable current and voltage-responsive devices that their result-ant time of operation varies directly in accordance with the voltage and inversely in accordance with the current traversing the circuit.

3. A time-limit relay for an electric circuit comprising a retarded current-responsive movable member operatively connected to the, circuit. a voltage-responsive movable memberoperatively connected to the circuit and resilient means for so connecting the two members that the time of operation of the relay will vary directly in accordance with the voltage and inversely in accordance with the current traversing the circuit.

4. A relay device for an electric circuit comprising a movable current-responsive device operatively connected to the circuit. an independently movable voltageresponsive device operatively connected to the circuit, and a dash pot and resilient member so operatively connected between the said movable current and voltage-responsive devices that,

their resultant time of operation varies-directly in accordance with the voltage and inversely in accordance with the current traversing the circuit.

In an electric circuit. the combination with two oppositely acting movable members. and means for causing them to be actuated in accordance with the current and voltage of the circuit. respectively. of a spring for operatively connecting the movable members together.

A relay for an electric circuit comprising a curretit-responsive movable member. a voltage responsive movable member. a movable contact member and means so connected between the said movable members that the movable contact member will require a time to operate that varies directly in proportion to the potential and inversely in proportion to the current traversing the circuit.

T. A short-circuit protective relay for an electric circuit comprising a movable member adapted to be actuated in accordance with. the current traversing the circuit. a restraining electromagnet adapted to be energized in accordance with the potential of the vi l't'llll and means for so connecting the movable member of the electromagnet to the currei'it-responsive movable member that the relay will operate in an interval of time that varies directly as its distance from ashort circuit on the circuit.

8. In an electric circuit. the combination with two oppositely acting movable inemher. and means for causing them to be actuated in accordance with the current and voltage of the circuit. respectively. of a spring and a dash pot operatively connected between the movable members. i

9. In an electric circuit. the combination with a current and a voltage responsive movable member adapted to oppose each other, of a circuit-controlling device operatively connected to the voltage responsive member, and resilient means for so Operatively connecting the movable members together that the circuit controlling means is actuated in a time proportional to the voltage and in versely proportional to the current in the circuit.

10. A relay for an electric circuit comprising two oppositely-acting movable members actuated in accordance with the current and voltage of the ciruit. respectively. an! means for so connecting the movable 1nemhers that the time of operation of the relay will vary directly as its distance from a fault on the circuit.

11. A circuit-controlling device comprising a time-element relay adapted to b responsive to overloading. an electromaguet for opposing the operation of the relay and a spring for operatively connecting the movable member of the electromagnet'to the movable member of the relay.

In testimony whereof. I have subscribed my name this 8th day of September 1 1i.

LESLIE X. CRICHTOX.

\Vitnesses D. L. BRUNDIGE,' N. J. MCMINN.

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