US1886985A

US1886985A - Protective relay system

Info

Publication number: US1886985A
Application number: US301404A
Authority: US
Inventors: Sunairi Shizuo
Original assignee: Individual
Current assignee: Individual
Priority date: 1927-09-13
Filing date: 1928-08-22
Publication date: 1932-11-08
Anticipated expiration: 1949-11-08

Description

Nov. 8, 1932. s. SUNAIRI PROTECTIVE RELAY SYSTEM Filed Aug. 22, 1928 Referring now to the drawing, wherein Figure' 1 shows a diagram of circuits and apparatus embodying my invention, a substation 1 receives alternating current electrical power from a power station 2, by way of a double-circuit high tension transmission line, comprising two

circuits

3 and 4, including

circuit interrupters

5 and 6 at the receiving end, and

circuit interruoters

7 and 8 at the sending end, r spectively. point of the system 2 is not grounded, or alternately, it may be grounded through a high limiting resistance as hercinbcfore described. But it will not be necessary to illustrate this grounding resistance, because such an arrangement may be readily understood.

l/Vith the sending ends oia the respective circuits are associated current transformers 9V and 10, whose secondaries are differentially or oppositely connected for respective corresponding phases, with their star points grounded, and energize a directional power relay 11.

The relay 11 comprises current windings 12 connected between respective phases of the current transformers and the ground, and potential windings 13 energized in accordance with the phase voltages at the power station. The potential windings may be conveniently energized from the low tension side oi lthe main transformers 14, through a potential transformer 15, it necessary. With this arrangement, considerable expenses in providing a high tension potential transformer may be avoided.

The directional power relay also comprises two opposed pairs of

contacts

16 and 17 ycontrolled by an armature 18 carrying a movable Contact, for selectively engaging the

contacts

16 and 17 in accordance with the energization of the actuating

windings

12 and 13. The

contacts

16 and 17 control the tripping circuits of the

circuit interrupters

7 and 8.

It must be noted that this relay 11 is so arranged that the armature 18 is actuated to one direction, say tothe lett when a shortcircuit current flows in one circuit, say 3, which current always lags from the normal voltage of the power system, while it is actuated to the opposite direction, i. e., to the right when a ground current flows in the same circuit 3, as hereinbeiore described.

In circuit with each current winding 12, there is` included the winding of an

overload relay

19, 29 or 21, and these windings are stanconnected at the outer terminals .of the overload relays. Between the star point and the earth is included the windings of two ground

current relays

22 and 23, in series. It will be readily understood that these ground current relays will not be energized unless a ground current flows therethrough due to the grounding ol one circuit, because he short circuit current or load current bal- 'llhe neutral n ances with each other within the star-connected windings of the

relays

11 and 19, 20 and 21.

The contacts of the

overload relays

19, 2O and 21, and of the ground current relay 22 are connected inparallel relation with each other, and connected between the

multiple contacts

16 and 17 of the directional power relay 11 and the negative side of a direct current control line, while the contact of the other ground relay 23 is included in the energizing circuit for a change-over relay 24 across the control line. The relay 24 is provided with four pairs of

contacts

25, 26, 27 and 28, and a movable armature 29, arranged so as to change over the circuits connecting the

contacts

16 and 17 and the

tripping coils

7 and 8 ot the

circuit interrupters

7 and 8, in a manner as hereinafter described.

ln order to rovide a better understandin@ oi the invention, I will now describe the operation of selective protection which takes place in case of one faulty circuit.

Now assume that a short-circuit has occurred in the circuit 3, while the other circuit el is normal. Unbalanced current will then flow through the current windings 12 and those of the

overload relays

19, 20, 21, but these currents balance with each other within these star-connected windings; no-

current will flow to the ground curr-

entrelays

22 and 23. The contacts of the overload relays are thus closed and the armature 18 is actuated by the lagging short-cir cuit current to eno'ae the contacts 16. The

tripping circuit of the iiaulty circuit 3 is thus comnleted from one side of the control l L line through the tripping coil 7,

contacts

25, 16, and

contacts

19, 20, 21 in multiple to the other side of the control line, and the interruptor 7 is tripped to its open position.

W hen one line of the circuit 3 is grounded by fault while the other circuit 1 is normal, a ground current will flow through the current windings 12 and the windings of the ground

current relays

22 and 23 to the ground,

and energize them. The armature 18 is then actuated in the direction to engage the contacts 17, while the relayY 23 closes its contacts, and completes the energizing circuit of the change-over relay 211. The armature 29 is then yoperated to the upper position shown. rhe tripping circuit of the circuit interrupter 7 is thus completed from one side Y of the control line through, the tripping coil 7 the

contacts

27, 17 and the contacts of the relay 22, which is now energized, to the otl ner side .of the control line. The interrupter 7 lil() circuit of the other trippingcoil 8 would be undesirably completed.

By some reason, such as in the case that the grounding would have occurred at a point adjacent to the receiving end, it would happen that the circuit Iinterruptor 5 is first tripped before the proper interrupter 7 is open. In this case, the whole load is transferred to the other circuit 4, increasing its load current, while in the grounded circuit 3 there flows the leading ground current only. As is obvious from the abovementioned special arrangement and setting of the relay 11, both the lagging current in the circuit e' and the leading current in the circuit 3, function to actuate the armature 18 in one and the same direction so as to complete the tripping circuit of the proper interruptor 7.

When a grounding and a short-circuiting should have occured simultaneously, the differential currents in the relay windings 12 and the

respective windings

19, 20, 21 are the sum of the large short-circuit current 1and the relatively small ground current,

whilel through the ground

current relays

22 and 23 there flows the ground current only. The relay 11 then operates its armature 18 to the left position, due to the fact that the vectorial sum of heavy short-circuit current d relatively small ground current has such a phase that the relay produces a torque in the same direction with the .short-circuit current only. The energizing circuit of the tripping coil 7 is thus completed across the control line through coil 7

contacts

25 and 16, and contacts of the

relays

19, 20, and 21 in multiple, and the faulty circuit 8 is interrupted at the interruptor 7. It will be readily understood that the overload relay must have a time limit sooner than that of the ground current relay 23, for the large short-circuit current.

In an ordinary watt-hour meter type rclay, the torque is maximum when the voltage current are in phase with each other, that is to say, the current in voltage winding is made to lag the terminal voltage thereof by 90 degrees, that is to say, the power factor of voltage winding circuit is made zero.

Consequently, the torque is maximum when the current in current winding is in phase with the terminal voltage of voltage winding, as the torque is maximum when the current flux and voltage iux have 90 degrees phase difference with each other. Therefore, the torque is zero when the current in current winding and the terminal voltage of voltage winding have 90 degrees phase difference.

In the present invention, the power factor of voltage winding circuit is not made zero, but has a suitable substantial value, and by proper selection of the power factor, the relay made to have its torque zero when 'I line current of the system leads line voltage by a certain angle. -With the connection of the relay 11 shown in the drawing, a vector diagram for the relay is given in Figure 4, wherein P1 represents the voltage impressed on the voltage winding of one phase, which is the line-to-line voltage of the system, while Il represents the current in the current winding of the same phase, which is in phase with the line current. According to the invention, assume thatthe power factor of voltage win ding circuit is made 0.5, that is to say, the current therein lags the terminal voltage by degrees. P11 then represents the current in voltage winding. The torque will be zero when Il and P11 are in phase or in opposite phase with each other. This condition occurs when Il is shifted forward by 80 degrees and takes the position of Il', and this signifies that the line current Il leads the phase voltage El by 30 degrees.

The directional relay has normally a zero torque relationship as taught by the position of the vectors Il and PI in Figure t and such zero torque relationship ceases to eXist when a. short circuit or ground occurs on the system to be protected because of the change of the position of these two vectors.

Although I have shown only one embodiment of my invention, it will be readily understood that various modifications and changes are possible, and l do not intend to limit myself by the specific disclosure out only insofar as xSet forth in the appended claims.

I claim as my invention:

1. A protective system adapted for use in a grounded neutral system including a high resistance to ground or a non-grounded system, a double-circuit transmission system of such a nature that the faulty ground current is often lower than the load current in the circuit, means for interrupting said two circuits at the power station end, respectively, a directional power relay for controlling said interrupting means and comprising current elements energized in accordance with the unbalance between said two circuits and potential elements energized in accordance with the normal phase voltages of the power station, and a change-over relay operated in accordance with a ground current for reversing the connection of said interrupting means with the contacts of said directional power relay.

2. A protective system adapted for use in a grounded neutral system including a high resistance to ground or a non-grounded system, a double-circuit transmission system of such a nature that the faulty ground current is often lower than the load current in the circuit, means for interrupting said two circuits at the power station end respectively, a directional power relay for selectively controlling said interrupting means in accordance with leading current and lagging current which flows in'one circuit when it is cuits respectively at the power station end,

`int-2ans 'for selectively controlling said interrupting means in accordance with. lagging current which flows in one circuit when it is short-circuited and means for reversing the function of said first means in accordance with a .grounding of said circuit.

4. A protective system adapted for use in a grounded neutral system including a high resistance to ground or a non-grounded system, a double-circuit transmission system of such a nature that the faulty ground current is often lower than the load current in the circuit, a directional power relay comprising an opposed pair of contacts, a plurality of current windings energized in accordance with the unbalance between respective corresponding phases of said two circuits, a plurality of potential windings energized in accordance with the respective phase voltages in the power station end, and a contact-carrying movable armature actuated thereby, said relay being so arranged that the actuating torque is zero when the current leads the phase voltage in phase by a predetermined degree, a change-over relay for reversing the connection of said pairs of contacts, and a ground current relay for energizing said change-over relay.

5. A protective system adapted for use in a grounded neutral system including a high resistance to ground or non-grounded system, a power-station, a transmission line of such a nature that the faulty ground current is often lower than the load current -in line.I a circuit interrupter having a tripping coil for cutting out said line from said power station, a directional power relay for controlling the circuit of said tripping coil of said interrupter, said relay comprising a contactcarrying movable armature which is actuated in one direction in accordance with the ground current when said line is grounded, so as to prepare one tripping circuit, and is actuated in the opposite direction in response to short-circuit current in said line, so as to prepare another tripping circuit, a current relay energized by said ground current for completing a control circuit, and a second cur- In witness whereof I affix my signature. f SHIZ SUNAIRI.