US1871822A - Alternating current protective relay - Google Patents

Description

Aug. 16, 1932.

F. OLLENDORFF ET AL 1,871,822

ALTERNATING CURRENT PROTECTIVE RELAY Filed Aug. 30, 1929 VVV INVENTOR 3/ Franz Ol/endorf Er/ch Fr/ed/d'nc/er 7 AT'TORNEY Patented Aug. 16, 1932 UNITED STATES PATENT OFFICE FRANZ OILENDORFF, F BERLIN-WILMERSDORF, AND ERICH FRIEDLANDER,-OF SPAN DAU, NEAR BERLIN, GERMANY, ASSIGNORS TO WESTINGHOUSE ELECTRIC & MANU- FACTURING COMPANY, A CORPORATION OF PENNSYLVANIA ALTRNATING CURRENT PROTECTIVE RELAY Application filed August 30, 1929, Serial No. 889,871, and in Germany September 22, 1928.

This invention relates to relay protective means for A. C. machines andA. C. systems. Heretofore relay schemes for over-current protection, differential protection, phase balancing and other known functions, have been controlled by any one of the A. C. quantities to be supervised. It is a recognized fact that it is not advisable to provide protective means for networks and the like which are responsive to all operative conditions of such systems for the same strength of the quantity to be supervised. For example, the same value of current may arise in an A. C. machine at a low value of the exciting current, in which case a disturbed operation would be the cause,

or the machine may be operating with the same value of current but with a higher exciting current in which case the machine would be operating under normal conditions.

However, the relay cannot take these conditions into consideration and will always respond at the same current.

According to this invention, therefore, the sensitiveness of the relay is dependent upon the exciting current of the A. C. machine, and in such a manner that the sensitivity is diminished by increasing excitation current, so that, with stronger excitation of the A. C. machine, it responds later than withweak excitation.

An object of this invention, therefore, is to provide a protective relay the sensitivity of which is proportional to the exciting current of an A. C. machine with which it is associated.

gized therefrom and a pivoted armature 13 in rotatable relation with respect thereto. The series connected coils 14 of the electro magnet tend to pull the armature 13 from its normally biased position, as shown, into a horizontal position, thereby closing the contacts 15 by the movement of the contact arm 16, which is substantially a portion of the armature 13. The biasing or damping efiect on the'armature 13 is obtained by means of the spring 17, one end of which is connected to the armature 13 and the other end to an iron core 18 which is magnetized by the coil 19.. The coil 19 is adapted to be energized from the exciter, not shown, or the excitation current of the A. C. machine 11. This magnetizing action of the coil 19 causes a tension or pull on the spring 17 in direct proportion to the amount of excitation current. The

armature will, therefore be moved to close thecontacts 15 on the occurrence of an unbalance in the system for any degree of excitation.

In the arrangement shown in Fi 2, a three phase star-connected A. C. mac ine 21 is adapted to be controlled in the event of a disturbance therein, in proportion to its degree of excitation. A circuit comprising a three phase auxiliary choke coil 23 and the primary of a current transformer 24 is interposed between the star connection of the A. C. machine 21 and its output circuit 22.

A dynamometer type relay 25 is interposed in the secondary circuit of the transformer 24 and is adapted to cause the disconnection of the A. C. machine by suitable switching means, not shown. On the occurrence of an unbalance between the phases of the circuit 22, a resultant current will flow through the transformer 24 and energize the windings of the relay 25. The sensitiveness of the relay is adapted to be dependent on the current in the exciting winding 26 of the A. C. machine by means of a resistance 27 which is inserted in that part of the exciter circuit which includes the Winding 26. The

voltage drop across the resistance 27 is impressed on the windings of the relay 25 in such a manner that the portion of the D. C. exciting current taken from the resistance 27 tends to flow in a direction opposite to that of the current from the transformer 24. The two coils of the relay 25 are in series in the secondary circuit of the transformer but are in parallel with respect to the applied D. C. exciting current. This result is obtained by providing an inductance 28 connected in parallel to the relay and having a central tap to which one of the D. C. conductors is connected. A blocking condenser 29 is provid ed to prevent the D. G. current from flowing into the circuit of the transformer 24. If the inductances and resistances of the relay are arranged symmetrically, an ordinary Wheatstone bridge results, and the blocking condenser 29 is not necessary.

yThe above arrangement produces a sensitivity of the relay which diminishes with increasing energization, the degree of the sensitivity being greater the smaller the degree of excitation. Without the directive force of the exciting current, the sensitivity of the relay is directly proportional to the energizing current. The proportionality factor can be controlled by selecting the distribution ratio between the relay direct-current and energizing current.

In Fig. 3 is shown a three phase A. C. machine 31 energized by an exciter 32 having a field winding 33 therefor, a current transformer 34 in one of the phases of the output circuit 35, of the said machine, adapted to energize the coil 36 of the relay 37 on the occurrence of an overcurrent. A choke coil 38 has one of its three legs energized by a direct current proportional to the exciting current, as from the D. C. source 39 through the winding 33 and the variable resistance 41. The other two legs of the choke coil are connected in series and paralleled with the coil 36 of the relay 37.

The energizing coil of the relay 37 and the series windings of the choke coil 38 are therefore energized in a proportionate amount determined by the amount of current flowing in the circuit 35 of the machine 31. With an increase of excitation current of the machine 31, the inductance of the choke coil 38 is diminished in increasing degree by the D. C. magnetization, so that the current delivered by the current transformer 34 flows for the greater part through the choke coil 38, and the current which flows through the energizing coil of the relay 37 is proportionately smaller. This distribution of the current in the parallel circuit, including the relay 37 and the choke coil 38, results "n a degree of sensitivity of the relay proportional to the relation between the exciting current and the outjput current of the A. C. machine.

In the oregoing arrangement, a usual type of relay may be used to actuate a control or protective system and the reaction of the A. C. current on the D. 0. current is avoided.

This invention as applied to the protection of A. 0. systems is not confined to the various arrangements shown in the drawing, and no limitations should be placed thereon other than those set forth in the appended claims.

We claim as our invention:

1. In combination with an alternatingcurrent machine, current-responsive means associated therewith and energized in accordance with the machine current, and means energized in accordance with the exciting current of said machine for Varying the sensitivity of said current-responsive means.

2. In combination with an alternatingcurrent machine, a current-responsive means associated therewith and energized in accordance with the machine current, and means energized in accordance with the exciting current of said machine for controlling the sensitivity of said current-responsive means.

3. A current-responsive device associated with an alternating-current circuit and responsive to the circuit current, and means energized in accordance with the circuit excitation current for varying the sensitivity of said device.

4. Protective means for an alternating currrent system including in combination a current-responsive device associated with said system and adapted to be energized in accordance with the current in said system and means energized in accordance with the system exciting current for predetermining the sensitivity of said device.

5. In a protective system for an alternating-current circuit, a current-responsive means associated therewith and responsive to the current thereof and means associated with the excitation circuit of said alternating-current circuit and with said current-re,

sponsive means for modifying the response of said protective system.

6. Protective means for an alternatingcurrent system, including a current-responsive relay energized therefrom in accordance with the current thereof, and damping means associated with the excitation circuit of said system and with said relay for varying the sensitivity of said relay inversely as the value of the exciting current.

7. A protective system for an alternatingcurrent machine connected in an electrical circuit, comprising a current-responsive relay, means for energizing said relay in accordance with the current traversing said circuit, and means associated with the excitation circuit of said machine for predetermining the sensitivity of said relay in accordance with the degree of excitation of said machine.

8.'Protective means 'for an alternatingcurrent electric circuit including a current relay associated with said circuit and adapted to be energized in accordance with the circuit current, and means energized in accordance with the circuit excitation current for biasing said relay.

In testimony whereof, we have hereunto subscribed our names at Berlin-Siemensstadt, Germany, this 16th day of July, 1929. Q FRANZ OLLENDORFF.

ERICH FRIEDLKNDER.

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