US2566974A - Close differential relay control - Google Patents

Description

Sept. 4, 1951 A. 1.. BAS TIAN 2,566,974

CLOSE DIFFERENTIAL RELAY CONTROL Filed Jan. 25, 1949 INVENTOR. 419x91?! 50.97740 BY W Patented Sept. 4, 1951 CLOSE DIFFERENTIAL RELAY CONTROL Arthur L. Bastian, Mount Vernon, N. Y., assignor to Ward Leonard Electric Company, a, corporation of New York Application January 25, 1949, Serial No. 72,709

7 Claims.

This improvement relates to a combined relay and self-saturating reactor in series with each other across a potential alternating current line circuit for the purpose of obtaining a close differential in response of the relay under comparatively small changes of potential applied to the relay circuit. This combined relay circuit is particularly useful for control purposes where the relay is required to pick up at a predetermined value of voltage applied to the relay circuit and to drop out upon the occurrence of a comparatively small decrease in value of the voltage.

When a potential relay is energized by an alternating current, there is a decided change in the impedance of the relay winding between the unattracted position of the relay and the attracted position. This is due to the fact that the air-gap in the path of the magnetic flux changes in length as the relay operates from open to closed position and vice-versa. The impedance of the relay winding in the attracted position of the armature or plunger is considerably larger than when in the unattracted position. Where conditions are such that a relatively wide range between the pick-up and drop-out values is permissible, this change in impedance of the relay winding circuit is not objectionable. This wide range may be reduced by adjustment techniques and mechanical design, but if it be attempted to narrow the range of control in this manner beyond a certain region, this characteristic of the impedance change becomes objectionable and results in chattering of the relay. This is due to the fact that when the relay moves to its attracted position, the increased impedance of the relay winding results in a decrease of current below the value of the drop-out current of the relay causing it to move to its unattracted position where it again picks up to cause the relay to assume its attracted position when it again drops out and thus continues to oscillate repeatedly closing and opening the circuit or circuits controlled by the relay. This objectionable condition may be stated to exist when the proportional change in current due to the change in impedance exceeds the proportional change in current due to the applied voltage change necessary to cause the relay to pick up and drop out.

The present invention overcomes this difilculty and the main object thereof is to obtain a close difierential between pick-up and drop-out response of the relay under comparatively small changes of voltage appliedto the relay circuit and to avoid chattering or an unstable or oscillating condition of the relay armature or plunger. A

further object is to accomplish these results by simple and durable means at comparatively low cost and which will occupy small space. Other objects and advantages and various applications will be understood from the following description.

The improvement comprises the placing of a self-saturating reactor in series with the winding of the relay across the supply lines of an alternating current circuit where for control purposes it is desired that the change of potential or voltage of the supply lines over a comparatively small amount will cause the relay to drop out or pick up. The reactor is designed to have low resistance and high reactance in the circuit of its winding. With such a reactor a curve plotted with applied voltage as ordinates and current in the winding as abscissas, shows only a small increase in current as the voltage is increased from zero until near saturation, then the curve forms a knee and just beyond the knee, a small increase or decrease in the applied voltage results in a pronounced increase or decrease in the current. The reactor is preferably designed to have an operating current range from pick-up to drop-out values in the region of such a curve just over the knee of the curve on the saturated side and thereby produces a pronounced change in the value of the current passing through the reactor winding under small changes of applied voltage. Also, the impedance of the sell-saturating reactor is made considerably more than the impedance of the relay winding when its armature or plunger is in its attracted position and may be several times more. The ratio of the reactor impedance to this relay impedance may be of any order according to the requirements of the differential control.

With this combined relay and reactor series circuit connection across the lines, when the relay picks up at a predetermined voltage, the increase in impedance of the circuit of the combined relay and reactor windings is not sufficient to reduce the current below the drop-out current value of the relay because the change in the impedance of the relay winding is proportionately small as compared with the impedance of the combined relay and reactor circuit. It follows that the relay does not drop out upon being picked up and chattering or an unstable condition of the relay is avoided.

Furthermore, when the voltage 01' the source or of the supply lines to which the relay and reactor circuit is connected falls somewhat below the normal voltage, the current in the combined relay and reactor circuit is decreased in much greater proportion than the proportional of the motor.

drop in voltage of the supply lines. This comparatively large decrease in current in the relay circuit will reduce the current therein below the drop-out currenLvalue of the relay circuit and cause the relay to assume its unattracted position. Thus not only is chattering of the relay avoided-but a closediflerential between pick-up,

a starting winding; and Fig. 2 is a simplified diagram showing the combined relay and reactor circuit incorporated in a system for the control of a transfer switch for automatically changing a load circuit from a main circuit to a standby circuit when the voltage of the main circuit drops below a predetermined value.

' Referring to Fig. 1, a source i of alternating current is indicated as supplying the lines 2 and 2a. A relay having a U-shaped magnetic frame 3, an armature 3a and a winding 3b is shown connected in series with a reactor winding 6 wound on a core do. The series connected windings of the relay and reactor are connected across the supply lines 2 and Ed. at the right of the 'figure an induction motor is indicated having a rotor 5, a main winding 5a and a starting winding 5b which latter has in series therewith a capacitor 50. A second relay indicated as of the solenoid type is shown having a winding 5, and a plunger to controlling a movable contact element 6b. When the relay winding 32) is energized sufficiently to attract its armature 3a, a circuit is closed from the supply line 52 to the fixed contact of the relay, then through the movable contact element 3a to the winding 6 of the second relay, thence through the main winding 5a of the motor to the other supply line 2a. The current through the winding 65 is then suificiently Ilarge to cause its plunger to be attracted and move the contact element to into engagement with the fixed contact 50. This closes the circuit through the starting winding 5b from the supply line 2 through the winding 51), capacitor .50 and contact elements to and 6b to the line contact 60: and the separation of these contacts opens the circuit of the starting winding of the motor. The normal running condition is then established.

However, if the voltage of the supply lines or of the source i should fall and cause the current supplied to the motor to increase sufliciently, the current through the winding 6 would cause the movable contact 6b to be moved to engage the fixed contact 60, thereby again connecting the starting winding of the motor in circuit. If this condition then continued long enough it might result in burning out the starting winding Such a condition is avoided however, by the action of the combined relay and reactor circuit due to the fact that before the load current is increased sufficiently to permit the starting winding to be reconnected in circuit, the armature 3a of the first relay would be released from engagement with the contact 3c and protect the motor from damage by opening the circuit thereto. Thus bythe close differential relay action of the combined relay and reactor circuit, a comparatively small drop in voltage of the supply lines results in a pronounced decrease of current in the relay to a value below its dropout value and thus protects the motor from damage. As soon as the voltage of the supply lines increases to normal value, the armature 3a will be attracted and again start the motor. In this manner the relay reactor circuit combination serves to protect the motor from any damage which might result from decrease of the supply voltage below a predetermined value.

In cases where the voltage of the line drops considerably due to the high inrush of the motor starting current, the relay of the combined relay and reactor circuit might drop out and prevent starting of the motor. This can be avoided in such cases by adding to the relay an additional winding 3d, as shown in Fig. 1, which winding is of only a few turns connected in series in the supply line to the motor circuit and acting cumulatively' with the potential winding 3b. The added magnetomotive force of the series winding will prevent the relay from dropping out during the starting period; but it will permit the proper dropping out of the relay at a predetermined small decrease in the supply voltage at other times because under the normal running load condition of the motor, the current is then much less than the starting current; and on account of the few turns of the series winding its proportional efiect on the action of the relay in relation to the efiect of the potential winding of the relay is small. Although Fig. 1 shows one particular type of motor starter, this invention may be applied to other forms thereof.

Fig. 2 shows an automatically movable transfer switch for transferring a load circuit from a preferred source of alternatingcurrent to a stand-by source of alternating current whenthe voltage of the preferred source, or preferred sup- .ply lines, drops below a predetermined value.

The preferred source It is indicated as supplying the lines i i and I to. The stand-by source I2 is indicated as supplying the lines I3; and 13a. The I combined relay reactor circuit combination is indicated by the same characters as in Fig. 1 and is connected across the lines I! and Ha. The movable contact element 3a of the relay is connected to one terminal of a relay winding H. the other terminal thereof being connected to the line Ma. The winding I4 is indicated, as having a solenoid core Ha which in turn controls the movement of a pair of contact elements [5 and 15a connected to the load circuit. When' the winding i4 is not sufficiently energized to attract its plunger, the contact elements l5 and l5a engage fixed contacts i6 and Mia respectively. These fixed contacts are connected respectively to the supply lines i3 and He of the stand-by source. When the winding is' energized sufficiently to attract its plunger, the contact elements I5 and Ma engage the fixed contacts I! and Ila respectively, the latter contacts being connected to the supply lines II and Ila of the preferred source. When the voltage of the supply lines I I and Ha is at or near its normal value, the current through the relay winding '81: and

reactor winding 4 is suflicient to cause the contact element Ia to be attracted and engage the rind contact 30. This closes the circuit from the supply line H through contact 30 and contact element 3a to the winding I4 and thence to the other supply line Ha. This energization of the relay winding M then connects the load circuit to the supply lines of the preferred source. However, if the voltage of the supply lines falls to a predetermined amount which may have a value only of a comparatively small amount less than the normal voltage, the current in the combined relay winding 3b and reactor winding 4 will decrease considerably to a value below the drop-out current value of the relay and the contact element 3a will be released. This opens the circuit of the winding ll and permits the load circult to be transferred to the stand-by circuit. As soon as the voltage of the preferred source, or preferred supply lines, is restored at or near its normal value, the current in the combined relay and reactor circuit is increased sufiiciently to cause the contact element 3a to be attracted and thereby cause the load circuit to be transferred back to the preferred source.

In the diagrams, a close differential acting relay having a pivoted armature is indicated, but it will be understood that it may be of any other suitable type or form, such as a solenoid type or contactor type of an electromagnetic switch. Also, although the core of the reactor is shown as circular, it may be of rectangular form or of any other design. Similarly the relays controlled by the close differential relay combination, although shown of the plunger type, may be of any other form or type suitable for the particular requirements.

It will likewise be understood that although particular embodiments of this improvement have been described and shown, many other embodiments of the invention may be made without departing from the scope thereof.

1 claim:

1. The combination of a relay and a saturable reactor having their windings connected in series with each other and adapted for connection across a pair of alternating current supply lines subject to variation in voltage, said relay having make and break contacts for afiecting a controlled circuit, said reactor winding having relatively low resistance and high reactance, and the winding of said reactor having higher impedance than the winding of said relay.

2. The combination of a relay and a saturable reactor having their windings connected in series with each other and adapted for connection across a pair of alternating current supply lines subject to variation in voltage, said relay having make and break contacts for afiecting a controlled circuit, said reactor winding having relatively low resistance and high reactance, and the winding of said reactor having at least several times the impedance of the winding of said relay.

3. The combination of a relay and a saturable reactor having their windings permanently connected in series with each other and adapted Ior connection across a pair of alternating current supply lines subject to variation in voltage, said reactor having relatively low resistance and high reactance, and the winding of said reactor having at least several times the impedance of the winding of said relay, an electric motor, and a second relay for controlling the starting of said motor by connection of a circuit of said having make and and break contacts for controlling the supply of current from said supply lines to the winding of said second relay when the voltage of the supply lines is normal and for discontinuing the supply of current thereto when the voltage of the supply lines falls below a predetermined value.

4. The combination of a relay and a saturable reactor having their windings connected in series with each other and adapted for connection across a pair of alternating current supply lines subject to variation in voltage, said reactor having relatively low resistance and high reactance, an electric motor, and a second relay for controlling the starting of said motor by connection of a circuit of said motor to said supply lines, said first named relay having contacts for controlling the supply of current from said supply lines to the winding of said second relay when the voltage of the supply lines is normal and for discontinuing the supply of current thereto when the voltage of the supply lines falls below a predetermined value, and said first named relay having an additional winding connected in series in one of the supply lines and acting cumulatively with the winding of said first named relay for avoiding discontinuing the supply of current to the winding of said second relay during the starting of the motor.

5. The combination of a source of alternating current, a second source of alternating current, a relay and a saturable reactor having their windings connected in series with each other across first named source, said reactor winding having relatively low resistance and high reactance, a second relay having contacts for connecting a load circuit to each of said sources respectively, said first named relay having make and break contacts for controlling the winding and energization of said second relay when the voltage of said first named source is above a predetermined value for causing said second relay to connect the load circuit to said first named source and for deenergizing said second relay when the voltage of said first named source falls below a predetermined value for then causing said second relay to connect the load circuit to said second source.

6. The combination of a relay and a saturable reactor having their windings connected in series with each other and adapted for connection across a pair of alternating current supply lines subject to variation in voltage, said reactor having relatively low resistance and high reactance, and the winding of said reactor having higher impedance than the winding of said relay, a load circuit, and a second relay for connecting the load circuit to said supply lines, said first named relay having make and break contacts for controlling the supply of current from said supply lines to the winding of said second relay when the voltage of the supply lines is normal and for disconnecting the supply of current thereto when the voltage of the supply lines falls below a predetermined value.

7. The combination of a relay and a saturable reactor having their windings connected in series with each other and adapted for connection across a pair of alternating current supply lines subject to variation in voltage, said reactor having relatively low resistance and high reactance, a load circuit, and a second relay for connecting the load circuit to said supply lines,

motor to said supply lines, said first named relay said first named relay having make and break contacts for controlling the supgly of currexilg REFERENCES CITED from said supply lines to the w dll'lg of sa second relay when the voltage of the supply lines g if ig gwa g are of record in the is normal and for disconnecting the supply of current thereto when the-voltage of the supply 5 UNITED STATES PATENTS lines falls below a predetermined value, and Number Name Date the winding of said reactor having at least 887,612 Everest May 12, 1908 several times the impedance of the winding Of 1,943,524 Godsey Jan. 16, 1934 said first named relay; 2,333,210 Stern Nov. 2, 1943 2,388,639 Marbury Nov. 6,1945

MD ARTHUR. L. BASTEAN. 2.456.541 Stoecklln Dec. 14, 1948

Images