US2654052A

US2654052A - Overload reset circuit

Info

Publication number: US2654052A
Application number: US243897A
Authority: US
Inventors: Harry F Mayer
Original assignee: Individual
Current assignee: Individual
Priority date: 1951-08-27
Filing date: 1951-08-27
Publication date: 1953-09-29
Anticipated expiration: 1970-09-29

Description

Sept. 29, 1953 H. F, MAYER 2,654,052

OVERLOAD RESET CIRCUIT Filed Aug. 27, 1951 Z2 n Z5' -fZiL/Ar. f

. INVENTOR.

Patented Sept. 29, 1953 OVERLOAD RESET CIRCUIT Harry F. Mayer, Baldwinsville, N. Y., assignor to the United States of Am the Secretary of the Air Application August 27, 1951, Serial No. 243,897

3 Claims.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without payment to me of any royalty thereon.

This device relates to overload re-set circuits which have for their function the removal of primary power from a load upon the occurrence of an overload and which will restore the power after a predetermined time interval.

One object of the invention is to provide a circuit of the class described, which is especially adapted to radar modulators and other kinds of electronic equipment. Heavy currents such as are necessary to operate re-setting overload circuit-breakers are not necessary for this circuit.

Another object of the invention is to provide a device of the above character iny which the resetting time delay is adjustable over wide limits.

In radar modulators and in many other types of electronic equipment overload is apt to occur due to occasional intermittent malfunctioning of a tube in the load circuit. For example, the thyratron in the modulator may arc back, or may fail to extinguish after a pulse; or the magnetron load may spark over. Any of these occurrences will cause excessive current to 4be drawn from the rectier which supplies the power. It is common practice to include a current-sensitive fault responsive relay in the output circuit of the rectier, connected so as to interrupt primary power` when the output current exceeds a certain value. If the relay returns to its normal position when the primary power is removed and the output current falls to zero, then primary power is immediately re-a'pplied. This happens so quickly that generally the malfunctioning which caused the overload will continue, and the relay will oscillate rapidly, turning power on and oi to no avail.

An alternative is to use a holding circuit which will cause the primary power to stay oil when interrupted by an overload, until a manual reset switch is operated. This is satisfactory in some applications, but not in others. In particular, it is not satisfactory in a re control radar system, where the necessity for operating the re-set switch in the middle of a shooting engagement would be disastrous.

The circuit here described removes the primary power, waits a predetermined time (adjustable over wide limits, but for application to radar sets xed at approximately 1A? second), and then restores primary power.

With reference to the drawing, the reference numerals I and 2 designate conductors in a primary alternating power circuit such as the input to the power rectifying equipment of a radar set erica as represented by Force and connected in series by the normally closed contacts 3 and 4, the latter contact being mounted on the movable armature 5 of a circuit breaking relay generally indicated at 6. The coil 'I of the relay E has one terminal grounded and the other terminal connected by conductor 8 to the lower contact 9 of an overload control relay generally indicated by the reference numeral I5.

The armature I of relay I5 is connected to a suitable source of D. C. potential such as 28 volts and normally engages the lower contact 9 when the relay I5 is de-energized- Current from the 28 volt source thus normally ows to ground through the coil I of relay 6 maintaining the relay energized and primary circuit breaking contacts 3 and 4 normally closed.

The relay I5 has an upper contact II connected by means of a resistor I2 and conductor I3 to one terminal of a holding coil I4 the other terminal of which is grounded. When the relay armature itl engages contact II the holding coil is energized with direct current from the 28 volt source which is reduced across resistor I 2 to about 20 volts D. C.

The relay I5 is also provided with a coil IB connected in series with conductors I'I and I8 of the load circuit to be protected such that current overloads through the coil I6 activate the relay I5 to attract the armature I D against a suitable biasing force thus energizing the holding coil I4 to maintain the armature in engagement with the upper contact II until the holding coil circuit becomes de-energized by means later to be described. When the armature I0 of relay I5 breaks engagement with contact 9 the relay 8 is de-energized and the relay arm 5 drops breaking engagement of contacts 3 and 4 and opening the primary power circuit which also de-energizes the load circuit.

Means are provided for delaying the de-energizing of the holding coil I4 of relay I5 which means comprise a conductor I9 connected to conductor I 3 in parallel with the holding coil and which has an adjustable resistance 26 and a capacitance 2I connected in series therewith to ground. A conductor 22 connected to conductor I9 between the resistance 20 and capacitance 2| is connected to the grid of a conventional triode type vacuum tube 25. Whenever the relay I5 is activated, current from the 28 volt source connected to the armature I0 flows through relay contact II and resistance I2 to holding coil I4 with a potential of approximately 20 volts. This latter voltage is dropped across resistance 20 to charge condenser 2I with the charging time being dependent on the RC value of the resistance 20 and capacitance 2I and preferably chosen cated at 3e, the other terminator therelay coil.

being connected to a suitabiefhi-'gh 'voltage plate supply. The relay 30 has its armature 3l and contact 32 connected to ground `and Vtlieupper contact 33 connected by means of conductor 34 to conductor i9 above the resistance 23; The

contacts

32 and 33 of relay 30 are normally separated and engaged when relay 370 is energized by `conductance of tube 25 and the contact engagement .short Icircuits the holding coil I4 and lde --energizes the same.

.From the foregoing it will be apparent that so long :as -the current in the load circuit I7-I8 and in coil 'IS of relay i5 is below a 'predetermined safe vvalue the armature it of the relay will :remain in engagement with the contact 9 permitting current Vfrom, the 28 volt source Yto :flow through coil 'I of relay e maintaining the same energized and keeping the primary power :circuit closed.

Upon occurrence of an overload in the load circuit I'I-Irelay I5 will be activated to cause the armature ID to engage contact II which will fde-energize relay 6 and open the primary 'power circuit to relieve the overload by also de-energizing theload circuit. Engagement of the relay varmature I!) with contact II energizes holding ,coil =I4 to maintain relay I5 activated and simultaneously will charge condenser 2| at a rate vdetermined 'by the setting of resistance 20.

As the condenser 2I begins to charge the volt- 'a'ge -on the-grid of vacuum vtube 25 will risemak- -ing the 'grid less negative with respect to the voltage on 'the .cathode and eventually the tube will begin-to conduct current in Vits plate circuit. When the plate current rises suii'iciently, relay 30 will Ibeen'ergized and its contacts32 and 33 in engaging will complete a short circuit of holding coil I4 causing relay vI5 to drop out and relay 6 to becomelactive .to again close the power circuit. l

When'relay 30 becomes energized and its contacts 33 and 34 short circuit the holding coil I4 of relay "I the charge on condenser 2l is discharged to ground and the bias voltage'on the cathode of tube drives y'the"tube25 -to cut-01T, rie-energizing the plate circuit and relay which in dropping out, removes the Vshort circuit on holding lcoil *IIL restoring initial conditions.

Tf `the overload condition persists, the vabove cycle of operations will be repeated with the primarycircuit'being opened for a one-'half second period during each cycle of the overload protectivev system.

Having now described the invention what I desire to "protect by United States Letters Patentis dened in the appended claims.

I claim:

l. A protective arrangement fora power lcircuit comprising a fault-responsive relay having a first set of contacts, means responsive to the closing of the rst set of contacts for closing said power circuit, a second set of contacts closed when said first set of contacts is open, means responsive to a fault condition in said power circuit for causing said rst set of contacts to open and said second set of contacts to close, a holding coil means responsive to the closing of said second set of' contacts vfor'holding 's aid rst set lof contacts open and said second set ofcontacts closed and means energized in response to clos- :ing of said second set of contacts for de-energizing said holding coil means after a predetermined time delay, whereby said second set of contacts will/then `be opened and said rst set fof contacts willthen be closed.

2. A protective arrangement for a power circuit comprising za VVfault-responsive relay having na Iflrvstlset oi? contacts, means responsive to the closing fof the first set of contacts for closing said power circuit, a second set of contacts closed when said rst set of contacts is open, means responsive to a fault condition in said power circuit for causing said rst set of contacts toy open and said second set of contacts to close, holding coil means responsive to the closing of said second set of contacts for holding said rst set `of contacts open and said second set of contacts rclosed and means 'including an electronic discharge device Lhaving at least an anode, a cathode and a control grid, which device is normally Anon-conducting and means including an adjustable resistor and condenser for applying a potential to the control grid of said electronic discharge device and said potential being of sufcient value to cause said electronic discharge device yto be made conducting `in :response `to the ciosing of said'second set vof contacts andmeans responsive to the conductivity of said electronic discharge device for de-energizing said holding coil means.

3. A protective arrangement for a power circuit comprising a fault-responsive relay having a rst winding, a second winding, va first set of contacts closed in the non-operative condition ofthe relay and a second set of contacts closed in :the operated condition of the relay, and an electromagnetic `power-controlling relay having contacts `controlling the flow of power in said `power circuit, said contacts Ybeing normally open and closed when said electromagnetic 'powercontrolling relay isenergized, circuit means including said rst set of contacts for Yenergizing said lelectromagnetic power-controlling relay, circuit means including said second set ofvcontacts forenergizing said second winding, circuit means including a resistor and a condenser for producing Va Voltage which increases as a function of time, and an electronic discharge device having at least an anode, a cathode and a control grid, circuit means for applying said voltage to said control grid, and an anode-cathode circuit `for said electronic discharge device including an electromagnetic relay having an energizing winding, contacts controlled by said electromagnetic relay and circuit means for short circuiting said second winding when said contacts are closed.

HARRY F. MAY-ER. l

:References lCited 'in the le of this patent 'UNITED STATES PATENTS Number Name Date I 2,451,953 Ingram Oct. 19, 1948 2,473,344 yMcCown June 14, 1949 2,527,483 Klemperer Oct. 24, C)