US3626250A

US3626250A - Protective circuit for current regulator

Info

Publication number: US3626250A
Application number: US81411A
Authority: US
Inventors: Clair A Nodurft
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1970-10-16
Filing date: 1970-10-16
Publication date: 1971-12-07
Anticipated expiration: 1988-12-07

Abstract

Current regulator device comprises constant current transformer having lighting circuit in its secondary and an open circuit protective device with time delay means connected to the transformer primary. The time delay means includes an RC circuit for delaying turnoff of the regulator in the event of a break in the lighting circuit.

Description

United States Patent Clair A. Nodurft East Flat Rock, NC. 81,411

Oct. 16, 1970 Dec. 7, 1971 General Electric Company lnventor Appl. No. Filed Patented Assignee PROTECTIVE CIRCUIT FOR CURRENT REGULATOR 8 Claims, 1 Drawing Fig.

US. Cl 317/30, 7

I 3 17/36 TD, 323/6, 3l5/l93 lnt.Cl. ..l-l05b 37/02, GOln l9/l6 Field of Search 317/30, 36

References Cited UNITED STATES PATENTS 7/1951 Houser et al 317/30 3/1958 l-lauck et al..... 323/6 9/l958 Swasey 315/193 lll969 Minks... 323/22 8/1970 Jones.... 323/6 Primary Examiner-L. T. Hix I Attorneys-Sidney Greenberg, J. Wesley Haubner, Frank L.

Neuhauser, Oscar B. Waddell and Joseph B. F orman ABSTRACT: Current regulator device comprises constant current transformer having lighting circuit in its secondary and an open circuit protective device with time delay means connected to the transformer primary. The time delay means includes an RC circuit for delaying turnoff of the regulator in the event of a break in the lighting circuit.

PROTECTIVE CIRCUIT FOR CURRENT REGULATOR The present invention relatesto current regulator devices, and more particularly to constant current regulators such as use d,in lighting circuits for supplying selected current levels for desired lamp brightness.

Arnong'lighting circuits of the above type in which the invention may be advantageously employed are those used for lighting airport runways and taxiways.

It is an object of the invention to provide an open'circuit protective device with improved time-delay means for a current regulator.

It is a further object of the invention to provide a current regulator circuit with an open circuit protector device of the above type which is reliable inoperation even under varying ambient conditions, is relatively'low in cost, is readily-adjustable to provide the desire time delay period and is simple and compact in fonn.

Still another object of the invention is to provide a protective circuitof the above type which is immediately reset for further operation after being actuated.

Other objects and advantages will become apparent from the following'description and the appended claims.

With the above objects in view, the present invention relates in one of its aspects to a current regulator system comprising,

in combination, a transformer having a primary winding and a secondary winding, a load'circuit connected to the secondary winding, .terminal means for-connecting'the primary winding to a source of alternating current, main switch means connected between the primary winding andthe terminal means, sensing means in the load circuit responsive to current in the latter circuit, a protector circuit connected to the main switch means for controlling the operation thereof, means for supplyingcurrent to the protector circuit, the protector circuit comprising first operating means for operating the main switch means, RC time delay means connected to the current supply means and to the first operating means for actuating the latter following a predetermined interval after energization of the RC-time delay means, and second operating means connected to the RC time delay means and the sensing means and responsive to the latter means for controlling the energizaa'on of the RC time delay means in response to current condition in the load circuit, whereby upon interruption of current in the load circuit while the transformer primary winding is energized, the RC time delay means actuates the first operating means to open the main switch means after the predetermined intervalfor deenergizing the transformer primary winding, whereas return of current to the load circuit before the predetermined interval elapses renders the RC time delay rent regulator circuit with an open circuit protective system showing an embodiment of the present invention.

Referring now to the drawing, there is shown a constant current series lighting system applicable for airport lighting purposes. The system illustrated comprisesa load circuit 1 in which the load comprises a plurality of series connected lamps 2, which may be of incandescent, gaseous discharge or other type. Load circuit 1 is connected to the secondary winding 3b of a constant current transformer '3, such as a movable coil type, having its primary winding 3a connected to terminals 4 of a source of alternating current. Arranged in series in the supply leads 5a, 5b to transformer primary 3a are normally open switch contacts 6b, 6c of main switch 6 which controls the power to transformer 3, the main switch contacts being operated by relay coil 6a connected in the protector circuit as sociated with the constant current circuit, as described more fully below.

in circuits of the type described, it has been the practice to provide protection against the high open circuit voltage which occurs in the load circuit in the event of a break therein for any reason while the input circuit is still energized. ln known circuits of this type, delay means have been incorporated for preventing permanenttripping of the protector circuit in the event of momentary interruption of current in the-load circuit. Such momentary interruption may occur, for example; in certain circuits in the courseof changing the brightness levels of the lighting means, or as a result of flashing the light sources for signalling purposes. Delay devices heretofore used in such circuits have included mechanical devices suchasbimetallic thermal switches, but thesehave not been'fully satisfactory due to malfunctions resulting from rapidlyrepeated operation giving rise to excessive heat in the device. Transistor or like electronic delay devices are in general too costly for general use in such protector circuits.

ln'accordance with the. present invention, a protector circuit with an improved time delay means'is provided which avoids the disadvantages of the known devices and reliably effects-thedesired time delay in the operation of the open circuit protector device.

The protective system of the illustrated embodiment includes the provision of a current transformer 7 connected in secondary load'circuitl 'andhaving relay coil'9a of switch device 9 connected in its secondary as shown, along with series connected capacitor 8 which, by cancelling the inductance of relay coil 9a,'reduces the impedance presented to current transformer 7.

The protector circuit provided by the invention comprises supply lines 10a, lob'conne'cted to terminals -11 Ma source of alternating current, typically of 120 volts,"'-with a'switch 12, such as a manually operated type, connected in one of the supply lines; Connected acrossthe supply is relay coil 6a which when energized operates to close the normally open contacts 6b, 6c of main switch 6. Also connected across the supply in the protector circuit is an RC time delay network comprising chargingcapacitor 13 connected at one side in series with fixed resistor 14 and variable resistor 15. Resistor 14 serves to provide a minimum resistance in thisnetwork. Connected at the other side of capacitor 13 is'current limiting resister 16 which-in turn is connected to the pole of single pole, double throw relay switch 9 which has a normally open contact 9b and a normally closed contact 90. Contact 9b is connected across capacitor 13 and resistor 16 in series discharge relation therewithyand contact is connected to supply line 10b, as shown. Connected across capacitor 13 is DC relay coil 17s of switch device 17 which has a normally closed switch. I contact 17b arranged in supply line 10a between'switch l2 and relay coil 6a in series therewith.

Diode 18 is connected to supply line 10a in series with vari- While'shown as a-manually operable switch, switch 12 may be operated by a photoelectric control device or may be a time switch for initiating operation of the lighting'circuit during hours of darkness or other desired period.

When switch '12 is closed, current will flow through normally closed contact 17a thereby energizing relay coil 6a and closing contacts'6b, 6c. Current also flows through the branch including normally closed contact 90, resistor 16, capacitor 13,-resistors 14 and 15, and diode 18, thereby beginning to charge capacitor 13. The adjustment of variable resistor 15 andthe magnitude of capacitor 13, as well as of the other circuit components, are so chosen as to provide a desired period (e.g., one second), for charging capacitor 13 to a voltage which is sufiicient to energize relay coil 17a for operating the latter.

While the foregoing operation is taking place, power is being applied through closed switch 6 to constant current' the secondary of the latter transformer. As a result, normally open contact 9b in the protector circuit closes and normally closed contact 90, opens before the one second period for charging capacitor 13 has elapsed. This condition stops the charging of capacitor 13 and also results in discharging capacitor 13 instantaneously through resistor 16.

Normal operation of the lighting circuit thus continues until switch 12 is opened or until the power supply to relay coil 60 is otherwise interrupted, resulting in opening of switch contacts 6b, 6c and deenergizing the primary of transformer 3. Under these conditions, relay switch 9 is also deenergized and its contacts 9b, 9c revert to their normal positions.

If during normal operation a break occurs in lighting circuit 1 resulting in an open circuit while transformer 3 is still energized, relay switch 9 is deenergized with contact 9b opening and contact 90 closing. Current now flows through resistors l4, l and 16 and diode 18 to charge capacitor 13. After the charging period of about one' second has elapsed, the voltage on capacitor 13 is sufficient to energize relay coil 17a, opening its normally closed contact 17b, and deenergizing relay coil 60 so that its contacts 6b, 60 open and removed power from transformer 3.

In an illustrative circuit as described, the following components have typical values as shown:

relistor 14 8,200 ohms resistor l5 H.000 ohml resistor 16 22 ohms capacitor 13 33 microfarlds relay coil 17a l5,000 ohms pickup voltage- 30 volts In a usual case, terminals 11 of the protector circuit are connected to a relatively low voltage source, e.g., 120 volts AC, while terminals 4 of the main current regulator circuit are connected to a higher voltage source, e.g., 240 volts AC or higher. While separate power sources are indicated in the circuit diagram for these respective circuits, it will be understood that the same power source may be used for both circuits, with a suitable transformer, for example, being used to step up or step down the voltage as appropriate for the particular circuit. While the present invention has been described with reference to particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the scope of the invention. Therefore, the appended claims are intended cover all such equivalent variations as come within the true spirit and scope of the invention.

What I claim as new and desire to secure to Letters Patent of the United States is:

1. Circuit protective system comprising, in combination, a source of electrical current, a load circuit connected to said source, switch means connected between said source and said load circuit for controlling supply of current to said load circuit, sensing means in said load circuit responsive to current in the latter circuit, a protector circuit connected to said switch means for controlling the operation thereof, means for supplying current to said protector circuit, said protector circuit comprising first operating means for operating said switch means, RC time delay means connected to said current supply means and to said first operating means for actuating the latter following a predetermined interval after energization of said RC time delay means, and second operating means connected to said RC time delay means and said sensing means and responsive to the latter means for controlling the energization of said RC time delay means in response to current condition renders said RC time delay means ineffective to open said switch means. I

2. Current regulator system compnsing, In combination, a

transformer having a primary winding and a secondary winding a load circuit connected to said second winding, terminal means for connecting said primary winding to a source of alternating current, main switch means connected between said primary winding said terminal means, sensing means in said load circuit responsive to current in the latter circuit, a protector circuit connected to said main switch means, for controlling the operation thereof, means for supplying current to said protector circuit, said protector circuit comprising first operating means for operating said main switch means, RC time delay means connected to said current supply means and to said first operating means for actuating the latter following a predetermined interval after energization of said RC time delay means, and second operating means connected to said RC time delay means and said sensing means and responsive to the latter means for controlling the energization of said RC time delay means in response to current condition in said load circuit, whereby upon interruption of current in said load circuit while said transformer primary winding is energized, said RC time delay means actuates said first operating means to open said main switch means after said predetermined interval for deenergizing said transformer primary winding, whereas return of current to said load circuit before said predetermined interval elapses renders said RC time delay means ineffective to open said main switch means.

3. A system as defined in claim 2, said RC time delay means comprising series connected resistance means and a capacitor, said first operating means comprising first relay switch means having a first relay coil connected across said capacitor and first normally closed contact means connected to said current supply means for controlling supply of current therefrom, said main switch means comprising a second relay coil connected to said first normally closed contact means and having second normally open contact means connected between said primary winding and said terminal means.

4. A system as defined in claim 3, said second operating means comprising a third relay coil connected to said sensing means and having third normally open contact means and fourth normally closed contact means, said third contact means being connected across said capacitor in series discharge relation therewith, said fourth contact means being connected to said current supply means in series with said capacitor.

5. A system as defined in claim 2, including diode means connected to said current supply means in series with said RC time delay means.

6. A system as defined in claim 2, including operating switch means connected to said current supply means for controlling the power to said protector circuit.

7. A system as defined in claim 4, including a first resistor connected to said capacitor and the junction between said third and fourth contact means.

8. A system as defined in claim 3, said resistance means comprising a variable resistor.

It I t l i

Claims

1. Circuit protective system comprising, in combination, a source of electrical current, a load circuit connected to said source, switch means connected between said source and said load circuit for controlling supply of current to said load circuit, sensing means in said load circuit responsive to current in the latter circuit, a protector circuit connected to said switch means for controlling the operation thereof, means for supplying current to said protector circuit, said protector circuit comprising first operating means for operating said switch means, RC time delay means connected to said current supply means and to said first operating means for actuating the latter following a predetermined interval after energization of said RC time delay means, and second operating means connected to said RC time delay means and said sensing means and responsive to the latter means for controlling the energization of said RC time delay means in response to current condition in said load circuit, whereby upon interruption of current in said load circuit while said switch means is closed, said RC time delay means actuates said first operating means to open said switch means after said predetermined interval for removing power to said load circuit, whereas return of current to said load circuit before said predetermined interval elapses renders said RC time delay means ineffective to open said switch means.

2. Current regulator system comprising, in combination, a transformer having a primary winding and a secondary winding, a load circuit connected to said secondary winding, terminal means for connecting said primary winding to a source of alternating current, main switch means connected between said primary winding and said terminal means, sensing means in said load circuit responsive to current in the latter circuit, a protector circuit connected to said main switch means, for controlling the operation thereof, means for supplying current to said protector circuit, said protector circuit comprising first operating means for operating said main switch means, RC time delay means connected to said current supply means and to said first operating means for actuating the latter following a predetermined interval after energization of said RC time delay means, and second operating means connected to said RC time delay means and said sensing means and responsive to the latter means for controlling the energization of said RC time delay means in response to current condition in said load circuit, whereby upon interruption of current in said load circuit while said transformer primary winding is energized, said RC time delay means actuates said first operating means to open said main switch means after said predetermined interval for deenergizing said transformer primary winding, whereas return of current to said load circuit before said predetermined interval elapses renders said RC time delay means ineffective to open said main switch means.