US2561202A

US2561202A - Constant current open circuit protective system

Info

Publication number: US2561202A
Application number: US7004A
Authority: US
Inventors: Philip H Houser; Peterson Justin
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1948-02-07
Filing date: 1948-02-07
Publication date: 1951-07-17
Anticipated expiration: 1968-07-17

Description

y 1951 P. H. HOUSER ET AL 2,561,202

CONSTANT CURRENT OPEN CIRCUIT PROTECTIVE SYSTEM Filed Feb. 7, 1948 Inventor: Philip H Mouser", Justin Peterson His Attorngy Patented ]uly 17, 1951 CONSTANT CURRENT OPEN CIRCUIT PROTECTIVE SYSTEM Philip H. Houser and Justin Peterson, Swampscott, Mass., asslgnors to General Electric Company, a corporation of New York Application February 7, 1948, Serial No. 7,004

8 Claims. (Cl. 175-294) Our invention relates to electric protective systems, and more particularly to open circuit protective systems for constant current circuits and the like.

In series circuits of the constant current type, such as are commonly used for street and airport lighting and the like, electric translating devices of the resonant circuit type are often used to convert a constant voltage input to a constant current output. It is a characteristic of such constant current translating devices that if the output circuit is opened with the input circuit energized, there appears at the output terminals a voltage considerably in excess of the normal full load voltage. This high open circuit voltage is frequently of the order of twice the full load voltage, and if the open circuit is due to a broken conductor, this full open circuit voltage appears across the break. Such a condition is highly undesirable in series circuits and accordingly, it is advisable to provide some means for disconnecting the input circuit of the translating device if the output circuit is broken or opened for any reason.

Accordingly, it is a general object of our invention to provide a new and improved open circuit protective system for electric translatin devices.

It is anotherobject of our invention to provide a new and improved open circuit protective system for series lighting circuits and the like.

It is a still further object of Our invention to provide a new and improved open circuit protective system for constant current series circuits and the like.

It is a more specific object of our invention to provide, in a constant current series lighting cir-' cuit or the like, means responsive to a breaking or other opening of the series output circuit for disconnecting the constant current translating device from its supply'source.

Our invention will be more fully understood and its various objects and advantages further appreciated by referring now to the following detailed specification, taken in conjunction with the accompanying drawing, the single figure of which is a schematic circuit diagram of a constant current series lighting circuit including an open circuit protective system embodying my invention.

Referring now to the drawing, we have shown by way of illustration of one embodiment of our invention, a constant current series lighting system applicable to runway lighting for airports and the like. The system illustrated comprises a plurality of series lighting load circuits l, 2 and}, arranged for selective connection through a plurality of manually operable switches 4, li, and 6 to a pair of output terminals 1 and 8 of a constant current electric translating device 9. The translating device 9 is provided also with input terminals l0 and H connected through a circuit breaker l2 to a suitable source l3 of substantially constant voltage single phase alternating current supply of predetermined frequency.

The circuit breaker l2 connecting the input terminals of the translating device 9 to the supply source I3 is of the manually operable, current responsively tripped type, and may suitably be a three-pole breaker having an operating handle in,

contacts

14,15 and I6 and thermal tripping elements ll, l8 and I9, one associated with each pole of the breaker, the thermal elements l1," l8 and I9 being connected independently to trip the breaker through a common tripping member. A suitable breaker of this type is illustrated in Patent 2,047,816 issued on July 14, 1936 to Atwood.

The supply source i3 is connected through two poles of the circuit breaker l2 to a variable tap auto-transformer 20 provided with a tap selector switch 2i. The output terminals of the autotransformer 20 are connected to the input terminals l0 and II of the translating device 9.

The constant current translating device 9 comprises a transformer 22 having a variable tap primary winding 23 and a secondary winding 24. The primary winding is provided with a tap selector switch 23a. The secondary winding 24 is connected to an inductance 25 in series with 1 av capacitor 26, and the output terminals 1 and 8 of the device are at opposite ends of the inductance 25. If desired, of course, only a portion of the inductance 25 need be included between the output terminals 1 and 8. The transformer 22 and the inductance 25- are iron core devices and may, if desired, be wound upon a unitary magnetic structure. Preferably, this magnetic structure is of the air gap type, such as illustrated in Patent 2,195,969, issued to Minor, on April 2, 1.940.

When a translating device of the character described is so proportioned that the reactances of the capacitor 26 and the inductance 25 are substantially equal and opposite at the supply source frequency, the device has the characteristic of translating a substantially constant voltage alternating current input to a substantially constant current alternating current output. It is a further characteristic of such a device, however, that if the load circuit is opened. as by broken conductor, or if the output terminals are otherwise open circuited while the input terminals are connected to the constant voltage supply source, the voltage appearing at the output terminals rises sharply to something of the order of twice the output terminal, voltage under full load conditions. This open circuit output voltage is also distorted in shape and contains prominent harmonics of the supply source frequency, principally the third harmonic.

The output terminals 1 and 8 of the translating device 8 are arranged to be selectively connected to the series lighting load circuits i, I and 3 through the manual selector switches l, I and 6. It will be observed that if the switches I, I and I are all open, the load circuits I, 2 and 3 are connected in series circuit relation across the load terminals 1 and I. If however, any one or more of the selector switches I. 5 or 8 is closed, the load circuit associated with each closed switch is short circuited.

Because of the open circuit output voltage characteristic of the translating device 8, it is desirable to provide means responsive to an open load circuit condition for disconnecting the input terminals of the device 9 from the supply source 13. It will, of course, be appreciated that if the load circuit is broken for any reason and the output terminals I and 8 thus left open circuited, the whole of the excessive output terminal voltage appears across the break. This is a dangerous and undesirable condition in series circuits, and especially in series street or airport lighting circuits, where the high voltage across the broken ends of the load circuit constitute a danger to service personnel or to passers-by, as well as a potential fire hazard.

In order to protect against such open circuit condition, we provide means responsive to an open output circuit characteristic of the translating device 9 for disconnecting the device 8 from the supply source. In the illustrated embodiment of our invention, we utilize the third pole I6 and associate its thermal current responsive device I! of the circuit breaker l2. neither of which are connected in the single phase supply circuit, for tripping the breaker in response to heating current supplied to the device l9 under open output circuit conditions. To provide such current, we connect the primary winding 21 of a transformer 2| across the input terminals Ill and II of the translating device 9 in series with a normally open contact 29 of a control relay 3!]. The secondary winding ll of the transformer 2| i connected to the thermal current responsive device I! in series circuit relation with the pole it of the circuit breaker l2. The actuating winding 32 of the control relay 3|! is provided with a shunting capacitor 33a and connected for energization to the output terminals 1 and l of the device 9 through a tuning capacitor II. The inductance of the actuating winding 32 and the capacitance of the capacitors 33 and Na are so proportioned that the relay energizing circuit including these elements is resonant at the harmonic frequency prominent in the open circuit output voltage across the terminals 1 and 0. whereby the relay 30 is significantly responsive only to this harmonic voltage. It will of course be appreciated by those skilled in the art that the resonant circuit 32-43-3311 need not be connected directly across the terminals 1, I, but may equally well be connected across any other portion of the load circuit or of the transformer secondary winding 24 or inductance 25, and we intend in the appended claims to cover any such coupling to the output terminals 1, 8. I

In operation, when the translating device I i connected to its supply source I I through the circuit breaker l2 and the output terminals I and 8 are connected to a completed load circuit, the frequency of the output voltage is such that the tuned actuating circuit of the relay 3. is insuiilciently energized to pick up the relay. If, however, the output or load circuit is broken. the prominent harmonic frequency voltage appearing at the output terminals supplies sufllcient energization through the tuned circuit 3243- 33a to pick up the relay ll, thereby to connect the transformer primary winding 21 for energization across the input terminals I! and H, and thus across the supply source B through the breaker i2. With the transformer 2| so connected, the transformer secondary winding 3| supplies an output current through the thermal current responsive device I9 sufllcient to trip the circuit breaker I2, thereby to remove energizetion from the translating device 9 and the transformer 28.

While we have described only a preferred embodiment of our invention by way of illustration. many modifications will occur to those skilled in the art and we, therefore, wish to haveit understood that we intend in the appended claims to cover all such modifications as fall within the true spirit and scope of our invention.

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

1. In a constant current electric protective system, an electric translating device having input terminals for connection to a source of alternating current supply of predetermined frequency and output terminals for connection to a constant current load circuit, said translating device having an electrical characteristic such that said output terminals when open circuited supply a distorted voltage containing a prominent harmonic of said source frequency, switching means for disconnecting said translating device from said supply source, and control means connected to actuate said switching means and including a circuit coupled to said output terminals and significantly responsive only to said harmonic frequency voltage.

2. In an electric protective system for a constant current load circuit, a constant current electric translating device having input terminals for connection to a source of alternating current supply of substantially constant voltage and predetermined frequency and output terminals for connection to a load circuit, said translating devicewhen so connected supplying a substantially constant current to said load circuit and having an electrical characteristic such that said output terminals when open circuited supply a distorted voltage containing a prominent harmonic of said source frequency, switching means for disconnecting said translating means from said supply source, and control means connected to actuate said switching means and including a circuit coupled to said output terminals and significantly responsive only to said harmonic frequency voltage.

3. In a constant current electric protective system, an electric translating device having output terminals for connection to a constant current load circuit and input terminals, switching means for connecting said input terminals to a source of alternating current supply of predetermined frequency, said translating device having an electrical characteristic such that when said input circuit is connected to said supply source and said load circuit open said output terminals supply a distorted voltage containin a prominent harmonic of said source frequency, and means for disabling said switching means thereby to disconnect said translating device from said source comprising a control circuit coupled to said output terminals and resonont at said harmonic frequency.

4. In a constant current electric protective system, an electric translating device having output terminals for connection to a constant current load circuit and input terminals, switching means for connecting said input terminals to a source of alternating current supply of predetermined frequency, said translating device having an electrical characteristic such that said output terminals when open circuited supply a distorted voltage containing a prominent harmonic of said source frequency, thermal responsive means for disabling said switching means thereby to disconnect said translating device from said supply source, and means for energizing said thermal responsive means comprising a circuit resonant at said harmonic frequency and coupled for energization to said output terminals.

5. In a constant current electric protective system, an electric translating device having output terminals for connection to a constant current load circuit and input terminals, switching means for connecting said input terminals to a source of alternating current supply of predetermined frequency, said translating device having an electrical characteristic such that said output terminals when open circuited supply a distorted voltage containing a prominent harmonic of said source frequency, current responsive means for disablin said switching means thereby to disconnect said translating device from said supply source, and means for energizing said current responsive means including a control circuit coupled for energization to said output terminals and significantly responsive only to said harmonic frequency voltage.

6. In a constant current electric protective system, an electric translating device having output terminals for connection to a constant current load circuit and input terminals, a manually operable current responslvely tripped circuit breaker for connecting said input terminals to a source of alternating current supply of predetermined frequency, said translating device having an electrical characteristic such that said output terminals when open circuited supply a distorted voltage containing a prominent harmonic of said source frequency, and means for actuating the current responsive tripping means for said circuit breaker in response to opening of said load circuit comprising a source of electric current supply for said tripping means and means for rendering said last named current supply source effective in response to presence of said harmonic frequency voltage at said output terminals.

7. In a constant current electric protective system, an electric translating device having output terminals for connection to a constant current load circuit and input terminals, current responsively tripped switching means for connectin said input terminals to a source of alternating current supply of predetermined frequency, an electrical characteristic of said translating device being such that saidv output terminals when open circuited supply a distorted voltage containing a prominent harmonic of said source frequency, a second source of electric current supply for the current responsive tripping means of said circuit breaker, and means coupled to said output terminals and significantly responsive to said harmonic frequency only for connecting said second supply source to said current responsive tripping means.

8. In an electric protective system for a constant current load circuit, a constant current electric translating device having output terminals for connection to said load circuit and input terminals, switching means for connecting said input terminals to a source of alternating current supply of substantially constant voltage and predetermined frequency, said translating device when so connected supplying a substantially constant current to said load circuit and having an electrical characteristic such that when said load circuit is open a distorted voltage containing a prominent harmonic of said source frequency is supply to said output terminals, current responsive tripping means for said switching means, and means for connecting said current responsive tripping means to a source of electric current supply including a control circuit resonant at said harmonic frequency and coupled to said output terminals.

PHILIP H. HOUSER. JUSTIN PETERSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,298,665 Chubb Apr. 1, 1919 1,335,256 Peterson Mar. 30, 1920 1,821,342 Hellmund Sept. 1, 1931 2,177,900 Logan Oct. 31, 1939 2,226,041 Young Dec. 24, 1940 2,304,986 Young Dec. 15, 1942 2,350,610 Haug June 6, 1944