Low Force Low Oil Trip Mechanism

• US 20100142102A1
• Filed: 12/03/2009
• Published: 06/10/2010
• Est. Priority Date: 12/04/2008
• Status: Active Grant

• Current Assignee: Eaton Intelligent Power Limited (Eaton Corporation PLC.)
• Original Assignee: Cooper Technologies Company (Eaton Corporation PLC.)
• Inventors: Brusky, Nicholas Paul
• Granted Patent: US 8,331,066 B2
• Time in Patent Office: Days
• US Class Current: 361/35
• CPC Class Codes: H01H 33/555 Protective arrangements responsive to abnormal fluid pressure, liquid level or liquid displacement, e.g. Buchholz relays circuits H02H5/08; specially adapted for transformers H01F27/402

Abstract

A circuit breaker for a transformer includes means for interrupting circuitry in the transformer upon a fault condition in the transformer (the “fault interruption means”). The circuit breaker also includes means for interrupting the circuitry when a level of dielectric fluid in a tank of the transformer is unacceptably low (the “low oil trip means”). The fault interruption means includes a magnet, metal element, and first actuator. Upon the fault condition, the magnet and metal element separate, moving the first actuator to cause the electrical circuitry to open. The low oil trip means includes a float, insulating rod, and second actuator. When the dielectric fluid level drops to an unacceptably low level, the float and insulating rod drop, moving the second actuator to cause the circuitry to open. The low oil trip means operates independently of the fault interruption means, opening the circuitry without separating the magnet and metal element.

Claims

1. A circuit breaker for a transformer, comprising:

fault interrupting means for causing circuitry in the transformer to open upon a fault condition in the transformer; and

low oil trip means for causing the circuitry to open when a level of dielectric fluid in a tank of the transformer is below a threshold level,

wherein the low oil trip means operates independently of the fault interrupting means to open the circuitry without actuating any components of the fault interrupting means.

2. The circuit breaker of claim 1, wherein the fault interrupting means comprises:

a magnet; and

a curie metal element electrically coupled to the circuitry and configured to release a magnetic coupling between the magnet and the curie metal element to open the circuitry upon the fault condition,

wherein the low oil trip means causes the circuitry to open without releasing the magnetic coupling between the magnet and the curie metal element.

3. The circuit breaker of claim 2, wherein the fault interrupting means further comprises an actuator coupled to the magnet and configured to move in conjunction with the magnet,

wherein release of the magnetic coupling between the magnet and the curie metal element moves the actuator to cause the circuitry to open.

4. The circuit breaker of claim 1, wherein the low oil trip means comprises:

a float member configured to float in the dielectric fluid;

a rod coupled to the float member; and

a lever,

wherein the float member is configured to apply a force to the rod to actuate the lever when the level of dielectric fluid in the tank recedes below the threshold level, actuation of the lever causing the circuitry to open.

5. The circuit breaker of claim 1, further comprising tripping means for opening the circuitry, the tripping means being responsive to actuation from each of the fault interrupting means and the low oil trip means.

6. The circuit breaker of claim 5, wherein the circuit breaker further comprises:

a stationary contact electrically coupled to the circuitry;

a movable contact; and

a lever arm coupled to the movable contact,

wherein the tripping means comprises a spring-biased cam coupled to the lever arm, movement of the spring-biased cam causing the lever arm to move the movable contact relative to the stationary contact.

7. The circuit breaker of claim 6, wherein the low oil trip means comprises a lever that releases the spring-biased cam to cause the circuitry to open.

8. The circuit breaker of claim 7, wherein the fault interrupting means actuates the lever to release the spring-biased cam to cause the circuitry to open.

9. A circuit breaker for a transformer, comprising:

a stationary contact configured to be electrically coupled to a circuit of a transformer;

a movable contact;

a member coupled to the movable contact;

a tripping apparatus that moves the member to move the movable contact relative to the stationary contact to open and close the circuit;

a fault interrupting apparatus that causes the tripping apparatus to open the circuit upon a fault condition in the transformer; and

a low oil trip apparatus that causes the tripping apparatus to open the circuit when a level of dielectric fluid in a tank of the transformer is below a threshold level,

wherein the low oil trip apparatus operates independently of the fault interrupting apparatus to open the circuitry without actuating any components of the fault interrupting apparatus.

10. The circuit breaker of claim 9, wherein the fault interrupting apparatus comprises:

a magnet; and

a curie metal element electrically coupled to the circuit and configured to release a magnetic coupling between the magnet and the curie metal element upon the fault condition,

wherein the low oil trip apparatus causes the circuit to open without releasing the magnetic coupling between the magnet and the curie metal element.

11. The circuit breaker of claim 10, wherein the fault interrupting apparatus further comprises an actuator coupled to the magnet and configured to move in conjunction with the magnet,

wherein release of the magnetic coupling between the magnet and the curie metal element moves the actuator to cause the tripping apparatus to open the circuit.

12. The circuit breaker of claim 9, wherein the low oil trip apparatus comprises:

a float member configured to float in the dielectric fluid;

a rod coupled to the float member; and

a lever,

wherein the float member is configured to apply a force to the rod to actuate the lever when the level of dielectric fluid in the tank recedes below the threshold level, actuation of the lever causing the tripping apparatus to open the circuit.

13. The circuit breaker of claim 9, wherein the tripping apparatus comprises a spring-biased cam coupled to the member, movement of the spring-biased cam causing the member to move the movable contact relative to the stationary contact.

14. The circuit breaker of claim 13, wherein the low oil trip apparatus comprises a lever that releases the spring-biased cam to cause the circuit to open.

15. The circuit breaker of claim 14, wherein the fault interrupting apparatus actuates the lever to release the spring-biased cam to cause the circuit to open.

16. A circuit breaker assembly for a transformer, comprising:

a plurality of circuit breakers, each circuit breaker comprising;

a fault interrupting means for causing transformer circuitry associated with the circuit breaker to open upon a fault condition in the transformer, and

low oil trip means for causing the circuitry to open when a level of dielectric fluid in a tank of the transformer is below a threshold level,

wherein the low oil trip means operates independently of the fault interrupting means to open the circuitry without actuating any components of the fault interrupting means; and

a linkage bar coupled to each of the circuit breakers, the linkage bar rotating in response to the fault interrupting means of one of the circuit breakers causing the transformer circuitry associated with the one of the circuit breakers to open, the rotating of the linkage bar causing the fault interrupting means of each other circuit breaker to open the transformer circuitry associated with the other circuit breaker.

17. The circuit breaker assembly of claim 16, wherein the circuit breaker assembly comprises three circuit breakers, each circuit breaker being associated with a different phase of three phase power in the transformer.

18. The circuit breaker assembly of claim 16, wherein the fault interrupting means of each circuit breaker comprises:

a magnet; and

a curie metal element electrically coupled to the circuitry associated with the circuit breaker and configured to release a magnetic coupling between the magnet and the curie metal element to open the circuitry associated with the circuit breaker upon the fault condition,

wherein the low oil trip means causes the circuitry associated with the circuit breaker to open without releasing the magnetic coupling between the magnet and the curie metal element.

19. A method for protecting circuitry of a transformer, comprising the steps of:

determining whether a fault condition exists in a transformer;

in response to determining that a fault condition exists in the transformer, releasing a magnetic coupling to cause circuitry in the transformer to open;

determining whether a level of dielectric fluid in a tank of the transformer is below a threshold level; and

in response to determining that the level of dielectric fluid is below the threshold level, causing the circuitry in the transformer to open without releasing the magnetic coupling.