Electricity: power supply or regulation systems – Including a transformer or an inductor – Current transformer
Reexamination Certificate
1999-06-30
2001-03-06
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
Including a transformer or an inductor
Current transformer
Reexamination Certificate
active
06198268
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dual-rated current transformer circuit, and more particularly to a miniature dual-rated transformer circuit for use in a protective relay.
2. Discussion of the Prior Art
The use of protective relays for or in a circuit breaker or other electrical apparatus is well known. Traditionally, the relay detects a condition and generates a signal to operate, for example, a trip coil in a low ampere industrial rated circuit breaker. A current transformer assembly is utilized to provide operating power to the trip coil. Traditionally, a single current transformer core fits within the circuit breaker and supplies a sufficient current and operating power to the trip unit circuit for a number of ampere ratings.
One manner of decreasing size constraints but still allowing a circuit to operate over a wide range of ampere ratings is to utilize a fixed transformer size and a fixed secondary winding thereon. The number of primary turns are varied inversely with the circuit ampere rating. See U.S. Pat. No. 5,015,983, assigned to the assignee of the present invention. However, varying the number of primary turns in a current transformer circuit will not allow different input current ratings to produce the same current through the primary winding.
Moreover, larger breakers for industrial or utility applications traditionally utilize protective relays that have their own enclosures. The protective relays have a source of power to operate other than from the current transformer. The output of the protective relay is normally a contact or solid-state device to connect the trip coil to a source of power independent from the relay. For this application, the current transformers are used to replicate and isolate the input current and are normally rated one ampere or five amperes. The current transformer must work over a large current range that includes fault current, which is much greater than rated current for protection and metering, and metering current which can be less than rated current. Traditionally, a typical current transformer for a one ampere input rating would have a twenty turn primary and a separate design for a five ampere input rating which would have four turns.
SUMMARY OF THE INVENTION
It would be economically desirable, therefore, to provide a dual-rated current transformer circuit which allows for at least two different current input ratings to be delivered to the transformer. Moreover, it is desirable to utilize a circuit which can be miniaturized.
One aspect of the present invention is to provide a dual-rated current transformer circuit which utilizes a transformer having a reduced size.
Another aspect of the invention is a transformer circuit which will meet the application requirements using a typical magnetic material that has a relatively low cost. The number of turns can vary due to changes in the magnetic material or application.
Still another aspect of the invention is a transformer circuit which is designed to produce the same output current with a first rated current or a second rated current.
According to presently preferred embodiments of the present invention, a dual-rated current transformer circuit has a first current line which delivers a first current and a second current line which delivers a second current. A transformer is coupled to both the first and second current lines, wherein the transformer generates a current proportional to the current of each of the first and second current lines. The transformer of the circuit incorporates design features which reduce its overall size.
REFERENCES:
patent: 4140961 (1979-02-01), Akamatsu
patent: 4301491 (1981-11-01), Gryctko
patent: 5015983 (1991-05-01), Derosier et al.
General Electric Company
Horton Carl B.
Hunton & Williams
Riley Shawn
Schulman Robert M.
LandOfFree
Dual-rated current transformer circuit having at least two... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dual-rated current transformer circuit having at least two..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dual-rated current transformer circuit having at least two... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2526192