Isolating circuit breaker and circuit protection arrangement

Details Isolating circuit breaker and circuit protection arrangement Isolating circuit breaker and circuit protection arrangement

2001-12-03

2004-02-03

Toatley, Jr., Gregory J. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

High voltage dissipation

C361S064000, C337S142000, C337S172000, C337S171000

Reexamination Certificate

active

06687110

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to electrical switchgear and protection arrangements for electric power distribution networks. More particularly, the invention relates to an improved isolating circuit breaker and a circuit protection system for medium voltage distribution networks utilising a plurality of the improved isolating circuit breakers.
2. Discussion of the Background Art
Existing electrical switchgear includes a dual purpose assembly that may function as both an isolating switch and a fuse, and is generally known in the electric power industry as a “dropout fuse”. Examples of a fuse and a dropout fuse holder are disclosed in Australian Patent No. 667953 and Australian Patent No. 683191 (respectively), both in the name of Cooper Power Systems, Inc. Some of the problems and drawbacks of conventional fuses and associated fuse holders are discussed in the introductory paragraphs of the Cooper Power Systems patent specifications.
Electric power utilities generally use dropout fuses in relatively large numbers in medium voltage distribution networks, often in a pole-mounted configuration, for reasons of cost. However, the fuses must be manually replaced by linesmen, which delays restoration of supply subsequent to a fuse blowing. Isolating switches, with or without fuses, are used for operations in conjunction with separate line sectionalising circuit breakers or automatic re-closing type circuit breakers. In the present context, medium voltage includes the range from about 10 kV up to about 75 kV. There have also been previous attempts to combine on-load circuit breakers with isolating switches, as exemplified by U.S. Pat. No. 4,596,911 to Guery et al., wherein a common operating mechanism closes the isolating switch prior to the circuit breaker and vice versa during opening.
More recently, U.S. Pat. No. 5,959,398 to McKean describes a sequential isolating circuit breaker and actuator wherein a vacuum interrupter provides fast interruption of load current and the isolator provides a large visual gap in the open position for safety reasons. The actuator mechanism in the McKean patent is a complex rotary driven arrangement including spring loaded levers and lost motion linkages.
German Patent Application No. 3412399 in the name of Sachsenwerk, Licht & Kraft AG discloses a high voltage switch with a vacuum switching tube incorporated into a rotary arm carrying an isolating contact on the end of the arm. The rotary mounting for the other end of the rotary arm, that is driven by an actuator, has a cam slot and guide pin arrangement for synchronising the opening of the vacuum interrupter contacts with the isolator contacts.
The prior art arrangement of isolating switches and circuit breakers in series with common actuation does not allow for independent operation of the respective contact sets. In particular, this arrangement does not facilitate opening and automatic re-closing of the circuit breaker alone, to reconnect the load in the event of a transient fault on a protected line. Furthermore, the physical designs are generally suited to metal-clad or indoor use, rather than being more compact and suited to pole-mounting.
In distribution networks with three phase circuits it is desirable to detect faults such as a phase-to-phase fault or a phase-to-ground fault, that may compromise distribution network security. Fault detection can be arranged to control operation of circuit breakers associated with the conductors in order to prevent network damage and when endeavouring to clear the fault.
In obtaining measurements from phase conductors, substantial isolation arrangements are required in view of the potential difference which exists between individual phase conductors and the control equipment for circuit breakers. Conventionally control equipment for circuit breakers is mounted in a cabinet at ground potential.
Furthermore, circuit breakers for three-phase applications typically employ a common actuating mechanism for all three phases. This similarly calls for a relatively heavy and cumbersome device, resulting from the isolation requirements and the mechanical performance required to operate three sets on contacts. This also adds to the cost of acquiring and installing circuit breakers.
BRIEF SUMMARY OF THE INVENTION
Object of the Invention
It is an object of the present invention to provide an isolating circuit breaker which ameliorates or overcomes at least some of the problems associated with the prior art.
It is another object of the present invention to provide a compact isolating circuit breaker for pole mounted, medium voltage applications.
It is yet another object of the present invention to provide a self-contained isolating circuit breaker which can be retrofitted to electrical distribution networks in place of conventional dropout fuses and fuse holders.
It is a further object of the invention to provide a circuit protection arrangement including a plurality of isolating circuit breakers that effect coordinated protection of three phase circuits.
Further objects will be evident from the following description.
Disclosure of the Invention
In one form the invention resides in an isolating circuit breaker for pole mounting in relation to a electrical distribution line, said isolating circuit breaker including:
(a) an isolating switch with a pivoting link, said isolating switch having respective terminals for electrical coupling to load and supply conductors of the electrical distribution line;
(b) a circuit interrupter disposed in series with the isolating switch, intermediate said load and supply conductors;
(c) an actuator arranged for selectively opening and closing the circuit interrupter;
(d) an electronic controller controlling operation of the circuit breaker in response to electrical conditions in the distribution line; and
(e) said isolating switch, circuit interrupter, actuator and electronic controller arranged together on a mounting structure adapted for pole mounting.
Most preferably, the circuit interrupter is incorporated in the pivoting link of the isolating switch.
In one arrangement of the isolating circuit breaker the electronic controller is incorporated in the mounting structure; whilst in an alternative arrangement the electronic controller is incorporated in the pivoting link of the isolating switch.
The actuator and electronic controller are suitably not isolated from the distribution line so as to float at line potential. If required however, the actuator and electronic controller could be isolated from the distribution line.
Preferably the isolating circuit breaker further includes a sensor arrangement coupled to the electronic controller, the sensor arrangement arranged for producing signals in response to electrical conditions in the distribution line. In preference, the sensor arrangement is carried by the mounting structure. Suitably the sensor arrangement includes a current transformer for measuring current in the distribution line. The sensor arrangement may also include a voltage transformer for measuring voltage in the distribution line. If required, the sensor arrangement includes a resistive voltage divider or a capacitive voltage divider for measuring voltage in the distribution line.
The electronic controller may derive power supply from the distribution line. The electronic controller may derive power supply from a separate transformer or capacitor coupled to the distribution line. In preference, the electronic controller derives power supply from a primary or secondary storage cell.
The electronic controller preferably includes a integrated circuit device, such as a microprocessor, gate array or applications specific integrated circuit, with a memory for storing data. Preferably the data includes protection settings relating to operation of the isolating circuit breaker. Suitably the settings include parameters for an automatic re-closing sequence of the circuit interrupter. If required, the memory may also be arranged to store historical data relating to the electrical co

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