High-voltage switches with arc preventing or extinguishing devic – Arc preventing or extinguishing devices – Multiple break
Patent
1996-08-16
1999-01-12
Stright, Jr., Ronald
High-voltage switches with arc preventing or extinguishing devic
Arc preventing or extinguishing devices
Multiple break
218 10, 218 3, H01H 3314, H01H 3312
Patent
active
058593985
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a circuit breaker incorporating a vacuum interrupter or switch in series combination with a sequential isolator.
Circuit breakers incorporating vacuum interrupters or switches are usually restricted to operating on three phase systems up to and including 36 kV. This is mainly because vacuum interrupters or switches are essentially short stroke devices in which the gap between the electrical contacts when the interrupter is open is usually between 10 and 20 mm. Such devices can normally withstand a maximum impulse voltage of approximately 200 kVp, which is the level typically required of 36 kV systems. Vacuum interrupters and switches for ratings of 36 kV are usually much more expensive than devices rated at, for example, 12 kV because of the difficulty in meeting the higher impulse voltage standards required.
Another feature of vacuum interrupters and switches is that the moveable and fixed contacts are, in general, of the "butt" type. These must be pressed together, both when closing and when fully closed, with sufficient force to be able to withstand the electromagnetic repulsive forces particularly when operating under maximum fault conditions when the forces generated can be considerable.
A solution to the above problems has been to provide a circuit breaker which combines a vacuum interrupter in series with an isolator, in which the isolator provides very much greater contact-to-contact distance when in the open condition.
In various prior art systems, two separate actuating mechanisms are required to support such circuit breakers: a first, short stroke, actuator to actuate the vacuum interrupter or switch, and a second, long stroke, actuator to actuate the isolator. Actuators are typically electromagnetic devices chosen to meet the particular requirements of the system to be operated with respect to speed of operation, holding force, stroke length etc. With two actuators, as indicated above, an electronic control system is then required to ensure correctly linked operation of the two devices or alternatively the isolator maybe a manually operated device. Duplication of actuators, whilst providing actuators which can individually be matched to the requirements of both the vacuum interrupter and isolator, nevertheless increases cost and complexity.
It is desirable to provide a "common" mechanical control mechanism which can operate both the vacuum interrupter and the isolator. For the avoidance of doubt, the expression "common mechanism" is used to indicate that a single actuator is adapted to operate both the vacuum interrupter and the isolator. To do this, a number of problems must be overcome.
Firstly, to ensure optimum operation of the circuit breaker, it is preferable for the current to be both interrupted and resumed by the action of the vacuum interrupter, and not by the isolator; in other words, the isolator is preferably an "off-load" device, only opening or closing when the vacuum interrupter has already operated in the appropriate direction.
This prevents damage to the contacts of the off-load isolator which, being an inherently larger device and not having vacuum isolation between opening contacts, is slower to operate and more prone to arcing or electrostatic discharge damage such as pitting of the contacts. Thus it is preferred that the actuating mechanism should, from a closed circuit condition, firstly open the vacuum interrupter rapidly, and then open the off-load isolator. Conversely, from the open circuit condition, it is preferable that the actuating mechanism first close the off-load isolator, and then close the vacuum interrupter. Such a facility is not found, for example, in the prior art switch assembly of GB-2 217 916 which fails to close the isolator ("disconnector") prior to closing the vacuum interrupter.
Secondly, prior art systems have not solved another particular difficulty with common actuating mechanisms adapted to operate both the vacuum interrupter and off-load isolator. As has been stated earlier, vacuum interrupters and isolators ha
REFERENCES:
patent: 3824359 (1974-07-01), Date
patent: 4166938 (1979-09-01), Peek
patent: 4484046 (1984-11-01), Neuhouser
patent: 4591678 (1986-05-01), Yin
Brian McKean Associates Limited
Hayes Michael J.
Stright, Jr. Ronald
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