Metal working – Method of mechanical manufacture – Electrical device making
Patent
1996-03-07
2000-01-04
Donovan, Lincoln
Metal working
Method of mechanical manufacture
Electrical device making
29609, 335229, 335261, 335264, H01F 706
Patent
active
060096152
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to magnetic actuators, and in particular to actuators suitable for the operation of electric circuit breakers.
In all electric circuit breakers it is necessary to have a mechanism that will open and close contacts in order to interrupt or close an electric circuit.
Conventional high-voltage circuit breakers include mechanical systems for opening and closing the circuit breaker contacts that are very complex to build and require periodic and expensive overhaul and maintenance. The advent of modern vacuum interrupters for use in high voltage circuit breakers, requiring no maintenance or overhaul, has led to the desire to make available actuator mechanisms requiring little or no maintenance and ideally matched to the characteristics of the vacuum interrupter.
These characteristics typically include: short stroke of the moving contact between open and closed positions, usually of the order of 8 to 12 mm; low operating times, typically 10 milliseconds between open and closed positions during operation; high pressure force between contacts when closed to withstand electromagnetic forces during short circuits; and low operating energy.
Prior art bistable permanent magnet actuators meet some of the above characteristics but typically have a number of disadvantageous features.
For example, in UK Patent Application No. 2112212 there is described a relay which has a bistable permanent magnet actuator. This relay includes an electromagnetic coil wound around the armature to provide the necessary electromagnetic driving force to move the actuator between the two bistable positions. This design has a number of disadvantages, not least that the flux generated by the coil works in opposition to the permanent magnet flux, thus having a tendency to destroy the permanent magnets in time. Additionally, considerable flux must be generated to oppose and overcome the permanent magnet flux, and the movement of the actuator is thus rapid and substantially uncontrolled. These types of device are inherently unsuitable for actuators requiring large holding forces, as they will suffer considerable damage when electromagnetic fluxes large enough to overcome the permanent magnet flux are generated. They thus have application only in lower power roles. In addition, the coil is mounted on the moving part (the actuator) thereby requiring a more complex and less reliable configuration.
In a further example, UK Patent Application No. 2223357 there is described a bistable, magnetically actuated circuit breaker. This device includes a dual yoke construction, each yoke providing either the low reluctance permanent magnet flux path or the high reluctance path of the bistable configuration. The permanent magnet is housed between two halves of the actuator. Actuation is provided by one of two electromagnetic coils which operate to destabilise the armature without substantially reducing the flux in the permanent magnet. A substantial disadvantage of this device is that the magnet is located in the armature, and thus for actuators requiring large holding forces, is prone to physical damage under the impact of switching the armature position. A further substantial disadvantage of this device is that the conduction of permanent magnet flux around the device is inefficient and large magnets are required to achieve reasonable holding force. Similarly, generation of electromagnetic flux is inefficient and large switching currents are required.
Where prior art designs of actuator have been made to accommodate high power circuit breakers requiring large holding forces, it has always been necessary to provide electromagnetic coils capable of generating very large opposing fluxes in order to switch the actuator from one bistable position to the other. While this is not always a problem, it is particularly difficult where the breakers must have an independent source of power in order to switch, such as those which must be powered by integral batteries which are required to have a long, maintenance-free life. In addition, the use
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Lequesne, IEEE, "Fast-Acting, Long Stroke Solenoids With two Springs," pp. 194-202, 1989.
Kenworthy Derek
McKean Brian
Barrera Raymond
Brian McKean Associates Limited
Donovan Lincoln
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