Electricity: electrical systems and devices – Safety and protection of systems and devices – Arc suppression at switching point
Patent
1988-06-29
1989-12-05
Jennings, Derek S.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Arc suppression at switching point
361 6, 361 8, H02H 700
Patent
active
048856541
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION OF TECHNICAL FIELD
The invention relates to switching devices and, particularly, to a device for arcless switching of electrical circuits.
PRIOR ART
One of the promising trends in developing devices for arcless switching of electrical circuits is combining a mechanical contact and a controlled semiconductor device so that an additional, parallel path bypassing contacts for the switching current is provided. This combination retains the advantages of a controlled semiconductor device, which has high reliability, fast response, and a great number of switching cycles, and of a mechanical contact, which consists in low losses of the switching voltage. It also provides arcless switching of electrical circuits.
Conventionally, arcless switching devices comprise a make contact and a means for its protection, which can be made as a controlled semiconductor device connected parallel thereto and coupled to a control circuit. Further improvement of such devices are now focused on providing new control circuits.
At present, two groups of control circuits are employed: with and without a control input.
Known in the art is a switching device (SU, A, 1107186), comprising a controlled semiconductor device, a make contact of an electromagnetic relay being connected parallel to the power outputs of the semiconductor device and coupled to a supply source, a control output thereof is connected to a control circuit made up of a coil of the electromagnetic relay and a resistor whose connection point is the control input. The resistor is connected to one of the power outputs of the controlled semiconductor device, while the coil of the electromagnetic relay is coupled to a control output of the semiconductor device.
This switching device is deficient in that a control input provided in the circuit means the potential thereon is to be varied to control the operation of the device. This is impossible without some additional means, e.g. additional make contacts inserted into the supply source circuit. This, in turn, makes the device less reliable and more complicated. Since the coil of the electromagnetic relay is connected to the control output of the semiconductor device, current in the control circuit is limited and, therefore, saturation of the semiconductor device, which is necessary for arc extinction, becomes difficult and the speed of response is affected. In addition, the presence of the coil of the electromagnetic relay means that the device can only be used to protect contacts of electromagnetic relays.
Known in the art is a device for arcless switching (SU, A, 1159077), comprising a controlled semiconductor device whose power leads are coupled parallel to a make contact of a bistable electromagnetic relay having a memory and two control inputs, the control output of the semiconductor device being connected to a control circuit built around an OR element whose inputs are connected to control inputs of the bistable relay.
This device is deficient in that it has control inputs which also require control means generating on and off pulses, e.g. make contacts inserted in the supply source circuit. This makes the device less reliable and its circuitry more complicated, though the control built around an OR element has a higher speed of response as contrasted to the foregoing device. The use of a bistable relay means that the device can only be used to protect contacts of relays of this particular type.
To summarize, devices for arcless switching of electrical circuits, which are provided with a control input in their control circuits, are characterized by a higher speed of response but require additional means for generating control signals to be applied to these control inputs, and this makes the devices more complicated and less reliable. Besides, such devices have a narrow field of application and can be used only to protect contacts of electromagnetic relays.
The principal demand set to devices for arcless switching of electrical circuits is reliability and uncomplicated structure. The speed of response ma
REFERENCES:
patent: 3539775 (1970-11-01), Casson
patent: 3868549 (1975-02-01), Schaefer et al.
patent: 4438472 (1984-03-01), Wasdworth
patent: 4745511 (1988-05-01), Kugelman et al.
Budyko Viktor A.
Ivanchenko Andrei F.
Konovalenko Vladimir V.
Krokhmal Vladimir M.
Kutsov Valentin D.
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