Electricity: electrical systems and devices – Safety and protection of systems and devices
Patent
1990-06-11
1992-06-02
Pellinen, A. D.
Electricity: electrical systems and devices
Safety and protection of systems and devices
361 3, 361 8, H01H 954
Patent
active
051192616
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a circuit arrangement for switching current from a contact to a thyristor, whereby the thyristor is connected in parallel to the contact.
Circuit arrangements are known, in which the switching of current to the thyristor is effected by connecting inductances to the thyristor circuit.
The disadvantage thereby results that arcing occurs at the contact.
The object of the invention is to provide an arrangement by means of which arcing is prevented upon opening of the contact.
The object is achieved by the invention.
This is characterized in that at least one, preferably several ohmic resistances 7, 8, 9, 10 are connected in parallel to the contact, and that each resistance is individually disconnectable by means of a delayed-opening contact 3, 4, 5, 6, whereby the disconnection times are staggered, and that the voltage drop at the contact 1 and at the delayed-opening contacts 3, 4, 5, 6, respectively, is smaller than 30 volt.
By the circuit arrangement according to the invention it is possible to accomplish stepwise switching of the current. The advantage thereby is that arcing and thus burning at the contact is reliably prevented.
A further development of the invention consists in that, in place of the contact and the ohmic resistances connected in parallel, there is provided a movable laminated contact piece which consists of individual laminations of electrically conductive material and insulated from one another, whereby these laminations are mutually displaceable relative to each other in the lifting direction of the contact piece and preferably comprise different resistance values, and that during the opening operation the laminations sequentially lift off from one or several opposite contact pieces.
In this manner, it is possible to switch very high currents and to finely grade the increase of the contact resistance.
The feature of a further development of the invention consists in that the stationary contact piece opposite the movable laminated contact piece consists of individual laminations of electrically conductive material and insulated from one another, whereby the resistance values of these laminations are preferably variable. The advantage results therefrom that the increase of the contact resistance is graduatable in a substantially more exact manner.
A further development of the invention consists in that the stationary contact piece opposite the movable laminated contact piece consists of individual laminations of electrically conductive material and insulated from one another, whereby the resistance values of the laminations are equal, and that each two adjacent laminations are conductively connected together by means of a separate ohmic resistance, and that the resistance values of the ohmic resistances are preferably different.
It is thereby advantageous that the circuit arrangement can be optimally construed by means of the separate ohmic resistances and by means of the large possibility of variation thereof with the most diverse resistance values.
According to an embodiment of the invention there is provided as a sliding contact, in place of the contact and the ohmic resistances connected in parallel, a movable or stationary lamination of electrically conductive material structured to be wedge-shaped in the lifting direction, the cross section of the lamination decreasing toward the contact piece or the contact pieces.
The advantage thereby is that the increase of the contact resistance during the switching-off operation is no longer stepwise, but continuously effected.
The invention will now be described in still greater detail with reference to a circuit diagram.
When current is switched from contacts to thyristors connected in parallel thereto, the current rise in the thyristors should not exceed an upper value of approximately 100 ampere per microsecond. It is customary that this current rise is maintained at a permissible value by switching inductances to the thyristor branch. This has the disadvantage that the voltage drop at the opening contact is so high
REFERENCES:
patent: 4525762 (1985-06-01), Norris
Elin-Union Aktiengesellschaft fur Elektrische Industrie
Jackson S.
Pellinen A. D.
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