Bbc Brown, Boveri & Company, Limited

Gerhard Guth

Hans Glavitsch

Kadry Sadek

Gerhard Linhofer

Walter Kuhn

Where different 3-phase systems are connected to each other via two static converters having an intermediate direct-current circuit, the exchange of power via the intermediate direct-current circuit can be interrupted by a severe disturbance, for example by failure of a static-converter or by line or busbar faults causing a short-circuiting of one of the static converters. This interruption means a change in the balance of effective power and, associated with this, a shedding of reactive load for the other undisturbed 3-phase system. To reduce high dynamic overvoltages which can lead to plant components being endangered or to operational disturbances, the firing angle of the static converter remaining in operation is regulated with dependence on the alternating voltage of the alternating-current system connected to this static converter, in such a manner that the overvoltage is reduced. This is carried out by regulating the current. The firing angle can be adjusted simultaneously with the short circuiting of the intermediate direct-current circuit by means of a short circuit device.

Method for reducing dynamic overvoltages in an alternating-current

A transformer which is suitable for connecting with a compound network and renders possible shifting the phase angle of the secondary side-output voltage in relation to the primary side-input voltage. The secondary windings are divided into winding stages and there are provided lines and switches, by means of which these winding stages can be selectively connected in series. Since the phase angle of the voltage in each winding stage coincides with the angle of the corresponding winding, it is possible to vectorially add in this manner partial voltages with different phase angles, so that at the output terminal of one winding there appears a composite voltage whose phase angle is aligned in the same direction as said one winding or, in relation to such direction, is shifted through a predetermined angle value in clockwise direction or in counterclockwise direction.

Transformer for the controllable shifting of the phase angle of output

Controllable phase shifters containing reactances and valve switching devices are used for compensation and stabilizing purposes in alternating current-energy transmission systems. There is desired a phase shift which can be continuously controlled within variable limits and with comparatively low expenditure in circuit components. There is provided at least one shunt circuit branch between primary terminals having mutual phase shifted voltages, and a tap provided as a secondary terminal supplies a secondary voltage or potential having a phase between that of the primary terminals. At both sides of the secondary terminal there are arranged in the shunt circuit branch preferably complementary reactive impedances. At least one valve switching device, controllable with respect to its gating behavior, is arranged in series or parallel to one such impedance and renders possible changing the magnitude of the impedance which is effective for the fundamental oscillation, and thus, a change of the control phase angle. Preferably valve switching devices are provided at both sides, and, if desired, in combination parallel and in series with the impedances to both sides of the secondary terminal, thereby realizing the advantage of a phase angle control in both directions and over wide ranges of the primary phase angle.

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Baden, Switzerland

Gerhard Guth