No abstract

A new device -a dc multimodule fuse (DCMF) -and a method of using it to limit short-circuit currents in the networks of large cities are proposed. Future short-circuit currents for the power system of the Moscow region are estimated, and from the results of investigations the optimum position for inserting the DCMF is found. It is shown that the use of the DCMF to limit short-circuit currents is more effective compared with using ordinary fuses and resonance-type devices.

The paper deals with transients attendant on filtercompensating capacitive units (FCU) switching-off. The transients disturbs the converter operating mode, breaks the valves commutation, which may caused a converter turn-off. Such processes are caused the saturation of the voltage transformers, used for control of the converter, at FCU switching-off. The problem can be solved by the use of voltage transformer with insulated neutral or ungrounded FCU. These means allow avoiding dangerous current values of primary windings of voltage transformers. To verify the efficiency of proposed means, the digital simulation and natural experiments on back-to-back link between the Russian and Finnish grids were carried out.

The features of the tuning of filters, connected with the tertiary windings of converter transformers, is considered. It is shown that such a connection is effective, but encounters difficulties due to the fact that the tunable filters have impedances as low as the external circuits. A theory and practical methods are given on how to overcome these difficulties. Positive results, obtained when tuning the filters in the Vyborg dc installation are described.

It is shown that the fourth converter unit with a capacity of 350 MW commissioned in 2000 at the Vyborg back-to-back direct-current converter station connecting the power systems of Russia and Finland increased the total installed power of the converter units to 1400 MW. The circuitry of the converter station and its connections permits two independent transmissions through the Vyborg substation with mutual redundancy and with allowance for the requirements of the receiving power system with respect to the maximum power of each transmission. Normal and emergency operating conditions are described. Difficulties encountered in the course of the work and measures taken for their elimination are discussed.