Upgrading of the VVN air-blast circuit breakers with shunting betel resistor equipment

Abstract

It is shown that the betel resistor shunting equipment enables the nominal disconnection current of the VVN series air-blast circuit breakers, operating at a voltage of 110 - 330 kV and a current of up to 31.5 kA, to be in- creased. The upgraded circuit breakers satisfy the requirements of the Russian Federation standards. Values of the resistance of the resistors and methods of mounting them are presented, and also measures which must be taken to upgrade all types of circuit breakers. The VVN series of circuit breakers are the most widely used air-blast circuit breakers in Russia operating at a voltage of 110 - 330 kV. They began to be developed during the pe- riod in which the State Standard GOST 687-41 and the time standards for reestablishing the voltage operated. These stan- dards were considerably below those adopted in subsequent standards. Moreover, in the development period no require- ments were imposed on the switching capability when dis- connecting local short circuits. The increase in the operating level of power systems was accompanied by an increase in the short-circuit currents at the points where circuit breakers were placed. The increase in the number of substations and the reduction in the lengths of the power transmission lines led to a considerable increase in the number of short circuits, which could be regarded as local discharges. As a result, the switching capability of cir- cuit breakers of the VVN series, and primarily of the 110 kV circuit breakers, at the beginning of the Seventies of the last century ceased to correspond to the operating conditions in the power systems. Research and tests of circuit breakers, carried at the Ural Polytechnic Institute, under Professor M. M. Akodis, showed that the switching capability of the VVN-110 circuit breakers under factory conditions with a ShS-300 shunting resistor had to be limited to a current of 12.5 kA as against the certi- fied value of 31.5 kA. Improvements in the methods of test- ing the switching capability and repeated tests of circuit breakers showed that the switching capability of circuit breakers had to be limited to a current of 20 kA. Since the replacement of the large number of established VVN-series circuit breakers by other types of circuit break- ers involve considerable technical and economic difficulties, the Scientific-Research Center for Testing of High-Voltage Apparatus and the Energotekhprom enterprise were commis- sioned to develop a method of upgrading the VVN-series of circuit breakers in order to increase their switching capa- bility.