IEEE International Symposium
on Discharges and Electrical Insulation in Vacuum,
Berkeley, 1996

RUSSIAN VACUUM CIRCUIT BREAKERS FOR ELECTRICAL NETWORKS
"ELVEST'S high voltage VCB"

Scientific and Production Enterprise "ELVEST" has been engaged in the development and production of powerful circuit breakers rated for voltage 10 - 110 kV for 10 years. The first VBU circuit breakers for 110 kV were put into operation in 1980 and were intended for commutation of transformers of arc steel melting furnaces. They were developed to replace American VCB produced by the "JOSLYN" company. The main characteristics of these circuit breakers are:

• long mechanical life-time - 40000 cycles "On-Off" which resulted from customers requirements and conditions of operation (normally a circuit breaker performs up to 50 commutations per day)
• higher level of electro-dynamical stability
• maximum short-circuit current in a circuit of the big arc furnace could be as high as 80 kA, with the protection for short-circuit currents being rated for currents up to 5 kA
• fire/explosion safety which is a result of using non-combustible materials and the breaker design preventing it from destruction even in case of an open arc in a distributor.

Since 1990 OEMK has been replacing the JOSLYN circuit breakers by VBU developed by "ELVEST" for. Since 1994 these circuit breakers are installed in electrical power systems (first circuit breakers were installed at a power station in Bashkiria).

VCB for inside installation of the VBC-35 type rated for 35 kV, interrupting current up to 31,5 kA and nominal current up to 1600 A were initially also developed for electrometallurgy. These VCB have mechanical life up to 100000 cycles "On-Off" (no analogy anywhere else in the world), they are equipped with built-in over-voltage limiting device which ensure safe operation in all conditions (including arc transformers) with interrupting current being as high as 1250 A. These VBC-35 are used at the electrometallurgical plants all over Russia and CIS.

High reliability of VCB is ensured by optimizing the conditions of VCB drive operation and primarily by optimizing the operating conditions of the bellow of the vacuum interrupter (VI) which life-time determines the mechanical life-time of the VCB. The rate of VI movable contact displacement is controlled by two double-acting pneumatic compensators and electrodynamical compensators demphering the shock loads at switching on. Besides, the optimal rate of contacts displacement decreases the probability of secondary breakdowns, because it decreases the number of microparticles emerging in the between-contact gap.

The built-in device limiting the overvoltages eliminates the possibility of virtual current chopping and thus of dangerous overvoltages caused by them.

It should be mentioned that "ELVEST" tests not only 100% of all parts and nodes, but also each of the VCB manufactured with the first 1500 cycles "On-Off" being worked out at the manufacturing cite.

Vacuum circuit breakers of outdoor installation with porcelain isolation of VBN-35 and VBN-27,5 types rated for 27,5 kV (one-pole modification) and 35 kV (three-pole modification) with interrupting current 25 kA and nominal current up to 1600 A are intended for industrial enterprises, power systems and other electrical installations with frequent communications.

Currently "ELVEST" offers a wide range of VCB rated for 10 kV with nominal currents up to 1600 A and interrupting current up to 31,5 kA including VCB with spring-electromagnetic drivers. "ELVEST" developed and tested a block of deep overvoltages limitation for the cases when for high-power electrical motors commutation which totally eliminates the possibility of overvoltages.

Chistjakov S.P. et al, "Russian Vacuum Circuit Breakers for Electrical Networks. 2.2. ELVEST's high voltage VCB", IEEE International Symposium on Discharges and Electrical Insulation in Vacuum, Berkeley, 1996, pp. 1055-1056