The Effective Solution for Switching and Protection of Transmission-Voltage Capacitor Banks.

A large utility in the Philippines needed to add several 115-kV, 50-MVAR capacitor banks to their system. Originally, the utility purchasing committee has specified controlled-closing circuit breakers to switch the capacitor banks.

S&C asked them to consider a better alternative — the Mark V Circuit-Switcher with Pre-Insertion Inductors. Its restrike-free interrupting performance and reliable, repeatable operation is ideal for these applications. The pre-insertion inductors provide a very reliable means to limit:

Inrush current and overvoltage at the capacitor bank bus — curbing induced transients in substation low-voltage circuits that can cause spurious signals, insulation puncture, and component damage.
Phase-to-phase switching-surge overvoltages at remote transformers — a phenomenon that can lead to decrease transformer life, or even failure, due to high-voltage stress across the transformer windings.
Overvoltages on long, open-ended lines, which can cause nuisance operation of surge arresters.
Transient overvoltages on users’ utilitzation-voltage bus — voltage magnification of capacitor-switching transients can cause nuisance tripping of adjustable-speed drives and other sensitive electronic devices.

The utility found that Mark V Circuit Switchers with Pre-insertion Inductors offer a number of advantages over controlled-closing devices as well. Among the major factors that they considered in making their decision were the following:

Low maintenance — Circuit-Switcher eliminates the timing and adjustment issues of controlled-closing devices, reducing maintenance requirements.
Reliability — A private utility located 100 km away had been using the older model S&C Mark II Circuit-Switcher for transformer protection since 1973, and despite a big volcanic eruption that happened in the region, the Mark II Circuit-Switcher had experienced no problems in its operation.
Ease of assembly and installation — The utility found installation of the Mark V Circuit Switcher to be very simple and straightforward.

In the end, the utility purchased Mark V Circuit-Switchers with Pre-Insertion Inductors . . . and the utility is thoroughly satisfied with their performance and maintenance records.