January 12, 2004

Trans-Rupter II® Model EX Enhances Protection at Wind-Turbine Generation Stations . . . At an Economical Installed Cost.

Background

A power generation company in the southwest was faced with a dilemma involving their new 160-MW wind generation facilities, comprised of 262 660-kW wind turbines.

The facilities tie into a 36-mile stretch of 138-kV transmission line that supports several oil and natural gas mining fields. The utility that purchases power from the facilities required that the generation company install breaker failure protection for the interconnecting circuit breakers at two generation substations, which were in turn protecting the substation’s 52.4-87.5 MVA 34.5-138-kV step-up transformers.

Examining the options

The total installed cost was a key consideration in the evaluation of protection schemes. Several options were considered, including high-speed grounding switch and direct transfer-trip switching schemes.

The utility would not accept the grounding switch scheme. The direct faults created by the grounding switches would trip the utility’s remote breakers . . . and interrupt the entire transmission line. This scheme would also take too long to clear faults because of its sequential operation of the line breakers and the local disconnect switch.

The transfer-trip scheme was rejected as well. Its eight-second operating time would take even longer to clear faults than the grounding switch scheme.

And, further, the direct transfer-trip scheme would require a communication system to integrate with the existing line breaker zone distance-relay scheme. This would require installing either fiber optic cable, a microwave communications system or wave traps for power line communications. Such equipment would well exceed the generation facilities’ budget.

Trans-Rupter II was the right answer

The generation company ultimately chose the economical S&C Trans-Rupter II Transformer Protector, Model EX as the back-up transformer protective device for each substation. Each Trans-Rupter II was connected to the substation’s existing control power supply and a breaker failure relay.

If the interconnecting breaker fails to trip for a fault in the wind farm facility, the associated Trans-Rupter II is tripped by the substation breaker-failure relays . . . providing the redundant isolation required by the utility at an economical installed cost. Since Trans-Rupter II provides three-cycle interrupting performance, the transmission line will experience only a slight voltage dip (and possibly a single trip-and-reclose operation by the line circuit breakers).

Results

Trans-Rupter II’s space-saving design made installation simple. Since commissioning, the Trans-Rupter IIs have provided excellent performance.

Their non-tracking composite-polymer silicone insulation has provided superior dielectric performance in the dusty mesa environment. And Trans-Rupter II’s 31.5-kA fault-interrupting rating is more than sufficient to handle future increases in available fault current . . . a possibility if generating capacity at the wind facility ever increases.

The generation company installed Trans-Rupter II at several other facilities to provide circuit breaker back-up protection. And the company is considering Trans-Rupter II as an alternative to substation circuit breakers for future wind-generation substation installations.