CPFL Paulista — a subsidiary of CPFL Energia, one of the largest electric utilities in Brazil — uses circuit breakers to protect the transformers in its 90 distribution substations.
The bus arrangement in the substations doesn’t allow the use of local bypass or transfer-tie schemes. So when a breaker needs maintenance or repair, the utility has two choices: either transfer protection of the load to an upstream substation or bypass the substation with the utility’s one and only mobile substation.
Transferring protection to an upstream substation is not desirable because it opens up more of the system to damage from fault currents. But bringing in the mobile substation presents a variety of problems. It requires special shipping permits and, in some areas, an escort car. With 90 substations requiring periodic maintenance, fast response can’t be assured. Further, commissioning the mobile substation requires that the load be dropped during the changeover. And, importantly, using the mobile substation for routine maintenance means that it it’s available for emergencies.
Procuring additional mobile substations was not feasible . . . they’re much too expensive. The maintenance engineering division of CPFL Paulista contacted S&C Electric Co. for a viable solution.
At first, S&C’s protection experts considered Type SMD-1A power fuses, mounted on a mobile base. But after further analysis, S&C recommended the Trans-Rupter II Transformer Protector. Trans-Rupter II provides a number of advantages. It works with the existing protective relays at a distribution substation, thus avoiding the need to properly coordinate power fuses. Trans-Rupter II also offers a higher 31.5-kA fault interrupting rating.
An inexpensive mobile-base Trans-Rupter II Transformer Protector was subsequently developed, featuring “quick-connect” conduit for easy assembly and disassembly. CPFL Paulista supplied a disconnect switch for use in series with the Trans-Rupter II.
The new, maintenance-free “mobile Trans-Rupter II” significantly reduces the cost of taking a circuit breaker off line for maintenance or repair. No outage is required . . . just rerouting of connections from the protective relays. And no special licensing is required for the truck and no escort car is needed, also providing significant cost savings.
The mobile Trans-Rupter II allows CPFL Paulista to reserve its mobile substation for emergency situations. CPFL Paulista is now considering specifying Trans-Rupter II for new substations and as a replacement for some of its aging circuit breakers.