January 3, 2005
First Trans-Rupter II® Installation in Brazil.
Brazil’s ongoing national initiative, “Luz no campo” (“Light in the countryside”), promises to upgrade the electrical infrastructure of rural areas, providing economic stimulus and improved quality of life for residents. This program requires construction of many new substations.
With limited monetary resources available, one regional electrical utility, Companhia Energética de Minas Gerais (CEMIG), sought ways to save on the purchased and installed costs of equipment. They turned to S&C Brasil for suggestions. S&C Brasil offered Trans-Rupter II Transformer Protector as an alternative to the costly circuit breakers CEMIG typically uses for transformer protection. The utility was attracted to Trans-Rupter II’s initial cost savings, plus its no-maintenance operating mechanism. They planned a trial Trans-Rupter II installation at a new substation located close to Montes Claros, one of the most economically underdeveloped areas of Minas Gerais, where low-cost power is crucial. But there were a few hurdles to overcome . . .
Meeting specifications
The utility’s specifications for transformer protective devices are based on circuit breakers. Trans-Rupter II offers many functions of a breaker but has been tailored specifically for transformer protection. It thus doesn’t have—or need—the expensive features of a general-purpose breaker. CEMIG requested a number of modifications to the low-voltage enclosure to help Trans-Rupter II meet the specifications, including:
- A trip-coil monitoring circuit.
- Additional auxiliary contacts, for use with CEMIG’s SCADA system.
- An electrical operation counter. The peak value of every fault current interrupted would be stored in the coordinating digital protection relay.
- Additional remote gas-density indicator contacts.
- A loss-of-dc-voltage relay.
- A pole-unit monitoring circuit. This circuit prevents the transformer from being energized until all three Trans-Rupter II pole-units have been closed and charged.
- A separate dc control-power protector.
- A space heater, convenience light, and power outlet.
Passing the test
Besides meeting their specifications for transformer protection devices, CEMIG required that Trans-Rupter II pass a series of qualifying tests, including:
- A temperature-rise test, utilizing thermocouples installed inside specially designed pole-units.
- A 5000-operation mechanical test.
- An ultraviolet radiation test, to verify that the polymer-silicone insulation would hold up under the extreme equatorial sunshine of the Brazilian highlands.
- A radio-influence voltage test.
- A lightning-impulse test.
- A pole-unit trip simultaneity test.
S&C performed the first three tests at the Nicolas J. Conrad Laboratory at its U.S. headquarters in Chicago, Illinois, with representatives of CEMIG in attendance. The last three tests were performed in Brazil. Trans-Rupter II passed CEMIG’s test requirements with flying colors.
The results
CEMIG placed a trial order for a specially modified 138-kV Trans-Rupter II Model EX as discussed above, with optional motor operators for charging and closing the pole-units.
Installation took just one day, with another day for completion of the control-circuit wiring connections. Technicians from S&C Brasil supervised the installation and provided training to CEMIG’s substation engineering group. The Trans-Rupter II protects a 10-MVA, 138- to 13.8-kV transformer serving rural customers and small farming communities.
CEMIG is well pleased with the performance of their trial Trans-Rupter II. They have seven other substations planned for the area and are considering using Trans-Rupter II for these installations as well. CEMIG appreciated how quickly S&C Headquarters in Chicago and S&C Brasil coordinated testing and engineering services to accommodate the specification requirements, and satisfactorily meet all testing and product delivery dates.