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Global warming caused by such gases as CO is a subject of great concern. Automobile emissions are an especially great problem in this respect. Therefore, hybrid cars are being widely developed and used. Because hybrid cars use electric power and gasoline, their emissions of CO are reduced. The electric motor of a hybrid car is driven by a battery, which has large capacity. Therefore, relays must interrupt a high DC current on switching between the electric motor and the gasoline engine, and hydrogen gas-filled relays are used for the purpose. In interruption tests in which we investigated the basic characteristics of hydrogen gas, the DC current did not reach a current-zero point. Thus, the current must be coerced to zero by using a high arc voltage. The loss coefficient and arc voltages of hydrogen are high, and we therefore performed interruption tests using a high arc voltage. Interruption tests and dielectric breakdowns test of air, pure hydrogen, and a hydrogen-nitrogen mixture indicated that an 80%-20% H-N mixture is the most effective. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(2): 9-17, 2011; Published online in Wiley Online Library (). DOI 10.1002/eej.21042 [ABSTRACT FROM AUTHOR]

Many alternative energy power generation systems create dc electricity. Also, many devices consume dc converted from ac. Therefore, it may be possible to reduce conversion losses and CO[sub2] emissions by adopting dc distribution. We assume that superconducting cables will be used for dc distribution because their electrical resistance is almost zero. However, if a superconducting cable is adopted, it is of great concern that if an excessive current flows because of, for instance, a short circuit, then there is a possibility that this current cannot be interrupted by a circuit breaker alone. We propose that the fault current be limited by a superconducting fault-current limiter (SFCL) and that this limited current is then interrupted by a dc circuit breaker. In this paper, we have separately investigated the SFCL and dc breaker and their use in combination. [ABSTRACT FROM AUTHOR]