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Distribution networks are normally formed by interconnecting a number of ring shaped grids. Distribution transformers are then connected to the system by T-offs. Instead of specifying and selecting individual components required for a T-off, the required components are frequently available in an integrated package known as a ring-main unit (RMU).
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Ring-main units normally consist of switches on both sides of the T-off, one to open the ring and another at the connection to the distribution transformer using one of the following:- Switch and a fuse separately
- Switch-fuse combination
- Circuit breaker
The earthing switch of the transformer is also usually integrated into the RMU. Each component must first be certified to the IEC Standard applicable to that component.
To insure the safety of the overall design, internal arcing tests according to IEC 62271-200 should be performed.
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Fused RMU
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[download] Brochure KEMA High-Power and High-Voltage Laboratories (.pdf 1.493 kb)
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