A typical ring main unit, known as an RMU for short, is a medium voltage switchgear that is used in electrical power distribution systems، provide continuous power with the added ability to switch power sources in the event that a repair or emergency happens.
For large-scale PV plants connected to higher voltage levels, the plant will be divided into stations and equipped with medium-voltage (MV) components such as MV transformers. In such cases, the installation of RMU is essential to connect the plant electrically.
The function of the ring main unit (RMU) is to link the loop network. This helps to increase the stability of the power supply i.e. the loop function of the loop system or the load cut of the ring network.
What is Ring Main Unit (RMU) and its function in a solar project?
A standard piece of switchgear in distribution systems comprising of switches for switching power cable rings and of switches in series with fuses for the protection of distribution transformers.
RMU is having 2 or 3 numbers of switches (Circuit Breakers or Isolators or LBS), it is used for two inputs with mechanical or electrical interlock and one outgoing to the load. Either one input with two outgoings. RMU used for redundancy feeder’s purpose.
Ring main unit is used in a secondary distribution system. It is basically used for an uninterrupted power supply. Alongside, it also protects your secondary side transformer from the occasional transient currents. Depending on your applications and loading conditions you can use a switch fuse combination or a circuit breaker to protect the transformer. Ring main Units come in standard ratings of 11/22/33 kV, 630/1250 A, 21 KA/3 secs.
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