Definition of RMU
RMU stands for Ring Main Unit.
It is a typical piece of switchgear in distribution systems that are composed of:
- Switches in series with fuses
- Switches for switching power cable rings and;
for the safeguard of distribution transformers.
RMU has three switches.
These are utilized for two inputs along with electrical or mechanical interlock and one outgoing to the load.
Either one input with 2 outgoings.
Ring main unit is utilized for redundancy feeder’s purpose.
It is employed in a secondary distribution system.
Basically, it is used for an uninterrupted power supply.
The metal enclosed unit links to the transformer either via:
- cables and typically installed indoors or
- bus throat of identical dimensions
Ring main cables enter and leave the cabinet.
This kind of switchgear is utilized for MV power distribution from 7,200V to at least 3,6000V.
RMU was introduced in the UK and is now widely utilized by other nations.
Throughout the North American distribution practice, the equivalent of RMU is created into a pad-mounted transformer.
This incorporates transformer and switches into a single cabinet.
The Function of RMU
The metal surrounded unit links to the transformer either over a bus throat of standardized dimensions.
It could also link through cables.
Normally, it is installed outdoors.
The main ring cables enter and leave the cabinet.
This kind of switchgear is utilized for medium-voltage distribution, from 7200 to at least 36,000 volts.
Advantages of RMU
As you can see:
RMU is an innovative solution, which makes it simpler to handle the different challenges of electrical distribution.
It’s a complete solution.
It’s simple to install, safe and maintenance-free.
It helps the utilities enhance reliability.
It also lowers operational expenses.
Below are some of the amazing benefits of using a ring main unit to all your applications:
- Simple to integrate
If you fit this equipment to an intelligent electrical device, you will notice that it’s simple to integrate.
- Offers efficiency
Have you ever seen modern RMU?
Its latest technology and compact design offer efficiency, reliability, connectivity, and safety.
- Saves time
As mentioned earlier, a ring main unit is easy to install.
Therefore, it enables you to save time and saving costs on installation and commissions.
Furthermore,
They are independent of climate as well.
They are resistant to any environmental conditions.
The maintenance and operation expenses of RMUs are comparatively low too.
- Loaded with features
RMU is an SF6 insulated compact switchgear.
It is geared along with a vacuum circuit breaker and an SF6 switch disconnector.
Ultimately, the compact design of the equipment needs less space to set up and operate.
Isn’t it amazing?
Diagram of RMU
Below is a simplified schematic diagram of a ring main unit.
Different Types of RMU
Ring main unit is categorized into three different types.
They can be characterized by their type:
- Gas
- Oil
- Insulated
The switch utilized to isolate the transformer could be a fusible switch.
It might also be a circuit breaking that utilizes:
- gas-insulated interrupters or;
- vacuum interrupters
The unit might also have protective relays to run the circuit breaker in case of a fault.