# What is role of Quad Ring Main Unit (QRM) in Substation?

1. Jan 28, 2014

### tipu_sultan

Below is the typical diagram of a Substation in which MIL and MIR are with TR-1 and TR-2 respectively. Where TR-1 and TR-2 are the transformers whose function is to step down the voltage.

I have also confusion about the flow(path) of the electricity with in substation.
The confusion is that either MV comes into switch gear or Transformer first. If the electricity comes first between them then please state reason?

In the diagram there are also two 18-way LV panels. Are these LV panels connect with transformer or switchgear?

I need a help and will be thankful to whom who draw a block diagram of the wiring connection of substation.

http://www.edaboard.com/attachments/99861d1387109892-ss.jpg

2. Jan 31, 2014

Sorry, I cannot see the diagram.May be you can revise the link.

3. Feb 1, 2014

### tipu_sultan

Diagram Attached

Dear now I have attached the diagram.

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• ###### SS.jpg
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4. Feb 1, 2014

In my opinion MIL and MIR are the main [medium voltage cables] risers-one Left and one Right.
According to switchgear dimensions there are three cells -one for incoming feeder and two for outgoing. The incoming feeder is routed from outside through a pipe and then under the floor. [The A-A cross section drawing could explain more.]
The outgoing feeders run under the floor up to 150 mm [PVC] pipe and through pipe up to the riser MIL or MIR and from here up to transformer 11 kV terminals.
The low voltage supply cables from each transformer up to the low voltage panel run under the floor.
If the riser MIL or MIR is starting from the ground floor the supply cable could be routed through one of them.

5. Feb 2, 2014

### tipu_sultan

According to you that the HV voltage from outside fed directly into the Switchgear, the two output of switchgear connected to the transformers at their respective points MIL & MIR. The transformers step down the voltage and send it to the respective LV panels and from LV panels output we get our desire voltage.

So I have a diagrams in which the substation have ratings of 11/0.4KV. The output of substation goes to the Feeder Pillar (FP) and Service Turret.
If the demand load is high then the building directly connect to FP but if demand load is low then the building is connect with ST which is in series with FP.

So my question is that How we supply the electricity to wiring if the wire used is 4Cx70mm2.
I am little confused in it. ( 4C means 4 core having three live, one neutral, and one earth).
I think if we take one live wire and other neutral wire than the output is 220V.

Can any one help me to build this concept?

6. Feb 2, 2014

If the meaning of MI=”Main Interrupter” this could be a one cell [CB] Ring Main Unit but could be also three cells and then the transformer are in “open loop” connection. Since the O.P.title it is “Quad” then it is possible the “11 kV Switchgear it is actually a four cells R.M.U. but the length is more then usual one[1.5 m instead of 2.5 m].However the schematic one line diagram could be as attached.
About the Low voltage. The four cores cable conveys the power from transformer to LV panel, I guess. The voltage between live-to-live will be 400 V and live-to-neutral 400/sqrt(3)=231 V[rated] [this is the new standard 380/220 V was the old one].
In free air at 30oC if the conductor is copper and the insulation is XLPE [90oC maximum permissible temperature] then –according to IEC 60364-5-52 for type E installation I=264 A. It is a small transformer S=SQRT(3)*0.4*264= 182 kVA.
However, according to dimensions-could be 2500 kVA dry-type transformer [3600 A!!!].

#### Attached Files:

• ###### Quad Ring Main Unit.jpg
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7. Feb 2, 2014

Sorry, it is not what I intended to send!.This one could the actual:

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8. Feb 3, 2014

### tipu_sultan

I built a block diagram just have a look.

Please have some look on the attached diagram and correct me if I am wRong.

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• ###### Combined Wiring Diagram.jpg
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9. Feb 3, 2014

1)The transformers- T1 and T2- are oil filled transformers and according to safety rules a trench under the transformer has to be provided in order to collect the spilled oil [mainly if the transformer would explode!].
2) The diagram shown in the sketch it is one possible, but in this case it is not connected to the ring main units, at all. The advantage of the RMU is its reduced dimensions-it is filled with SF6- gas with higher dielectric strength than the air –and one may employ three-or four cells usually in a supply loop –one may supply both transformers from one end or the other in case of one cable section damaged.
The medium voltage cable [11 kV]- I think it has to be 15/8.7 kV rated according to IEC 60502-2-minimum conductor cross sectional area it has to withstand the maximum short-circuit current in the time set to clear the fault- by protection.
Let's say Isc[rms]=30 kA, time 1 sec.Then the minimum copper conductor has to be:210 mm^2 [250 oC XLPE emergency].
According to IEC60502-2 Table B.2 – this cable permissible maximum current [ampacity] in single-way duct embedded in 1.5 K.m/w earth thermal resistance will be 400 A [shield grounded at one end only].
3) Low voltage cables have to be chosen according to the load. A single-core cable of 300 mm^2 in air at 30oC withstand- according to IEC 60364-5-52 for type F installation [Table A.52-12]: 547 A. But you need 5 parallel group of cables, so you have a derating factor [Tableau A.52-17 pos.5 k=0.8]=437.6 A. Then you need 5*4 single core cables laid on a ladder cable tray [300 mm^2 copper conductors XLPE insulated].

#### Attached Files:

• ###### Not RMU layout.jpg
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10. Jun 22, 2016

### highvoltpower

Quad ring main unit is used to connect two no of transformers at their high voltage side to the distribution systems.