8 Schemes To Supply MV Switchboard

MV switchboard supply solutions //

Medium voltage networks are made up of switchboards and the connections feeding them. Let’s take a look at the eight different supply modes of these medium voltage switchboards. We’ll start with the main power supply solutions of an MV switchboard, regardless of its place in the network.

NOTE // The number of sources and the complexity of the switchboard differ according to the level of power supply security required.

8 most common power supply modes //

1. 1 busbar, 1 supply source
2. 1 busbar with no coupler, 2 supply sources
3. 2 bus sections with coupler, 2 supply sources
4. 1 busbar with no coupler, 3 supply sources
5. 3 bus sections with couplers, 3 supply sources
6. 2 busbars, 2 connections per outgoing feeder, 2 supply sources
7. 2 interconnected double busbars
8. “Duplex” distribution system

I – 1 busbar, 1 supply source

Operation // If the supply source is lost, the busbar is put out of service until the fault is repaired.

Go back to Power Supply Modes ↑

II – 1 busbar with no coupler, 2 supply sources

Operation // One source feeds the busbar, the other provides a back-up supply. If a fault occurs on the busbar (or maintenance is carried out on it), the outgoing feeders are no longer fed.

Go back to Power Supply Modes ↑

III – 2 bus sections with coupler, 2 supply sources

Operation // Each source feeds one bus section. The bus coupler circuit-breaker can be kept closed or open. If one source is lost, the coupler circuit-breaker is closed and the other source feeds both bus sections.

If a fault occurs in a bus section (or maintenance is carried out on it), only one part of the outgoing feeders is no longer fed.

Go back to Power Supply Modes ↑

IV – 1 busbar with no coupler, 3 supply sources

Operation // The power supply is normally provided by two parallel-connected sources. If one of these two sources is lost, the third provides a back-up supply. If a fault occurs on the busbar (or maintenance is carried out on it), the outgoing feeders are no longer fed.

Go back to Power Supply Modes ↑

V – 3 bus sections with couplers, 3 supply sources

Operation // Both bus coupler circuit-breakers can be kept open or closed. Each supply source feeds its own bus section. If one source is lost, the associated coupler circuit-breaker is closed, one source feeds two bus sections and the other feeds one bus section.

If a fault occurs on one bus section (or if maintenance is carried out on it), only one part of the outgoing feeders is no longer fed.

Go back to Power Supply Modes ↑

VI – 2 busbars, 2 connections per outgoing feeder, 2 supply sources

Operation // Each outgoing feeder can be fed by one or other of the busbars, depending on the state of the isolators which are associated with it, and only one isolator per outgoing feeder must be closed.

If one source is lost, the other source takes over the total power supply. If a fault occurs on a busbar (or maintenance is carried out on it), the coupler circuit-breaker is opened and the other busbar feeds all the outgoing feeders.

Go back to Power Supply Modes ↑

VII – 2 interconnected double busbars

Operation // This arrangement is almost identical to the previous one (two busbars, two connections per feeder, two supply sources). The splitting up of the double busbars into two switchboards with coupler (via CB1 and CB2) provides greater operating flexibility.

Each busbar feeds a smaller number of feeders during normal operation.

Go back to Power Supply Modes ↑

VIII – “Duplex” distribution system

Operation // Each source can feed one or other of the busbars via its two drawout circuit-breaker cubicles. For economic reasons, there is only one circuit-breaker for the two drawout cubicles, which are installed alongside one another. It is thus easy to move the circuit-breaker from one cubicle to the other.

Thus, if source 1 is to feed busbar BB2, the circuit-breaker is moved into the other cubicle associated with source 1.

The same principle is used for the outgoing feeders. Thus, there are two drawout cubicles and only one circuit-breaker associated with each outgoing feeder. Each outgoing feeder can be fed by one or other of the busbars depending on where the circuit-breaker is positioned.

If one source is lost, the other source provides the total power supply. If maintenance is carried out on one of the busbars, the coupler circuit-breaker is opened and each circuit-breaker is placed on the busbar in service, so that all the outgoing feeders are fed. If a fault occurs on a busbar, it is put out of service.

Go back to Power Supply Modes ↑

Reference // Protection of Electrical Network – Christophe Prévé