Bus-bar is one of the vital elements in electric power stations and substations. The term bus is derived from the word omnibus which means collector of things. Thus the electrical bus bar is the collector of electrical energy at one location. Bus bar are convenient means of connecting switches and other equipment’s into various arrangements.
Bus-bar used in substations are usually bare rectangular cross-section bars. Aluminum is used for the construction of bus bar as it has several advantages over copper such as higher conductivity on weight basis, lower cost for equal current capacity, excellent corrosion resistance. For proper reliable electrical connections aluminum buses are coated with silver. The most common sizes of bus-bars are 40 *4mm;40*5mm;50*5mm;50*6mm;60*8mm;80*8mm;100*10mm.
Whenever the fault occurs in bus bar, considerable damage and disruption of supply will occur and system stability is adversely affected. Hence, the proper protection of bus bar is needed.
Types of Bus-bar
There are several types of bus-bar arrangements. The choice for the particular arrangements depends upon system voltage, position of substation in the system, reliability of supply, flexibility and cost. The factors for the selection of the bus bar arrangements are:
- Maintenance possibility without interruption of the power supply.
- Provision of extension with the load growth.
- In case of the outage other alternative arrangements must be possible.
- Load and local conditions.
The various bus bar arrangements are as follows:
- Single Bus-bar arrangement
- Single Bus-bar arrangement with bus sectionalization
- Main and transfer Bus Arrangement
- Double Bus Double Breaker Arrangement
- Sectionalized Double Bus Arrangement
- One –and –a Half Breaker Arrangement
- Ring Main Arrangement
- Mesh Arrangement
Single Bus-bar arrangement
- This is the simplest arrangement consisting of a single set of bus bar for the full length of switch board and to the set of generator, transformers and feeder.
- The main drawback of this system is that in case of fault in bus bar whole of the system is collapsed and all the healthy feeders are disconnected.
- It is employed for switchboards, small and medium size substation, small power station and DC station.
2. Single Bus-bar arrangement with bus sectionalization
- This bus bar is sectionalized by a circuit breaker and isolating switches so that a fault on one part does not cause a complete shutdown.
- Sectionalization of bus bar is done in the large substations where the large units are installed.
- There are basically 2 or 3 number of section of bus-bar.
- In case of occurrence of fault on any section of the bus-bar the faulty section can be isolated without affecting the supply of other sections.
- One section can be completely shut down for maintenance and repairs without affecting the supply of other sections.
- Adding a current limiting reactor between the sections the fault level(MVA) can be reduced thereby the circuit breakers of lower capacity can be used.
Main and transfer Bus Arrangement
- This arrangement is done where the loads and continuity of supply are to be done.
- This provides additional flexibility, continuity of supply and allows periodic maintenance without total shutdown.
- It consists of two bus bar as main bus bar and transfer bus bar used as an auxiliary bus bar.
- The power from main bus can be totally transferred to auxiliary bus bar as needed through bus coupler, since there will be high degree of reliability.
- While transferring the load to reserve bus
- Close the bus coupler.
- Close isolators on the reserve bus.
- Open isolators on the main bus.
- Cost index for this type of arrangement is 1.6.
- Repair and maintenance can be carried out on the main bus without the interruption of the supply.
- The maintenance cost of substation is lowered.
Double Bus Double Breaker Arrangement
- Two circuit breaker are employed for each circuit.
- This type of arrangement doesn’t require any bus coupler.
- This type of arrangement can permit switch-over from one bus to other bus without interruption.
- Costly and maintenance cost is high.
- Provides maximum flexibility and reliability.
- In case of maintenance of a circuit breaker load can be shifted to other circuit breaker.
Sectionalized Double Bus Arrangement
- Duplicate bus-bars are used with the main bus-bar in sections connected through a bus coupler.
- Any section can be isolated for maintenance.
- Any section may be synchronized with any other through the auxiliary bus bar.
One –and –a Half Breaker Arrangement
- This arrangement is the improvement of Double bus double breaker arrangement and reduces in the number of circuit breaker.
- It needs three circuit breaker for two circuits.
- This arrangement is used in important large stations where power handled per circuit is large.
- Provides a high security against loss of supply.
- The main drawbacks of this type of system is complications in relaying system because at the time of fault two breakers are to be opened.
- The maintenance cost is higher.
Ring Main Arrangement
- Higher reliability.
- Less number of circuit breaker is needed.
- Difficulties in addition of any new circuit in the ring.
- Possibilities of overloading of circuit in opening of any of section of breaker.
- Necessity of supplying demand potential to relay separately to each of the circuit.
- This arrangement provides greater flexibility as each feeder is supplied by two path, so the failure of the section doesn’t cause any interruption of supply.
- Economical use of circuit breaker in the substation.
- Circuit breaker are installed in the mesh formed by the buses.
- When the fault occurs in any section two circuit breakers have to open resulting in opening of the mesh.
- Provides the security against bus-bar faults.
- Lacks switching facility.
- Needs less number of circuit breakers than required by one-and –a –half breaker arrangement.
- Used in substations having large number of circuits.
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