Need of Parallel Operation of Alternators and Condition for Satisfactory Parallel Operation.
Q. Why the alternators are connected in parallel ? What are the conditions to be fulfilled successful parallel operation of alternators?
Need of parallel operation of alternators and condition for satisfactory parallel operation :
- Load growth : Load demand is now a days increasing due to increasing use of electric power Existing system may not be sufficient to meet with the increased demand and hence addition units of alternators to be added to satisfy the increased demand.
- Continuity of service : Instead of only one unit supplying the power many smaller units the run on the system so that if any of the unit fails the other can meet the demand and continuity be maintained.
- Repairs : The units are some times to be taken off from the system for repair works In its place other unit is to be paralleled to the circuit so that faulty unit can be taken off for repair work.
- Maintenance : As per the maintenance schedule the units are to be switched off and taken off electrically so the other unit shall continue the supply and one unit may be paralled to the system.
- Efficiency : The machine works to its maximum efficiency at nearly to its full load capacity. If the demand on the system decreases, then that unit may operate at a lower load conditions lower frequency. This is not economical. Hence bigger unit is to be shut off and smaller unit may be introduced so that smaller unit can work to its full capacity at higher efficiency.
Conditions for satisfactory parallel operation of alternators :
- A stationary Alternator must not be connected to live bus-bars as its E = 0 and hence short circuit may occur.
- The terminal voltage of the incoming Alternator must be same as the bus – bar voltage (R.M.S. Values.)
- The generated frequency of the incoming Alternator must be same as the bus-bar frequency 4 .
- The phase sequence of the incoming alternator (three phase alternator) must be same as the phase sequence of bus bar.
- The polarity of the incoming alternator terminals must be same as the bus-bar terminals.
