What Is Parallel Operation Of D.C. Generators And Its Conditions

  • What Is Parallel Operation Of D.C. Generators

Parallel Operation Of D.C. Generators:— It is necessary for most power stations, To supply power from several small units (generators) rather than from a single large unit so that the number of the working generator at any time can be varied according to the magnitude of the load on the power station. this helps the machines loaded up to their rated capacity and increases the efficiency of operation.
What Is Parallel Operation Of D.C. Generators And Its Conditions

⇒ The other advantage of several small units over a single large unit is—
(1) The small cost of the standby unit.

(2) Increased reliability.

(3) More convenient and economical repairing.

(4) The possibility of installation of an additional unit.

When required with the growth of the Load.
⇒ There are two ways in which the D.C. generators can be connected to the load. i.e.
› in series.

› in parallel.

when several generators are connected in series, all the units deliver the same current and load on any unit is proportional to the terminal voltage. the letter arrangement i.e. parallel connection of generators is almost universally adopted, in which all the generators work at the same voltage and load on any unit is proportional to the current delivered by it. it is desirable that the generators operating in parallel should have the same voltage regulation, so as to share the total load is proportional to their respective rated capacity. to take the generator running in parallel with another out of service, its main switch should never be opened suddenly when it is sharing load, why because if it is done so it will cause violent sparking at the switch contacts and also whole of the load will be transferred to another machine causing a sudden fall in terminal voltage.

Shunt wound generator due to their drooping characteristic is best suited for parallel operation. In practice, When the load on the generator increases, Speed tends to decreases and will do so by an amount sufficient to cause the Governor gear to operate, Increasing the engine power and torque to balance the retarding effect of the increased load. If any change occurs in the load of the system, Each unit must share some of the increased or decreased load.
Parallel operation of D.C. series generator is inherently unstable. D.C. series generator is not usually employed for the supply of power. But D.C. series motor is frequently arranged to operate as D.C. series generator during electric braking.
What Is Parallel Operation Of D.C. Generators And Its Conditions

For the satisfactory parallel operation of D.C. series generators, It is necessary to connect the armature of the two machines through a heavy copper bar, Called the equalizing bar, or by cross-connecting their field windings.
The compound wound D.C. generator is paralleled to the bus-bar in the same way as D.C. shunt wound generators. Load transfer or disconnecting one machine from the line may also be accomplished in the same way. For satisfactory parallel operation it is necessary that the resistance of the equalizing bar is very low in comparison to that of series field winding and it is desirable that all the compound D.C. generators operating in parallel have identical external characteristics, So as to share the total load is proportional to the ratings, as explained in case of shunt wound generators.

when added capacity is required, The new unit can be simply paralleled with the old units to increase the plant capacity. During generators are being operated in parallel, the routine or emergency operations can be performed by isolating the affected generator while the load is being supplied by other units. This leads to both safety and economy.
  • Conditions for paralleling of D.C. Generators:

› Polarity must be the same.
› Output voltage must be the same.

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