How Does Cross-Current Compensation in Parallel Generators Work?

This a simplistic explanation but it may help.

http://www.patentgenius.com/patent/6218813.html

Thanks Eagle !

This is a very valuable piece of information you had there !

Exactly what i needed !

Plenty of thanks to the other members who have helped me with this question.

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Newbie Enginner

Reactive current compensation circuitry ensures that two or more generators operating in parallel will carry their proportionate share of reactive (kVAR) load.

Reactive current is current that circulates between paralleled generators. The result of kVAR's is energy expended in the form of heat in the load conductors between the generators. If kVAR's are not shared, the generator will reach current and temperature ratings before actually carrying full amperage at the rated load.

A current transformer allows a signal from the generator load current to be applied across an adjustable potentiometer. A portion of this signal is applied to the sensing circuit and causes a voltage droop condition.

When a single generator is used, a shorting unit parallel switch can be used to omit the signal. In parallel operation, kVAR load sharing is achieved by applying the same signal through the potentiometers to the sensing circuits of all the regulators.

An alternative method of kVAR load sharing is the no-droop method. In this mode, the signal from all parallel generators passes through all current transformers and potentiometers in a series loop.

Crosscurrent compensation can be used only if the regulators on all the generators operating on a common bus are interconnected into the crosscurrent loop. Generators of different kill ratings may be operated with crosscurrent operation if parallel transformers are selected that give approximately the same secondary current at each generators rated load.

On parallel crosscurrent compensation applications consisting of more than two generators, the unit-parallel switch (also referred to as the isoch-droop or CCCR in-out) should be placed in the unit position on any generating system that is not on the load bus or a voltage droop will be introduced into the system. An unloaded generator parallel transformer does not supply a compensating signal, but allows a voltage droop to occur across it. This drop also causes the voltage of the oncoming generator to fluctuate prior to paralleling. This fluctuation can be eliminated by utilising an auxiliary contact on the main generator circuit breaker. The auxiliary contact should be connected across the parallel transformer secondary and be closed when the main generator circuit is open. The contact opens when the main generator circuit breaker closes. When this auxiliary contact is used, the Unit-Parallel switch in the paralleling modules is left in the "parallel" position.

hmmmm...its good to understand sir... but as u told that the signal from the potentimeter in form of voltage droop condition is taken....now my que is this....as we get voltage signal from potentiometer and then superimpose it or add it to the signal coming from PT from any one phase and then we apply the three phase signal to the three phase bridge rectifire from where it goes to AVR where after manipulation AVR generate signals or pulses to the field current increement or decriment to share kVARs and it is end of story.....now come to another point as i said the Voltage droop signal is added to the one of the phase PT signal then HOW ADDED SIGNALS TELL OR BEHAVE TO TELL THE AVR THAT IT HAS TO ORIGNATE THE SIGNAL TO INCREASE OR DECREASE kVARs SHARING...???? . . In simple words how from the output signal of droop voltage we can or AVR can analyse that kVARs sharing should b increase or decrease...?????

Extraordinary response... THANKS!

If you parallel two generators and the voltage of one is set higher than the other, reactive current (90 degrees out of phase with voltage) will flow between the two, serving no other purpose than heating up the windings. The current transformer detects this current and adjusts the voltage regulators to minimize this current.