Hydro Generator Synchronicing


Thread Starter

Wajira Priyankara

We have a hydro generator with a turbine, but do not have a fly wheel. When jets are open gradually generator speed up, As we need to synchronise this with national grid (50Hz) we connect a resistive load (50Kw) to the generator o/p through a contactor, contactor coil is energised only when generator voltage is build up gradually. But we experiance a sudden blast near the contactor terminals. What could be the reason for this, have any one tried something like this.

Responding to Wajira's Jun 28, 2:40pm, query:

The following observation is being made without knowing installation specifics nor hardware parameters> Also I have assumed that "sudden blast" means arcing.

One possible cause is contact "chattering" of the loading resistor relay. The relay's coil is responding to not only the generator's increasing voltage but it's increasing frequency as well. Thus, early during voltage and frequency buildup, the coil's impedance is low. The result is a high current to the relay coil. Essentially, the current is limited by only the coil's resistance. The high current causes the relay to "pull-in!" As the armature moves to close the relay, the coil's impedance increases. This causes a reduction of coil current and the relay will "drop-out!" This process repeats resulting in contact

The observation noted above can be proven by monitoring coil current via a scope, during generator runup.

Phil Corso, PE
(Boca Raton, FL)