Our turbine has a permanent magnet synchronous generator and full converter system (rectifier diods for rectification and IGBTs for chopping dc link voltage and as inverters) which means its generator doesnt need excitation current to start. Then why does it draw reactive power whenever turbine is in stop mode due to no wind or if it is manually stopped? What is purpose of this reactive power? I have been searching for this for over a month now but could not find any answer.

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    \$\begingroup\$ How much power? Just enough to keep it in a ready state or 75% of rated output? \$\endgroup\$ – Solar Mike Jul 11 '18 at 21:29
  • \$\begingroup\$ With zero back EMF current is limited by series DCR but current rises dI/dt = V / L and that leaves Remanence which can result in saturation. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 11 '18 at 21:55
  • \$\begingroup\$ @SolarMike its value is very low around 1kw or low. But it exists continuosly. As Mr Charles Cowie has already suggested it comes from capacitors in converter syatems but i still have one more confusion which is," the charge on these capacitors come from grid power and are these being charged continuosly during this time"? \$\endgroup\$ – Jason Jul 12 '18 at 5:12
  • \$\begingroup\$ I would not class 1kW as low... \$\endgroup\$ – Solar Mike Jul 12 '18 at 5:15
  • \$\begingroup\$ @solar mike its sometimes even higher. I have asked my supervisors about it as to why and from where does it come but they dont answer me clearly they sort of ignore it \$\endgroup\$ – Jason Jul 12 '18 at 6:09

The converter system should have provisions to provide reactive volt-amperes to inductive loads supplied by the generator. If the converter remains connected to an active grid when the generator is shut down, it may continue to supply reactive VA to those loads. Capacitors in the converter would be supplying VA to inductive loads, not drawing reactive power from the grid.

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  • \$\begingroup\$ So that means these capacitors are being charged by grid power when turbines are in stop mode and then these capacitors delivers reactive power to inductive loads? Because this power has to come from somewhere and it is continuous \$\endgroup\$ – Jason Jul 12 '18 at 5:07
  • \$\begingroup\$ @Jason My understanding is that a grid tie inverter is operated by grid power and stands ready to receive power from a DC source and transfer that power to the grid. It stands ready to exchange a certain level of reactive power with the grid whenever is is operating regardless of the level of real power received. Sources other than wound-field synchronous generators do not have reactive power capability except when provided by a grid-tie inverter or a conventional power-factor compensation capacitor bank. \$\endgroup\$ – Charles Cowie Jul 12 '18 at 12:35

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