Generator synchronising

What do you mean by KVAR?

you can use PLC or capacitor banks

KVAR is adjusted using the generator excitation. Lowering the excitation of a generator causes it to reduce the KVAR on that generator.

Raising the excitation increases the voltage output of the generator, thus causing the generator to provide more KVAR, i.e., circulating current. The excitation on the other generators connected must be reduced to keep system voltage constant.

The power output of the generator is determined by the throttle setting. To increase KW on a generator, open the throttle and throttle back on the other connected generators to keep the frequency constant.

Answer no.3 is perfect and no.2 is not well elaborated regarding the use of a plc.

A perfect solution will be to use a digital excitation system DECS 15, 200 or 300 from basler electric which has a mode selector which can be controlled with the use of a plc for different applications to enable your set of generators to be automatically set as desired.

Mode 1 = voltage control, meaning you running only one machine and you not connected to the utility.

Mode 2 = voltage droop control meaning running two or more machine in parallel and still not connected to the utility. In this mode what the droop does is to ensure that both or all machines are running as generators and not motors(meaning drawing power instead of supplying) contributes equally to the the load at all times.

Mode 3 = Power factor/Var control means you running one or two machines paralleled to the utility, then from here what's being explained in answer no.3 applies.

excitation plays a very critical part on generators, and at the same time over or under excitation can also destroy your machine.

My best advice is to have a good Dec's relay to monitor your excitation and volt/Hz, rump up and etc.

Before paralleling get the voltage the same on both sets by the voltage adjust rheostat on the panel door keeping in mind you probably have 3% meters (0.5% switchboard grade should be utilised if you don't have them now). Then synchronise and adjust the voltage until the amps are as low as you can get on each machine back and forth and still maintain the bus voltage you want.

Summary:

* VAR (or kVAR or amps) is voltage sensitive

* Watts or kW or MW is speed sensitive (fuel and governor adjust).

You can upgrade to automatic VAR sharing with a Basler or equal SSR or SR series regulator with a "Cross Current Compensation CT". This is old analog type and there are digital versions now. The current transformer goes on phase B and connects to its regulator in that cubical and the same for the other regulator. There is also some wonderful black boxes 'all in one' now such as Basler DGC 2020 and Woodward EasYGen. Very cool things now.

You adjust the output voltage to control the kVAR, in the older manual synchronisation systems this was done via a potentiometer on the control panel. you are trying to equalise the voltage so there is minimum recirculating current. If you are synchronising a gen.set with another gen.set (or the mains which is slightly different) one gen.set, if its voltage is higher, can end up driving the other alternator as if it were a motor. Once adjusted, if the load stays the same the system should be relatively stable. If there are changing loads; the power factor will change, also the AVR (Automatic Voltage Regulator) will try to adjust voltage (via the excitation circuit) and so the balance will be disrupted. manual systems have to be continually monitored as there is danger of burning out the alternator as they are not designed to be 'motored'.

Automatic systems will adjust the voltage of the to reduce the kVAR and are now very effective whether gen.set to gen.set (master & slave) or gen.set(s) to mains. With gen.set to mains the output will also have to be controlled as the gen.set sees the mains as an infinite load, so will go to overload strait away. the set is usually limited to only give 90 to 95% max output.

The answers are all very good, and did briefly touch on "damaging" if you take the voltage too far leading or lagging kVAR's, limit kVARS to 10% of generator amps to limit heating in the generator, you can get the generator "out of step" or out of synchroization or "slipping poles" all of which will cause severe mechanical stresses and damage to the generator and if it isn't doweled will actually cause a "rub" of the rotor and stator, which a friend once did by momentarily removing the excitiation and then reconnecting it. Safer to trip the breaker and let it shut down. Loss of excitiation on a synchronous generator causes all the kVAR's available to flow to the generator, a loss of excitiation relay is a good investment. Especially if you use a manual voltage regulator, which were used for eon's and there are some still in use, checked and adjusted once a day.

Envision a graph with the base being KW the vertical line is generator amps and a 45 degree line is generator voltage as I recall, using the unity power factor (0 kVAR's, all KW) equation I made these up for different voltages so I could check the panel meters at unity pwer factor to know volts and amps were wired correctly.

At unity power factor generator amps (winding heat) are minimum for the KW being prodcued.