KW & KVAr Load Sharing on Alternator

1. Increase in kVAR load alone- will increase the lossess and consequently will increase the kW. However, this might also result in reduced load bus voltage and consequent decrease in both kVAR and kW. This is because the load power is likely to be non-linear and depends also on load characteristics with respect to load bus voltage. Examples are motor loads and impedance loads which have different load characteristics with respect to applied bus voltage.

2. PF cannot be maintained with constant voltage at the loads. Variation of kW varies PF depending on the kW and kVAR components of the load. As mentioned in point 1, kW and kVAR components are also functions of the load bus voltage and the phenomenon needs understanding of the load power with respect to load-bus voltage also.

Sir,

Thank you for your reply. I am happy that you are from bangalore, because I am also in Bangalore.I have a doubt in your reply,"Increase in kVAR load alone- will increase the lossess and consequently will increase the kw" we know Kw = apparent power - reactive power, so if reactive power KVAr increases the KW should decrease but how you are saying that the KW is increasing?

We know as Kvar(inductive load) increases pf decreases and current increases so to maintain constant power factor we are decreasing voltage as KVAr(indcutive load) load increases and the pf is maintained as 0.8-1. But if Kw changes and then pf changes, how it can be maintained between 0.8-1.

Assume that KWL represents the load KW, KVARL represents load KVAR.

if KVARL - load kVAR is increased, this has to come from the generator via the transmission, distribution system. This extra flow in transmission and distribution system will result in additional KW losses in the T&D. Thus, even though the load KW is same, generator KW increases because of the increase in load KVAR. This is one scenario.

In the second scenario, things can happen as follows.

Assume that load KVAR is increased. This is supplied from the same generator using the same T&D. However, this increase in the load KVAR decreases the load bus voltage. If the load is sensitive to bus voltage and the effective load decreases[both KW and KVAR may decrease], we have reduced KW as well as reduced KVAR at load due to reduction in load bus voltage. In this case the generator output power can reduce or still increase due to increased T&D losses during low voltage conditions.

I hope I am clear.

What I am highlighting is the non-linear nature of the power system voltage and load relation. Power Flow study solves these non-linear equations to get the voltage solution.

If u increase KW load on KVAR then pf increases viceversa. u maintain pf constant put capacitor with auto correction parallel with the load.

increase in kvar on kw produces losses affect alternators in parallel. so maitaining voltage at rated value by more excitation which inturn increasing rotor temperature.

increase in kw on kvar is done by increasing prime mover torque on the alternators if increase one alternator only then producing syncronising current and syn.torque make one as alternator and the other as motor.