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	Subject - Leading power factor jackleung I heard some devices got leading power factor. e.g. some UPS or converters. However, in power generation plant, it usually generates lagging power factor power and try to maintain it around 0.85. I knew it is because the inductive loads of the power system. So, my questions are: 1. Are there any problems to operate power generation in leading power factor or very close to unity power factor? Will the generator become unstable? 2. Any kind of power generations are operated in leading power factor? e.g. Hydro-power plant? JimmyDee Not an area of total expertise with me but it is my understanding that the generator will generate with 100% or unity PF. The inductive loads such as under loaded substations will give a perceived lower PF. Yes 85% is the goal and can be improved only by adding large capacitors or synchronous motors on the load some where. The problem with a low PF is that the generator still has to produce the KVA and the customer only pays on the KWatt usage so the power company will charge for a low PF. Since I believe that all generators generate at unity, I don't think they will become unstable. Generators are controlled by controlling the DC current to the rotor. (exciter current) To my knowledge, this is done to increase or decrease the total output of the generator and has nothing to do with PF. Question 2, I don't think the generator will care what the power source is that turns it, so no. Since I'm not 100% sure of what I just said (99.9%) I would invite response from anyone that is 100% sure. Jim JimmyDee After a brief study on this subject, I found that I was correct that a generator does generate at unity PF. There is a PF rating on the generator and that is there so the operator can tell at what the load PF the generator will tolerate. When the load PF drops below the generators design, usually 80%, it tends to cause the armature to demagnetize and to be able to maintain output voltage, a large increase in DC exciter current is necessary. This will cause an excessive increase in the field (armature) temperature. (Not Good) I am going to assume that a leading PF would be harmfull as well but don't know. Jim Chris Clement A source (generator) can have pf as well. It is all a balancing act from end to end to keep the circuits "tuned" to 60Hz, just like a radio. Most big industrial loads, as well as distribution equipment, are inductive so capacitor banks are used along the way so everything is made resonant at the design frequency. Pf hurts us by forcing us to carry more current back and forth than is needed to do the work. Power is lost in the wires as heat. jackleung I think avoiding voltage drop due to the reactive power is reason to have good power factor as well. By the way, as I know, reactive power makes no work done on the load side because it just moves back and forth on the load. Thus, there is no work done, no power loss...etc. However, are there any power losses in the transmission induced by reactive power? JimmyDee I would think the only losses will be from the additional load caused by the induction. Jim robertw19026 To the best of my memory, unity represents a concident overlay of current and voltage waveforms. Inductive reactance induces a delay in the transmission of the current in relation to the voltage wave, causing a lagging non-unity power factor. A capacitive reactance induces a leading power factor. Both interfere with use of power because true power is reflective of momentary current X momentary voltage. The difference between measured current x measured voltage and the momentary value is the "lost" power. The reason capacitors are added is to attempt to draw the retarded inductive load current wave into unity with the voltage wave.The trick is balancing their use so you don't create a leading wave imbalance at times when the motors or ballasts are out of circuit. JimmyDee Yes, you are correct as far as I know. Jim