How Do I Can Estimate Electricity Usage, Drive by GenSet?

Estimate or measure amps of all the loads you want to put on gen-set.

Multiply that with your required voltage

divide result by 1000. thats KVA Required,

http://en.wikipedia.org/wiki/Volt-amperes_reactive

Hello billy79,

This explains the difference between KVA and KVAr, or var it is simply the sign of reactive power.

Hope it helps.

AC electric power system. 1 VAr = 1 V·A.^[1]

Electric power (watts) is transmitted by the simultaneous product of electric voltage and current in a wire. If large amounts of current are present when there is less voltage, the wires, transformers and other power equipment are heated, but less power is transmitted by the equipment. Since equipment is designed to remain cool up to a certain amount of current, VArs waste some of the power unnecessarily as excess heat

Since AC power has a varying voltage, efficient power systems must therefore vary the current in synchrony with the voltage. VArs measure unsynchronized "leading" or "lagging" currents. These currents are usually caused by the side effects of powering equipment that behaves like coils (e.g. motors) or capacitors (e.g. arc welders).

Technically, VArs are the product of the rms voltage and current, or the apparent power, multiplied by the sine of the phase angle between the voltage and the current. Or in mathematical terms, the reactive power Q, (measured in units of volt-amperes reactive or VAr), is given by

,

where φ is the phase angle between the voltage and current.

The term VAR was introduced in 1930 by the IEC in Stockholm, which has adopted it as the unit for reactive power (name: var, symbol: var [and not VAr], conversion factor: 1 var = 1 V·A^[1])

Note 1: The unit VAr represents the power consumed by a reactive load, i.e. when there is a phase difference between the applied voltage and the current.

Note 2: Only effective power, i.e. the actual power delivered to or consumed by the load, is expressed in watts. Imaginary power is properly expressed in volt-amperes reactive.

Note 3: To maximize transmission efficiency, VArs must be minimized by balancing capacitive and inductive loads, or by the addition of an appropriate (off-setting) capacitive or inductive reactance to the load.

Source: from Federal Standard 1037C

Note 4: Apparent power, or the product of the rms voltage and current, measured in volt-amperes (VA), graphically presented as the hypotenuse of the power triangle, is typically the power rating measure of transmission or distribution equipment. Except in purely resistive circuits, apparent power is always larger than effective power (watts), hence the use of VA as the power rating measure in alternating circuits.

It is best to measure actual usage over time rather than trying to estimate it, because the load will vary significantly during different periods of the day. If you are looking at a backup generator system, this is easily done by measuring the energy consumed at the point of entry (if you have a modern electronic power meter, this already has a record of the information you need, but you will have to catch your local meter reader in the act to figure out how to access the information).

If you are looking to size a unit for off-grid application, the only thing you can do is make a list of all the equipment you plan to use and the maximum amperage it will draw. Add this all up and calculate kVA by multiplying volts times amps.

Most small generator sets with which I am familiar are rated in kW at 80% power factor, and the manufacturers generally insist that the capacity be decreased if the power factor is closer to 1 (the instruction manual that comes with the equipment, assuming it is quality equipment) will discuss proper rating. Typically, if you have only resistive loads (incandescent lighting, heating units like hot water heaters, stove tops, etc.) and no motors, your power factor will be close to 1. If you are trying to drive a lot of electric motors (i.e., air concitioner compressors, water pumps and the like), these are inductive loads that decrease the power factor.

The more detailed your list of equipment to be powered, the better your estimate. After completing the estimate, at 50% for future expansion. I can pretty much guarantee that, once you have your generator installed, you will find more things to add to the load...