Why are alternators rated in KVA and not in kw?

Why are alternators rated in KVA and not in kw?

If we connect inductive or capasitive load (When power factor is not at least unity), The output would differ than as there are losses occurs due to low power factor. For this reason, KVA is an apparent power which does not take in to account the PF (Power factor) instead of KW (Real Power). And kVA = KW / Cos θ.

What is the effect of changing of excitation in alternator?

A change in the excitation of an alternator running in parallel with other affects only its KVA output; it does not affect the KW output. A change in the excitation, thus, affects only the power factor of its output.

What is the effect of change in excitation on the power factor of the synchronous motor?

As the excitation is increased, the power factor improves till it becomes unity at normal excitation. Under such conditions, the current drawn from the supply is minimum. If the excitation is further increased (i.e., over excitation), the motor power factor becomes leading. Note.

What factors do the generated EMF in an alternator depend upon?

Due to relative motion between armature conductors and the main field, an emf is induced in the armature windings whose magnitude depends upon the relative speed and as well as the magnetic flux.

Is kVA bigger than kW?

What is the difference between kW and kVa? kW is the unit of real power and kVA is a unit of apparent power (or real power plus re-active power). The power factor, unless it is defined and known, is therefore an approximate value (typically 0.8), and the kVA value will always be higher than the value for kW.

Why motor is rated in kVA?

A kVA rating is more useful in determining the % loss. Volt Amp. rating, is just the Kilowatt rating determined at unity power factor (V.A = Watts / power factor). All AC devices that supply power, such as transformers, UPS, generators, etc are rated in kVA.

When an alternator is connected to infinite bus bar what will be the effect of change in excitation for alternator?

When the excitation of an alternator connected to infinite bus-bars and supplying load at lagging of is increased, the alternator falls back (i.e., load angle decreases), power factor further drops and armature current increases due to reduced power factor; active component being constant.

When an alternator is connected to an infinite bus bar change in excitation for alternator will?

When alternator is connected to infinite bus bar, change in excitation for alternator will change terminal voltage & power factor.

What is normal excitation?

Synchronous motor excitation refers to the DC supply given to rotor which is used to produce the required magnetic flux. The field current, which causes this unity power factor is called normal excitation or normal field current.

Which type of rotor is best for turbo alternator?

Smooth cylindrical type rotor is generally used for high speed alternators or turbo alternators.

What is the emf equation of alternator?

V = 4.44 Kf KC KD f ΦT Volts. Where: V = Actual generated Voltage per phase.

Why are alternator and generator rated in kVA instead of kW?

If we put the value of Cos θ as 1, The real power (kW) would be equal to the appearnt power (kVA) In case of inductive or capacitive load, suppose the power factor is 0.80. Now the real power would be. kW= KVA X Cos θ. kW = 100 X 0.80. kW= 80 kW. Now you now that why alternators, generators, transformer and UPS etc are rated in kVA instead of kW.

What happens when the excitation of an alternator is changed?

A change in the excitation of an alternator running in parallel with other affects only its KVA output; it does not affect the KW output. A change in the excitation, thus, affects only the power factor of its output. Let two similar alternators of the same rating be operating in parallel, receiving equal power inputs from their prime movers.

Why are alternators rated on current and voltage?

So the alternator is rated only based on current and voltage that is VA, KVA or MVA. (2) When engineers design an alternator they do not know what type of load will be connected with the alternator so they cannot decide the power factor as the power factor depends on types of load.

How does a change in the excitation affect the output?

A change in the excitation, thus, affects only the power factor of its output. Let two similar alternators of the same rating be operating in parallel, receiving equal power inputs from their prime movers. Neglecting losses, their kW outputs are therefore equal.