Hello Every One - Question About Transformers

A Transformer is not a load, so it is not rated in Watts, which is a measure of power consumption. A transformer is a transmission device and so it's rating is based on the amount of power it can transfer. That power transfer is measured in kVA. The transmission of power in a transformer has two limits, the breakdown voltage of the insulation of the windings and the current carrying capacity of the windings. kVA sets the limit of both. Inductive loads and high-current loads put different stresses on the transmission circuit. So, by using a rating that limits both the current and the voltage, a safe opperating range can be applied with one number.

A primer on KVA,and KW.

1:KVA is apparent power.2:KW is real power, or power used to perform actual work.3.In a Direct current Circuit, KVA is equal to KW.4.In an AC circuit, they are seldom equal,and the Power Factor must be considered.5.The power factor is a measure of the phase relationship between current and voltage.6.If you have a Power Factor of 80%,then 20% of the KVA is basically being used to maintain the magnetic field of the inductive load, and is not performing any actual "work". However, the current must still be supplied regardless, and this means that everything supplying the circuit must be capable of supplying and carrying this (non working) current.Generators must be large enough to handle this inductive load, transformers must also be sufficiently large.This means larger generators, transformers,and conductors.A typical power meter can only measure the KW of a circuit,which in a normal house situation is nearly 100%. The small difference is usually corrected by pole mounted capacitors at a central distribution point for an entire neighborhood.Utility companies charge industrial users for KW and KVAR,and low power factors are penalized by a higher rate,because of the extra facilities required to generate and carry this extra burden,which does not produce any actual work.Industries will install large capacitors to bring the power factor closer to unity,to minimize the charge.KVAR is Killovolt Amps Reactive,which means the current is lagging the voltage.A leading current (KVAC) is rarely seen.So in effect, a transformer and generators are rated in KVA, instead of KW because the designers do not know what the current/voltage relationship will be in the application.The KVA will equal the KW if the circuit is purely resistive, such as a resistive heater load.If you add an inductive load, such as an A/C motor,the Power Factor of the motor must be considered.The reactive current is merely circulating without producing any real "work",but it must still be there.Now ..Clear as mud?