Because the transformer designer does not know the power factors of the different loads that might be connected to it. The way round this probem is to specify the voltage and the maximum current that the transformer can supply, then multply them together and print the VA, kVA or MVA rating on the transformer. Then it's up to the user to comply with this rating to avoid damaging the transformer.
transformer transforms constant power from input circuit to output circuit so there is no factorization of power.so power factor is not considered in their ratings.
zero volatge regulation means the terminal volatge of transformer at full load on a given power factor become equal to the rated teriminal volatge of transformer , it happens only for leading power factor in transformer
Hi, First understand one thing seriously!! The transformer only can be rated in KVA. Bcoz, its power factor not depends on the load connected.
It tells us how much is the transformer utilised in a given process. For a rectifier,TUF =(D.c.power delivered to the load)/(power rating of transformer secondary)
Transformers are rated in KVA because that is a more accurate way to measure their capacity requirements. KWH is apparent power, while KVA is true power, and the ratio between them is power factor. The power factor is a function of the load, and not the transformer, so a poor power factor would make KWA look less to the transformer while, in fact, the true power, if not met by the transformer, could overload the transformer.
When power factor is at unity, the voltage and current waves are aligned or in phase with one another. Since power is the product of voltage and current, power transfer is maximized at unity power factor. When power is transmitted at a lower power factor, greater current is required to deliver the same amount of power. When current is increased, the size of the transmission, distribution and generation systems, all have to be increased accordingly, along with the price of the killowatt-hour at the meter.
It isn't! A transformer operating at no load has a very low power factor.
Power factor is determined by the nature (resistive, inductive, capacitive) of a load, not whether it is a low load or a high load.
When its load has a leading power factor.
When it supplies a resistive load.
With varying power factor the load current drawn changes, which in turn affects the voltage regulation
Same
Transformer utilization factor is the ration of power delivered to the load and ac rating of the transformer secondary.
The inductance of the transformer is much higher than the resistance of the transformer, resulting in very low real power losses (in watts), but some reactive power (vars).
zero volatge regulation means the terminal volatge of transformer at full load on a given power factor become equal to the rated teriminal volatge of transformer , it happens only for leading power factor in transformer
It depends on the power factor of the load, but for a load power factor of 0.7 on a 2000 kVA transformer the real power and reactive power are both 1400 kilo (watts and VAR). So a 1400 kVAR capacitor on the load would restore the power factor to 1, allowing 2000 kW to be drawn instead of only 1400 kW.
Hi, First understand one thing seriously!! The transformer only can be rated in KVA. Bcoz, its power factor not depends on the load connected.
There is no such thing as a 'low power-factor' wattmeter. A wattmeter always reads true power, regardless of the load's power factor.