Why transformer is rating kva?

Answer 1

the short answer: to distinguish as an AC transformer, as opposed to a DC transformer.

The long answer:

A Kva stands for Kilo-Volt-Amps. The Transformers mounted on telephone poles work with hundreds of thousands of volts so rather than 750,000 V, we use the abbreviation kilo, being the metric prefix for thousand and write 750 kV. As for 'VA' some high school physics tells us Voltage*Current=Power. voltage being measured in volts (V), current in amperes or amps for short (A), and power being Watts (W). However alternating current is a very fickle beast and the voltage and current vary in a wave like fashion causing the power to reverse direction. Other factors come into play such as power sag, types of electrical loads, and wasted energy, the equation soon becomes very messy. at times the power is actually negative and is flowing away from your house! so to simplify things they use Volt-Amps to represent the maximum amount of power as an absolute value that the electricity can deliver. as opposed to the USEFUL amount of power which is lower due to resistances in the wires and other loses. Engineers have to worry about the KVA when designing a system so it can handle everything thrown at it, keeping the wires from melting and that transformer from blowing up!

Answer 2

Transformers are rated in KVA because voltage refers to iron loss or core loss and ampere
refers to copper loss.
iron loss or core loss are of two type
1) Hysteresis losses
2) Eddy current losses

Answer 3

KVA rating indicates the transformers maximum power output capacity. Power is power to a transformer, it does not matter if it is reactive or real, the transformer rating is based on the amount of current that is flowing through it. If it was rated in Watts you would have to factor in Power Factor which would only lower this capacity. Since this will be load dependant it is not as convenient as a rating.

Answer 4

The watt is a measure of true power, which is the product of the supply voltage, load current, and load power factor. The volt ampere is a measure of apparent power, which is the product of the supply voltage and the load current.

A transformer manufacturer has no means of knowing the power factor of the load its transformer will supply. Accordingly, transformers are rated in volt amperes -the product of their rated secondary voltage and their rated secondary current.

Answer 5

Power rating of any equipment depends on power consumed by that equipment,

in other wordspower depend on Voltage, Current & Phase angle between Voltage & Current vactor.

P = V * I * cosØ

In case of transformer, there are two types of losses occure in transformer one is iron loss & other is copper loss.

Iron loss occcure in core of the transformer and its value depends on supply voltage, whereas copper loss occures in winding of the transformer and its value depends on load current.

there is not any relation with supply voltage & load current in case of transformer, so power rating isdepends onSupply voltage & Load current

P = V * I

There is not any role of power factor in calculation of power of transformer so, its rating is defines as VA (Volt-amp, or KVA).

Answer 6

Power is voltage times current times power factor. The power factor is determined by the load. As the transformer manufacturer has no idea of the power factor of the load the transformer is to supply, he can only specify the transformer's rated current and rated voltage, the product of which is apparent power, expressed in volt amperes.

Answer 7

in transformer the losses never depends on power factor depends only on voltage (constant losses) and current (variable losses) so...