In an electric device, the power rating is mentioned on the label. Few devices have power specifications mentioned in watt ( W ) while few are specified in kilo volt-ampere ( kVA ) ratings. The value may look similar but they differ according to the electric circuit.
what is the difference between watt (W) and kilo volt-ampere (kVA)?
Watt (W) – In an electric device, the power which is used in the circuit is measured in terms of a watt ( W ) and is also called useful power or the actual power of the electric circuit.
1 kilowatt ( kW ) = 1000 watt ( W )
Kilo volt-ampere (kVA) – It can be said as the apparent power of the electric device. It may also be calculated as the product of the current and voltage ratings of the electrical circuit. The values of kilo volt-ampere ( kVA ) are not the same as a kilowatt (kW) for every device. It depends upon the loads in the circuit and the phase difference of the circuit. It also depends on the factor by which the values may change known as the power factor of the electrical device.
What is the power factor and how does it differ for every device?
In an electric power system, the power factor is the ratio of power that can be utilized in the circuit to the apparent power of the electric circuit.
Power factor ( pf ) = kW/kVA ….. ( 1 kW = 1000 W )
Power factor is always equal to unity in DC circuit devices because the current and voltage are always in phase. So, the kilowatt (kW) rating is always equal to the kilo volt-ampere ( kVA ) rating in DC voltage devices. In AC circuit devices, the current and voltage are not in phase due to which the kilowatt ( kW ) and kilo volt-ampere ( kVA ) ratings would not be the same. This is also due to different types of loads acting on it such as inductive loads and capacitive loads, etc. The value of the Power factor may vary from 0-1 in AC circuit devices. We can understand the relationship between active power and apparent power in an explanation given below :
Conversion of kilo volt-ampere ( kVA ) to watt ( W ) is very simple. By the relation given below, we can convert the values.
Power factor, pf = kW/kVA ….. ( 1 kW = 1000 W )
kW = kVA x Pf
Let us consider a device having an apparent power of 10 kVA having a power factor of 0.8. We can convert it into watt ( W ) by simply using the above relation.
kW = kVA x pf
So , kW = 10 x 0.8 = 8
8 kW = 8000 W
As per the power factor of 0.8, we get the value of 10 kVA as 8000 W.
2) Similarly we can convert the kilo volt-ampere (kVA) into watt (W) for a different device. Let's say an electrical device having an apparent power of 25 kVA has a power factor of 0.6. We will apply the same relation for converting.
kW = kVA x pf
So, kW = 25 x 0.6 = 15
15 kW = 15000 W
As per the power factor of 0.6, we get the value of 25 kVA as 15000 W.
This is how we can calculate the value of watt for any electrical device by understanding the relation of kilo volt-ampere and watt.
Due to different loads acting on the device, the power output is less, and the power that can be utilized for doing work is less. low power factor may cause many issues in the performance of the device. Some major causes of the low power factor have been listed below.
Causes of a low power factor in an electrical device :
Due to inductive loads in an inductive machine such as generators, heating furnaces, etc the power factor gets decreased. Inductive loads cause a high voltage flow in the circuit which can also destroy the circuit
The voltage and current drawn from the device are more when the circuit is loaded lightly which results in a low power factor.
The power factor becomes low due to improper wiring of the electric circuit because the device will heat up easily.
Induction motors are used in many applications which operate on low power factors. In less load conditions, the power factor is very low i.e. 0.2 – 0.3 whereas it performs better in full load conditions at 0.7 – 0.9 power factor.
Disadvantages of low power factor of an electrical device :
There are many disadvantages of the low power factor.
Low power factor affects the performance of the electrical device, Hence, the power factor should be corrected for better operation of the electrical device. The power factor correction may lead to many advantages including the efficiency of the system, power-saving, life cycle of the device, and many other benefits. Some of the benefits of improving the power factor are listed below.
Benefits of improving the power factor in the electrical device :