Watts to kVA
Relationship between Watt (W) and kilo volt ampere (kVA) ratings of an electric device
In an electric device, there is the power specifications or power rating mentioned on it. Some devices have power ratings mentioned in watt ( W ) whereas some are specified in kilo volt ampere ( kVA ). They both seem similar to each other but they are different. There is a relationship between both the power ratings. Let us understand what is the difference between watt ( W ) and kilo volt ampere ( kVA ).
Watt (W) – In an electric circuit, the power which can be utilised in the circuit is measured in terms of watt ( W ) which is also called as active power or the useful power of the electric circuit.
1000 watt ( W ) = 1 kilo watt ( kW )
Kilo volt ampere (kVA) – It resembles the apparent power of an electric circuit of the electric device. It may also be formulated as the product of the current and voltage ratings of the electrical device. The values of kilo volt ampere ( kVA ) may not be the same as watt ( W ) . It depends upon the loads and losses in the circuit, phase difference of the circuit etc. The factor by which the values may change is called as the power factor of the electrical device.
Power factor of the electric power system is defined as the ratio of power which can be utilised in the circuit to the apparent power flowing the an electric circuit.
Power factor (pf) = kW/kVA
In dc circuits, the values of current and voltage are always in phase. So the power factor is always equal to unity. Therefore the kilo watt rating is always equal to kilo volt ampere rating. But in AC circuit devices, the current and voltage are not in phase. Due to different type of loads acting on it such as inductive loads and capacitive loads, the kilo watt and kilo volt ampere value may be different. Power factor may vary from zero to one in an AC circuit devices. We can understand the relationship between real power and apparent power in the examples below :
Conversion of watt (W) and kilo volt ampere (kVA) ratings in the particular device
Conversion of watt ( W ) to kilo volt ampere ( kVA ) is very simple. By the simple relation we can convert the values.
Power factor, pf = kW/kVA
kVA = kW/Pf …… ( where 1 kW = 1000 W )
Let us consider a device having an actual power of 5000 W having a power factor of 0.8. We can convert it into kVA by simply using the above relation.
kVA = kW/Pf
actual power = 5000 W = 5 kW
So , kVA = 5/0.8 = 6.25
As per the power factor of 0.8, we get the value of 5000 W as 6.25 kVA.
2) Similarly we can convert the watt ( W ) into kilo volt ampere ( kVA ) for a different device. Lets say an electrical device having a active power of 20000 W having a power factor of 0.5. We will have to apply the same relation for converting.
kVA = kW/Pf
actual power = 20000 W = 20 kW
So , kVA = 20/0.5 = 40
As per the power factor of 0.5, we get the value of 20000 W as 40 kVA.
This is how we can calculate the value of kilo volt ampere for any electrical device by understanding the relation of watt ( W ) and kilo volt ampere ( kVA ).
The power output is less and power which can be utilized for doing work is less due to different loads acting on the device. low power factor can cause many difficulties in the performance of the device. Some major causes of the low power factor has been listed below.
Causes of a low power factor in the electrical device :
Low power factor is caused by inductive loads in the inductive machines such as generators, heating devices, transformers etc. Due to inductive loads, high voltage flows in the circuit which can destroy the electric circuit.
When the load is less, the voltage and current drawn from the device is more which results in low power factor.
In many applications, induction motors are used which operate on low power factor. In less load condition, power factor is very low i.e. 0.2 – 0.3 whereas in full load condition it performs better at 0.8-0.9 power factor.
Due to improper wiring, the device will heat up easily which causes low power factor.
Disadvantages of low power factor in the electrical device :
- Efficiency of the system is reduced.
- Current and Voltage levels are not stable.
- High current flows in the circuit which leads to more energy loss in the system.
- More wiring will be required due to more energy loss in the electric cirvuit.
- Power losses in the distribution system are more.
- Costly power factor correction equipments are needed in the system.
- Less amount of power can be used by the electric circuit.
The power factor should be improved for better operation of the electrical device. Low power factor may affect the performance of the electrical device. Improving the power factor may lead to many benefits including the efficiency of the system, power output, life cycle of the device and many other factors. Some of the advantages of improving the power factor are listed below.
Advantages of improving the power factor in an electrical device :
- The efficiency of the system will be more.
- Voltage and current will be stable.
- More power can be used by the distribution system.
- Losses in power are decreased.
- Saving in the overall energy of the system.
- The cost of additional power factor correction devices will be less.
- Saving in the electricity bill.