kVA ≠ kW, 90% of people confuse the concept of electric power

'I have an old 1000kVA transformer with an existing load of approximately 200kW. If I add a new load of approximately 600kW, can this transformer handle it?'

Understanding kVA and kW

kVA: It's kilovolt-amperes. Baidu Encyclopedia defines it as: 'A unit of capacity for electrical equipment (such as transformers and motors). In an AC circuit, voltage (kilovolts) / current (amperes) = capacity (kilovolt-amperes). Transformer capacity is expressed in kilovolt-amperes.'

kW: It's a kilowatt. The encyclopedia defines it as: 'A kilowatt is a unit of power equal to 1,000 watts. The kilowatt is commonly used to express the power of generators, engines, motors, tools, machines, electric heaters, etc. It is also a common unit of electromagnetic power used by radio and television transmission towers.

Of course, the definition on the encyclopedia is just basic.

We also need to know that kVA (kilovolt-ampere) is the unit of apparent power, while kW (kilowatt) is the unit of active power. In addition to apparent power and active power, there is also reactive power, and the unit of reactive power is kvar (kilovar).

So, what are the differences between the three types of power mentioned here: apparent power, active power, and reactive power?

1. Apparent power refers to the total power provided by the power supply;

2. Active power refers to the power actually consumed by electrical appliances, that is, the power converted from electrical energy to other forms of energy. For example, the electricity bills we pay in our daily lives are for active power.

3. Reactive power refers to the power that some devices temporarily store but don't actually consume. For example, if a device contains a capacitor or coil, the capacitor or coil will be constantly charging and discharging while the device is operating. Because the capacitor or coil is constantly charging and discharging, it doesn't actually consume power, so this power is called reactive power.

How much active power can a power supply provide? This requires the introduction of a concept: power factor.

Power factor refers to the ratio of active power (P) to apparent power (S), and is generally expressed as cosφ.

Let's take an example. A 1000kVA transformer can output 600kW of active power when the power factor cosφ=0.6; when the power factor cosφ=0.9, it can output 900kW of active power.

Calculated at 1 yuan per kWh, when the power factor is 0.6, the transformer can generate an economic benefit of 600 yuan per hour; when the power factor reaches 0.9, the transformer can generate an economic benefit of 900 yuan per hour. In fact, the role of improving the power factor is far more than just this simple, there are many more, which I will not elaborate on here.

After understanding the relevant knowledge above, it will be easier to look at the questions at the beginning of the article.

We need to know that the capacity unit of the transformer is kVA (kilovolt-ampere), while the power unit of the electrical equipment is kW (kilowatt). The difference between the two is that when calculating the power kW of the equipment, it is necessary to multiply the power factor. That is to say: a transformer with a capacity of 1000kVA can only output 1000kW of power at full load when the power factor is 1, but this is basically impossible in actual applications.

For example, when designing, it's more economical and reasonable to calculate based on a 90% compliance rate. This is also the requirement of power companies, which require a power factor of at least 0.9, or penalties will apply. However, it cannot exceed 1, otherwise the system voltage will increase, affecting normal operation.

The question says that the 1000kVA transformer originally supplied power to 200kW of electrical equipment, and now 600kW of electrical equipment has been added. The total active power of the electrical equipment has reached 800kW, which still does not exceed the calculated value.

Therefore, a 1000kVA transformer originally supplied power to 200kW electrical equipment, and now 600kW electrical equipment has been added. As long as we can increase the power factor to the required value, the transformer can operate safely for a long time.