"There is an old 1000kVA transformer with an existing load of about 200kW, if a new load of about 600kW is to be added, can this transformer handle it?"

This question first deals with the concept of the relationship and difference between kVA and kW.

kVA (kilovolt-amperes) is the unit of apparent power, while kW (kilowatts) is the unit of active power. In addition to apparent power and active power, there is also reactive power, which is measured in kvar (kilo-volts).

What is the difference between active power, reactive power and apparent power?

Active power is the actual power consumed by appliances, that is, the conversion of electrical energy into other forms of energy.

For example, the electricity we pay everyday is the active power.

Reactive power refers to some equipment does not really consume electricity, it is only temporarily store the power of that part of the power.

For example, if there is a capacitor/coil inside a power device, the capacitor/coil will be charging and discharging all the time when this device is working. Because the capacitor/coil is charging and discharging all the time, it does not really consume electricity, so this part of the power is called reactive power.

The apparent power is the total power provided by the power supply.

A power supply (usually a transformer or a generator) needs to provide reactive power in addition to active power to the power-using equipment. The reason is simple, although the capacitor inside the equipment does not consume electricity, but it has been charging and discharging, so it also needs to occupy part of the power supply capacity.

After these are clear, we then look at the relationship between them, which will come to another concept - power factor. A power supply can provide how much active power, which depends on the power factor.

[Power Factor]

Power factor is the ratio of active power to apparent power, generally expressed as cosφ.

As an example, a 1000kVA transformer, at a power factor cosφ=0.6, it can output 600kW of active power; but when the power factor cosφ=0.9, it can output 900kW of active power.

If it is 1 yuan per kWh, the transformer can produce 600 yuan/hour of economic benefit when the power factor is 0.6; but when the power factor reaches 0.9, the transformer can produce 900 yuan/hour of economic benefit. In fact, the role of improving the power factor is much more than that simple, there are many, here will not say more.

With the above foundation, and then to explain the problem will be easy.

Transformer capacity unit is kVA (kVA), while the power unit of power equipment is kW (kilowatt), the difference between the two is the calculation of equipment power kW is required to multiply the power factor, that is, 1000 kVA capacity transformer, only in the case of power factor of 1, will be able to full-load output of 1000kW of power, but in the actual application of basic impossible.

In the design time, need to leave a certain amount of margin, generally calculated according to 90% compliance rate, more economical and reasonable, that is, 1000 × 0.9 = 900 kVA. if we compensate the power factor to 0.95 and above through power compensation, then the transformer can output 900 × 0.95 = 855kW active power.

Note: The power company requires that the power factor must be above 0.9 or there will be a penalty; however, the power factor cannot exceed 1, otherwise the system voltage will rise and affect the normal operation of the system.

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