1. 1 power factor: electrical equipment, motors, transformers, etc. It is an inductive load with both inductance and resistance in the power grid. There is a phase difference between the phasor of voltage and current of inductive load. COSφ of phase angle is the power factor, that is, the ratio of active power to apparent power, that is, cos φ = p/s. The power factor reflects the rational use of electrical equipment, the utilization degree of electric energy and the electricity consumption of power users.

1.2 reactive power compensation: connect capacitive power equipment and inductive load in the same loop. When the capacitive device releases energy, the inductive load absorbs energy, and when the inductive load releases energy, the capacitive device absorbs energy and the energy is converted to each other. Reactive power absorbed by inductive load can be compensated by reactive power output by capacitive equipment.

2. The purpose and function of reactive power compensation

2. 1 Compensate reactive power and improve power factor.

In the operation of power grid, due to the operation of a large number of nonlinear loads, not only active power but also reactive power is consumed. When the load current passes through the line and transformer, it will cause power and electric energy loss. According to the power loss formula, when the active power and voltage transmitted by the line or transformer are constant, the line loss is inversely proportional to the square of the power factor. The lower the power factor, the more reactive power the power grid needs and the greater the line loss. Therefore, installing a reactive power compensation device at the receiving end can reduce the reactive power loss of the load, improve the power factor and reduce the line loss.

2.2 improve the power supply capacity of equipment

It can be seen from P=S.COSφ that when the apparent power S of the equipment is constant, if the power factor COSφ increases, P in the above formula will also increase, and the active output of the electrical equipment will also increase.

2.3 Reduce the power loss and electric energy loss in the power grid.

From the formula I=P/(3. U.COSφ), it is known that when the active power p is constant, the load current I is inversely proportional to COSφ. After installing the reactive power compensation device, the power factor is improved, and the current in the line is reduced, thus reducing the power loss: Δ δP = I2R Reducing the power loss in the power grid is the main purpose of installing the reactive power compensation device.

2.4 improve the voltage quality

The calculation formula of line voltage loss δ u is as follows:

Where: Δ u-Voltage loss in the line kV.

P- active power MW

Q- reactive power Mvar

UE- rated voltage KV

R- total line resistance ω

XL line inductance ω

As can be seen from the above formula, when the reactive power Q in the line decreases, the voltage loss δ u also decreases.

2.5 Reduce the user's electricity expenditure and reduce the production cost.

2.6 Reduce equipment capacity and save power grid investment.

3. Selection of reactive power compensation capacity

3. 1 Determine the compensation capacity Qc according to the increased power factor.

Where p is the monthly average active power KW of the load.

Cosφ 1 cosφ2- power factor value before and after compensation.

For example, the monthly average active power of a processing plant is 300KW, and the power factor COSφ=0.6. If the power factor is to be increased to 0.9, the selected capacitor capacity is:

3.3 Determine the compensation capacity according to the no-load current value of the induction motor.

Under normal circumstances, the reactive power compensation of the motor adopts the local compensation method, and the capacitor switches back and forth with the operation and stop of the motor, and the capacity should not exceed the reactive power loss when the motor is empty. The calculation formula is as follows:

Where, Ue—— refers to the rated voltage (kV) of the motor.

Io—— No-load current of motor can be measured by clamp ammeter. If you make a rough estimate, you can also use the following formula:

Qc=( 1/4~ 1/2)Pn

Where Pn—— is the rated power KW of the motor.

3.4 Determine the compensation capacity according to the capacity of distribution transformer.

When installing capacitors on the low voltage side of distribution transformer, the following principles should be considered: when the load is light, prevent reactive power from being sent back to 10KV distribution network to achieve energy-saving effect. According to the capacity of distribution transformer, the following formula is calculated:

QC =(0. 10 ~ 0. 15)Sn(Kvar)

Sn-kVA capacity of distribution transformer

In short, the configuration of reactive power compensation equipment should be based on the principle of "overall planning, reasonable layout, grading compensation and local balance", combining loss reduction with voltage regulation, with loss reduction as the main factor; It is also necessary to combine centralized compensation with decentralized compensation, focusing on decentralized compensation; At the same time, the compensation of power supply department should be combined with the compensation of users, giving priority to local balance, and doing a good job in the configuration and management of reactive power compensation in order to obtain the economic benefits of reactive power compensation.