Analysis on the significance of reactive power compensation in heating boiler room
In AC circuits, there are two types of load ratios supplied by the power supply: one is active power and the other is reactive power.
Active power is the electrical power required to maintain the normal operation of electrical equipment, that is, the electrical power that converts electrical energy into other forms of energy (mechanical energy, light energy, heat energy). For example, a 5.5-kW electric motor converts 5.5-kW electric energy into mechanical energy, driving a pump to pump water or a thresher to thresh; various lighting equipment converts electric energy into light energy for people's life and work lighting. The symbol of active power is represented by P, and the unit is watt (W), kilowatt (KW), megawatt (MW).
Reactive power is relatively abstract. It is used for the exchange of electric and magnetic fields in the circuit, and is used to establish and maintain the electric power of the magnetic field in electrical equipment. It does not work externally, but transforms into other forms of energy. All electrical equipment with electromagnetic coils must consume reactive power to establish a magnetic field. For example, a 40-watt fluorescent lamp requires more than 40 watts of active power (the ballast also consumes part of the active power) to emit light, and about 80 watts of reactive power is required for the alternating current magnetic field of the ballast coil. Because it does not do work externally, it is called "reactive". The symbol of reactive power is represented by Q, and the unit is Var or kVar.
1. Introduction Due to historical reasons, China's heating industry has always attached importance to only active load and active power, ignoring reactive load and reactive power, thinking that energy is exchanged for active power, and reactive power is not energy. The heating station itself has no benefits, etc. The main electrical equipment of the heating boiler room is an electric motor, which consumes a lot of reactive power, and there is no reactive power compensation facility for a long time, resulting in a long-term low power factor in the heating station boiler room and a serious waste of electrical energy. Therefore, in addition to improving the natural power factor of the equipment itself, the heating station should adopt manual compensation measures to improve the power factor, reduce electrical energy consumption, reduce operating costs, give full play to the potential of power supply and distribution equipment, improve power supply efficiency, and save electricity the amount.
Second, the principle of reactive power compensation When the waveform of the grid voltage is a sine wave and the voltage and current are in phase, the power P obtained by the resistive electrical equipment such as incandescent lamps and electric heaters from the grid is equal to the product of the voltage U and the current I , Namely: P = U × I.
Inductive electrical equipment such as motors and transformers need to establish a magnetic field during operation, and the energy consumed at this time cannot be converted into active power, so it is called reactive power Q. At this time, the current lags the voltage by an angle a. The selection of substation equipment is based on apparent power S, the geometric sum of active and reactive power:
S = (P2 + Q2) 1/2
Reactive power is: Q = (S2-P2) 1/2
The ratio of active power to apparent power is the power factor: cosa = P / S
Reactive power is by no means useless power, it is very useful. The rotor magnetic field of the motor is established by obtaining useless power from the power source. Transformers also require reactive power in order for the primary coil of the transformer to generate a magnetic field and induce a voltage in the secondary coil. Therefore, without reactive power, the motor will not rotate, the transformer will not change voltage, and the AC contactor will not pull in. In order to illustrate the problem visually, here is an example: rural water conservancy needs excavation to carry soil. When carrying soil, it is filled with bamboo baskets. The picked soil is like active power. Baskets are not useless. How can the soil be transported to the embankment without bamboo baskets?
Under normal circumstances, electrical equipment not only needs to obtain active power from the power supply, but also needs to obtain reactive power from the power supply. If the reactive power supply in the power grid is in short supply, and the electrical equipment does not have enough reactive power to establish a normal electromagnetic field, then these electrical equipment cannot maintain the rated conditions, the terminal voltage of the electrical equipment will drop Thereby affecting the normal operation of electrical equipment.
The reactive power supplied from the generator and the high-voltage wire cannot meet the needs of the load, so some reactive power compensation devices should be installed in the power grid to supplement the reactive power to ensure the user's need for reactive power. The equipment can only work under the rated voltage. This is the reason why the grid needs to install reactive power compensation devices.
3. Benefit analysis of reactive power compensation (1) Reduce line power loss, save electricity and reduce reactive power, which can reduce power consumption in power supply and distribution lines and transformers. When the current passes through the wire, the calculation formula for the line loss is:
△ P = 3I2R × 10-3 = [P / （Uecosφ）] 2 × R × 10-3
Among them, I is the current that the line or transformer passes through; R is the resistance of each phase in the line or transformer; Ue is the rated voltage of the line; P is the active power delivered by the line or transformer; cosφ is the power factor of the load. After the power factor is increased from cosφ1 to cosφ2, if the effect of reducing the voltage loss due to the increase of the power factor on the load voltage is ignored, the percentage reduction of the active power in the line or transformer is:
△ P% = (△ P1- △ P2) / △ P1 × 100%
= [1- (cosφ1 / cosφ2) 2] × 100%
For example: when the power factor is increased from cosφ1 = 0.8 to cosφ2 = 0.95, the power loss can be reduced by 29%; if the power factor is reduced from cosφ1 = 0.95 to cosφ2 = 0.8, the line loss will increase by 41%.
It can be seen from the above analysis that when transmitting the same power, due to different power factors, the active loss caused in the power grid varies greatly. The power saving effect of reactive power compensation is extremely significant.
(2) Increase the load capacity of power supply and distribution equipment and reduce investment costs Under the condition of the same apparent power, adding reactive power compensation can increase the active power. The apparent power delivered by the line or transformer is S, and after the compensation capacity QC is installed, the power factor is improved. Under the condition that the apparent power is constant, the ability to deliver active power is increased by ΔP.
△ P = P2-P1 = S (cosφ2-cosφ1)
Among them, P1 is the maximum active power before compensation; P2 is the maximum active power after compensation; cosφ1 is the maximum power factor before compensation; cosφ2 is the maximum power factor after compensation.
The reactive power required to increase â–³ P, that is, the reactive compensation capacity is:
QC = Q1-Q2 = S (cosφ1tanφ1-cosφ2tanφ2)
For example: when cosφ1 = 0.8, a 1000kVA transformer can supply a load of 800kVA under full load; if cosφ2 is increased to 0.95, then a load of 950kVA can be provided under full load, which can increase △ P = 1000 × 0.95-0.8) = 150kVA, which increases the active power transmission capacity by 19%.
2. Under the same active load conditions, increase capacitance compensation. The apparent power can be reduced. Under the condition that the active power P is constant, when QC is compensated, the apparent power can be reduced. After reactive power compensation, the apparent power that the transformer can reduce is:
△ S = S1-S2 = P (1 / cosφ1-1 / cosφ2)
Among them, S1 is the maximum apparent power before compensation; S2 is the maximum apparent power after compensation; P is the active power of the transformer; cosφ1 is the maximum power factor before compensation; cosφ2 is the maximum power factor after compensation.
For example, the electrical load of a heating boiler room is 450kW, and the power factor is 0.8. After the power factor is increased to 0.95, the transformer capacity is reduced by 89kVA. The selected rated capacity of the transformer can be reduced from 630kVA to 500kVA, and the capacity is reduced by one level. In addition, when the transmission power is fixed, due to the increase of the load power factor, the total current will be reduced accordingly, and the distribution equipment and conductor cross-sections can also be selected to be smaller, which reduces the investment cost and reduces the burden on the enterprise.
(3) Reduce voltage loss, improve operating conditions, reduce reactive power, and reduce voltage loss in lines and transformers. Under a three-phase symmetrical load, the voltage loss is:
Among them, P is the active power transmitted by the line; Q is the reactive power transmitted by the line; R is the resistance of the line; X is the reactance of the line; Ue is the rated voltage of the line.
After the compensation capacity Qc is installed on the low voltage side of the transformer, its voltage loss (ie, voltage rise) is:
△ Ub = △ U1- △ U2 = QcX / （10Ue2） ≈Qc / Se × Ud
After the compensation capacity Qc is installed at the end of the line, the value of the line voltage loss reduction (end voltage rise) can be calculated as follows:
△ U2% = Qc / （1000Ue2） × XL × 100%
Among them, Qc is the operational capacity of the compensation capacitor; Sc is the rated capacity of the transformer; Ud is the impedance voltage of the transformer; the reactance of the XL line. For the distribution transformer below 1000kVA and the low voltage distribution line below 1000V, the capacitor compensation is more significant for improving the voltage quality.
4. Conclusion It can be seen from the above that the addition of capacitors in the heating boiler room for reactive power compensation can not only improve the power factor, save active power, reduce line losses and transformer losses, reduce operating costs, but also improve the boiler room. The load capacity of the power supply and distribution equipment reduces the investment cost of the newly built boiler room, reduces the voltage loss, improves the operating conditions, and makes the circulation pump and blast fan motor of the heating station easier to start.
With the rapid development of China's economy, the contradiction between energy supply and demand has become increasingly prominent, and people's awareness of energy conservation has also continued to increase. The heating industry should also actively carry out technical transformation, reduce production costs, save energy, and better serve the people
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