| The choice of reactive power compensation devices |
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| 发布日期：2011-03-30 07:49:07 |
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The choice of reactive power compensation devices
The role of reactive power compensation are summarized in this paper, analysis of the types of low voltage parallel capacitor reactive power compensation, selection of capacitance compensation control and the determination of compensation capacity, etc.
Reactive power is to maintain normal operation Power Factor Capacitor of power system, one of the main factors. Matter in power system reactive power balance and improve the power factor of load, can reduce the active power loss of lines and transformers and other electrical energy loss, improve power quality, reduce the loss of electricity, and ensure the stability of the power system operation and the user of the power supply quality.
First, the role of reactive power compensation
1. Improve the utilization rate of variable distribution equipment to reduce the investment cost.
For low power factor of load reactive power compensation, access to the parallel capacitor, due to the reactive current compensation, reduces the load current, because of the increase and make the power factor of variable distribution equipment power saver capacitor to reduce capacity (kVA) calculate formula 1: Δ S = P/COS P/COS phi phi 1-2 = P * 2 - COS (COS phi phi 1)/(COS phi 2 x COS phi. 1). Type: S - to reduce the equipment capacity, active power P - for load, COS phi 1 - as the before the load power factor compensation, COS phi after 2 - to compensate the load power factor.
Before such as the load capacity of 1000 kw, compensation power factor is 0.7, when the power factor can be calculated from the formula 1 compensation to 0.95, for the distribution of load transmission equipment can reduce 376 kva capacity, can reduce the investment costs for the new project (variable distribution equipment to reduce 376 kva capacity, can reduce the spending of the basic electricity), economic benefit is obvious.
2. Reduce the power loss in the power grid.
When the power factor of load from 1 to COS phi, grid power loss will increase in the percentage of about the delta p (%) = (1 / COS2 phi - 1) x 100%
3. Reduce the line pressure drop.
Due to the improvement of power factor, small wire, current, line voltage loss decreases in the system, to improve the end of the power quality.
4. To improve the power factor and reduce electricity accordingly.
By the state price bureau in 1983, according to the national ministry of water conservancy "power factor adjustment charge way" regulation standard three kinds of power factor, accordingly to reduce electricity bills:
Standard 0.90 (1) power factor, high voltage power supply industrial users that applies to more than 160 kva, equipped with load adjusting voltage device of high voltage power supply electric power users and more than 3200 kva and high voltage power 7.5 kvar capacitor supply electric power irrigation and drainage pumping station. Standard 0.85 (2) the power factor, applies to more than 100 kva (kw) and other industrial users, more than 100 kva (kw) and non-industrial users and more than 100 kva (kw) and electric power irrigation and drainage pumping station. Standard 0.80, (3) power factor that applies to more than 100 kva (kw) and agricultural users and wholesale.
Second, the kinds of reactive power compensation
1. The concentrated compensation.
In low voltage power distribution within several group of capacitor on the power distribution busbar, configuration of reactive power compensation of power supply scope
2. To compensate.
Install the compensation capacitor near a load, or directly in parallel on the electrical equipment
On-site compensation is divided into two kinds: one is the dispersion compensation on-spot, electric power capacitor in low voltage power distribution equipment or power box on the bus, the power equipment of the nearby reactive power compensation. 2 it is to separate compensation on-spot, the condenser directly or the end of the protection equipment on terminal electrical equipment, generally don't need a capacitor with the operation of the protection equipment.
Three, capacitor compensation on the technical problems that should be paid attention to
(1) to prevent the flow. When the capacitor input, usually with large flow, In IEC publication 831 capacitor capacitor In the calculation formula Is the 30 kvar capacitor flow 2 s/Q = In x). Type: the flow when the input Is -- - for the capacitor (A). The In - A capacitor rated current (A). S - for capacitor installation place of short circuit power (MVA). Q - a capacitor capacity (Mvar).
In the low voltage capacitor circuit, can adopt the following methods: one is the series reactor; Second, increase for capacitor's capacity; Three is to use special capacitor contactor.
(2) to prevent the influence of the system harmonic. Due to the capacitor circuit is a LC circuit, for some harmonic is easy to produce resonance caused by harmonic amplification, increase the current and voltage rise. Can be used for this series inductance value of the reactor in order to avoid the resonance, such as the percentage of the reactor as K, when the power grid harmonic five is higher, and 3 times without too much harmonic, K appropriate USES 4.5%; Such as in 3 times higher harmonic, K appropriate USES 12%, when the power grid harmonic is not high, K should be 0.5%.
(3) to prevent producing self-excited. Using capacitor to compensate reactive power of the motor, capacitor in parallel on the motor directly, when the power is cut off, motor in the inertial effect continues to run, capacitor discharge current to be exciting current at this time. If the capacity of compensation capacitor is too big, can make the magnetic field Industrial capacitors of the motor to get motivated and produce voltage, the motor is running on power condition, so the compensation capacity is less than the motor no-load capacity can be avoided, generally take 0.9 times as it doesn't matter.
QC = 0.9 x 3 ui0. Type: Qc - to compensate capacitor capacity. U - for the system voltage. I0 - for motor no-load current.
Four, selection of capacitance compensation control and determination of compensation capacity
The choice of the ways of capacitor Banks for 4.1
Capacitor Banks for break up dynamic and automatic two ways. For basic reactive power compensation of low voltage and stable high voltage capacitor Banks, appropriate USES manual cutting; In order to avoid any compensation or light load voltage is too high, easy to cause equipment damage, appropriate USES automatic cutting. High and low voltage compensation effect at the same time, appropriate USES low voltage automatic compensation device.
4.2 the determination of capacitor compensation capacity
To load calculation, determine the active power P and reactive power Q, natural power factor of cos phi 1 before compensation, compensation to the 50 kvar capacitor power factor of for cos phi 2. The QC = P 1 - tg (tg phi phi 2). Type: Qc - as the compensation capacitor capacity, active power P - for load, COS phi 1 - as the before the load power factor compensation, COS phi after 2 - to compensate the load power factor.
To determine the reactive power compensation capacity, but also should pay attention to the following three points: (1) to avoid any compensation when light load, delivers the reactive power loss increase, also is not economic. (2) the higher power factor, the role of compensation capacity and each kvar, reducing wear and tear will be smaller, as is often the case, to increase the power factor to 0.95 is reasonable compensation. (3) on-site compensation capacitor capacity selection of main parameters, excitation current, because they do not cause the capacitor self-excitation is the necessary condition to choose the capacitor capacity, calculate formula 4.
Using reactive power compensation can improve the power factor, is a less investment, short-term energy saving measures. Principle of parallel MPP Capacitor compensation capacitor is simple, easy to use, economic operation, can also be grouped for guarantee the voltage qualified rate and reasonable power factor. The average power factor of power distribution network in many regions and site on the low side, through the adoption of reasonable compensation capacitor compensation, will be able to improve the quality of power supply and obtain obvious economic benefit.
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