At present, the reactive power compensation of industrial and mining enterprises mostly uses grouped automatic tracking compensation, and the capacity of a single group is mostly below 900kvar. Generally, power capacitors, series reactors and vacuum contactors are installed in the same cabinet. This requires reactors to be small in size and performance. Good, light weight, easy to install and maintain; the purpose and performance of series reactor for reactive power compensation are introduced as follows.
1. Types of series reactors 1. Oil-immersed iron-core reactor; 2. Dry-type iron-core reactor; 3. Dry-type air-core reactor; 4. Dry-type half-core reactor; 5. Dry-type magnetic shield Reactor
2. The purpose of reactive power compensation reactor is divided into: 1. Current-limiting reactor; 2. Suppressing harmonic reactor; 3. Filtering reactor;
3. The role of series reactor is multi-functional, mainly: 1. Reduce the inrush current multiple and inrush frequency of the capacitor bank, and facilitate the selection of supporting equipment and protective capacitors. According to the GB50227 standard, the inrush current should be limited to less than 10 times the rated current of the capacitor. In order to avoid harmonic amplification (harmonic traction), the volt-ampere characteristics of the series reactor are required to be as linear as possible. When the network harmonics are small, use a reactor that limits the inrush current; the reactance rate is about 0.1%-1%, that is: the inrush current can be limited to less than 10 times the rated current to reduce the active power loss of the reactor, and the size of the reactor is small , Small footprint, easy to install in the capacitor cabinet. The use of this type of reactor is both economical and energy-saving. 2. The series filter reactor, the impedance of the reactor and the capacitive reactance of the capacitor are fully tuned to form an AC filter for a certain harmonic. Filter out a certain order of higher harmonics, and reduce the voltage value of this order of harmonics on the bus, so that there is no higher harmonic current on the line, and improve the voltage quality of the power grid. Tuning degree of filter reactor: XL=ωL=1/n2XC=AXC where A-tuning degree (%) XL- reactance value (Ω) XC- capacitive reactance value (Ω) n- harmonic order L- inductance value ( μH) ω----314 The reactance rate of each harmonic filter reactor is 11.12% for the 3rd harmonic, 4% for the 5th harmonic, and 2.04% for the 7th harmonic, and 0.83% for the 11th harmonic. The reactor is configured according to the above tuning degree for 0.53%, which can filter out all harmonics. 3. The prerequisite for the reactor to suppress harmonics is to know the harmonic situation of the power grid, and check whether the surrounding electricity users have large-scale rectifier equipment, electric arcs, steelmaking and other equipment that can generate harmonics, and whether they have poor performance For high-voltage transformers and high-voltage motors, try to measure the actual value of the grid harmonics as much as possible, and then configure appropriate reactors according to the actual harmonics. The iron core reactor has poor linearity and noise. The air-core reactor runs without noise, has good linearity and low loss. The standard stipulates that when the capacity of air-core reactor is below 100KVAR, the loss per volt-ampere is not more than 0.03W. For example: a single 12000VA reactor with a reactance rate of 6% has a loss of 360W, and a three-phase active loss of 1080W, which is not a small number. When the harmonics on the power grid are small, the use of current-limiting reactors can save energy. 4. Since the series reactor is set, the short-circuit current value provided by the system to the parallel capacitor device or the capacitor device to the system is reduced. 5. It can reduce the discharge current of the capacitor bank to the faulty capacitor bank and protect the power capacitor. 6. It can reduce the inrush current of the capacitor bank, help the contactor to extinguish the arc, and reduce the amplitude of the operating overvoltage. 7. Reduce the overvoltage amplitude caused by operating the parallel capacitor bank, which is beneficial to the overvoltage protection of the power grid.
4. The selection principle of series reactors. Electricity companies have their own characteristics and have different requirements for equipment. Dry-type reactors have the characteristics of low noise, good linearity of the reactor, high mechanical strength, and simple installation; oil The immersion reactor has small loss, small footprint, poor linearity, and high noise. Therefore, what kind of reactor should be considered comprehensively. The main function of series reactor is to suppress harmonics, limit inrush current and filter harmonics. The reactance rate is the main parameter of the reactor, and the size of the reactor directly affects its function. The reactance rate of the current-limiting reactor is 0.1-1%, and the reactance rate of the reactor that suppresses harmonics is 4.5%-13%. The current-limiting reactor limits the inrush current to less than 10 times the rated current of the capacitor. When configuring current-limiting reactors, line reactance (1μH/M) should be considered.
5. Inrush current when switching capacitors: 1. Inrush current when a single group of capacitors is switched on Iym=√2 IΣ[1-√(XΣ/Xl)] Xl=2 IΣ* XΣ/( Iym-√3* IΣ)2ψy= ψ√(XΣ/Xl) where Iym---the maximum amplitude of closing inrush current (peak value) (KA) IΣ---the rated phase current of the group capacitor device (A) XΣ---the total rated reactance of the group capacitor phase ( Ω) X_l---Rated reactance of system inductance and series reactor (Ω) fy ----Inrush current frequency Μ---Grid frequency 2. When the capacity of each capacitor bank is equal, the following formula Iym=((M-1 )/M]*√[2 000QΣ/3ωL] (kA) L=[(M-1)/M]2*[2 000QΣ/3ωIym2] (μH) where QΣ- rated capacity of a single group capacitor (kvar) Μ ---Number of capacitor banks L---Inductance value (μh) ω---Angular frequency (314) Iym-peak current (ka) Line reactance XL′=(1μH/Μ) fy=103/[2л√(LCΣ) )] When the power grid has harmonics that cannot be ignored, a reactor that suppresses harmonics should be used. In order to determine a reasonable reactance rate, the background content of harmonics in the power grid should be ascertained so that the type and reactance rate of the reactor can be selected appropriately.
6. Equipped with reactors in the following way: 1, even harmonics 2, 4, 6, 8..., the harmonics cancel each other out symmetrically, so it is not considered. 2 Odd harmonics are 3, 5, 7, 11, 13 and above harmonics. These harmonics are mostly caused by large-scale rectifier equipment, electric arcs, steelmaking, electric locomotives and other loads. When there is this kind of equipment in the user's power grid, there is a harmonic source. The order and content of the harmonic should be measured. If the harmonic does not exceed the national standard, then the reactor parameters that should be configured are calculated. The reactor with the 3rd harmonic configuration 13%, the reactor with the 5th harmonic configuration 4.5%-6%, the 4.5%-6% reactor can cover the 5th harmonic. After the reactor is configured, it should be converted to whether it can produce harmonic amplification. If the following situations occur, the parameters of the reactor should be changed.
7. The criterion of harmonic amplification phenomenon
1. Configuring a reactance rate of 6% may amplify the 3rd harmonic. If the network has 3rd harmonics, a 13% reactor should be configured. 2. Harmonic amplification can be generated after the reactor is installed, the measured harmonic content, and the appropriate reactance rate according to the actual situation. 3. The terminal voltage of the reactor is UD=UN ╳ reactance rate (0.1%-13%) (V) where: UD---terminal voltage (V) UN---capacitor rated voltage (KV) reactor terminal Voltage refers to the working voltage of the reactor itself, not the grid voltage, such as a reactance rate of 13%, 10KV grid voltage, the phase voltage of the capacitor is 6936V, and the terminal voltage of the reactor is 6936 ╳ 13% = 900V.
8. The quality factor of the reactor The quality factor of the series reactor of the single-pass filter is an important index, generally between 30-60, and the quality factor should be high, that is, the DC resistance of the reactor coil is as small as possible. Q= nXl/RL=(30~60) the quality factor of the single-pass filter The quality factor of the high-pass filter reactor is the same as above, but a parallel resistor is required. Rb=√XLXC=BXL=XC/B.
9. The characteristics of the reactor 1. The iron core reactor has high noise and poor linearity, which can cause magnetic leakage, local overheating, magnetic saturation, and burn out the coil. The influence of system overvoltage, overcurrent and harmonics causes the iron core oversaturation reactance value to drop sharply, the ability to suppress harmonics is reduced, and the ability to resist short-circuit current is low. In addition to the above shortcomings, dry-type iron core reactors cannot be operated outdoors. 2. Dry-type air-core reactor has good linearity, no noise, strong flow capacity, strong heat dissipation capacity, simple and solid mechanical structure, and can be used indoors and outdoors, basically maintenance-free. The disadvantage is that the volume is larger and the loss is larger. 3. Half-core reactor The half-core reactor is a new type of reactor between the iron-core reactor and the air-core reactor. An iron core that does not close the magnetic circuit is added to the winding of the air-core reactor. , So that the half-core reactor has the advantages of iron-core reactor and air-core reactor. A new half-core reactor is formed. The coil diameter of the half-core reactor is 20% smaller than that of the air-core reactor. The loss of the reactor is 25% lower, the linearity is close to a straight line, the impedance does not decrease with the increase of current, and the noise is less than 50db. It is easy to install in the cabinet and is a series reactor with better reactive power compensation. The ideal reactor should have the following characteristics: 1. No oil 2. No noise 3. Small size 4. Good linearity 5. No magnetic leakage 6. Strong over-current capability The upcoming development direction is dry-type half-core magnetic shielded reactor Device.
10. The capacitor voltage rises after the series reactor. After the series reactor, the capacitor terminal voltage will increase, and the magnitude of the increase is related to the percentage of the series reactor; the higher the percentage, the higher the capacitor terminal voltage, calculate according to the following table . The relationship between the percentage of series reactor and the increase in capacitor voltage.
11. Why use percentage to calculate reactor? Current-limiting reactor is to ensure that the closing inrush current does not exceed ten times the rated current of the capacitor, which can reduce the copper consumption of the reactor and reduce the volume. 4.5%-13% of reactors suppress harmonics. If the network harmonics are large, such as the 3rd, 5th, 7th, 11th and high-pass harmonics, only 13% of the reactors can suppress 3 For harmonics above the 5th order, if there is no 3rd harmonic, a 6% reactor can be used to cover the harmonics above the 5th order, because the harmonics above the 5th order require less reactance than the 5th harmonic. .
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