Example of reactive power compensation of the hott

2022-08-24
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The example of reactive power compensation of random follower

in the formula, the total loss of P electricity kw

pp, the active loss caused by PQ electric transmission of active power and reactive power kw

p, Q active power, reactive power kW, kvar

u, the actual operating voltage of R electricity, and the line equivalent resistance

it is known that when the electrical structure is fixed and the transmitted active power is certain, the size of P depends on the change of Q, that is, it is proportional to the square of Q. The following table shows the change of P caused by Q that needs to be transmitted by electricity under different load power factors

relationship between load power factor and reactive power and power loss of electric transmission:

it can be seen from the above table that when the load power factor COS is lower than 0.7, because the reactive power Q required by the load is greater than the active power P, the lower the load power factor cos, the greater the reactive power required by the load, and the greater the reactive power of electric transmission and the resulting active power loss. Therefore, in order to reduce the reactive power transmitted by electricity and reduce the loss of active power in electricity, when the load power factor COS is low (COS < 0.8), reactive compensation must be carried out at the load point or in electricity, so as to improve the load power factor and balance the reactive power of electricity locally

I. advantages and disadvantages of random follower reactive power compensation

(I) advantages

Random follower reactive power compensation is to directly install low-voltage capacitors in parallel on inductive electrical equipment such as transformers and motors in order to improve the power factor of electrical loads. The biggest advantage of this installation method is that the reactive power compensation is input when the electric equipment is running, and the reactive power compensation is withdrawn when the electric equipment is stopped. There is no need to adjust the compensation capacitance frequently. It has the advantages of less investment, small space occupation, light weight, easy installation, convenient and flexible configuration, simple maintenance, less accident rate, and no need for special personnel to take care of it

(II) shortcomings

random follower compensation, although it has many advantages that we should make use of, but it also has its shortcomings: (1) it cannot automatically switch, which is the main disadvantage of random follower compensation compared with the automatic switching device of capacitance compensation. It cannot follow the cleaning machine like the automatic switching device: high-density polyethylene In general polystyrene, the reactive power is balanced by changing the number of capacitors according to the change of power factor in the power supply network. (2) Reverse power transmission during shutdown. Since the random follow-up compensation is to connect the capacitors directly in parallel with the electrical equipment, during the transient process after the power supply of the electrical equipment is cut off, the capacitor reverses the discharge of the electrical equipment. If the selection of the compensation capacitor is unreasonable, overvoltage will occur, which may damage the electrical equipment and capacitance. Therefore, the selection of capacitor compensation capacity must be scientific and reasonable. For frequently started electrical equipment, especially motors, we should pay more attention to the harm of overvoltage

II. Precautions for installing random follower

(-) selection of shunt capacitor capacity

when the shunt capacitor compensates the motor, its capacity should be calculated according to the following formula

where UE motor rated voltage kV

I0 no-load current a

the estimation method of rated capacity (kw) 30% ± 0.5 (kvar) for 1500 rpm and 3000 rpm motors with the most consumption, It can quickly and easily calculate the capacity of the compensation capacitor expected to be needed by 2019. Take 30kW motor as the standard, if the motor capacity is less than 30kW, increase 0.5kvar for each motor. Each unit with a capacity greater than 30kW will be reduced by 0.5kvar

the table of compensation capacitance required by various single motors calculated by formula is listed below:

(II) wiring of shunt capacitor

(1) selection of wire diameter. The size of wire diameter connecting compensation capacitor must be selected according to the rated current of capacitor. The rated current of the capacitor is:

Where, the rated current of IC capacitor a

the rated power of QC capacitor kvar

manual control button box! The operation is more humanized. The rated voltage of UE capacitor kV

the rated current of the capacitor can also be calculated by estimation, that is, 1kvar is equivalent to 2a, which is slightly larger than the actual current

(2) wiring method: for small capacitors below 10kvar, if a single connection is made, the line can be directly connected to the terminal post of the capacitor, while for capacitors with larger capacity above 10kvar, the connection card must be used for connection, because the rated current of these capacitors is above 20a, the wire is thick, especially the cable wiring. There are many burrs, and the distance between the terminal posts of the capacitors is very close, It is often easy to cause discharge short circuit and damage equipment

(3) shunt capacitors should not be placed in places that are overheated, leaking rain, dripping water, easy to squeeze, easy to press, easy to smash and hinder traffic, nor should they be placed too far away from the compensation equipment, so as to avoid unnecessary losses

III. energy saving benefits of random anti trap compensation

after installing anti trap capacitor compensation, the power factor can be increased and the variable loss can be reduced. When the power factor is increased from COA 1, which is composed of the main machine part, control part and power system of the experimental machine, to Cos 2, The percentage of variable loss reduction can be obtained from the following formula:

from the above formula, the benefit of reducing variable loss when the power factor is increased from cos 1 to Cos 2 can be calculated

up to now, our county has put 370 low-voltage random capacitor compensation capacitors 4440kvar, which can save 1.777 million KW h per year. After installing the random capacitance compensation, it can also reduce the equipment capacity, improve the power transmission capacity of the line, so that the overloaded transformer is no longer overloaded, so that the transformer that needs to be increased may not need to be increased, and the economic benefit is very good

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