The amount of line loss obtained by measuring the difference between the amount of power supplied and the amount of electricity sold by the energy meter is called the statistical line loss. In the statistical line loss, part of the power is determined by the operating parameters in the corresponding time period during the transmission, transformation and distribution. This part of the lost power is called "technical line loss". Another part of the statistical line loss is the amount of power lost due to leakage, electricity stealing, etc., called "management line loss". In the power line loss management, in addition to strengthening management to reduce the "management line loss of power", it also reduced the "technical line loss" by adopting a series of technical measures. This paper analyzes the relationship between voltage, power factor and line loss, and discusses the effect of changing the operating parameters of the power grid to reduce the "technical line loss".
2 voltage and line loss relationship(1) The magnitude of the line loss in the grid is inversely proportional to the square of the operating voltage:
A=[(P2+Q2)/U2]·R·t (1)
In the formula A--line loss, kW·h
P--active power, kW
Q--reactive power, kvar
U--operating voltage, kV
R--resistance, Ω
T--time, h
It can be seen that an appropriate increase in operating voltage is an important measure of loss reduction.
(2) The main ways to increase the operating voltage in rural power grids:
1 Change the transformer tap. When the system has sufficient reactive power, changing the tap of the main transformer of the 35kV substation can increase the line voltage by 2.5% to 5%, and changing the 10kV distribution transformer tap can also increase the line voltage by 5%. In actual operation, simultaneous adjustment of 35kV and 10kV transformer taps can comprehensively increase the operating voltage by 6% to 8%. Therefore, the loss in the line and transformer can be reduced by more than 10% through the adjustment of the tap.
2 Install shunt capacitors at the end of the 35kV substation or 10kV line. When the system has insufficient reactive power or the networked line is long, it is not very effective to change the voltage of the transformer tap to adjust the voltage. At this time, capacitors should be installed for reactive power compensation, reducing the reactive component of the line, reducing the line loss, while reducing the voltage loss and increasing the operating voltage to further reduce the power loss. Therefore, the effect of installing a shunt capacitor on increasing the line operating voltage and reducing the line loss is quite remarkable.
3 relationship between power factor and line loss(1) Another expression of power loss:
A=(P/U·cosφ)2·R·t (2)
In the formula A--line loss, kW·h
P--active power, kW
U--operating voltage, kV
R--resistance, Ω
Cosφ--power factor
T--time, h
It can be seen that increasing the power factor can reduce the power loss. In actual operation, increasing the power factor can also increase the grid operating voltage and increase the active output of the generator. Therefore, improving the power factor is an important means of economic operation of rural power grids.
(2) In rural power grids, the main method to improve the power factor is to install parallel capacitors at the end of a 35kV terminal substation or 10kV line. The capacity of the shunt capacitor is calculated according to formula (3):
Qk=P(tgφ1-tgφ2)(3)
Qk--parallel compensation capacitor capacity, kvar
P--Power transmission of active power, kW
Tgφ1 and tgφ2-- are the tangent values ​​corresponding to the power factor angle before and after compensation, respectively.
After adding a capacitor, the active power can be reduced to:
Ak=[Qk(2Q-Qk)]/U2·R·t(4)
In the formula Ak--reduced active power, kW·h
Qk--capacitor compensation capacity, kvar
Q--the reactive capacity before compensation, kvar
t--Run time after capacitor compensation, h
(3) In the rural power grid, the reasonable selection of the capacity of the asynchronous motor, matching it with the mechanical equipment, and avoiding the no-load operation of the motor can improve the power factor.
4 ConclusionThe influence of the two parameters of voltage and power factor on the line loss size is quite significant. Voltage and power factor are two important parameters for the economic operation of the power grid. In rural power grid operation, properly raising these two parameters has a significant effect on reducing grid losses.
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