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The power factor and power efficiency


abstract in the process of power supply, a user power factor of the high and low, directly related to the power grid in the power loss and power loss, is related to the voltage of the power supply line loss and voltage fluctuation, and relates to save power and the power supply quality of the regional power supply.The article introduces the main factors influencing the grid power factor and low voltage reactive power compensation of several practical methods.

Power factor refers to the apparent power supply in the power grid line active power consumption accounts for a percentage.In the operation of the network, we hope to see is the power factor of the bigger the better, if you can do this, the apparent power in the circuit will be most used for active power supply, in order to reduce the consumption of reactive power.A user power factor of the high and low, hair, offer, electricity for electric power systemequipmentMake full use of, have a significant impact.Appropriate progress the power factor of the user, not only can fully exert, power supplyequipmentProduction capacity, reduce line losses, improve the quality of voltage, and can improve user efficiency of electrical equipment and itself for the user to save electricity.Therefore, for the national general power supply enterprises, especially for some kinds of present national modified rural power grids, if can effectively improve the low voltage compensation, not only can reduce the pressure of a grid compensation at the next higher level, to improve the progress the user the power factor, but also can effectively reduce the power loss, reduce electricity users.The social benefit and economic benefit is very significant.

First, the main factors influencing the power factor

First of all we have to get to know the main reason for the power factor to produce.The generation of power factor is mainly due to the ac electrical equipment in the process of their work, in addition to the consumption of active power, reactive power is needed.When active power P have certain, such as reducing reactive power P, the power factor can progress.In extreme cases, when P = 0, without its power factor = 1.The essence of the subject therefore progress power factor is to reduce the reactive power requirement of electrical equipment.Affect the power factor is mainly the following several aspects.

(a) asynchronous motor and powertransformerIs the main consumption of reactive power equipment

Asynchronous motor stator and rotor asynchronous motor is the air gap between the main factors that need to be more reactive.The asynchronous motor is the reactive power consumption by its light the reactive power and under a certain load, the added value of reactive power which is composed of two parts.So to improve the power factor of asynchronous motor to prevent the no-load running and progress as much as possible of the motor load rate.Transformer consumes reactive ingredient is its no load reactive power, it has nothing to do with the size of the load factor.Therefore, in order to improve the power factor of power system and the enterprise, the transformer should not be running light or its long in low load operation condition.

(2) the power supply voltage within the prescribed scope of power factor have a big impact

When the voltage is higher than 10% of the rating, because of the influence of the magnetic circuit saturation, reactive power will grow quickly, accounts for the relevant statistics, when the power supply voltage is 110% of the rated value, the general factory reactive power will increase by about 35%.When the power supply voltage is lower than the rating, reactive power and to reduce the power factor of making them accordingly improved.But lowering power supply voltage will affect the normal work of the electrical equipment.So, should take measures to make the power system voltage stability as soon as possible.

(3) the grid frequency fluctuation of asynchronous motor and transformer magnetizing reactive power caused certain effect

We know that some of the main factors affecting the power system, power factor, so we need to seek some effective, can make advances some practical methods of low voltage power grid power factor, make DiYaWang can realize the balance of reactive of, to achieve the effect of loss reduction and energy saving.

Second, DiYaWang common methods of reactive power compensation

We usually adopt the low voltage reactive power compensation method mainly has three kinds: random compensation, as compensation, tracking compensation.The following simple introduce the scope of application of the three compensation mode and the advantages and disadvantages of using this compensation mode.

1. The random compensation

Compensation is the low voltage capacitor groups at random with motor and, through the control, protection and motor, cutting at the same time.Random compensation applicable to compensate the reactive power consumption of the motor, with magnetic reactive power compensation is given priority to, this way can be better to limit the rural electric reactive power peak load.

Random compensation is: the advantages of electricity equipment is running, reactive power compensation into, electricity equipment stoppage, compensation equipment also quit, and does not need frequent adjustment compensation capacity.Has the advantages of low investment, small placeholder, easy installation, configuration, convenient and flexible, simple maintenance, low accident rate, etc.

2. Along with the implement compensation

With unit refers to the low voltage capacitor compensation through low-pressure insurance in distribution transformer secondary side, to compensate for reactive power compensation of distribution transformer no-load mode.With change in light load or no-load reactive load reactive power, mainly for transformer no-load excitation with no-load changeable reactive power is the main part of the site to reactive load, for light load distribution change, this part of the loss accounts for a large proportion of supply, leading to the increase of electricity price, against electricity network with the same price.

With implement compensation is: the advantages of simple connection, convenient maintenance management, can effectively match variable light reactive power compensation, reactive power base in rural power grid limit load, the balance of the part of reactive power on the spot, and progress with utilization, reduce reactive power network loss, has high efficiency, is currently one of the most effective means of reactive power compensation.

3. Tracking compensation

Tracking compensation refers to reactive power compensation as control protection device, cutting device will group low voltage capacitor compensation on the large user 0.4 kv busbar compensation mode.Applies to more than 100 kva dedicated with users, changeable can replace randomized, with two kinds of compensation mode and the compensation effect is good.

Tracking compensation is: the advantages of flexible operation mode, operation maintenance workload small, than the previous two compensation mode relative to extend the service life, more reliable operation.But the disadvantage is that the control protection device complex, relatively large initial investment.But when the three compensation ways of economy approaches, priority tracking compensation mode selection.

Third, take appropriate measures to progress idea system natural power factor

Progress of natural power factor is not acquire any compensation equipment, the lower the power equipment of reactive power required to reduce load taking reactive power to advance the method of power factor of the industrial and mining enterprises, it does not need to increase investment, is the power factor method of economic progress.Progress of natural power factor measures below some brief introduction.

1. The reasonable use of motor (page 122)

(on page 199)

Reasonable selection of the type and specification of the motor and capacity, so that it is close to full load operation.When choosing motor, should not only pay attention to their mechanical properties, and to consider their appliance standards.If the motor under low load operation for a long time, both increases power consumption, and make the power factor and efficiency are significantly worse.So the progress from save power and power factor, from the viewpoint of the fair must be properly choose the capacity of the motor.

2. The progress of asynchronous motor inspection quality

Experiments show that the asynchronous motor stator winding circle number changes, changes in the air gap between the rotor and the motor when the size of the reactive power of asynchronous motor has a big impact.

3. Using synchronous motor synchronous or asynchronous motor power factor operation progress

Principle know by motor, synchronous motor on the active power consumption depends on the motor with the size of the mechanical load, and reactive power depends on the size of excitation current in the rotor, when under excitation state, "learn" the stator winding to the grid reactive power, in extreme condition, the stator winding to the power grid reactive "send".Therefore, as long as adjust the excitation current of the motor, make its in extreme condition, can cause the synchronous motor "sent" to the power grid reactive power, reduce the power grid reactive power given to the industrial and mining enterprises, thus advances the power factor of industrial and mining enterprises.Asynchronous motor synchronous operation is to connect the three-phase asynchronous motor rotor winding is appropriate and pass into the dc excitation current, to assume the synchronous motor running, this is "asynchronous motor synchronization.So as long as adjust the dc excitation current of motor, to assume the extreme condition, which can output reactive power to the grid, so as to achieve the goal of progress DiYaWang power factor.

4. Reasonable choice with variable capacity, improve the distribution operation mode

To change with the load factor is lower, generally take the "withdraw, change, and, stop" methods, such as the load rate of progress to the optimal value, thus improving the natural power factor of power grid.

Through the above progress evenly weighted power factor and natural power factor of the narrative, perhaps we have the simple power term "power factor" had a deeper understanding of and familiar.


[1] XiaoYunXin. Electricity monitoring [M]. Water power press, 2003.

JinLongZhang Ding Yushan. Power grid reactive power compensation and practical technology [M]. China water conservancy and hydropower press, 2004.

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