What are the causes of three -phase imbalances?

There are many reasons that cause three -phase voltage imbalances, such as: single -phase ground ground, disconnected resonance, etc., can operate managers quickly deal with it can only be quickly distinguished.

1. Dispel line failure

If a broken line but not ground, or a circuit breaker or isolation switch is not connected, the voltage transformer fuse melting will cause three -phase parameter asymmetry. When the previous voltage level line is disconnected, the voltage of the next voltage level is reduced as three phase voltage, one of which is low, and the other two are high but the voltage value of the two is close. When the lines at this level are disconnected, the disconnection phase voltage is zero, and the non -disconnected phase voltage is still phase voltage.

2. Floor failure

When the line is disconnected and grounded in single -phase, although the three -phase voltage is unbalanced, the voltage value after grounding does not change. Single -phase land is divided into two types: metallic grounding and non -metallic grounded ground. Metal grounding, the fault phase voltage is zero or close to zero, the non -fault phase voltage increases by 1.732 times, and the lasting unchanged; non -metallic grounding, the grounding phase voltage is not zero, but the value is reduced to a certain value. It is less than 1.732 times.

3. Resonant cause

With the rapid development of the industry, the load of non -linear power has increased largely. Some loads not only produce harmonic, but also cause the power supply voltage fluctuations and flashing, and even cause three -phase voltage imbalance.

There are two types of resonance caused by imbalance of three -phase voltage:

(1) Base frequency resonance

Base frequency resonance, characteristic is similar to single -phase ground ground, that is, a one -phase voltage decreases, and the other two phase voltage increases. It is not easy to find the fault point when finding the cause of the failure. At this time, you can check the special users. Essence

(2) Frequent resonance

The other is frequency resonance or high -frequency resonance, which is characterized by three -phase voltage increase at the same time. Three -phase voltage increases exceeding the wire voltage. In this case, it is generally caused by resonance.

4. Unreasonable allocation of three -phase load

Many staff members of the meter have no professional concept of knowledge about the balance of three -phase load. Therefore, when the electricity is connected, I did not notice that the three -phase load balance should be controlled, but it is blindly and casually carried out. Table, which has largely caused unbalance of three -phase load.

Secondly, most circuits in my country are integrated with power and lighting, so when using single -phase power equipment, the efficiency of electricity consumption will be reduced. Balance status.

5. Continuously changing with electric load

Causes of unstable electricity load include the increasing demolition of local II, increasing the increase in tables or electricity users; the instability of temporary electricity and seasonal electricity consumption. In this way, the uncertainty and inadequateness in time and time make the load of electricity use also have to follow the actual situation.

6. Weaken the surveillance of the distribution load

In the management of the power distribution network, it is often ignored the management problems in the three -phase load distribution. In the detection of the distribution network, the three -phase load of the power distribution transformer did not conduct regular detection and adjustment. In addition, there are many factors that cause three -phase imbalances, such as the influence of lines and the incompatibility of the three -phase load.

What are the hazards of three -phase imbalances?

1. Increase the electrical loss of the line

In the three -phase and four -line power supply network, when the current passes through the line wire, the power loss will be generated due to the existence of impedance, and the loss is proportional to the square of the current. When the low -voltage grid is powered by three -phase and four -line, it is inevitable that the three -phase load is unbalanced due to the existence of single -phase loads. When the three -phase load is unbalanced, the neutral line is passed. In this way, not only the phase line is lost, but also the neutral line also generates loss, which increases the loss of the grid line.

2. Increase the electric energy loss of the power distribution transformer

The power distribution transformer is a power supply owner equipment for low -voltage grids. When it runs under the imbalance of the three -phase load, it will increase the increase in deformation loss. Because the power loss of the distribution changes with the imbalance of the load.

3. Decreased matching forces

During the transformation design, the winding structure is designed according to the load balance. Its winding performance is basically the same, and the rated capacity of each phase is equal. The maximum allowance of the distribution is limited by the rated capacity per phase. If the distribution is running under the unbalanced work conditions of the three -phase load, a light load has a rich surplus capacity, which reduces the power of the matching. The degree of contribution is related to the imbalance of the three -phase load.

The greater the imbalance of the three -phase load, the more decreased the power of the matching. To this end, the output capacity cannot reach the rated value when the three -phase load is unbalanced, and its output capacity can be reduced accordingly, and its spare capacity decreases accordingly, and the overload capacity is reduced. If the distribution is running under overload conditions, it is easy to cause the distribution and heat, and in severe cases, it will even cause degeneration burns.

4. Disposal generates zero -order current

The distribution is running under the conditions of the three -phase load imbalance, which will generate zero -sequential current. The current will change with the degree of unbalanced three -phase load. The greater the unbalancedness, the larger the zero -order current. If there is a zero -sequential current in the running, zero -order magnetic flux will be generated in its iron core.

(There is no zero -sequential current on the high -voltage side) This forcing the zero -sequential magnetic flux can only be passed by the fuel tank wall and steel components as a channel, and the magnetic rate of the steel component is low. When the zero -sequential current passes through the steel component Losses, so as to increase the local temperature of the dilated steel component. The extension of the wound -changing winding is accelerated by overheating, resulting in a decrease in the life of the equipment. At the same time, the deposit of zero -sequential current will also increase the loss of ditching.

5. It affects the safe operation of electric equipment

The distribution is designed according to the three -phase load balancing operating conditions, and the resistance, leakage resistance and excitement impedance of each section are basically the same. When the deformation runs when the three -phase load is balanced, the three -phase current is basically equal, and the per phase voltage of each phase of the configuration is basically the same, and the three -phase voltage of the distribution output is also balanced. If the distribution runs when the three -phase load is imbalanced, the output current of each phase is not equal, and its internal three -phase voltage drop will not be equal.

At the same time, the matching runs when the three -phase load is imbalanced, and the three -phase output current is different, and the neutral line will pass. As a result, the neutral lines generate the impedance voltage drop, which causes the neutral point to drift, causing the voltage of each phase to change. A phase voltage of the load is reduced, and the voltage of the light load is rising.

Power supply under the imbalance of voltage, that is, the user's electric equipment that is easy to cause a high voltage is burned out, and the user's electric equipment with low voltage band may not be used. Therefore, when the three -phase load is unbalanced, it will seriously endanger the safe operation of electric equipment.

6. Decrease motor efficiency

The running under the imbalance of the three -phase load will cause the output voltage to be unbalanced. Because there are three voltage components: positive, negative, and zero -order voltage components, when this unbalanced voltage inputs the motor, the negative order voltage generates the rotating magnetic field and the rotating magnetic field generated by the positive sequence voltage is opposite, which plays a braking. effect.

However, because the positive magnetic field is much stronger than the negative -sequential magnetic field, the motor is still rotating in the direction of the positive magnetic field. Due to the braking effect of the negative -sequential magnetic field, the power output power of the motor will be reduced, which will lead to a reduction in motor efficiency.

At the same time, the temperature rise and non -power loss of the motor will also increase with the imbalance of the three -phase voltage. Therefore, the motor runs under the imbalance of the three -phase voltage, which is very economical and unsafe.

How to improve the three -phase imbalance?

1: Pay attention to the reasonable allocation of three -phase load

In terms of distribution of three -phase load, power staff should carefully collect and record relevant data in actual work to achieve a state of electricity loading to a certain extent. Secondly, the problem of better three -phase balance can be achieved by installing a balanced device.

In some places G, which uses low -voltage three -phase and four -line system, you can add adjustment of unbalanced current compensation devices to solve the various consequences caused by the unbalanced current phenomenon in the frequent power grid. Such a device can not only compensate the system without success, but also adjust the effect of imbalanced and merit.

In addition, according to the different situations of the load torque in the actual situation, proper adjustment of the wiring method also has a certain impact on the reasonable allocation of three -phase load.

2: The treatment method of imbalanced current in the load of three -phase load

According to the compensation principle of unbalanced current power, at any time that can be determined, the unbalanced load of three -phase is not grounded, so each of them can form a parallel form in the same resistance and capacitance in each of them.

Therefore, under the guidance of imbalanced current governance electricity compensation theory, the equivalent of different properties can be analyzed to determine the disarm and relative powerless compensation. When the power distribution transformer is compensated for unbalanced current, a few principles should be met. First, it is necessary to notice that the governance of the current should have two contents, one is the compensation power factor, and the other is to adjust the imbalance of the three -phase current. The two jointly determine the non -effective power required for compensation.

Secondly, in actual engineering construction, a full -capacity governance method should be adopted, which is distinguished from inductive compensation to avoid serious compensation. The third point is to consider that the load changes with time changes. Based on this characteristic, the amount of compensation should also be adjusted appropriately according to the changes in the load.

The fourth point is manifested in the limit of the number of shots and compensation devices in the device switch, and the optimization scheme of the day of the day should be managed. In short, when the proportional adjustment coefficient is set, the limit conditions of the power factor and the conditions for compensation limit need to be considered at the same time.

3: Increase the detection and adjustment of the three -phase load

It is also necessary to regularly open a three -phase load detection work. After the reasonable allocation and control of the three consistency, the relevant departments should open a testing work.

The balance of electricity cannot be absolute. It can only be done to make a relative balance. In actual testing, various departments should use the measurement indicator of the balanced degree of balance set by the state and related departments as a standard. The results of the test results are professional for professionalism The records and analysis of each phase of each phase are regularly detected in order to timely discover some unbalanced situations of three phases in time. When the parts with hidden safety hazards are found during the testing process, adjust and modify it in a timely manner.

For parts that are not found during the testing process, you should also be able to improve your vigilance. After the test is over, not only the data is organized and analyzed, but also timely feedback must be performed. The feedback here mainly refers to the adjustment of the three phases in inferred by the test results, and the possibility prediction of the new technologies in the three phases.

Through reasonable testing and in -depth analysis of the test results, we can avoid the occurrence of unbalanced phenomena to the greatest extent and reduce the emergence of electricity use accidents.

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