由于大多数家庭是单相负荷和三相负荷一起，所以负荷大小和功耗时间是不同的

Since most households are single-phase and three-phase load with the load, the load size and power consumption are different times. Thus, three-phase unbalanced current grid relative presence, this imbalance power consumption is irregular, can not be predicted in advance. A carrier having a three-phase voltage power supply system affect long-term non-uniform. For three-phase unbalanced current, in addition to the power sector as reasonably possible load distribution, almost no effective solution. Phase imbalance is one of power quality problems. With the development and application connectivity, power electronics and other high-tech, three-phase unbalanced power source of more and more diverse. With the development of science and technology and the national economy, increasing demand for electricity, power quality requirements are also increasing. Based on the analysis and research, in the three-phase unbalanced distribution network, we look for the causes phase imbalance, resulting in unbalanced three-phase devices and equipment, safe and economic operation of electrical equipment and power grid, as well as on the order of national life It has far-reaching significance. In this paper, three-phase unbalanced 35kV distribution network engineering background, through modeling, simulation and research to identify the causes of the three-phase voltage imbalance, and proposed solutions and measures. Research methods and results of this paper, not only solve the practical problems, but also provides an effective method of theoretical analysis to improve grid management level. Key: unbalanced three-phase voltage with the same amount, according to the order, B, C, two-thirds of the angle, a similar condition called three-phase equilibrium, on the contrary, it is called unbalanced three-phase system for the latter, under normal circumstances, It can be divided into two types of normal and accident. Generally, a three-phase imbalance is due to the component or system load caused by asymmetry. Phase voltage imbalance as to measure the power quality is determined according to the normal operating conditions of imbalance to some extent. Generally, a three-phase three-phase voltage imbalance caused by load imbalance. Unbalanced Voltage is applied to the three-phase motor, negative sequence current generated by the rotor, the damping torque, and heat loss. In particular, when a single-phase open, two-phase motor is running, in the case of constant load, the motor may burn out. Three phase load distribution unreasonably large power load changes, insufficient load distribution transformer monitoring line impact of large, three-phase load torque are not equal. If the magnitude of the three-phase voltage and current are equal, the phase difference is 120 degrees, three-phase power system is called balanced or symmetrical. If one or both of these conditions are not met, the system is called asymmetric or unbalanced. If the same three phases of the load impedance and the impedance is linear, then this three-phase sinusoidal current, and the same the same frequency, the same amplitude, the same phase, they are 120 degrees. Generally use positive sequence, negative sequence and zero sequence concept of unbalanced three-phase system to quantify the voltage or current, into a three-phase symmetrical components asymmetrical components (the positive and negative sequence) and with the zero-sequence component. As long as the three-phase system, we can solve these three parts. For an ideal power system, due to the symmetrical three-phase, negative sequence and zero-sequence components are zero (which is why we often say that only positive sequence component under normal conditions). When the system fails, the three-phase asymmetric phase transition can be decomposed negative sequence components and zero-sequence component amplitude. Thus, by detecting these two components should not normally occur, we can know that the system has failed. Normal-phase imbalance is mainly due to asymmetric elements, parameters, or the load caused. Since the three-phase load uncertainty factor, phase voltage, current supply point and an unbalanced line losses occur easily. Not only that, but also adversely affect the feed point of the motor, endanger the normal operation of the motor. Therefore, if more than three-phase unbalanced distribution network can bear, it will affect the overall security of the power system. System failure caused by a three-phase (or two-phase). For example: a single-phase or two-phase circuit breaker, single-phase ground failure. In this case, the system is allowed to run, the system in question must be restored to normal in a short time. Intensive phase current imbalance is too large (3-fold increase), overload is too large, it may lead to overheating of the windings and transformer oil. Overheated windings, insulation aging fast; hot transformer oil, oil deterioration, rapidly reducing the insulation performance of the transformer, the transformer reduces the lifetime (every Single-phase or two-phase circuit breaker, single-phase ground failure. In this case, the system is allowed to run, the system in question must be restored to normal in a short time. Intensive phase current imbalance is too large (3-fold increase), overload is too large, it may lead to overheating of the windings and transformer oil. Overheated windings, insulation aging fast; hot transformer oil, oil deterioration, rapidly reducing the insulation performance of the transformer, the transformer reduces the lifetime (every Single-phase or two-phase circuit breaker, single-phase ground failure. In this case, the system is allowed to run, the system in question must be restored to normal in a short time. Intensive phase current imbalance is too large (3-fold increase), overload is too large, it may lead to overheating of the windings and transformer oil. Overheated windings, insulation aging fast; hot transformer oil, oil deterioration, rapidly reducing the insulation performance of the transformer, the transformer reduces the lifetime (every

Since most households are single-phase loads and three-phase loads together, load sizes and power consumption times are different. Therefore, the three-phase imbalance discurrent in the power grid is relatively present, and the power consumption of this unbalanced state is irregular and cannot be predicted in advance. The three-phase carrier of low-voltage power supply system has a long-term uneven effect. For three-phase unbalanced currents, the power sector has few effective solutions except for distributing loads as reasonably as possible. Three-phase imbalance is one of the problems of power quality. With the development and application of high-tech such as connection and power electronics, the sources of three-phase imbalance of power grid are more and more diversified. With the progress of science and technology and the development of national economy, the demand for electricity is increasing, and the demand for power quality is getting higher and higher. On the basis of analysis and research, in the distribution network three-phase imbalance, this paper looks for the three-phase imbalance causes, resulting in the three-phase imbalance of devices and equipment, the safety of the power grid and economic operation and electrical equipment, as well as the national living order has far-reaching significance. Based on the three-phase imbalance project of 35kV distribution network, the three-phase voltage imbalance is found out through modeling, simulation and research, and the solutions and measures are put forward. The research methods and results of this paper not only solve the practical problems, but also provide an effective theoretical analysis method to improve the level of power grid management. Key point: the three-phase unbalanced voltage phase is the same, according to the order, B, C, two-thirds of the angle, similar situation called three-phase balance, on the contrary, it is called a three-phase imbalance system, for the latter, under normal circumstances, it can be divided into two types of normal and accident. In general, the imbalance is caused by the asymmetry of the three-phase component or system load. The three-phase voltage allowed imbalance as a measure of power quality is determined according to normal unbalanced operating conditions to a certain extent. In general, the three-phase voltage imbalance is caused by the three-phase load imbalance. When the three-phase unbalanced voltage acts on the three-phase motor, the rotor produces negative sequence current, damping torque and heat loss. Especially when the single phase opens, the motor is in a two-phase operation state, in the case of constant load, the motor will burn. The distribution of three-phase load is unreasonable, the power load changeist swells, the power distribution transformer load monitoring is insufficient, the line impact is large, and the torque of the three-phase load is not equal. If the three-phase voltage and current are equal in magnitude and the phase difference is 120 degrees, the three-phase power system is called balanced or symmetrical. If one or both conditions are not met, the system is called asymmetry or imbalance. If the load impedance of the three phases is the same and linear, the currents of the three phases are sine, the same frequency, the same amplitude, the same phase difference, they are 120 degrees. The concepts of positive, negative and zero sequence are generally used to quantify the imbalance of voltage or current in the three-phase system, and the three-phase asymmetric components are divided into symmetrical components (positive and negative sequence) and hoveal zero components. As long as it is a three-phase system, we can solve the above three parts. For ideal power systems, the negative and zero sequence components are zero due to the three relatives (which is why we often say that only positive sequence components are in normal conditions). When the system fails, the three-phase phase change is asymmetric, and the amplitude of the negative and zero sequence components can be broken down. Therefore, by detecting these two components that should not occur properly, we can know that the system has failed. Normal imbalance is mainly caused by asymmetry of three-phase components, parameters or loads. Due to the uncertainty of the three-phase load factor, the three-phase voltage and current power points are prone to imbalance and line loss. Not only that, but also on the power supply point of the motor adversely affect, endangering the normal operation of the motor. Therefore, if the three-phase imbalance exceeds the range that the distribution network can withstand, it will affect the overall safety of the power system. Caused by a three-phase (or two-phase) system failure. For example: single-phase or two-phase break, single-phase ground failure, etc. In this case, the system is not allowed to run and the system in question must return to normal within a short period of time. Unbalanced heavy-duty phase currents are too large (to triple) and overloads are too large, which can cause windings and transformer oils to overheat. The windings overheat, the insulation ages quickly, the transformer oil overheats and the oil deteriorates, which rapidly reduces the insulation performance of the transformer and reduces the service life of the transformer (per

Because most families are single-phase load and three-phase load together, so the load size and power consumption time are different. Therefore, the three-phase unbalanced current in the power grid exists relatively, and the power consumption in this unbalanced state is irregular and cannot be predicted in advance. The three-phase carrier of low-voltage power supply system has long-term uneven influence. For the three-phase unbalanced current, the power sector has almost no effective solution except to distribute the load as reasonably as possible. Three phase unbalance is one of the problems of power quality. With the development and application of connection, power electronics and other high-tech, the sources of three-phase imbalance in power grid are more and more diversified. With the progress of science and technology and the development of national economy, the demand for power is increasing, and the demand for power quality is also increasing. On the basis of analysis and research, in the distribution network three-phase imbalance, this paper looks for the causes of three-phase imbalance, resulting in three-phase unbalanced devices and equipment, which has far-reaching significance for the safety and economic operation of the power grid and electrical equipment, as well as the order of national life. In this paper, based on the 35kV distribution network three-phase imbalance project, through modeling, simulation and research, the causes of three-phase voltage imbalance are found out, and the solutions and measures are put forward. The research methods and results of this paper not only solve the practical problems, but also provide an effective theoretical analysis method for improving the level of power grid management. Key point: the three-phase unbalanced voltage phasor is the same, according to the order, B, C, two thirds of the angle, similar situation is called three-phase balance, on the contrary, it is called three-phase unbalanced system, for the latter, under normal conditions, it can be divided into two types of normal and accident. Generally speaking, unbalance is caused by the load asymmetry of three-phase components or system. The allowable unbalance of three-phase voltage is taken as the measurement index of power quality, which is determined to a certain extent according to the normal unbalanced operation conditions. Generally speaking, three-phase voltage imbalance is caused by three-phase load imbalance. When the three-phase unbalanced voltage acts on the three-phase motor, the rotor produces negative sequence current, damping torque and heat loss. Especially when the single-phase open circuit, the motor is in two-phase operation state, in the case of constant load, it will burn out the motor. The three-phase load distribution is unreasonable, the power load changes greatly, the load monitoring of distribution transformer is insufficient, the line impact is large, and the three-phase load torque is not equal. If the amplitude of three-phase voltage and current is equal and the phase difference is 120 degrees, then the three-phase power system is called balance or symmetry. If one or both conditions are not satisfied, the system is said to be asymmetric or unbalanced. If the load impedances of these three phases are the same and all of them are linear impedances, then the current of these three phases is sinusoidal, the same frequency, the same amplitude and the same phase difference, they are all 120 degrees. In general, the concepts of positive sequence, negative sequence and zero sequence are used to quantify the voltage or current imbalance of three-phase system, and the three-phase asymmetric components are divided into symmetrical components (positive sequence and negative sequence) and zero sequence components in the same direction. As long as it is a three-phase system, we can solve the above three parts. For an ideal power system, due to the three-phase symmetry, both the negative sequence component and the zero sequence component are zero (that's why we often say that there are only positive sequence components in the normal state). When the system fails, the three-phase phase transition is asymmetric, which can decompose the amplitude of negative sequence component and zero sequence component. Therefore, by detecting these two components that should not happen normally, we can know that the system has failed. The normal imbalance is mainly caused by the asymmetry of three-phase components, parameters or loads. Because of the uncertainty of three-phase load factor, three-phase voltage and current supply points are prone to unbalance and line loss. Not only that, but also has an adverse impact on the power supply point of the motor, endangering the normal operation of the motor. Therefore, if the three-phase imbalance exceeds the range that the distribution network can bear, it will affect the overall security of the power system. Caused by three-phase (or two-phase) system failure. For example: single-phase or two-phase open circuit, single-phase ground fault, etc. In this case, the system is not allowed to run, and the system in question must return to normal state in a short time. Unbalanced large load phase current is too large (increased to 3 times), overload is too large, which may cause overheating of winding and transformer oil. The winding is overheated and the insulation aging is fast; the transformer oil is overheated and the oil is deteriorated, which rapidly reduces the insulation performance and service life of the transformer<br>