Influence of voltage sag on single-phase V/V traction transformers Li Huawei, Fan Yu (School of Electrical Engineering, Beijing Jiaotong University, Beijing 100044, China) The mechanism of the ringing mechanism shows that the voltage sag causes the transformer to generate magnetizing inrush current, and the moment of voltage sag determines the aperiodic The magnitude of the component flux, which determines whether the core is saturated or not, and thus determines whether the transformer magnetizing inrush current occurs. The positive and negative of the flux at this time will affect the positive and negative of the inrush current. The duration of the voltage sag has a certain influence on the magnitude of the inrush current, and the value varies between 1.2 and 1.8 pu. When the transformer is in operation, the voltage sag will also excite the transformer magnetizing inrush current.
3 Logo Code: A fund project: National Natural Science Foundation of China (60776830); Ministry of Education, Doctoral Fund Project Funding (2009009110025); Beijing Jiaotong University Basic Research Business Fees Project Power Quality Issues can be divided according to the length of production and duration It is both steady state and transient. The steady-state power quality problem is characterized by waveform distortion and the duration is usually greater than 1 min. Transient power quality is usually characterized by transient duration, including voltage flicker, voltage swell and dip. Because the load of electric locomotive has nonlinearity, mobility, randomness of operating conditions, etc., transient characteristics are obvious. Therefore, transient power quality is the main problem in electric power quality research of electrified railway. This paper focuses on the voltage sag problem.
It drops to 0.1~0.9pu, and the duration is half a cycle to 1min under the power frequency, also called depression, dip and voltage drop. Most of the causes are due to short-circuit faults, the start-up of large-capacity asynchronous motors and circuit breakers, and capacitor switching. The voltage sag causes the sensitive controller to trip unnecessarily, and the inverter stops.
The research on voltage sag mainly includes the following types: research on feature quantity and detection and identification methods, such as research on suppression methods and devices, such as. At present, there are few articles on the impact of voltage sag on traction transformers in China. Tao Shun studied the transfer matrix of voltage sag between transformers and neglected the transformer excitation circuit. 12. Foreign, Styvaktakis first pointed out that voltage sag will cause transformers. Saturated, L. Sainz,. Pedraand Shakarami studied the effects of voltage sag on three-phase transformers based on PSPICE and MATLAB, respectively.
1.1 The phasor model is the magnetic permeability of the yoke, P4 and P5 are the leakage flux, and Y is the magnetic flux. The corresponding formula is Akå©0å©r where A and /, respectively indicate the cross-sectional area and length of each part. Magnetic permeability. Thus, by writing the magnetic circuit equation, the expression of the magnetic flux can be obtained as follows: A is a matrix that describes the relationship between the node and the branch in the circuit, and represents the correlation matrix of the magnetic circuit; P represents the permeance matrix; N represents A matrix of turns; I represents an identity matrix; represents a current matrix. According to the voltage and magnetic flux equations, it is obtained from the Journal of Beijing Jiaotong University, where u represents the voltage matrix. Substituting the magnetic flux matrix in equation (6) into equation (5), the current equation can be obtained from equation (7). In the magnetic equivalent circuit model, the magnetic circuit equation is finally converted into current and voltage to solve It is only in the calculation process that the magnetic circuit characteristics are considered more detailed.
1.3 In the calculation of transformer parameters, the single-phase V/V wiring transformer parameters are 110/ 27.5kV, 50MVA, short-circuit reactance 10%, no-load loss 0.09%, short-circuit loss is 0.46%. The ratio of core column to yoke length is 2, area ratio As 1, the saturation curve is shown in Table 1.
Table 1 Transformer core saturation characteristics system as shown, where the power supply voltage is 110kv, short-circuit capacity is 2400MVA. Single-line line, contact line is GLCA-100/215, load cable is G-70, rail is 50kg/m, line length 15s. The locomotive is a straight-through locomotive, the power factor is 0.8 (hysteresis), the locomotive current is 150A. When the system is in the 0.2s, the power supply side single-phase short circuit (voltage sag is B), the sag duration is 0. 11s When the transformer is unloaded, the primary current of the transformer is as shown in the sum.
It is a partial enlarged view of the current waveform, and the waveform has obvious discontinuity angle, which is one of the remarkable characteristics of the transformer magnetizing inrush current. 2 The effect of voltage sag on the transformer The book2 voltage sag can be balanced or unbalanced. It is mainly determined by the reasons for its occurrence. Depending on the magnitude and phase of the voltage sag, the voltage sag can be divided into seven categories, showing the common three types of sag. Class A represents the voltage sag caused by the three-phase short circuit, Class B represents the voltage sag caused by the single-phase short circuit, and Class C represents the voltage sag caused by the two-phase short circuit. A voltage waveform diagram for the class B sag.
Harmonic/secondary visible, the transformer current waveform has quite rich harmonics, wherein the second harmonic component is 80% of the fundamental wave, and the waveform is a cusp wave, which has the characteristics of typical magnetizing inrush current. Therefore, the voltage sag causes the transformer magnetizing inrush current, and its amplitude reaches nearly 1.8 times the rated current, which is suppressed.
3 Simulation analysis of the effect of voltage sag on the transformer From and visible during the voltage sag, the system does not generate magnetizing inrush current, only when the voltage is restored, the excitation inrush current is excited. This is because the voltage recovery process is similar to the transformer closing process, in which the transformer core is saturated.
When the voltage sag occurs in the system, the magnetic flux of the transformer is a certain value, which depends on the voltage at which the voltage sag occurs. If the voltage at the moment of voltage dip occurs is zero, then the flux is positive (negative) maximum, as shown by the aperiodic component flux. In the figure, the aperiodic component flux is positively largest. When the voltage sag is restored, the transformer winding voltage also increases. Based on the principle of flux linkage conservation, at this time, the composite magnetic flux in the magnetic circuit of the transformer will be the superposition of the non-periodic component flux and the periodic component flux. It is such that the magnetic flux at the time of voltage recovery does not abruptly and is equal to the non-periodic component flux. If the periodic component flux is not equal to zero at the voltage recovery time, the value of the resultant flux will be larger. As shown, the voltage phase is assumed to be 90. Thus, the transformer core will enter the saturation region, as indicated by zero.
Single-phase transformer voltage sag core flux When the core enters the saturation region, a large amplitude inrush current phenomenon will occur, as shown by zero. Since the current i0 when the core is not saturated is very small compared with the rated current of the transformer, the approximate processing is zero in the figure, and the discontinuous angle of the magnetizing inrush current is 0 = 01 + (2: - 02).
0 Single-phase transformer voltage dip Magnetizing inrush current The key factor of the magnetizing inrush current is the flux size in the core. Among them, the influencing factors of the periodic component flux are voltage magnitude and phase, voltage sag recovery time and the magnitude and direction of the core flux at this time. The influencing factors of the non-periodic component flux are the voltage magnitude and phase, and the voltage sag occurs. Wait.
Due to the large amplitude of the magnetizing inrush current, in addition to causing the transformer to overheat, the differential protection of the transformer will be mis-operated, and the adjacent transformer will be triggered and the current will be accidentally tripped. In severe cases, a large area will be caused. 5 The influence of the moment of the different voltage sag of the ink toe 1 is generated. When the voltage sag occurs at t = 0.2 s, the voltage is zero. Since the flux lag voltage 90 is non-periodic, the flux is negative and maximum, so the superposition is combined. The magnetic flux has a maximum value of 2 times the aperiodic component flux, which is sufficient to saturate the core, so a magnetizing inrush current occurs, as shown in 2(a) (compared to the composite flux below the voltage). When the voltage sag occurs at t=0.205s, the voltage is a positive maximum, and at this time, the non-periodic component flux is zero, and the result of the synthesized magnetic flux is that the maximum value is equal to the periodic component flux, so the core is not saturated. Therefore, the magnetizing inrush current does not occur, as shown in 2(b) (compared to the magnetic flux with only the periodic component).
3 is the current waveform and its spectrogram of the voltage sag moment equal to 0. 21s, and the corresponding voltage and flux waveform. It can be seen that the magneto-current current still occurs, but only the inrush current. The value becomes positive. Compared with the Journal of Beijing Jiaotong University, when the duration of the voltage sag changes from 0.11s to 012s, the magnetizing inrush current also occurs, but the inrush current value decreases from 1.8pu to 1. 2p.u This reason is caused by the difference in the periodic component flux caused by the voltage sag recovery, as shown in 5.
5 voltage and flux at different voltage sag durations Fig.15Voltageandfluxindifferentsag 3.3 Voltage sag at different load rates The electrified railway under heavy load conditions, the average load factor up to 50% 60% under normal circumstances, average The load factor is 30% and 60%. The single-line no-load running time can reach 40% and 50%. This paper compares the influence of voltage sag on the magnetizing inrush current of the transformer under no-load and load conditions, and sets the locomotive current 150A. The harmonic content is shown in Table 3. The harmonic current distortion rate is 23.63%. The result of the transformer under load is shown as 6.
Table 3: Harmonic current harmonic order ratio/% of locomotive 4 Conclusion Based on the UMEC model, the influence mechanism of voltage sag on the operating characteristics of single-phase V/V wiring traction transformer is studied. The research shows that the voltage sag will cause the traction transformer to generate excitation. Inrush current, which may cause misoperation of protection.
The magnitude of the non-periodic component flux at the time of voltage dip will determine whether the core is saturated or not, thereby determining whether the transformer magnetizing inrush current occurs. If the magnetic flux at this moment is zero, an inrush current will occur. The positive and negative of the flux at this time will determine the positive and negative of the inrush current.
The duration of the voltage sag has a certain effect on the magnitude of the inrush current, and its value varies between 1.21.8 pu.
When the transformer is in operation, when the voltage sag occurs, the transformer magnetizing inrush current will also be excited.
3 Logo Code: A fund project: National Natural Science Foundation of China (60776830); Ministry of Education, Doctoral Fund Project Funding (2009009110025); Beijing Jiaotong University Basic Research Business Fees Project Power Quality Issues can be divided according to the length of production and duration It is both steady state and transient. The steady-state power quality problem is characterized by waveform distortion and the duration is usually greater than 1 min. Transient power quality is usually characterized by transient duration, including voltage flicker, voltage swell and dip. Because the load of electric locomotive has nonlinearity, mobility, randomness of operating conditions, etc., transient characteristics are obvious. Therefore, transient power quality is the main problem in electric power quality research of electrified railway. This paper focuses on the voltage sag problem.
It drops to 0.1~0.9pu, and the duration is half a cycle to 1min under the power frequency, also called depression, dip and voltage drop. Most of the causes are due to short-circuit faults, the start-up of large-capacity asynchronous motors and circuit breakers, and capacitor switching. The voltage sag causes the sensitive controller to trip unnecessarily, and the inverter stops.
The research on voltage sag mainly includes the following types: research on feature quantity and detection and identification methods, such as research on suppression methods and devices, such as. At present, there are few articles on the impact of voltage sag on traction transformers in China. Tao Shun studied the transfer matrix of voltage sag between transformers and neglected the transformer excitation circuit. 12. Foreign, Styvaktakis first pointed out that voltage sag will cause transformers. Saturated, L. Sainz,. Pedraand Shakarami studied the effects of voltage sag on three-phase transformers based on PSPICE and MATLAB, respectively.
1.1 The phasor model is the magnetic permeability of the yoke, P4 and P5 are the leakage flux, and Y is the magnetic flux. The corresponding formula is Akå©0å©r where A and /, respectively indicate the cross-sectional area and length of each part. Magnetic permeability. Thus, by writing the magnetic circuit equation, the expression of the magnetic flux can be obtained as follows: A is a matrix that describes the relationship between the node and the branch in the circuit, and represents the correlation matrix of the magnetic circuit; P represents the permeance matrix; N represents A matrix of turns; I represents an identity matrix; represents a current matrix. According to the voltage and magnetic flux equations, it is obtained from the Journal of Beijing Jiaotong University, where u represents the voltage matrix. Substituting the magnetic flux matrix in equation (6) into equation (5), the current equation can be obtained from equation (7). In the magnetic equivalent circuit model, the magnetic circuit equation is finally converted into current and voltage to solve It is only in the calculation process that the magnetic circuit characteristics are considered more detailed.
1.3 In the calculation of transformer parameters, the single-phase V/V wiring transformer parameters are 110/ 27.5kV, 50MVA, short-circuit reactance 10%, no-load loss 0.09%, short-circuit loss is 0.46%. The ratio of core column to yoke length is 2, area ratio As 1, the saturation curve is shown in Table 1.
Table 1 Transformer core saturation characteristics system as shown, where the power supply voltage is 110kv, short-circuit capacity is 2400MVA. Single-line line, contact line is GLCA-100/215, load cable is G-70, rail is 50kg/m, line length 15s. The locomotive is a straight-through locomotive, the power factor is 0.8 (hysteresis), the locomotive current is 150A. When the system is in the 0.2s, the power supply side single-phase short circuit (voltage sag is B), the sag duration is 0. 11s When the transformer is unloaded, the primary current of the transformer is as shown in the sum.
It is a partial enlarged view of the current waveform, and the waveform has obvious discontinuity angle, which is one of the remarkable characteristics of the transformer magnetizing inrush current. 2 The effect of voltage sag on the transformer The book2 voltage sag can be balanced or unbalanced. It is mainly determined by the reasons for its occurrence. Depending on the magnitude and phase of the voltage sag, the voltage sag can be divided into seven categories, showing the common three types of sag. Class A represents the voltage sag caused by the three-phase short circuit, Class B represents the voltage sag caused by the single-phase short circuit, and Class C represents the voltage sag caused by the two-phase short circuit. A voltage waveform diagram for the class B sag.
Harmonic/secondary visible, the transformer current waveform has quite rich harmonics, wherein the second harmonic component is 80% of the fundamental wave, and the waveform is a cusp wave, which has the characteristics of typical magnetizing inrush current. Therefore, the voltage sag causes the transformer magnetizing inrush current, and its amplitude reaches nearly 1.8 times the rated current, which is suppressed.
3 Simulation analysis of the effect of voltage sag on the transformer From and visible during the voltage sag, the system does not generate magnetizing inrush current, only when the voltage is restored, the excitation inrush current is excited. This is because the voltage recovery process is similar to the transformer closing process, in which the transformer core is saturated.
When the voltage sag occurs in the system, the magnetic flux of the transformer is a certain value, which depends on the voltage at which the voltage sag occurs. If the voltage at the moment of voltage dip occurs is zero, then the flux is positive (negative) maximum, as shown by the aperiodic component flux. In the figure, the aperiodic component flux is positively largest. When the voltage sag is restored, the transformer winding voltage also increases. Based on the principle of flux linkage conservation, at this time, the composite magnetic flux in the magnetic circuit of the transformer will be the superposition of the non-periodic component flux and the periodic component flux. It is such that the magnetic flux at the time of voltage recovery does not abruptly and is equal to the non-periodic component flux. If the periodic component flux is not equal to zero at the voltage recovery time, the value of the resultant flux will be larger. As shown, the voltage phase is assumed to be 90. Thus, the transformer core will enter the saturation region, as indicated by zero.
Single-phase transformer voltage sag core flux When the core enters the saturation region, a large amplitude inrush current phenomenon will occur, as shown by zero. Since the current i0 when the core is not saturated is very small compared with the rated current of the transformer, the approximate processing is zero in the figure, and the discontinuous angle of the magnetizing inrush current is 0 = 01 + (2: - 02).
0 Single-phase transformer voltage dip Magnetizing inrush current The key factor of the magnetizing inrush current is the flux size in the core. Among them, the influencing factors of the periodic component flux are voltage magnitude and phase, voltage sag recovery time and the magnitude and direction of the core flux at this time. The influencing factors of the non-periodic component flux are the voltage magnitude and phase, and the voltage sag occurs. Wait.
Due to the large amplitude of the magnetizing inrush current, in addition to causing the transformer to overheat, the differential protection of the transformer will be mis-operated, and the adjacent transformer will be triggered and the current will be accidentally tripped. In severe cases, a large area will be caused. 5 The influence of the moment of the different voltage sag of the ink toe 1 is generated. When the voltage sag occurs at t = 0.2 s, the voltage is zero. Since the flux lag voltage 90 is non-periodic, the flux is negative and maximum, so the superposition is combined. The magnetic flux has a maximum value of 2 times the aperiodic component flux, which is sufficient to saturate the core, so a magnetizing inrush current occurs, as shown in 2(a) (compared to the composite flux below the voltage). When the voltage sag occurs at t=0.205s, the voltage is a positive maximum, and at this time, the non-periodic component flux is zero, and the result of the synthesized magnetic flux is that the maximum value is equal to the periodic component flux, so the core is not saturated. Therefore, the magnetizing inrush current does not occur, as shown in 2(b) (compared to the magnetic flux with only the periodic component).
3 is the current waveform and its spectrogram of the voltage sag moment equal to 0. 21s, and the corresponding voltage and flux waveform. It can be seen that the magneto-current current still occurs, but only the inrush current. The value becomes positive. Compared with the Journal of Beijing Jiaotong University, when the duration of the voltage sag changes from 0.11s to 012s, the magnetizing inrush current also occurs, but the inrush current value decreases from 1.8pu to 1. 2p.u This reason is caused by the difference in the periodic component flux caused by the voltage sag recovery, as shown in 5.
5 voltage and flux at different voltage sag durations Fig.15Voltageandfluxindifferentsag 3.3 Voltage sag at different load rates The electrified railway under heavy load conditions, the average load factor up to 50% 60% under normal circumstances, average The load factor is 30% and 60%. The single-line no-load running time can reach 40% and 50%. This paper compares the influence of voltage sag on the magnetizing inrush current of the transformer under no-load and load conditions, and sets the locomotive current 150A. The harmonic content is shown in Table 3. The harmonic current distortion rate is 23.63%. The result of the transformer under load is shown as 6.
Table 3: Harmonic current harmonic order ratio/% of locomotive 4 Conclusion Based on the UMEC model, the influence mechanism of voltage sag on the operating characteristics of single-phase V/V wiring traction transformer is studied. The research shows that the voltage sag will cause the traction transformer to generate excitation. Inrush current, which may cause misoperation of protection.
The magnitude of the non-periodic component flux at the time of voltage dip will determine whether the core is saturated or not, thereby determining whether the transformer magnetizing inrush current occurs. If the magnetic flux at this moment is zero, an inrush current will occur. The positive and negative of the flux at this time will determine the positive and negative of the inrush current.
The duration of the voltage sag has a certain effect on the magnitude of the inrush current, and its value varies between 1.21.8 pu.
When the transformer is in operation, when the voltage sag occurs, the transformer magnetizing inrush current will also be excited.