High-power motors generate large current surges at the moment of starting, which has a great impact on the stable power grid. In engineering practice, certain control measures are often used to improve and limit the adverse effects on the power grid during motor starting. . This article mainly introduces this!
Motors are ubiquitous in industrial applications. In particular, high-power motors generate large current surges at the moment of starting. This is a corresponding impact on the stable power grid. In engineering practice, certain control measures are often used to improve and limit the motor. Unfavorable phenomena to the power grid generated during the startup process.
At present, a large number of AC asynchronous motors are used in industrial and mining enterprises, and most of the motors adopt direct start mode. This starting method is very simple, but it will bring great harm.
1. Grid impact: excessive starting current (no-load starting current can reach 4~7 times of rated current, and 8~10 times or more when starting with load), which will cause the grid voltage to drop, affecting other power consumption. The normal operation of the equipment can also make the undervoltage protection action, resulting in harmful tripping of the equipment. At the same time, excessive starting current will cause the motor winding to heat up, which will accelerate the insulation aging and affect the life of the motor.
2. Mechanical shock: excessive impact torque often causes the motor cage bar, the end ring breaks and the insulation of the stator end winding is damaged, resulting in breakdown of the burning machine, distortion of the rotating shaft, coupling, transmission gear damage and belt tearing;
3. Impact on production machinery: sudden changes in pressure during start-up often cause damage to the piping and valves of the pump system, shortening the service life; affecting transmission accuracy and even affecting normal process control.
All of this poses a threat to the safe and reliable operation of the equipment, as well as excessive starting energy losses, especially when frequent starts and stops. In order to avoid serious impact on the power grid and equipment, high-power motors generally use the following two methods when starting up.
1, step-down start
Buck start is often said to start the star triangle. At the beginning of the start-up, the voltage of 220V should be supplied to the winding of 380V (buck-down use), and after the motor is rotated, a certain speed is reached, and the circuit is switched to 380V power supply to reduce the starting current. The motor is rotated by the action of a rotating magnetic field generated by an alternating current. The higher the frequency of the alternating current, the faster the rotational speed of the rotating magnetic field.
2, frequency conversion start
The frequency conversion start is to use the frequency converter to reduce the frequency of the 50Hz mains to a low frequency alternating current and supply it to the motor. When the motor is started, it will be activated slowly by the action of a very slow magnetic field, and the starting current will be relatively small. In theory, the inductive reactance of the motor coil is proportional to the frequency of the alternating current. When the inverter is started, if the voltage applied to the motor is still 380V, the current will still be relatively large, so when the frequency converter is started, the voltage is also reduced.
Second, voltage dips monitoring
Zhiyuan Electronics E6500 power quality and energy efficiency analyzer sampling using chip, 200kHz high-speed fixed-frequency sampling, can capture the shortest 50μs waveform transient pulse, while supporting the transient event non-destructive recording function, allowing users to find the hard-to-detect power quality sudden changes.
Through the E6500, the imbalance of the motor can be observed. Due to the unbalanced load of each phase, the three-phase unbalance will occur. The unbalance function page provides monitoring of the unbalanced phase parameters. The monitoring parameters are: unbalanced. Degree, sequence component, voltage, current value, and phase angle.
Figure 5
Zhiyuan Electronics E6500 Power Quality Analyzer supports 50Hz/60Hz power grid power system measurement. It can record all power quality parameters such as harmonics, voltage, current, frequency, fluctuation, flicker, power and three-phase unbalance in the analysis site. With advanced power quality measurement function, it also provides professional PC analysis software for secondary analysis, providing users with the most accurate power fault diagnosis analysis.
Motors are ubiquitous in industrial applications. In particular, high-power motors generate large current surges at the moment of starting. This is a corresponding impact on the stable power grid. In engineering practice, certain control measures are often used to improve and limit the motor. Unfavorable phenomena to the power grid generated during the startup process.
At present, a large number of AC asynchronous motors are used in industrial and mining enterprises, and most of the motors adopt direct start mode. This starting method is very simple, but it will bring great harm.
1. Grid impact: excessive starting current (no-load starting current can reach 4~7 times of rated current, and 8~10 times or more when starting with load), which will cause the grid voltage to drop, affecting other power consumption. The normal operation of the equipment can also make the undervoltage protection action, resulting in harmful tripping of the equipment. At the same time, excessive starting current will cause the motor winding to heat up, which will accelerate the insulation aging and affect the life of the motor.
figure 1
2. Mechanical shock: excessive impact torque often causes the motor cage bar, the end ring breaks and the insulation of the stator end winding is damaged, resulting in breakdown of the burning machine, distortion of the rotating shaft, coupling, transmission gear damage and belt tearing;
3. Impact on production machinery: sudden changes in pressure during start-up often cause damage to the piping and valves of the pump system, shortening the service life; affecting transmission accuracy and even affecting normal process control.
All of this poses a threat to the safe and reliable operation of the equipment, as well as excessive starting energy losses, especially when frequent starts and stops. In order to avoid serious impact on the power grid and equipment, high-power motors generally use the following two methods when starting up.
figure 2
1, step-down start
Buck start is often said to start the star triangle. At the beginning of the start-up, the voltage of 220V should be supplied to the winding of 380V (buck-down use), and after the motor is rotated, a certain speed is reached, and the circuit is switched to 380V power supply to reduce the starting current. The motor is rotated by the action of a rotating magnetic field generated by an alternating current. The higher the frequency of the alternating current, the faster the rotational speed of the rotating magnetic field.
image 3
2, frequency conversion start
The frequency conversion start is to use the frequency converter to reduce the frequency of the 50Hz mains to a low frequency alternating current and supply it to the motor. When the motor is started, it will be activated slowly by the action of a very slow magnetic field, and the starting current will be relatively small. In theory, the inductive reactance of the motor coil is proportional to the frequency of the alternating current. When the inverter is started, if the voltage applied to the motor is still 380V, the current will still be relatively large, so when the frequency converter is started, the voltage is also reduced.
Second, voltage dips monitoring
Zhiyuan Electronics E6500 power quality and energy efficiency analyzer sampling using chip, 200kHz high-speed fixed-frequency sampling, can capture the shortest 50μs waveform transient pulse, while supporting the transient event non-destructive recording function, allowing users to find the hard-to-detect power quality sudden changes.
Through the E6500, the imbalance of the motor can be observed. Due to the unbalanced load of each phase, the three-phase unbalance will occur. The unbalance function page provides monitoring of the unbalanced phase parameters. The monitoring parameters are: unbalanced. Degree, sequence component, voltage, current value, and phase angle.
Figure 5
Zhiyuan Electronics E6500 Power Quality Analyzer supports 50Hz/60Hz power grid power system measurement. It can record all power quality parameters such as harmonics, voltage, current, frequency, fluctuation, flicker, power and three-phase unbalance in the analysis site. With advanced power quality measurement function, it also provides professional PC analysis software for secondary analysis, providing users with the most accurate power fault diagnosis analysis.
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