Are you aware of these starting methods of the motor?

Add Date: 2019/6/4    Views: 2535

The most familiar electric equipment for electrical workers should be the electric motor. There are many ways to start the motor, including direct start, auto-decompression start, Y-Δ step-down start, soft starter start, drive start, etc. the way. So what is the difference between them?

1, full pressure direct start
In the case of full-voltage direct start in both grid capacity and load, full-voltage direct start can be considered.
The advantages are convenient operation control, simple maintenance and economical. It is mainly used for the starting of small power motors. From the perspective of saving electric energy, this method should not be used for motors larger than 11kw.
2, auto-decompression start
The multi-tap decompression of the autotransformer can not only meet the needs of different load starting, but also obtain a larger starting torque. It is a decompression starting method that is often used to start a large capacity motor.
Its biggest advantage is that the starting torque is large. When its winding tap is at 80%, the starting torque can reach 64% of the direct starting. And the starting torque can be adjusted by tapping. It is still widely used today.
3, Y-Δ start
For a squirrel-cage asynchronous motor in which the normal running stator winding is a delta connection, if the stator winding is connected to a star at the start, and then connected to the triangle after the start, the starting current can be reduced and the grid can be reduced. The impact. Such a starting method is called a star-delta decompression starting, or simply a star-delta starting (Y-Δ starting).
When starting with the star-delta, the starting current is only 1/3 of the original starting directly by the delta connection. If the starting current at the time of direct start is 6 to 7 Ie, the starting current is only 2 to 2.3 times when the star-delta is started. This means that when starting with the star-delta, the starting torque is also reduced to 1/3 of the original direct start by the delta connection. For more related knowledge, please pay attention to the WeChat public number "Electrical and Electrical Learning".
Suitable for applications with no load or light load start. And compared to any other decompression starter, the structure is the simplest and the cheapest. In addition, the star-delta starting method has the advantage that when the load is light, the motor can be operated in star connection. At this time, the rated torque can be matched with the load, which can improve the efficiency of the motor and save power consumption.
4, soft starter
This is the use of the phase shift voltage regulation principle of the thyristor to achieve the voltage regulation start of the motor, mainly used for the start control of the motor, the starting effect is good but the cost is high. Due to the use of thyristor components, the thyristor has a large harmonic interference during operation and has a certain impact on the power grid. In addition, fluctuations in the grid can also affect the conduction of the thyristor components, especially when there are multiple thyristors in the same grid. Therefore, the failure rate of the thyristor component is high, and since the power electronics technology is involved, the requirements for the maintenance technician are also high.
5, the frequency converter
The frequency converter is the motor control device with the highest technical content, the most complete control function and the best control effect in the field of modern motor control. It adjusts the speed and torque of the motor by changing the frequency of the power grid. Because it involves power electronics technology and microcomputer technology, it is costly and has high requirements for maintenance technicians. Therefore, it is mainly used in areas where speed regulation is required and speed control is required.

The advantages and disadvantages of decompression start, soft start, and frequency conversion start.
Decompression start, the common is the star-delta start, the disadvantage is that the starting torque is small, only suitable for no-load or light-load start. The advantage is that the price is cheap.
Soft start, can set the start time and starting initial torque to achieve soft start and soft stop for the device, and can limit the starting current, the price is moderate.
Variable frequency start, can start smoothly according to the set time, and let the equipment run at the set frequency, the price is higher.
Soft start, frequency converter, decompression start performance principle comparison.
1. The soft starter is a combination of thyristor AC voltage regulation technology and power factor control technology. It is a soft start and soft stop of the motor through thyristor voltage regulation, and does not have a speed regulation function.
2. The frequency converter is a motor control (speed regulation) device that converts the power frequency power source into another frequency by using the on/off function of the power semiconductor device. The motor is controlled by frequency conversion (the voltage also changes with frequency, such as v/f constant), which is a true high-efficiency speed regulation method with high efficiency. The frequency converter enables true soft start, soft stop and efficient speed regulation.
3, the common way to start the decompression is auto-decompression start-up and Y-Δ start. The biggest advantage of auto-coupling and decompression is that the starting torque is large. When the winding tap is at 80%, start. The torque can reach 64% of the direct start. And the starting torque can be adjusted by tapping. It is still widely used today.
Y-Δ is suitable for applications where there is no load or light load starting. Www.diangon.com is copyrighted and compared to any other decompression starter, the structure is the simplest and the cheapest. In addition, the star-delta starting method has the advantage that when the load is light, the motor can be operated in star connection. At this time, the rated torque can be matched with the load, which can improve the efficiency of the motor and save power consumption.
Soft start, frequency converter, decompression start comprehensive analysis
1, the price problem.
Naturally, the inverter is the most expensive, and Y-Δ and auto-decompression start-up are relatively inexpensive. For projects with smaller investments, economics will be the first choice;
2. Controllable problems.
Y-Δ, auto-coupling decompression is simple to start, but it is just a start. However, in the case of high degree of automation, it is estimated that it will be used less, or even softer. The regulation of the motor through the frequency converter, including the speed and voltage, is far from being comparable to the decompression start and soft start. Therefore, the inverter is the first choice for large or highly automated production lines.
3. Network communication.
The frequency converter itself can be monitored by its own integrated or extended communication port. Soft start can also do some monitoring, but real-time monitoring of the motor is also unmatched by decompression start and soft start.
4. Maintenance.
Since the Y-Δ, auto-coupling decompression startup itself is relatively simple, it is also the easiest to maintain naturally. I am actually against the use of soft start, if you do not choose the inverter, you will definitely choose Y-Δ or auto-decompression start.
5. The inverter can complete the soft start and soft stop of the motor, so in the case of relatively large load, Y-Δ, auto-decompression start or soft start can not compare with the inverter.
Supplementary knowledge comparison
1: soft starter and inverter
Both the inverter and the soft start device belong to the buck start range. The inverter achieves the purpose of step-down startup by changing the frequency.
Soft start is achieved by changing the conduction angle of the thyristor to start from voltage 0 to full voltage.
The frequency converter is controlled in full range, and the motor speed can be controlled by the instrument signal at any time. The soft starter can only be used for voltage reduction when the motor starts and stops.
2: Motor analog mode is a large analogy
Common methods for starting the motor: full-voltage direct start, auto-decompression start-up, Y-Δ start, soft start, variable frequency start, etc.
In the case where both the grid and the load are allowed, the motor is preferably started directly because the steering control is convenient and economical.
Auto-coupling decompression is often used to start larger-capacity squirrel-cage asynchronous motors. Although auto-coupling decompression is an old-fashioned starting device, multi-tap decompression using autotransformers can accommodate multiple loads. The need for starting, but also to get a larger starting torque, coupled with the installation of thermal relays and low voltage trips with perfect overload and loss of pressure protection is widely used.
The star-delta starting mode has good current characteristics and poor torque characteristics, so it is only suitable for occasions with no load or light load starting, but this method is the simplest and the cheapest, and can save power consumption in light load operation.
All of the above starting methods belong to the staged decompression starting, and there are obvious disadvantages, that is, secondary inrush current occurs during starting.
3: Comparison between soft start and traditional decompression start mode
The difference between soft start and traditional decompression start mode is:
1 no inrush current. When the soft starter starts the motor, the motor starting current is linearly increased from zero to a set value by gradually increasing the conduction angle of the thyristor. No impact on the motor, improve the reliability of power supply, start smoothly, reduce the impact torque on the load machine, and extend the service life of the machine.
2 There is a soft parking function, that is, smooth deceleration, and gradually stop, it can overcome the shortcomings of instantaneous power failure, reduce the impact on heavy-duty machinery, avoid the water hammer effect of the elevation water supply system, and reduce equipment damage.
3 The starting parameters are adjustable, and can be adjusted steplessly to the optimal starting current according to the load condition and the grid relay protection characteristics.
Soft starters and frequency converters are two completely different applications.