Motor starting methods, performance, advantages and disadvantages

Update date:2018-04-20 Source:MAXGE

Motor starting methods, performance, advantages and disadvantages

  The electrical equipment most familiar to electricians should be the electric motor. There are many ways to start the electric motor, including direct start, auto decompression start, Y-Δ step down, soft start, inverter startup, etc. the way. What is the difference between them?

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First, the general motor start mode.

1, full pressure direct start

In the case where both the grid capacity and the load are allowed to start directly at full pressure, a full-pressure direct start can be considered.

The advantages are easy to operate and control, easy to maintain, and more economical. It is mainly used for the starting of small-power motors. From the viewpoint of saving electric energy, motors with more than 11kw are not suitable for this method.

2, auto-coupling decompression start

Multi-tap decompression using an autotransformer can not only meet the requirements of different load starting, but also can 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 larger. When its winding tap is at 80%, the starting torque can reach 64% when it starts directly. And the tapping torque can be adjusted by tapping. It is still widely used today.

3, Y-Δ start

For a squirrel-cage induction motor with a delta-connected stator winding for normal operation, if the stator windings are star-connected at start-up and then connected to a triangle after starting, the starting current can be reduced and it can be reduced to the grid. The impact. Such a starting method is called a star-delta decompression start, or simply called a star-delta start (Y-delta start).

When starting with the star-delta, the starting current is only 1/3 of the original starting with the delta connection. If the starting current at the time of direct start is 6-7 Ie, the starting current will only be 2 – 2.3 times when the star delta starts. This means that when starting with the star-delta, the starting torque is also reduced to 1/3 of the original starting with the delta connection.

Applicable to no-load or light-load starting occasions. And compared with any other decompression starter, its structure is the simplest and the price is the cheapest. In addition, the star delta startup method has an advantage that when the load is light, the motor can be operated under star connection. At this time, the rated torque and load can be matched, which can improve the efficiency of the motor and save power consumption.

4, soft starter

This is the use of the thyristor phase shift regulator principle to achieve the motor voltage regulator start, mainly used for motor start control, start-up effect is good but the cost is higher. Due to the use of thyristor components, thyristors work with greater harmonic disturbances and have a certain influence on the power grid. In addition, the fluctuation of the power grid will also affect the conduction of the SCR components, especially when there are multiple SCR devices in the same power grid. Therefore, the failure rate of thyristor components is relatively high, because it involves the power electronics technology, so the requirements for maintenance technicians are also high.

5, inverter

Inverter is a 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 electronic technology and microcomputer technology, it is costly and has high requirements for maintenance technicians. Therefore, it is mainly used in areas where speed control is required and speed control is required.

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Second, decompression start, soft start, contrast the advantages and disadvantages of the frequency conversion start

Decompression starts, common is the star-delta start, the disadvantage is that the starting torque is small, only for no-load or light-load start. The advantage is that the price is cheap.

Soft start, you can set the start time and start the initial torque of the device to achieve soft start and soft stop, and can limit the starting current, the price is moderate.

Inverter start, can start smoothly according to the set time, and let the equipment run at the set frequency, the price is higher.

Third, soft start, inverter, decompression start performance principle comparison

1. The soft starter is a combination of thyristor AC voltage regulation technology and power factor control technology. It realizes soft start and soft stop of the motor through thyristor voltage regulation, and it does not have speed regulation function.


2. A frequency converter is a motor control (speed control) device that uses the on-off function of a power semiconductor device to convert an industrial frequency power supply to another frequency. The frequency conversion control of motor operation (voltage also varies with frequency, such as v/f constant) is a true high-efficiency speed control method with high efficiency. The frequency converter can achieve true soft start, soft stop and high speed regulation.

3. The common common ways of decompression start are auto decompression start and Y-Δ start. The biggest advantage of auto decompression start is that the starting torque is larger. When the winding tap is at 80%, the start Torque up to 64% when starting directly. And the tapping torque can be adjusted by tapping. It is still widely used today.

Y-Δ is suitable for no-load or light-load starting. And compared with any other decompression starter, its structure is the simplest and the price is the cheapest. In addition, the star delta startup method has an advantage that when the load is light, the motor can be operated under star connection. At this time, the rated torque and load can be matched, which can improve the efficiency of the motor and save power consumption.

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Fourth, soft start, inverter, decompression start comprehensive analysis

1, the price issue

Naturally, the inverter is the most expensive, and the Y-Δ and auto-coupling decompression start are relatively inexpensive. Economics will become the first choice for projects with smaller investment;

2. Controllable issues

Y-Δ, auto-reducing start-up is simple, but it is only started. However, in areas with a high degree of automation, the estimates will be used less frequently, and even less softening. The inverter control of the motor, including speed, voltage, etc. is far less than the decompression start, soft start can match. Therefore, inverters are preferred in large-scale or automated production lines.

3, network communication

The inverter itself can realize network monitoring through its own integrated or extended communication port. Soft start can also do some monitoring, but to achieve real-time monitoring of the motor, but also decompression start, soft start can not be compared.

4, maintenance aspects

Since Y-Δ, auto-reducing start-up itself is relatively simple, it is naturally the simplest to maintain. In fact, I am very opposed to using soft start. If I do not choose the inverter, I will definitely choose Y-Δ or auto decompression to start directly.


5, the frequency changer can finish to realize the soft rise and soft stop of the electrical machinery, so in the occasion that the relative load is relatively large, Y- Δ, auto decompression start or soft start can't compare with the frequency converter.

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V. Complementary knowledge comparison

1: soft starter and frequency converter

Both frequency converters and soft-start devices belong to the category of step-down startup. The frequency converter is designed to achieve step-down startup by changing the frequency.

Soft start is achieved by changing the conduction angle of the thyristor to start the process from voltage 0 to full voltage. The inverter is in full control, and the motor speed can be controlled by the instrument signal at any time. The soft starter can only start and stop the motor. It is the purpose of stepping down.

2: Motor starter type analogy.

Motor start commonly used methods: full pressure direct start, auto decompression start, Y-Δ start, soft start, frequency conversion start.

In the case that both the grid and the load are allowed, the motor is suitable for direct start, because it is easy to operate and control, and it is more economical.

Auto decompression start-up is often used to start larger-capacity squirrel cage induction motors. Although auto decompression start-up is an old-fashioned starting device, multi-tap decompression using an autotransformer 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 release and has a perfect overload and loss of pressure protection has been widely used.

The star-delta starting method has good current characteristics and poor torque characteristics, so it is only suitable for applications with no-load or light-load starting. However, this method has the simplest structure and the cheapest price, and can save power consumption during light-load operation.

The above starting methods all belong to stepped decompression starting, and there are obvious shortcomings, that is, secondary inrush current occurs during starting.

3: Comparison between soft start and traditional decompression start

The difference between soft start and traditional decompression start mode is。

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