Electrical Encyclopedia: The main role of large motor soft start and variable frequency start

What is the difference between a frequency converter and a soft starter?

Frequency converter:

definition:

An inverter that converts alternating current with constant voltage and frequency into alternating current with variable voltage and frequency is called a frequency converter.

effect:

Reduce the impact load caused by the start of the motor, control the speed of the motor, lengthen the start-up time, smooth the current, and achieve the purpose of soft start.

At the same time, it can improve the efficiency of the grid and motor. In fact, the frequency converter is mainly used in energy saving, and the output voltage, current and frequency are changed by adjustment. The general speed calculation motor uses a frequency converter.

Disadvantages:

1. The cost is high, and the price is much more expensive than the microcomputer protection.

2. Since the current inverter almost adopts the PWM control mode, such a pulse modulation form causes the inverter to generate a high current on the power supply side during operation, and causes the voltage waveform to be distorted. After the power system is subjected to harmonic pollution, the system affects the system. Operational efficiency, in particular, damages equipment and even jeopardizes the safe operation of the power system.

3. Overload makes the inverter jump more frequently. When the overload occurs normally, the motor is generally overloaded. As long as the motor parameters of the inverter parameter table are set properly, the motor overload is generally not present. The inverter itself is overloaded. Poor capacity is prone to overload alarms.

Soft starter:

Definition and role:

It is connected in series between the power supply and the controlled motor, and the internal thyristor is triggered by the microcomputer to trigger the conduction voltage to realize the AC voltage regulation, so that the input voltage of the motor gradually rises from zero with a preset function relationship until the end of the start, and the motor is given full voltage. That is, soft start, during the soft start process, the motor starting torque is gradually increased, and the rotational speed is gradually increased until the thyristor is fully turned on, and the motor operates on the mechanical characteristic of the rated voltage to achieve a smooth start.

Reduce the starting current. Avoid starting overcurrent trips. When the motor reaches the rated number of revolutions, the starting process ends and the rated voltage is supplied for the normal operation of the motor.

Disadvantages:

1. The power frequency cannot be adjusted, so the motor cannot be started from zero voltage and zero frequency, and zero impact start cannot be achieved.

2. Can not adjust speed.

3. The soft starter exits the system after starting the motor and loses its protection function.

1. The frequency converter is used for places that require speed regulation.

The output of the frequency converter not only changes the voltage but also changes the frequency at the same time.

2. The soft starter is actually a voltage regulator that protects the motor. When the motor is stepped down, the soft starter output only changes the voltage without changing the frequency.

3. The frequency converter has all the functions of the soft starter, but its structure is complicated and the price is much more expensive than the soft starter.

4. The frequency converter controls the electrical equipment by adjusting the frequency, and can be adjusted and started, such as the industrial frequency conversion pump. The soft start is basically far away by changing the resistance connected in the circuit to make the current from small to large. This way is used to start a high-power motor, which is used to reduce the fluctuation of the high-power motor directly to the grid, or cause some The trouble of important load unloading.

Electrical Encyclopedia: What are the advantages and disadvantages of large motor soft start and variable frequency start?

What are the advantages and disadvantages of large motor soft start and variable frequency start?

1. Frequency:

The output frequency of the soft starter is fixed to the power frequency, and the frequency is not adjustable; the inverter has an adjustable output frequency.

2. Voltage:

The soft starter controls the output voltage by controlling the conduction angle of the thyristor (or other power electronic components), and its output voltage is gradually increased from 0V to the rated voltage; the voltage of the inverter is adjustable.

3. Motor speed:

The soft starter does not adjust the motor speed; the frequency converter can adjust the motor to run at any speed.

Electrical Encyclopedia: Why should the motor start with a soft starter? And the role of the soft starter?

Motor Why start with a soft starter? And the role of the soft starter?

We know that the rated current of the motor is 4 to 7 times of the rated current. If the power of the motor is relatively small, then the impact on the grid is not very large. We allow it to start directly. Generally, the motor power is below 7.5KW. Directly launched.

But for large motors, the power is particularly large, so it is not allowed to start directly. If his rated current is 100A, then the current can reach several hundred amps at the moment of starting. The impact of such a large current on the grid is very The large ones will affect the normal operation of other loads carried by the same power grid. In this case, we can often see that, for example, when a large load starts, the light bulb will be darkened, etc., and we sometimes have this situation at home. For example, when the TV is turned on, the light bulb sometimes suddenly darkens, and also because the starting current of the load is too large, and the insulation of the motor winding is also extremely disadvantageous.

Therefore, for large motors, soft start is generally required. The so-called soft start is that the voltage we add to the initial stage is lower than the rated voltage.

Common soft starters include soft starter start-up and autotransformer step-down start. The autotransformer step-down start-up is applied to a voltage of 60% to 80% of the rated voltage at the beginning of the motor start-up. Let it move first. When it is turned, let him switch to the rated voltage to work. This is a simple soft start process, and the soft starter is more advanced than the autotransformer step-down start. The principle is the same, the soft start When the voltage of the motor is gradually increased from 0 to the rated voltage, his starting process is smoother, the starting effect is better, and the impact on the power grid and the winding is also minimal, which is better than the auto-transformer step-down starting. This is the advantage of soft starters in industrial applications.

The most commonly used in today's transmission engineering is the three-phase AC induction motor. In many cases, these motors are directly connected to the power system due to their starting characteristics. If you start directly online, it will generate up to 6 times the rated current of the motor. This current overloads the power supply system and the switching devices in series. If it is started directly, it will also produce a higher peak torque, which will not only impact the drive motor, but also damage the mechanical device. For example: auxiliary power transmission unit (V-belt, gear). In order to reduce the direct current, the starting auxiliary device, such as the starting reactor or the autotransformer, should be used, but the conventional method such as starting the reactor or autotransformer can only gradually reduce the voltage, and the soft starter can smoothly raise the terminal. The voltage can be achieved without impact starting.

Therefore, the power system and the motor can be optimally protected.

1. Reduce the starting current of the motor, reduce the distribution capacity, and avoid the investment of capacity expansion;

2. Reduce the starting stress and extend the service life of the motor and related equipment;

3. Smooth start and soft stop avoid the surge problem and water hammer effect of traditional starting equipment;

4, a variety of starting modes and a wide range of current, voltage and other settings, can adapt to a variety of load conditions;

5. Improve the reliable protection function and protect the safety of the motor and related equipment more effectively;

6. It can smoothly start/stop the motor without stepping, avoiding mechanical and electrical shocks caused by starting the motor in the traditional starting mode such as direct start, star/delta start, auto-decompression start-up, etc.

7, can effectively reduce the starting current and distribution capacity, to avoid capacity expansion investment.

Electrical Encyclopedia: The main role of the motor soft starter of the motor soft starter

The main function of the motor soft starter of the motor soft starter:

First: Effectively reduce the starting current of the motor; reduce the distribution capacity and avoid the investment in grid capacity increase.

Second: reduce the starting stress of the motor and load equipment; extend the service life of the motor and related equipment.

Third: the soft stop function effectively solves the problem of parking surge of the inertia system; it is impossible for conventional starting equipment.

Fourth: There are six unique starting modes; to adapt to complex motor and load conditions, to achieve a perfect starting effect.

Fifth: It has perfect and reliable protection function; it effectively protects the safety of the motor and related production equipment.

Sixth: The application of intelligent and networked technology of motor soft starter makes the motor control technology adapt to the higher requirements of the rapidly developing power automation technology.

Electrical Encyclopedia: The disadvantage of the soft start built-in bypass

First of all, we need to clarify one thing. The application of the soft starter is mainly applied to the start-up phase of the motor. After the motor enters the power frequency, it must enter the bypass contact work.

The bypass contactor is divided into an external bypass and a built-in bypass.

The external bypass can realize the cascade function, and one soft start can continuously start multiple motors, but the cost is high.

The built-in bypass can only control one motor, does not support the cascade function, the power segment is relatively narrow, and the cost is lower. Use some users who only control one motor without cascading function, saving cost and reducing wiring time due to built-in bypass.

So what is the disadvantage of using the built-in bypass?

1 The current passes through the soft starter for a long time, which will reduce the service life of the internal thyristor;

2 causing pollution to the front-end power supply;

3 Reduce the efficiency of power usage.

Electrical Encyclopedia: The Necessity and Difference of Soft Starter Built-in and External Bypass Contactor

Why do you want a previous contactor on the soft starter?

The contactor that is connected to the soft starter is called a bypass contactor. Because the soft starter is used for a long time, it will cause great pressure on the thyristor.

The long-term excessive current of the thyristor is unfavorable to it. At the same time, it is easy to cause the thyristor to be triggered by the circuit board. It is better to use the traditional contactor to keep it, because the soft start is only useful during the motor starting process, and it is operated at the power frequency. It is the same as the ordinary motor, so it is still reliable with the traditional contactor.

Soft start is a device that can reduce the starting current of the AC motor when starting. When the motor completes the starting process, the device can start the bypass contactor according to the set time to cut the soft start from the main circuit of the motor. The main contactor of the motor and motor is connected to the motor power circuit.

There are also two kinds of soft starters, one that does not use an external contactor and runs directly after starting. It is a built-in bypass contactor.

The other is the need for an external bypass contactor, which is less expensive and automatically switches to contactor operation after startup. This kind of soft start can start multiple motors at the same time, so that one machine can be used more.