Application Basics of the hottest soft starter

2022-07-30
  • Detail

Basic knowledge of soft starter application

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

soft starter is a novel motor control device that integrates motor soft start, soft stop, light load energy saving and a variety of protection functions. It is called soft start plastic drag friction and wear experimental machine in foreign countries. The key is composed of experimental server and intelligent automatic control system. Its main structure is a three-phase anti parallel thyristor and its electronic control circuit connected in series between the power supply and the controlled motor

different functions can be realized by using different methods to control the conduction angle of the three-phase anti parallel thyristor so that the input voltage of the controlled motor changes according to different requirements

soft starter and frequency converter are two completely different products. The frequency converter is used where speed regulation is required. Its output not only changes the voltage, but also changes the frequency 1kW at the same time; The soft starter is actually a voltage regulator. When the motor is started, the output only changes the voltage without changing the frequency. The frequency converter has all the functions of soft starter, but its price is much more expensive than the soft starter, and its structure is much more complex

2. What is the soft start of motor? What are the starting modes

the soft starter connected in series between the power supply and the controlled motor is used to control the conduction angle of its internal thyristor, so that the motor input voltage gradually rises from zero with a preset functional relationship until the end of starting, and the motor is given full voltage, that is, soft starting. In the process of soft starting, the starting torque of the motor gradually increases, and the speed also gradually increases. Soft start generally has the following starting modes

(1) ramp boost soft start. This starting method is the simplest, without current closed-loop control, and only the thyristor conduction angle is adjusted to increase as a function of time. Its disadvantage is that, due to no current limitation, sometimes a large impulse current will be generated during motor starting to damage the thyristor, which has a great impact on the film, and is rarely used in practice

(2) slope constant current soft start. This starting method is to gradually increase the starting current at the initial stage of motor starting, and keep it constant after the current reaches the preset value (T1 to T2 stages) until the starting is completed. During the starting process, the rate of current rise and change can be adjusted and set according to the motor load. If the current rising rate is large, the starting torque is large and the starting time is short

this starting mode is the most widely used starting mode, especially applicable to the starting of fan and pump loads

(3) step start. Start up, that is, make the starting current quickly reach the set value in the shortest time, that is, step start. By adjusting the set value of starting current, the effect of fast starting can be achieved

(4) impulse impulse starting. At the start-up stage, let the thyristor conduct for a period of time with a large current within a short period of time, then fall back, and then rise linearly according to the original set value, and connect it to the constant current for starting

this starting method is rarely used in general loads and is suitable for starting occasions with heavy loads and large static friction

3. What is the difference between soft start and traditional reduced pressure start

the traditional decompression starting modes of cage motor include y-q starting, auto coupling decompression starting, reactor starting, etc. These starting methods belong to step-by-step reduced voltage starting, which has obvious disadvantages, that is, there is a secondary impulse current during the starting process. The difference between soft start and traditional reduced voltage start is:

(1) no impulse current. When the soft starter starts the motor, the starting current of the motor rises linearly from zero to the set value by gradually increasing the conduction angle of the thyristor

(2) constant current starting. The soft starter can introduce current closed-loop control, so that the motor can maintain constant current during the starting process to ensure the smooth starting of the motor

(3) according to the load conditions and the selection of electrical relay protection characteristics, it can be freely and steplessly adjusted to the optimal starting current

4. What is the soft stop of motor

when the motor is stopped, the traditional control mode is completed by instantaneous power failure. However, in many applications, the motor is not allowed to shut down instantaneously. For example, if the water pump system of high-rise buildings and buildings is shut down instantaneously, it will produce a huge "water hammer" effect, causing damage to pipelines and even pumps. In order to reduce and prevent the "water hammer" effect, the motor needs to stop gradually, i.e. soft stop. The soft starter can meet this requirement. In the pump station, the application of soft parking technology can avoid the damage of the "flap door" of the pump station and reduce the maintenance cost and workload

the soft stop function in the soft starter is that after receiving the stop command, the thyristor gradually reduces the conduction angle from full conduction to full closure after a certain period of time. The parking time can be adjusted within 0 ~ 120s according to actual needs

5. How does soft starter realize light load and energy saving

cage asynchronous motor is an inductive load. During operation, the current in the stator coil winding lags behind the voltage. If the working voltage of the motor remains unchanged, the power factor is low under light load and high under heavy load. The soft starter can achieve the purpose of energy saving under light load by reducing the motor terminal voltage, improving the power factor, reducing the copper and iron consumption of the motor; When the load is heavy, increase the motor terminal voltage to ensure the normal operation of the motor

6. What protection functions does the soft starter have

(1) overload protection function: the soft starter introduces a current control loop, so it can track and detect the change of motor current at any time. By adding the setting of overload current and inverse time limit control mode, the overload protection function is realized. When the motor is overloaded, the thyristor is turned off and an alarm signal is sent

(2) phase failure protection function: during operation, the soft starter detects the change of three-phase line current at any time, and can make phase failure protection response in case of current interruption

(3) overheat protection function: detect the temperature of the thyristor radiator through the internal thermal relay of the soft starter. Once the radiator temperature exceeds the allowable value, the thyristor will be automatically shut off and an alarm signal will be sent

(4) other functions: other interlocking protection can be realized in the system through the combination of electronic circuits

7. What is soft start MCC control cabinet

mcc (motor control center) control cabinet, namely motor control center. Soft start MCC control cabinet is composed of the following parts: (1) circuit breaker at the input end, (2) soft starter (including electronic control circuit and three-phase thyristor), (3) bypass contactor of soft starter, (4) secondary side control circuit (to complete the selection and operation of manual start, remote start, soft start and direct start functions), with voltage, current display, fault, operation, working status and other indicator lights

8. Why are some soft starters equipped with bypass contactors

most soft starters have bypass contactor contacts on both sides of the thyristor, which has the following advantages:

(1) the control cabinet has two starting modes (direct starting and soft starting)

(2) at the end of soft start, the bypass contactor is closed, so that the soft starter is out of operation until it is put into operation again when it is stopped, which not only prolongs the service life of the soft starter, but also avoids harmonic pollution and reduces the heat loss of thyristor in the soft starter

9. What are the extended functions of soft start MCC control cabinet

the soft start MCC control cabinet can be further combined to realize a variety of composite functions. For example, adding two control cabinets with control logic can form a "one for use and one for standby" scheme, which is used for the fire protection system, sprinkler pump, domestic pump and other systems of the building. If a PC (programmable controller) is equipped, the fire pump can be automatically detected at a fixed time (such as half a month) and automatically shut down at a fixed time; With the corresponding control logic, the fire pump and each system can be regularly operated at low speed and low water pressure (no water outlet) during normal inspection; In case of fire fighting, full speed and full load operation shall be implemented. Several motors can be combined with control logic to form a living pump system or other special systems. Each motor can be turned on step by step according to the demand, and the motors can also be reduced step by step to achieve the best efficiency operation. According to customer requirements, it can also realize the automatic switching operation of multiple motors each time, so that each motor is in the same operating life

10. Where is the soft starter applicable

in principle, the cage asynchronous motor can be used in various applications where speed regulation is not required. The current application range is AC 380V (or 660V), and the motor power ranges from several thousand watts to 800KW

the soft starter is especially suitable for various pump loads or fan loads. There are many kinds of soft starter and impact testing machines, and the prices of different impact testing machines are also very different In order to control the cost, many enterprises pay too much attention to the price when purchasing impact testing machines, resulting in various problems in their later use Next, soft parking. Similarly, for variable load conditions and fire rating of insulation materials, the motor is in light load operation for a long time, and only in heavy load situations for a short time or instantaneously, the application of soft starter (without bypass contactor) has the effect of light load and energy saving

(end)

Copyright © 2011 JIN SHI