The working principle and selection of Siemens soft starter 3RW44

The working principle of Siemens soft starter 3RW44

The device has two anti-parallel thyristors on each phase, one thyristor for the positive half-wave and the other for the negative half-wave. The rms value of the motor voltage (from the adjustable starting voltage or starting torque), through the Siemens soft starter 3RW44 leading phase to increase the motor rated voltage within a definable starting time, which is achieved through a variety of control methods.

The motor current changes in proportion to the voltage applied to the motor, so the reduction in the starting current is proportional to the voltage applied to the motor. The torque is proportional to the square of the voltage applied to the motor, so the reduction in the start conversion is proportional to the square of the voltage applied to the motor.

◆Example description

The rated data of SIEMENS 1LG4253AA motor (55 kW) at 400V is as follows:

Pe: 55kW

Ie: 100A

I direct start: about 700A

Me: 355Nm

Ne: 1480rpm

M direct start: about 700Nm

Set starting voltage: 50% (1/2 line voltage)

=> I start 1/2 direct start current (about 350A)

=> Mstarting1/4 the starting torque of direct starting (about 175Nm)

◆Starting current and torque characteristics of three-phase asynchronous motor combined with soft starter.

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The above figure is the current characteristic drop curve of the three-phase asynchronous motor during the start-up period of the Siemens soft starter 3RW44.

Transmitter|Encoder|Soft starter|Power supply|VFD|Light curtain|Servo products|Human-machine interface|Solenoid valve|Cylinder|Actuator|Flow meter|Transformer|Thyristor|Sensor|Deceleration drive gearbox reducer|Linear guide|Circuit breaker|Refrigeration compressorAll industrial products of okplazas are purchased from the original factory or formal channels of agents to ensure the original authenticity, which perfectly solves the problem of industrial product sample procurement and small-batch procurement for the majority of engineers and purchasing personnel.

The above figure is the torque characteristic drop curve of the three-phase asynchronous motor during the start-up period of the Siemens soft starter 3RW44.

◆Start

This means that since the electronic soft starter is used to control the motor voltage during the starting process, the incoming line current and the starting torque generated in the motor will also be adjusted. The same principle applies to the stopping process, so that the torque generated in the motor can be slowly reduced, so as to achieve the applied soft stop effect.

Contrary to the frequency modulation start and stop process of the inverter, the frequency remains constant and equal to the power supply frequency during this process. After the motor starts correctly, the thyristor will be fully turned on, that is, all the line voltage will be applied to the motor terminals. Since it is not necessary to control the motor voltage during operation, thyristor bridging can be achieved through the bypass contact integrated in the Siemens soft starter. This can minimize the waste heat generated during continuous operation (caused by the power consumption of the thyristor) and also reduce the temperature rise in the area around the switching device.

◆Working mode of Siemens soft starter 3RW44

Transmitter|Encoder|Soft starter|Power supply|VFD|Light curtain|Servo products|Human-machine interface|Solenoid valve|Cylinder|Actuator|Flow meter|Transformer|Thyristor|Sensor|Deceleration drive gearbox reducer|Linear guide|Circuit breaker|Refrigeration compressorAll industrial products of okplazas are purchased from the original factory or formal channels of agents to ensure the original authenticity, which perfectly solves the problem of industrial product sample procurement and small-batch procurement for the majority of engineers and purchasing personnel.

The figure above is the principle diagram of phase angle control and soft starter with internal bypass contacts.

Siemens soft starter 3RW44 selection instructions

Transmitter|Encoder|Soft starter|Power supply|VFD|Light curtain|Servo products|Human-machine interface|Solenoid valve|Cylinder|Actuator|Flow meter|Transformer|Thyristor|Sensor|Deceleration drive gearbox reducer|Linear guide|Circuit breaker|Refrigeration compressorAll industrial products of okplazas are purchased from the original factory or formal channels of agents to ensure the original authenticity, which perfectly solves the problem of industrial product sample procurement and small-batch procurement for the majority of engineers and purchasing personnel.

Siemens soft starter 3RW44 application selection

This device is a substitute for star-delta starters and frequency converters. Its main feature is compact size and can perform soft start, soft stop and uninterrupted switching without generating current peaks that burden the system. For many drive devices that can only be operated with frequency converters, as long as they do not require speed control, do not have particularly high starting torque or require starting current close to the rated current, this type of Siemens soft starter can be selected.

◆Typical applications: conveyor belts, conveyors, compressors, exhaust fans, mixers, centrifuges, crushers, mills, milling machines, circular saws, band saws, fans, pumps and other places.

◆Play a major role:

1. It can play the role of smooth starting and smooth braking in the conveyor belt conveying system;

2. It can play the role of no pressure fluctuation and prolong the service life of the pipeline system in the rotary pump and piston pump;

3. It can reduce the starting current in mixers and mixers;

4. It can reduce the pressure of the gear box and the V-belt in the fan.

◆Storage and operating conditions:

1. Allowable ambient temperature requirements for storage: -25°C...+80°C;

2. Allowable ambient temperature requirements for operation: 0°C...+60°C, but drop from 40°C;

3. Allowable relative humidity requirements: 10...90%;

4. The maximum allowable installation altitude: 5000 meters, but it drops from 1000 meters.

Note: Do not allow liquid, dust or conductive objects to enter the Siemens soft starter.

◆Starting level:

If you want to choose a suitable and reasonable soft starter when selecting, you must understand the starting time (that is, the starting level) of the application. The longer the starting time, the greater the thermal load on the thyristor of the equipment. Therefore, the Siemens soft starter 3RW44 can work continuously under normal starting conditions (CLASS10), 40°C ambient temperature, and fixed switching frequency. At the same time, the corresponding value can be found in the "Technical Data of the Power Supply Unit". If there is a deviation from this data parameter, the size of the soft starter needs to be increased.

◆Selection criteria: The soft starter specifications must be selected according to the motor rating (rated current ≥ motor rated current), if it is for a motor with a high starting current ratio (usually I/Ie ≥ 8), the correct soft starter specifications must be selected.

◆Application examples:

1.CLASS10 starts normally (maximum 20 seconds when the motor is 350%In), and the rated value of the soft starter equal to the rated value of the motor used can be selected. The specific parameters are shown in the figure below.

Transmitter|Encoder|Soft starter|Power supply|VFD|Light curtain|Servo products|Human-machine interface|Solenoid valve|Cylinder|Actuator|Flow meter|Transformer|Thyristor|Sensor|Deceleration drive gearbox reducer|Linear guide|Circuit breaker|Refrigeration compressorAll industrial products of okplazas are purchased from the original factory or formal channels of agents to ensure the original authenticity, which perfectly solves the problem of industrial product sample procurement and small-batch procurement for the majority of engineers and purchasing personnel.

2.For level 20 heavy-load start (up to 40 seconds at 350% In motor), the power level of the selected soft starter must be one level higher than the power level of the motor used. The specific parameters are shown in the figure below.

Transmitter|Encoder|Soft starter|Power supply|VFD|Light curtain|Servo products|Human-machine interface|Solenoid valve|Cylinder|Actuator|Flow meter|Transformer|Thyristor|Sensor|Deceleration drive gearbox reducer|Linear guide|Circuit breaker|Refrigeration compressorAll industrial products of okplazas are purchased from the original factory or formal channels of agents to ensure the original authenticity, which perfectly solves the problem of industrial product sample procurement and small-batch procurement for the majority of engineers and purchasing personnel.

3.For heavy load starting at level 30 (maximum 60 seconds at 350% In motor), the power level of the selected soft starter must be two levels higher than the power level of the motor used. The specific parameters are shown in the figure below.

Transmitter|Encoder|Soft starter|Power supply|VFD|Light curtain|Servo products|Human-machine interface|Solenoid valve|Cylinder|Actuator|Flow meter|Transformer|Thyristor|Sensor|Deceleration drive gearbox reducer|Linear guide|Circuit breaker|Refrigeration compressorAll industrial products of okplazas are purchased from the original factory or formal channels of agents to ensure the original authenticity, which perfectly solves the problem of industrial product sample procurement and small-batch procurement for the majority of engineers and purchasing personnel.

Note: The settings and equipment specifications in the above figure are only examples, for reference only and not binding. The set value depends on the relevant application and must be optimized when debugging Siemens soft starters.

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