Siemens soft starter 3RW55 working principle and circuit diagram

The working principle of Siemens soft starter 3RW55

The soft starter can be used to start a three-phase induction motor with a smaller torque and a lower starting current. After the start command is issued, the Siemens soft starter 3RW55 will immediately start the motor (t1). During the ramp-up period (t1 to t3), the current is conducted through the power semiconductor to make the motor start smoothly.

The 3RW55 soft starter has an internal starting detection function. If it detects that the motor has reached its rated operating speed before the end of the ramp-up time, the motor voltage will immediately increase to 100% of the line voltage (t2). The internal bypass contactor will be closed, the power semiconductor will be bypassed, and the Siemens soft starter will then enter the bypass state.

When the open command (4) is canceled, the coast to stop will be activated and the motor will be turned off. The power semiconductor can also ensure that the motor stops smoothly until it stops. The power of the motor is maintained until the end of the stop time (t4 to t5), and the actual free stop to standstill time of the motor may be longer (t6). The working principle diagram of the Siemens soft starter 3RW55 is shown below.

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①Speed;

②Voltage;

t1 motor starts with the set starting voltage US;

t2 reaches the rated speed ne;

The ramp-up time set by t3 ends (t3-t1);

The t4 open command is cancelled and the motor is turned off;

The stop time set by t5 ends (t5-t4);

t6 motor is stationary;

Starting voltage set by US;

Ue rated working voltage;

ne rated motor speed.

Siemens soft starter 3RW55 has functions

◆Soft start can be parameterized for smooth drive start;

◆Soft stop can be parameterized, used to realize smooth drive stop;

◆The current limit can be parameterized to avoid current peaks;

◆Integrated motor overload protection with adjustable trip level (OFF, CLASS 10A, 10E, 20E, 30E level);

◆Universal intrinsically safe equipment protection function can prevent 3RW55 soft starter from overload;

◆Extended omni-directional motor protection that can be realized by the thermistor protection of the motor, used to connect the temperature sensor;

◆Analog output, used to display a set of measured values

​​using an external display device;

◆Automatic parameterization simplifies system debugging;

◆Support 4 separate limit current limit monitoring;

◆Monitor the switching frequency to meet the waiting/cooling time requirements related to the application;

◆Condition monitoring for factory monitoring;

◆ Parameterizable digital input and output;

◆Basic unit with tracking function (evaluated by soft starter ES);

◆Motor connection options using inline circuit or inner delta circuit;

◆Emergency start function allows the system to continue running in the event of a system failure;

◆Phase asymmetry monitoring function can prevent asymmetric current consumption of the motor;

◆The heating of the motor can minimize the condensed water inside the motor, which is suitable for drives used outdoors;

◆Pump cleaning function, used to eliminate the clogging phenomenon of water pipes, filters and pump blades, and remove dirt from them;

◆Starting pulse, used to overcome high static friction (such as in a mill);

◆Access protection through PIN and user account;

◆Micro SD card, used to save data;

◆Optional communication module;

◆Slow speed function, suitable for applications with low anti-torque, such as machine tool positioning;

◆The application wizard supports debugging various applications;

◆Parameter group changes, suitable for applications with different load conditions;

◆ Cascade, used to connect the output of Siemens 3RW55 to the input of other soft starters;

◆Serial connection can turn on and off up to 3 different motors in sequence.

Siemens soft starter 3RW55 circuit example

◆Feeder assembly, matching type 1 without fuse (main circuit connection)

The equipment is connected between the motor starter protector of the motor feeder and the motor, which realizes the coordination type 1. The specific circuit diagram is shown 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: Q1 motor starter protector (such as 3RV2 or 3VA); Q11 soft starter; M motor; PE protective conductor.

◆Feeder assembly, matching type 1 with fuse (main circuit connection)

If a main contactor or line contactor is used, it should not be connected between the soft starter and the motor. In the case that the start command is connected to the relay of the contactor, the soft starter can indicate a "missing load voltage" fault. If galvanic isolation is required, a main contactor or line contactor can be installed between the Siemens soft starter and the fuse. The specific circuit diagram is shown 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: F1 is used for cable and line protection; gG full range fuse (such as 3NA3); Q21 is used for galvanic isolation main contactor or line contactor; Q11 soft starter; M1 motor; PE protective conductor.

◆Feeder installation, coordination type 2 (main circuit connection)

In order to obtain coordination type 2, a special semiconductor fuse (such as Siemens SITOR fuse) must be used to provide short-circuit protection for all thyristors. A short circuit may occur, for example, caused by motor winding or motor power supply cable failure. The specific circuit diagram is shown 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: Q1 motor starter protector; F3 aR partial fuse used to protect semiconductors (such as SITOR 3NE3/4 or 3NC3); F3* gR full range fuse used to protect semiconductors (such as SITOR 3NE1); Q11 soft start Device; M1 motor; PE protective conductor.

◆Inner delta start (main circuit connection)

Inner delta starting requires that the motor coil can be connected to the delta circuit under wired voltage. If the soft starter runs in the inner delta circuit, the motor power output of each independent device increases by a factor of 3. At the front end of the device after the rotary cover, you can find the value table for the increased current value of the inner delta circuit. If there is a load voltage and the motor is connected to the device, the Siemens soft starter 3RW55 will automatically detect the connection type.

●The circuit diagram of the motor rotating along the line phase direction is shown 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: Q1 motor starter protector; F3 aR partial fuse used to protect semiconductors (such as SITOR 3NE3/4 or 3NC); F3* gR full range fuse used to protect semiconductors (such as SITOR 3NE1); Q11 soft start Q21 main contactor or line contactor for galvanic isolation; M1 motor; PE protective conductor.

●The circuit diagram of the motor rotating in the opposite direction along the line phase is shown 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: Q1 motor starter protector; F3 aR partial fuse used to protect semiconductors (such as SITOR 3NE3/4 or 3NC); F3* gR full range fuse used to protect semiconductors (such as SITOR 3NE1); Q11 soft start Q21 main contactor or line contactor for galvanic isolation; M1 motor; PE protective conductor.

◆PLC control (control circuit connection)

Warning: automatic restart may cause casualties.

If the start command is pending, the restart operation will be automatically triggered after reset. This applies especially when the motor protection device has tripped. May cause the system to be in a dangerous state. Reset the start command (for example via PLC or switch) before performing the reset. For example, the group error output (terminals 95 and 96) can be connected to the control system for this purpose.

Requirements: need to be parameterized.

●The control circuit diagram of Siemens soft starter 3RW55 controlled by PLC is shown 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: F1 fuse; Q1 motor starter protector; Q11 soft starter; Q21 PLC; M1 motor; PE protective conductor.

◆Controlled by switch

Warning: automatic restart may cause casualties.

If the start command is pending, the restart operation will be automatically triggered after reset. This applies especially when the motor protection device has tripped. May cause the system to be in a dangerous state. Reset the start command (for example via PLC or switch) before performing the reset. For example, the group error output (terminals 95 and 96) can be connected to the control system for this purpose.

Requirements: need to be parameterized.

●The control circuit diagram of Siemens soft starter 3RW55 controlled by switch is shown 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: F1 fuse; S1 motor on/off switch; S4 reset button; Q1 motor starter protector; Q11 soft starter; P1 indicator light; M1 motor; PE protective conductor.

◆Line contactor operation

Warning: automatic restart may cause casualties.

If the start command is pending, the restart operation will be automatically triggered after reset. This applies especially when the motor protection device has tripped. May cause the system to be in a dangerous state. Reset the start command (for example via PLC or switch) before performing the reset. For example, the group error output (terminals 95 and 96) can be connected to the control system for this purpose.

Requirements: need to be parameterized.

●The control circuit diagram of Siemens soft starter 3RW55 control line contactor is shown 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: F1 fuse; S1 motor on/off switch; S2 reset button; Q1 motor starter protector; Q11 soft starter; Q21 line contactor; P1 indicator light; M1 motor; PE protective conductor.

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