The difference between the soft start of the motor and the starting of the decompression
The soft start of the motor is widely used in metallurgy, chemical industry, electricity, coal, water conservancy, light industry and other industries.
- The rotor current of three-phase asynchronous motor starts at 5~8 times of rated state because the rotor current is induced from the stator winding so that the current in the stator winding is increased to 4~7 times of the rated value.
- Such a large starting current will bring the following negative consequences: make the grid voltage fluctuate (especially when the larger capacity motor starts). So what’s the difference between the soft start and the traditional decompression start?
- No shock current. When the soft starter starts the motor, the starting current of the motor is increased from zero linear to the set value by increasing the conduction angle of the thyristor gradually.
- The constant current starts. The soft starter can introduce the current closed-loop control to keep the motor constant in the starting process and ensure the motor to start smoothly.
According to the load situation and the selection of power grid relay protection characteristics, it can be freely adjusted to the best starting current.
Flashball, soft starter is superior to star-delta starter and autotransformer starter, is because it has a lot of functions, there is the “intelligence” to achieve human-computer dialogue, through the keyboard, computer or manual remote operation, not only can realize the soft stop, also has many protection functions.
These are all the requirements of new humanized equipment, so it is highly praised.
Soft start operation has the following characteristics
- It can make the starting voltage of the motor rise steadily with a constant slope, small start current, no impact current to the power grid, and reduce the mechanical impact of the load.
- The rising voltage of the starting voltage can be adjusted to ensure the smoothness of the starting voltage. The starting voltage can be continuously adjusted according to the different loads in the range of (30% to 70%) Gong (rated voltage).
- The start time can be set according to the different load.
In order to adapt to the modern production, reduce the impact on the power grid, wear the machinery and reduce the maintenance of the starting device, the soft starter also has thyristor short circuit overload protection, phase failure protection, overheating protection and other protection functions.
The overload protection function of soft starter based on current control loop can keep track of changes in the detection of the motor current, by increasing the overload current setting and inverse control mode realizes the function of overload protection, turn off thyristor and alarm signal in motor overload.
When working, the soft starter can detect the change of the three-phase current at any time. As soon as the current breaks down, the phase protection reaction can be made.
The overheating protection function is used to detect the temperature of the thyristor radiator through the thermal relay inside the soft starter. Once the radiator temperature exceeds the allowable value, the thyristor can be shut off automatically, and the alarm signal is sent out.
Other protection functions, through the combination of electronic circuits, can also implement all kinds of chain protection in the system.
Generally speaking, soft starters can be used in various applications without induction motor speed, and soft start is suitable for all kinds of pump loads or fans.
For variable load condition, motor running in long-term light load is only operated in a short time or full load. Soft starter (without bypass contactor) has the effect of light load and energy saving.
At present, there are many brands and models of soft starters. The working principles of several soft starters are introduced below.
WJR series soft starter
WJR series soft starter is Qigihar QILIDA Electronics Co. Ltd. production of a new generation of three-phase AC asynchronous motor control special products. The series of three-phase motor soft starters are divided into 3 types.
Electricity saving type: online operation, suitable for motor drag system with low load rate or intermittent load, such as plate shearing machine, press and punching machine, its active power saving rate can reach 20% to 40%. The lower the stamping frequency is, the higher the power saving rate is, if the load rate of the motor is over 40%, the power saving effect is not obvious. The panel is equipped with LED display lamp and operating keyboard. It can display and modify the system running parameters. It is convenient and fast. The connection form is the down line and the downline.
Bypass type: it is a soft start control device composed of the unit type as the main controller. The connection mode is the downline and the downline. W melon power saving soft starter based on single-chip microcomputer control technology, through the built-in special optimization control software, dynamically adjust the motor’s voltage and current during operation.
In the condition that the motor speed is not changed, the output torque of the motor is matched with the load demand, and the unloaded active power saving rate is as high as 50%. It not only has the soft start-up and stop function, can guarantee the smooth continuous motor start, current and avoid mechanical shock when the motor is started; has broken phase, overcurrent, overload, unbalance, thyristor, power inverse equal number overheating protection function, and fault state output (BK), the running state of the output (TR) function, can be used to control other chain equipment.
The WJR power saving soft starter can detect the faults in the operation of the motor intelligently, and the running state and the fault state are all displayed by the LED on the panel.
The bypass WJR soft starter has the functions of power supply reverse phase, thyristor overheating, motor overload, unbalanced three-phase and equal protection, and has the function of fault status output. It can be used to control (protect) other interlocking devices (output relay contact capacity is 250V/5A). The internal circuit board has an easy to identify fault diagnosis indicator, which can detect the fault in the running process intelligently.
When the soft boot is completed, the bypass contactor is put into normal operation. The contact contractor has no contact when it is closed and disconnected. This is a special effect that has been achieved by the electronic arc extinguishing device.
The WJR series soft start unit is a special control product of three-phase AC asynchronous motor. The voltage and time ramp mode is adopted and the current limit mode is started.
The unit has the function of soft start, soft stop and starting current limit. When starting and running, it has the function of fault diagnosis and fault protection, and remote operation can be carried out through external passive contact switch. The unit does not need an additional motor protector or thermal relay. It needs to be bypassed by AC contactor during operation, and no arcs are generated when the bypass contactor is sucked and broken.
Unit type: using the thyristor online operation mode, is the basic unit of three-phase asynchronous motor soft-start control and has a bypass signal output terminal, that is, after the completion of the completion, the bypass relay contacts are closed, and the contactor bypass operation is controlled.
Due to the adoption of the patented technology of “electronic arc extinguishing device”, the contractor is not generated when the contractor is being sucked up and broken, and the output terminals of the fault signal are equipped. When the system fails, the system stops automatically, and the contact points of the failure relay are closed. The connection form is the upper and lower lines.
When the unit is selected, the user needs the self-matching current closed loop sampling transformer, the bypass contactor, the start and stop buttons for normal use.When the unit is selected, the user needs the self-matching current closed loop sampling transformer, the bypass contactor, the start and stop buttons for normal use.