Crane Motor:Differences between soft start and decompression start of motor

As a new generation of industrial control mode, the soft starting of motor is widely used in crane equipment. The rotor current of the three-phase asynchronous motor is usually 5 ~ 8 times higher than that of the rated state.

Since the rotor current is induced from the stator winding, the current in the stator winding is increased to 4~7 times of the rated current. Such a large start-up current will have the following adverse consequences: fluctuating the grid voltage (especially when the larger motor starts). What is the difference between the soft start and the conventional decompression start of motor?

Soft start of motor and soft start connection drawing

• No impulse current. When the soft starter starts the motor, the starting current of the motor rises from zero linear to the set value by increasing the thyristor conduction angle gradually.
• Constant current start. The soft starter can introduce the current closed loop control to keep the constant current in the starting process of the motor and ensure the steady start of the motor.
• According to the load condition and relay protection characteristics, the optimal starting current can be adjusted freely and continuously.

Decompression start of motor and decompression start connection drawing

The reason why the soft starter is superior to the Star-Triangle starter and the self-coupling decompression starter is that it has many functions, such as "intelligence quotient", the realization of man-machine "dialogue", and the remote operation through the keyboard, computer or manual, not only soft stop can be realized, but also it has many protection functions. These are new humanized equipment requirements, so it is highly respected.

Soft start has the following characteristics

• a.It can make the starting voltage of the motor rise steadily with a constant slope, the starting current is small, and there is no impact current on the power network, which reduces the mechanical shock to the load.
• b.The rising slope of the starting voltage can be adjusted to ensure the smoothness of the starting voltage. The starting voltage can be continuously adjustable in the range of 30%~70% according to different loads.
• c.It can set startup times depending on the load.
• d.In order to meet the needs of modern production, reduce the impact on the power grid and the wear on the machinery, and reduce the maintenance of the starting device, the soft starter also has the thyristor short circuit overload protection, phase deficiency protection, overheat protection and other protection functions.

1.Overload protection function

The soft starter adopts the current control loop to track and detect the current change of the motor at any time. The overload protection function is realized by adding the setting of overload current and the anti-time-limited control mode. Turn off the thyristor and issue an alarm signal when the motor is overloaded.

2.Phase deficiency protection function

When it works, the soft starter detects the change of three-phase current at any time, once the current is cut off, a phase loss protection response can be made.

3.Overheat protection function

The temperature of the thyristor radiator is detected by the thermal relay inside the soft starter. Once the temperature of the radiator exceeds the allowable value, the thyristor is automatically turned off and an alarm signal is issued.

4.Other protection functions

Through the combination of electronic circuits, other kinds of chain protection can be implemented in the system.

We Yuantai crane ,Dongqi Group have overhead crane, gantry crane, jib crane, electric hoist and Electric Winch. The motor of all products has soft start now. Yuantai crane has strong technical team. Yuantai crane has been committed to the upgrading of product technology, and Yuantai crane is at the forefront of technology.So please connect us if you need crane equipment.