Comparison of soft starter performance
At present, there are mainly two kinds of medium and high voltage soft start products at home and abroad, one is soft start for applying soft start of high voltage inverter and the other is applied by thyristor. Here, the author briefly introduces the performance of the two devices.
(1) High-voltage inverter soft start
The inverter device is mainly used in the speed regulation of the AC motor and has obvious energy saving effect. If it is used on the soft start of the motor, its speed control performance should not be compared with our products. The frequency conversion device is used for soft start, the motor will not have over-current phenomenon during the whole starting process, the starting torque is large, and the starting performance is good. However, for the fan-pump type load with low starting torque, this advantage of the inverter device does not show up. At the same time, the following deficiencies exist:
1. The frequency conversion technology is still in the development stage. Because the switching loss is still relatively large, the reliability is still relatively low, and the failure rate is relatively high, which is a maintainable device. Each unit often has a long downtime due to the failure of maintenance technology. A steel company had a case where a 35,000 KW blast furnace blower started more than a week. There are also situations where you are not allowed to use it.
2. In the output voltage of the inverter device, the content of harmonics is large, which will cause local overheating on the tooth groove of the motor, burning the insulation and affecting the service life of the motor. This is why it is necessary to use a specially designed variable frequency motor for speed control applications.
3. Use the frequency conversion device for soft start. When the sub-synchronous speed is to be switched from the variable frequency power supply to the commercial frequency power supply, it must have a good synchronization function (some frequency conversion devices do not have this function), otherwise mechanical impact will occur, and the mechanical damage will occur. device.
4. Inverter is expensive
5. The circuit principle of the frequency conversion device is complicated, the maintenance technology level is high, and the maintenance time is long.
Conclusion
Medium voltage motor soft starters are now widely used in metallurgy, petrochemical, pharmaceutical, municipal and other fields. There are many defects in the traditional starting scheme, and the problem is more prominent for large-capacity equipment. With the continuous application of soft starters in production practice, selecting a soft starter motor will be an inevitable trend in the future.
