Development of Soft Start Technology for Medium and High Voltage Motors from Power Electronics Technology
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.
I. Introduction
Power electronics technology is an electronic technology applied in the field of electronic technology. It is closely related to electronics, control, and power. In 1957, the introduction of thyristors brought about a revolution in power electronics, and power electronics technology developed rapidly.
A thyristor is an abbreviation for a thyristor, also known as a thyristor, and is also referred to as a thyristor. Its characteristic is that the turn-on time can be controlled, and when the current crosses zero, it is turned off, which is a semi-controlled device. At the beginning of the invention of the thyristor, it was widely welcomed because its performance in all aspects was significantly better than that of the previous mercury arc rectifier, which opened up a new era of rapid development of power electronics technology. Since the 1980s, some applications of thyristors have been replaced by a variety of better-controlled fully-controlled devices, but because of their high voltage and current capacity, they are still the highest in current power devices, so in large-capacity applications. Still has an important position. Its characteristics are mainly as follows:
(1) High withstand voltage: 8500V products are currently available
(2) Large current: 5000A products are currently available
(3) Pressure reduction: tube pressure drop <2V when conducting
(4) Low power loss and long life
(5) Strong resistance to transient overcurrent and impact
Second, medium voltage (6 ~ 10kV) motor commonly used starting method
AC motor is the most widely used motor in various fields. In order to solve the impact of AC motor on the grid and machinery during the starting process, many methods have been adopted. Traditional series resistance start, series reactor start, star-angle Conversion start, auto-coupled step-down start, variable frequency start, etc.
The thyristor-controlled motor soft starter appeared in the 19th century. At that time, NASA had a "Frank" engineer who obtained a patent called "Power Cycle Controller", which uses the thyristor anti-parallel to adjust the conduction angle of the thyristor to achieve the purpose of AC voltage regulation, in order to solve the problem of no-load and light. This technology has been applied to the problem that the AC factor of the asynchronous motor is too low. Later, the current feedback technology was introduced to greatly improve the control level, which was widely adopted. The device using this technology in the United States was named “Power Saver”.
