The main circuit of the soft starter adopts the thyristor tube, which raises the voltage by gradually changing the on-on angle of the thyristor tube and completes the start-up process, which is the basic principle of the soft starter. In the low-voltage soft starter market, a wide range of products, but the high-voltage soft starter products are still relatively small. The basic principle of a high-voltage soft starter is the same as that of a low-voltage soft starter, but compared with a low-voltage soft starter, there are several differences:
(1) High-voltage soft starter in the high-voltage environment, a variety of electrical components must be good insulation performance, electronic chip anti-jamming capacity to be strong. When a high-voltage soft starter forms an electrical cabinet, the layout of the electrical components and the connection to the high-voltage soft starter and other electrical equipment are also very important.
(2) High-voltage soft starter must have a high-performance control core, the signal can be processed in a timely and fast manner. Therefore, this control core typically uses a high-performance dsp chip instead of a common single-chip movement of a low-voltage soft starter. The main circuit of the low-voltage soft starter consists of three sets of inversely parallelthionthing thyristors. In the high-voltage soft starter, because the pressure resistance of a single high-voltage thyristor is not enough, it must be divided by multiple high-voltage thyristors in series. However, the performance parameters of each thyristor are not exactly the same. Inconsistencies in the parameters of the thyristor tube will lead to inconsistent opening time of the thyristor, which will lead to damage to the thyristor. Therefore, in the selection of the thyristor, it is necessary to ensure that the crystalline tube parameters of each phase are as consistent as possible, and that the component parameters of the rc filter circuit of each phase thyristor are as consistent as possible.
(3) The working environment of the high-pressure soft starter is susceptible to various electromagnetic interferences, so the transmission of the trigger signal must be safe and reliable. In the high-voltage soft starter, the transmission of trigger signals, generally using optical fiber transmission, can effectively avoid all kinds of electromagnetic interference. There are also two ways to transmit signals through optical fiber: a multi-fibre approach and a single fiber-optic approach. Multi-optical mode, that is, each trigger plate has a fiber, a single fiber mode that is, each phase only one fiber, the signal is transmitted to a main trigger plate, and then by the main trigger plate to the other trigger plate of the same phase. Because the loss in the transmission of various optical fibers is not consistent, the single fiber is more reliable than multi-fiber in terms of trigger consistency.
(4) The detection of the signal by the high-pressure soft starter is more demanding than that of the low-pressure soft starter. There is a lot of electromagnetic interference in the environment where the high-voltage soft starter is located, and the vacuum contactor and vacuum circuit breaker used in the high-voltage soft starter will produce a lot of electromagnetic interference in the process of breaking and closing. Therefore, the detected signal should not only be hardware filtered, but also software filtering, remove interference signal.
(5) After the soft starter completes the start-up process, to switch to the bypass running state, how to smoothly switch to the running state, which is also a difficult point for the soft starter, how to select the bypass point is very important. The bypass point is early, the current impact is very large, even under low pressure conditions, will cause the three-phase power supply circuit breaker tripping, or even damage the circuit breaker. The hazards are greater under high pressure conditions. The bypass point is late and the motor shakes badly, affecting the normal operation of the load.Therefore, the hardware detection circuit of the bypass signal must be very accurate and the program handling must be just right.