Jul 26, 2018
The basic principle of soft starter is that the main circuit of soft starter adopts thyristor, and the voltage is raised by changing the conduction Angle of thyristor step by step to complete the start-up process. In the market of low voltage soft starter, there are many products, but there are few products of high voltage soft starter. The basic principle of the high-voltage soft starter is the same as that of the low-voltage soft starter. However, compared with the low-voltage soft starter, the high-voltage soft starter has its particularity in some aspects:
1. The high-voltage soft starter works in a high-voltage environment. The insulation performance of various electrical components must be good, and the anti-interference ability of electronic chips must be strong. The layout of the electrical components and the connection between the high-voltage soft starter and other electrical equipment are also very important when the high-voltage soft starter constitutes the electric cabinet.
2. The high-voltage soft starter must have a high-performance control core, which can process signals timely and quickly. Therefore, this control core generally USES high-performance DSP chip, rather than the common chip chip of low-voltage soft starter. The main circuit of the low-voltage soft starter is composed of three sets of inversely parallel thyristors. However, in the high-voltage soft starter, the voltage distribution must be carried out by multiple high-voltage thyristors in series due to the insufficient voltage withstand capacity of a single high-voltage thyristor. However, the performance parameters of each thyristor are not completely consistent. The inconsistency of thyristor parameters will lead to the inconsistency of thyristor opening time, which will lead to the damage of thyristor. Therefore, in the selection of thyristor, the thyristor parameters of each phase must be as consistent as possible, and the component parameters of RC filter circuit of each phase thyristor must be as consistent as possible.
3. The working environment of the high-voltage soft starter is vulnerable to various electromagnetic interference, so the transmission of the trigger signal must be safe and reliable. In the high-voltage soft starter, the trigger signal is transmitted, usually by optical fiber transmission, which can effectively avoid all kinds of electromagnetic interference. There are also two ways to transmit signals through optical fibers: one multi-fiber and one single-fiber. Multi-fiber mode means that each trigger board has one fiber; In the single-fiber mode, there is only one fiber in each phase, and the signal is transmitted to one main trigger board, and then from the main trigger board to other trigger boards in the same phase. Since the loss of each optical fiber is not consistent in the process of photoelectric transmission, the single optical fiber is more reliable than multiple optical fibers in terms of triggering consistency.
4. High voltage soft starter has higher requirements for signal detection than low voltage soft starter. There are a lot of electromagnetic interference in the environment of the high-voltage soft starter, 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 signals should be filtered not only by hardware, but also by software to remove interference signals.
5. After the soft starter completes the startup process, it is necessary to switch to the bypass operation state. How to smoothly switch to the operation state is also a difficulty for the soft starter. Bypass point early, the current impact is very big, even in low-voltage conditions, will cause the three-phase power supply circuit breaker trip, or even damage the circuit breaker. High pressure conditions are more harmful. The bypass point is late and the motor jitter is severe, which affects the normal work of the load. Therefore, the bypass signal hardware detection circuit must be very accurate, and the program processing must be just right.