Application of Solid State Relay in Electric Actuator

Author: solid state; relay; principle; failure; electric actuator Summary: Combining the use of power plant electric actuator in the solid state relay using large Tangwu Sha Shan, introduces the basic principle of AC solid state relay, when the practical application test And fault judgment, the problems that should be paid attention to when selecting solid state relays are proposed, which can provide reference for the commissioning and maintenance personnel. Datang Usha Power Plant 4 sets of supercritical 600mw desulfurization unit, chemical and refined processing system are selected Shanghai Automation Instrumentation Co., Ltd. produced ai series intelligent and Germany Deruimo (drehmo) electric actuators, in this category Solid state relay (ssr) is used in the actuator. In operation, the drehmo actuator and the actuator of the chemical system of the desulfurization system all have malfunctioned, the speed is slow or the air switch is faulty, and most maintenance personnel are not very familiar with the performance of the solid state relay. Difficulty. Therefore, it is necessary to further understand the principle, type, fault judgment and use of solid state relay. A typical AC solid state relay works Solid state relay (solid state relay, ssr) is a non-contact relay with relay characteristics. With long life, high reliability, switching speed, electromagnetic interference, noiseless, no sparks and so on. Exchange solid state relay (zero-crossing type) principle shown in Figure 1. Figure 1 AC solid state relay schematic Solid State Relay consists of three parts: the input circuit, isolation (coupling) and the output circuit, the signal input circuit control end, the phototransistor phototransistor is turned on, r1 series resistor Current limit on the input signal to ensure that the optical coupler will not damage. LED led indication input control signal, diode vd1 to prevent the positive and negative polarity of the input signal is reversed when the opto-coupler ic1 caused damage. v1 in the line to play the role of AC voltage detection, the solid state relay in the zero-crossing voltage is turned on, the load current zero off. When the ic1 phototransistor is off (the control signal is not input), v1 by r2 get the base current to saturation of conduction, so that SCR gate trigger voltage ugt was clamped at a low potential in the off state, Eventually lead to bta triac in the gate control terminal r6 without trigger pulse in the off state. When the ic1 phototransistor is turned on (the control terminal has a signal input), scr SCR work by the AC voltage zero detection transistor v1 to determine. Such as the supply voltage by the r2 and r3 partial pressure, a voltage is greater than the zero-crossing voltage (va> vbe1), v1 saturate the conduction state, scr, bta thyristor are in the off state; such as the supply voltage by r2 and r3 Partial pressure, a Department of voltage is less than zero voltage (va c1, r7). AC zero-crossing type solid state relay with voltage zero crossing open, load current zero off when the characteristics. Its maximum turn-on and turn-off time is half the power cycle, a complete sinusoidal waveform can be obtained on the load, and the impact on the load is reduced correspondingly. The radio frequency interference generated in the corresponding control loop is also greatly reduced. Three-phase solid state relay (ssr) can be directly used for three-phase motor control. The easiest way is to use 2 ssr motor on-off control, 4 ssr motor commutation control, the third phase is not controlled. The advantages and disadvantages of solid state relays and conventional electromagnetic relays are shown in Table 1.