Solid state phase failure relay protection circuit a

38. Solid-state phase failure relay is a new device used for three-phase AC phase failure monitoring, protection and control, referred to as SSPORR. It is a semiconductor
module with 5 terminals , among which terminals 1, 2 and 3 are three-phase monitoring input terminals. The phase sequence is arbitrary, the current absorbed is very small, and the total of the three terminals does not exceed 1mA; terminals 4 and 5 are switch terminals. The characteristics of this module are: wide operating range, no sparks and jitter, and large surge current capacity. When the three-phase power supply is normal, terminals 4 and 5 are on; when the phase is missing, terminals 4 and 5 are off, and the protection and control switches are disconnected. The phase failure protection circuit composed     of solid-state phase failure relay is shown in Figure 4-38.     When one phase of the power supply is missing, the output terminal of SSPORR is cut off, no voltage is output, the contactor KM is released, and the motor stops.