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Three-phase four-wire system power phase-lack protection cir

2016-09-18 17:49  
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Three-phase four-wire system power phase-lack protection circuit
When the power supply is in the phase lack operating state, one limb of the rectifier bridge has no current, and other limbs will be damaged by the overcurrent, and the operating of inverter will be abnormal, so we must protect the phase lack. We usually use the current transformer or the electronic phase lack detection circuit to detect the phase lack of the power grid. Because the testing cost of the current transformer is high, and the volume is large, so we usually use the electronic phase lack detection circuit in the switch power supply. The simple electronic phase lack detection circuit is as shown in the figure. When the three-phase is balanced, the level of the R1~R3's node H is low, the light coupling output is near zero.