This circuit is used to detect whether the phase sequence of three-phase alternating current is correct. If the phase sequence is correct, the output signal of the circuit drives the relay to attract the three-phase AC power supply connected to the electrical equipment; Otherwise, do not connect the power supply to protect the electrical equipment.

Circuit working principle:

As shown in the figure, the three-phase alternating current phase sequence detection circuit consists of a phase sequence detection circuit, a trigger and a control execution circuit. The phase sequence detection circuit consists of resistor R 1-R5, zener diode vs 1-VS3, capacitor C 1 and diode vd 1. The flip-flop circuit consists of a dual D flip-flop integrated circuit IC and a resistor R5.

This circuit is mainly composed of a CD40 13 double D flip-flop. Three-phase alternating current is converted into low-voltage pulse signal after step-down rectification, and input to terminals A, B and C of this circuit. The signals at terminal A and terminal B are respectively used as clock signals of two D flip-flops after being limited and shaped by resistors and Zener diodes, and the signals at terminal C are turned into sharp pulses through difference channel and act on the reset terminals R of the two flip-flops. If the phase sequence is correct, that is, positive pulses appear in the order of A, B and C, as shown in Figure 2(a), the rising edge of A first makes Q 1 output high level, then Q2 becomes high level under the action of the rising edge of B, and finally the sharp pulse generated by the rising edge of C at the R terminal resets the two D flip-flops, and Q 1 and Q2 return to low level, completing a cycle. Three-phase alternating current is a periodic signal, the frequency of Q2 output pulse is the same as that of three-phase alternating current, and the DC component of its voltage is the voltage on C2(22uF) capacitor. This voltage turns on the triode, and the relay turns on the three-phase power supply of the electrical equipment. If the phase sequence is wrong, the Q2 output remains low, and the triode is turned off to ensure that the three-phase AC power supply of the electrical equipment is not connected. The waveform of each point is shown in fig. 2(C). The following two pictures are similar, except that one of them draws a contactor symbol. )

The control execution circuit consists of transistors v 1, V2, relay K, diode VD2, resistor R6 and capacitor C2. The three-phase AC voltage is converted into a low-voltage pulse signal after being processed by a step-down rectifier circuit (not shown) and input to the A, B and C terminals of a single-phase AC phase sequence detector. The input signals at terminals A and B are limited and shaped by Rl, vs 1, R2 and VS2, and are respectively applied as clock pulse signals to the clock terminals (3 pins and 1 1 pin) of two flip-flops in IC; The input signal at terminal C is changed into a reset-tip pulse signal through Cl, R4, VDl and R5, which is applied to the two reset terminals of l C (pin 4 and pin 10).

If the phase sequence is correct (that is, the power pulses appear in the order of A, B and C), the L pin of IC (Ql terminal) and the Q2 pin of 13 both output high levels, so that Vl and V2 are turned on and K is attracted. Its normally open contact is connected to the working power supply (not shown in the circuit) of the AC contactor, and the load works with electricity. When the reset pulse is applied to the IC, the double D flip-flop is reset, and the 1 pin and 13 pin output low levels, completing one cycle. At this time, the charge on C2 keeps Vl and V2 conductive, and the working state of the load remains unchanged. When the next three-phase alternating current periodic signal comes, the L pin and 13 pin of ic output high level again ... and so on.

If the phase sequence of the three-phase AC power supply is wrong, the 13 pin of the IC remains low, Vl and V2 are in the off state, K does not pull in, and the load cannot be energized to work.

Component selection

Rl-R6 selects 1/4W metal film resistor.

Cl adopts high frequency porcelain capacitor; C2 selects aluminum electrolytic capacitor with withstand voltage of 16V.

Vd 1 and VD2 adopt 1N4007 silicon rectifier diode or 1N4 148 silicon switching diode.

Vs 1-VS3 all use 1/2W and lOV silicon zener diodes.

S 90 13 Vl and V2 use silicon NPN transistors.

LC adopts CD40 13 or MCl40 13 dual d flip-flop integrated circuits.

Part ii: integrated circuit TH22 1A(pdf data) of phase sequence detection protector for three-phase AC power supply part iii: simple three-phase AC phase sequence detection circuit.

Schematic diagram of phase sequence detection of three-phase alternating current