In the working process of 10kV utility transformer, the unbalanced three-phase load often causes the neutral line n-phase current. The neutral line current will not only cause line loss, but also bring a lot of losses to the power supply company. In severe cases, the neutral line will burn the neutral line when it flows through the neutral line, causing damage to household appliances. Therefore, adjusting the three-phase current to make the three-phase current too same and reducing the neutral line current is one of the daily operations of the power supply company. The traditional three-phase load adjustment method is to manually step on the pole to adjust the phase, the workload is relatively large, and the work must be done after power failure. Therefore, a phase modulation control circuit is designed, which combines three single-phase switches, three AC contactors (CJX2), control buttons and other electrical components to end the "one out of three" function of the switch. Integrate the equipment into a control box, place the equipment in the control box on the wall or the low-voltage pole, and lead the 4 wires on the low-voltage pole down to the control box.

The three-phase power supply a, B and C are connected to the small master card through the single-phase switch 1qf, 2qf, 3Qf and the normally open node 1km1 of the main circuit of the AC contactor (CJX2), and then connected to the house through the small card. In order to prevent the equipment damage caused by the short circuit of the three-phase power supply, the auxiliary s circuit of the AC contactor (CJX2) is used in the three-phase power supply In any case, only one phase power supply can be used for this locking. The principle is as follows. When selecting A-phase power supply, close the A-phase switch 1qf, and then press the I brake button 1sb. The control word of A-phase is conducted through the closing button 1sb, the opening button 1TB, the voltage coil of AC contactor (CJX2) 1km, the normally closed node 2km2 of AC contact ii2km, and the normally closed node 3km3 of AC contactor (CJX2) 3km Through the normally open node 1km4g of AC contactor (CJX2) 1km, the AC contactor (CJX2) 1km is charged, and its normally open node 1km1 of slave circuit is closed. The A-phase power supply supplies power to residents through single-phase switch 1qf and normally open node 1km1 of AC contactor (CJX2) 1km Assist the normally closed nodes 1km2 and 1km3 to turn over and lock the control loops of B-phase power supply and c-phase power supply. Even if the B-phase power switch 2qf is closed, the t start button 2Sb is pressed, the c-phase power switch 3Qf is closed, and the auxiliary button 3Sb is pressed, the B-phase power supply and c-phase power supply will not be connected, and the three-phase or two-phase short circuit fault will not be formed. When it is necessary to adjust the load, such as adjusting from phase a to phase C, just press the phase a break button 1TB first, and swing the phase a switch 1qf. At this time, the AC contactor (CJX2) 1km loses power, and its main fixed circuit normally open node 1km1 turns over; assist the normally closed point 1km3 to close s, and then close the phase C switch 3Qf, and press the brake button 3Sb to control the phase C The circuit is connected through the closing button 3Sb, the opening button 3TB, the voltage coil of AC contactor (CJX2) 3km, the normally closed node 1km3 of AC contactor (CJX2) 1km, and the normally closed node 2km3 of AC contactor (CJX2) 2km, and through the normally open node 3km4 of AC contactor (CJX2) 3km ）3km is electrified, its main circuit normally open node 3km1 is closed, and the c-phase power supply supplies power to residents through single-phase switch 3Qf and main 0-way normally open point 3km1 of AC contactor (CJX2) 3km, which can end the load adjustment. After the control box is put into operation, it has the advantages of greatly reducing the workload of power workers. Staff standing on the ground can end the phase modulation operation, do not have to climb the pole for phase modulation operation. The reliability of power supply is ensured. There is no need for power cut operation. The staff can finish the operation by pressing the button twice. The user only needs a short power cut time. Due to the convenience of phase modulation, the three-phase load can be adjusted in time on site, which makes the three-phase load tend to be balanced, greatly reduces the current on the neutral line, and prevents the loss of power users caused by the burning of the neutral line.