Three-phase power supply common fault analysis and improvement program
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First, the three-phase power supply common fault analysis Most of our power supply uses three-phase four-wire power supply. The following figure shows the schematic diagram of three-phase four-wire system. It can be seen from the figure that this kind of power supply can provide two different voltages—line voltage (380V) and phase voltage (220V), which can meet different needs of users. The ideal state of three-phase four-wire power supply is three-phase load balancing. At this time, the neutral current is zero. From the theoretical analysis, the neutral line at this time is optional, and it does not affect the normal operation of the equipment. But in reality, the three-phase balance is only relative, and the imbalance is absolute. Therefore, the middle line in practical applications is necessary, so as to ensure the stable output of each phase voltage. With the development of the economy, the use of electrical appliances has increased substantially, the probability of single-phase short-circuiting has inevitably increased, and zero-crossing voltage problems caused by single-phase short circuits and transient short circuits have become commonplace. Here we analyze some of the common faults and provide directions for the design of the power supply system of the power equipment so that the power supply system can operate stably and reliably. 
The open circuit of the transmission line is in the actual environment of the electricity environment, and the neutral line is often disconnected due to improper installation of the line or improper installation of the fuses and switches. If the neutral line breaks, the neutral point potential of the three-phase load will shift. The neutral point potential displacement directly leads to the unbalance of the output voltage of each phase, and the too high phase voltage will cause the device to overvoltage and directly burn, while the phase of the low phase voltage may damage the device due to the voltage drop and current increase. Because the calculation of the three-phase electric voltage is very complicated, due to the introduction of the load vector, the final detailed calculation formula is also very difficult to understand. The following is a simple way to explain the effect of the neutral short circuit on the line voltage. 
In addition to power lines, open circuit power equipment in the equipment is prone to failure, and equipment power input and socket failures may damage the equipment. Because most occasions use three-phase four-wire power supply, and three-phase four-wire power supply also has a more special application, and when using three-phase four-wire full-wave rectification, as long as any one phase of electrical equipment can be normal Operation. 
Second, three-phase power supply improvement measures Because there are more restrictions in practical applications, it is impossible to avoid the occurrence of many power failures, but we can reduce the probability of equipment damage through some means to improve product reliability. The specific improvement measures are as follows:
Single-phase short-circuit fault improvement measures This fault can properly improve the impact resistance of the input end of the power supply. Generally, it needs to resist the impact of 335VAC. This protects the post-circuit from damage due to overvoltage during transient short-circuits. In order to reduce the voltage increase caused by zero-floating, the cross-sectional area of ​​the zero line can be properly increased to reduce the zero drift, to reduce the voltage increase of the other two phases.
Open circuit improvement measures for the central line of the transmission line From the fault analysis we can see that the open circuit of the neutral line is mainly a current loop that affects the phase voltage, so that the current does not return to the neutral point. The loop can only be formed by two phase lines, which increases the risk of overvoltage in the equipment. In order to provide a reliable current loop for the phase voltage, the three-phase three-six-wire power supply mode can be adopted in the wiring, and the three-phase three-zero work independently. The disadvantage of this wiring is to increase the zero line investment and line loss, but this can effectively suppress zero drift and reduce the mutual influence of each phase voltage.
The open circuit improvement measures for equipment power supply neutral line The general equipment adopts a three-phase four-wire full-wave rectification circuit, mainly considering the redundant design of its power supply, as long as the three-phase power any one phase electric equipment can work normally. However, once the device is not connected to the neutral line, the voltage of the rectifier circuit will rise sharply. To solve this problem, it is necessary to cut off the post-stage circuit when the voltage increases, thereby protecting the post-stage circuit from being damaged. However, it is necessary to ensure that the detection control circuit is stable in power supply during design.
Third, from the root to solve the power system power failure With the development of society, the power of the power equipment is gradually increased, while the quality of various equipment is also uneven. These devices not only cause great interference to the power grid, but also have a greater risk of short circuit. There are many incentives for power failure and it is impossible to completely avoid its occurrence. But once the failure occurs, we need to feedback and handle it in a timely manner. At this point, there is a need for a power detection device to detect the power grid in real time, and take necessary measures when the fault occurs to avoid causing greater losses. 
PD2IHBxxD-10W Features:
Conversion efficiency up to 83%;
Input voltage: 56 ~ 700VDC;
Output voltage: 5V, 12V, 15V, 24V;
Working temperature: -40°C～+85°C;
Enable (EN) control function;
Isolation voltage: 4000VAC;
Sustained short circuit and self-recovery, with over-temperature protection function;
Single-phase circuit application features: Single-phase circuit is simple, can adapt to the mains voltage fluctuations.
Three-phase three-wire application features: Suitable for occasions without a midline, any one phase line open, the power supply can continue to work.
Three-phase four-wire application features: The biggest advantage of this circuit is that three-phase redundant power supply, the circuit can still work stably when there is no phase.
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