Causes of voltage dips-Shanghai Jingneng Power Technology Co., Ltd.

1, computer and electronic equipment voltage

The power supply structures of computers and electronic devices (such as televisions, copiers, fax machines, PLCs, etc.) are very similar, so their sensitivity mechanisms to voltage dips are also similar, and they are discussed here as a type.

The simplified structure of computer and electronic equipment power supply is shown in Figure 1. It is usually composed of a diode rectifier and a voltage regulator (DC/DC converter). The AC voltage is rectified by a rectifier to obtain several hundred volts DC voltage, which is then regulated by a voltage regulator to a DC voltage supply device with a voltage rating of 10V. If the voltage on the AC side decreases, the voltage on the DC side of the rectifier will also decrease. However, within a certain range of voltage variation, the voltage regulator can keep its output variation to a minimum and make the equipment work normally. However, if the voltage on the DC side of the rectifier is too low, the output voltage of the voltage regulator can no longer maintain the specified value. This will cause an internal error in the digital electronic device or cause the computer power supply to trip.

3, electromagnetic switch electromagnetic switch is mainly AC contactor and relay two types, generally used in low voltage industrial wiring and control motor start. There is a solenoid coil, a movable iron core and a spring. The principle is that when the current flows through the upper electromagnetic coil, the electromagnetic force generated by the upper iron core will attract the lower movable iron core, resulting in the closed core (NO) core closed, and the NC (normal closing point) because the movable iron sheet leaves Contact and open.

When the electromagnetic contact is disturbed by the voltage sag, the current flowing through the coil will become smaller as the voltage becomes smaller. When the current becomes smaller, the generated magnetic force is insufficient to attract the movable core, which may cause the electromagnetic switch in the industry. Controlled equipment malfunctions and stops. Studies have shown that when the voltage is less than 50% and the duration exceeds 20ms, the contactor will trip; some studies show that when the voltage is lower than 70%, it is even higher and the contactor may trip.

4. Most lighting fixtures will flash or temporarily darken when a voltage dip occurs, which will not cause serious consequences. The lighting devices discussed here are high-intensity dis-charge (HID) lamps, such as mercury lamps, metal halide lamps, and high pressure sodium lamps. HID not only has a high luminous efficiency, but also has a higher luminous quality than a fluorescent lamp, and has a longer life, and has extremely high economic benefits. From the above advantages, HID will become increasingly common in the application of lighting technology in the future and will occupy an important position.
HID is an arc discharge lamp, and the bulb current changes greatly during lighting, so a ballast is needed to stabilize its current and stabilize the light emitted by the bulb.
HID ballasts can be divided into electronic (see Figure 6) and electromagnetic (traditional, see Figure 7) two kinds of electronic ballasts with small size, high efficiency, long life and other advantages. At present, there is a tendency for electromagnetic ballasts to be replaced by electronic ballasts.