Factors causing surge voltage

What is surge voltage? What are its effects? Circuits often generate high operating overvoltages when struck by lightning and when switching on or off inductive loads or large loads. This instantaneous overvoltage (or overcurrent) is called Surge voltage (or surge current) is a kind of transient interference. For example, when a DC 6V relay coil is disconnected, a surge voltage of 300V to 600V will occur; when an incandescent lamp is connected, a surge current of 8 to 10 times the rated current will occur; when a large capacitive load such as a compensation capacitor bank is connected, a surge voltage of 300V to 600V will occur. A large surge current impact occurs, causing the power supply voltage to suddenly drop; when the no-load transformer is cut off, an operating overvoltage as high as 8 to 10 times the rated voltage will also occur.

The phenomenon of surge voltage is increasingly endangering the safe operation of automation equipment. Eliminating surge noise interference and preventing surge damage have always been core issues related to the safe and reliable operation of automation equipment. Modern electronic devices are becoming more integrated, but their ability to withstand surge voltages is declining. In most cases, surge voltage will damage the circuit and its components. The degree of damage is closely related to the withstand voltage strength of the components and the energy that can be converted in the circuit.

What causes surge voltage?

Surge is also called surge, which is an instantaneous overvoltage that exceeds the normal voltage. It generally refers to a large current caused by a short-term "wave"-like high voltage in the power grid. Essentially, a surge is a violent pulse that occurs in just a millionth of a second. There are two causes of surge voltage, one is lightning, and the other is generated when large loads on the power grid are turned on or off (including switching of compensation capacitors).

(1) Lightning is an extremely strong electromagnetic transient process that occurs in nature. It mainly affects power automation equipment through two channels. First, lightning directly hits lightning rods and lightning protection wires in substations or dispatch centers. The transient electromagnetic field generated exerts electromagnetic effects on electronic equipment in the surrounding space, produces piezoelectric current in closed metal circuits, and induces electromotive force in open metal circuits. Because the effect of lightning electromagnetic pulses is very strong, the induced voltage may be very high. The lightning current discharged into the ground through the ground wire causes the voltage of the ground network to increase, resulting in a large voltage difference between the grounding points in the grounding system. They may cause interference to the automation equipment, affecting normal operation in mild cases, and in severe cases May cause equipment damage. Second, lightning discharges between thunderclouds above the line, or discharges to the ground near the line, which will cause the line to generate lightning shock waves or surge voltages due to electromagnetic induction. This shock wave will invade along the line and into the power automation system connected to it. equipment, causing work errors or equipment damage. If lightning strikes a line directly, the surge voltage generated will be stronger and more harmful.

(2) When some large-capacity electrical equipment is turned on or off, due to the presence of inductance in the power grid, a "surge voltage" will be generated in the power grid, causing a surge current. Generally, surge voltage will exist regardless of the capacity of the equipment. The problem is that the surge voltage generated by small-capacity equipment is small and will not cause much harm, so it is often ignored by people. During startup of the off-line converter, a large current is generated due to charging of the bulk capacitor. This large current is several times or even dozens of times greater than the normal current of the system (the so-called surge current), and this may cause the voltage of the AC line to drop, thus affecting the operation of all equipment connected to the same AC line, and sometimes causing them to burn out. Components such as fuses and rectifier diodes.

The diversity of operating modes and fault forms determines the different categories of operating overvoltages, which mainly include: arc ground overvoltage in ungrounded neutral point systems, closing overvoltage of unloaded lines, unloaded lines, unloaded busbars and Breaking capacitive load overvoltage when capacitors are opened, breaking inductive load overvoltage when no-load transformers, reactors and motors are opened, etc. The above is an overview of surge voltage, I hope it can be helpful to you.