Sources, hazards and protection measures of surges
According to statistics, in the United States: the direct losses caused by surges to various industries, such as shutdowns, time loss, equipment maintenance, and premature equipment replacement, are as high as 26 billion US dollars each year. In China, according to relevant statistics, 63% of electrical products that have problems during the warranty period are caused by surges. Therefore, PCB design is indispensable for electrical products, so it is particularly important to understand surges and effectively avoid surges in design.
What is a surge?
Surges are called transient overcurrents. They are a short-term current and voltage fluctuation in the circuit, which usually lasts about one millionth of a second in the circuit. A voltage fluctuation of 5,000 or 10,000 volts that lasts for a moment (one millionth of a second) in a 220-volt circuit system is a surge or transient overcurrent.
Where does the surge come from?
Surges can come from outside the electrical device or from inside the electrical device, that is, from the electrical equipment inside the electrical device.
Surge from outside This surge is caused by lightning or the switching of public power grid switches. Both types of harmful power disturbances can disrupt the operation of computers and microcomputer information processing systems, causing shutdowns or permanent equipment damage.
1.Surge from outside:
The main source of external surges is lightning. When there is charge accumulation in the clouds and the ground below the clouds accumulates equal charges of opposite polarity, lightning discharge occurs. The charge potential between the clouds and the ground is as high as several million volts. When lightning strikes, several kiloamperes of current are discharged through lightning strikes, passing through all equipment and the earth and returning to the clouds, thus completing the path of electricity. Unfortunately, the path often takes important or valuable equipment. If lightning strikes a nearby power line, part of the current will enter the building along the line. This huge current will directly disrupt or destroy computers and other sensitive electrical equipment, and the speed is so fast that the whole process only takes one millionth of a second.
Another source of external surges is the overvoltage generated on the power line by the power company’s public grid switch.
2.Surge from inside: Surge from inside is common, 88% of surges are generated by equipment inside the building, such as air conditioners, elevators, welding machines, air compressors, water pumps, switching power supplies, copiers and other inductive loads.
Surge has certain harm to computers and other sensitive electrical equipment. With the development of computer technology, multi-layer, super-scale integrated chips, dense circuits, tend to be more integrated, smaller component gaps, and thinner wires. A few years ago, a square centimeter of computer chips had 2,000 transistors, while the current Pentium has more than 10,000,000. This increases the probability of computer damage by surge.
Due to the design and structure of the computer, it should work within a specific voltage range. When the surge exceeds the level that the computer can withstand, the computer will have garbled data, the chip will be damaged, and the components will age prematurely. These symptoms include: unexpected data errors, failure to receive/transmit data, loss of documents, abnormal operation, frequent maintenance, unexplained failures and hardware problems, etc.
Lightning surges far exceed the level that computers and other electrical equipment can withstand. In most cases, they cause immediate destruction of computers and other electrical equipment, or permanent loss of data. Even the start-up or shutdown of a small 20-horsepower induction engine will generate a surge of 3,000-5,000 volts, causing the computer sharing the same distribution box with it to be damaged or disturbed in every surge, and the number of such surges is very frequent.
What are the surge phenomena?
There are five types of surges from the perspective of phenomena:
- Arcing: leaving obvious arc marks on the damaged parts;
- Corona: There are obvious electrical corrosion marks on the surface of the insulator, and the insulation of the corroded part decreases;
- Damage to components such as IC of the control circuit;
- Damage to rectifier components and voltage stabilizing components of general electronic equipment and household appliances;
- Grounding fault causes equipment to be energized (single-phase grounding): causing phase-to-phase short circuit of equipment (phase-to-phase short circuit of motor).
What are the hazards of surges?
There are mainly two types: catastrophic hazards and cumulative hazards.
Catastrophic hazards: If a surge voltage exceeds the tolerance of the equipment, the equipment will be completely destroyed or its life will be greatly reduced.
The insulation voltage of the motor is usually 2 times the normal working voltage plus about 1000V, so the insulation voltage of a 220V motor is generally 1500V. The surge continuously impacts the insulation layer of the motor, causing the insulation layer to be broken down.
Accumulative hazards: The cumulative effect of multiple small surges causes the performance degradation of semiconductor devices, equipment failures and shortened life, and finally leads to shutdown or reduced productivity.
Surges can damage electrical equipment containing microprocessors, which are extremely susceptible to surge damage, including computers and computer auxiliary equipment, program controllers, PLCs, fax machines, telephones, answering machines, etc.; program-controlled switches, radio and television transmitters, microwave relay equipment; products in the home appliance industry include televisions, stereos, microwave ovens, video recorders, washing machines, dryers and refrigerators, etc.
How to achieve surge protection?
Surge protection should be implemented in stages to ultimately achieve the purpose of perfect protection of distribution systems and electronic equipment. The first step in implementing surge protection in a graded manner is to classify the surge environment.
The classification of surge environments is based on the intensity and frequency of surges. Internationally, surge environments are generally divided into three categories.
(1) Class C: refers to outdoor and incoming line main switches. These locations are prone to strong lightning surges. Specific locations include: the connection between the meter and the distribution board, the overhead lines between buildings, and the underground cables connected to the well;
(2) Class B: refers to locations with shorter connections to the Class C environment, as well as lighting systems in large buildings. Surges at these locations can be generated by lightning or internal electrical switches. Surges generated by lightning are attenuated by distribution lines and are already attenuated more than surges in Class C environments;
(3) Class A: refers to power sockets in rooms and terminals of longer distribution lines; longer means power sockets that are more than 10 meters away from the Class B location, or more than 20 meters away from the Class C location. Surges at these locations are mainly surge voltages generated by internal electrical switches.
