The source of power supply system surge is divided into external (lightning causes) and internal (electrical equipment start and stop and failure, etc.). Lightning surge overvoltage
The surge caused by lightning is the most harmful, in the lightning discharge, centered on the lightning strike within the range of 1.5 ~ 2KM, can produce dangerous overvoltage. Lightning caused (external) surge is characterized by a single-phase pulse type with huge energy. The voltage of an external surge can rise rapidly from a few hundred volts to 20,000V in a few microseconds and can be transmitted over considerable distances. According to ANSI/IEEE C62.41-1991 description, the instantaneous surge can be as high as 20,000 V, and the instantaneous current can be up to 10,000 A. According to the statistics, the surge outside the system mainly comes from lightning and other system impacts, which accounts for about 20%.
(1) induction lightning surge over-voltage: lightning strike lightning generated by high-speed changes in the electromagnetic field, the lightning radiation of the electric field on the conductor, the induction of a very high over-voltage, this type of over-voltage has a very steep leading edge and rapid decay.
(2) direct lightning surge overvoltage: direct lightning on the grid, due to the instantaneous energy is huge, extremely destructive, there is no one device can be protected against direct lightning.
(3) lightning conductive surge overvoltage: by the distant overhead line conduction, due to the equipment connected to the power grid has a different overvoltage suppression ability, so the conductive overvoltage energy with the extension of the line and weakened.
(4) oscillating surge overvoltage: the power line equivalent of an inductor, and the earth and the presence of distributed capacitance between the adjacent metal objects, constituting a parallel resonance circuit, in the TT, TN power supply system, when a single-phase grounding fault occurs at the moment, due to the high-frequency components of the resonance, the line produces a very high overvoltage, the main damage to the secondary instrumentation.
Direct lightning strikes are the most serious events, especially if the lightning strike hits an overhead transmission line near the customer's inlet. During these events, overhead transmission line voltages rise to hundreds of thousands of volts, often causing insulation flashover. Lightning currents travel over distances of one kilometer or more on power lines, with peak currents of 100 kA or more near the point of strike. The current in the low voltage line at the customer's inlet can reach 5kA to 10kA per phase, and in areas with high lightning activity, power facilities may be subjected to several direct lightning strikes per year causing severe lightning currents. In areas with high lightning activity, power facilities may experience several direct lightning strikes per year resulting in severe lightning currents. These events are rare when power is supplied by underground power cables or in areas where lightning activity is infrequent.
Indirect lightning strikes and internal surges have a higher probability of occurring, and the vast majority of damage to electrical equipment related to it. So the power supply surge prevention focus on this part of the surge energy absorption and suppression. Operation surge overvoltage
The reason for the occurrence of internal surge with the power supply system within the equipment start and stop and power supply network operation faults related:
Inside the power system, due to the operation of the circuit breaker, load input and removal or system failure and other internal state changes in the system, and the system parameters change, resulting in the power of the internal electromagnetic energy conversion or transmission of the transition process, there will be overvoltage within the system. Overvoltage will occur within the system. The surge within the system mainly comes from the impact of the electrical load within the system, accounting for about 80%. The causes of internal overvoltage in the power system can be broadly divided into:
(1) the input and removal of large loads of electricity;
(2) the input and removal of inductive loads;
(3) the input and removal of power factor compensation capacitors
(4) short-circuit faults
Power supply system due to the start and stop of high-power equipment, line faults, casting and cutting action and frequency conversion. Failure, casting and cutting action and the operation of frequency conversion equipment, etc., will bring internal surge, to the power equipment to bring adverse effects. Especially computers, communications and other microelectronic equipment to bring a fatal impact. Even if no permanent equipment damage is caused, abnormalities and stoppages in system operation can have very serious consequences. For example, nuclear power plants, medical systems, large-scale factory automation systems, stock exchange systems, telecommunication bureaus with switches, network hubs and so on.