Power line interference
Power quality issues play an important role in ensuring the sustainability of computers and peripherals and their longevity. Computers, like any electronic equipment that is powered by AC power, are exposed to various negative influences from this power supply. One of the reasons that reduce the reliability of computers is an abnormal change in the parameters of the power supply network. These changes in the parameters of the power supply can be caused by both external and internal factors. External factors include unpredictable changes in loads, generating negative disturbances of the primary network, lightning strikes, etc., as well as possible special effects. Internal factors are intra-system interference.
Among the above reasons leading to a change in the output voltage of power supplies, and therefore to a decrease in noise immunity of various computer nodes, the most difficult is the problem of eliminating the influence of changes in the supply voltage on the computer. Unfortunately, in real industrial networks, there are short-term or long-term unacceptable voltage changes, called network noise.
Network interference can be divided into two categories: long-term voltage dips and surges (low-frequency disturbances) and impulse noise (high-frequency disturbances).
Low-frequency disturbances are understood as voltage dips and surges, the duration of which is comparable with the duration of the voltage frequency of the AC mains or exceeds it (Fig. 1a). High-frequency disturbances are short-term impulse noise superimposed on the sinusoidal voltage of the primary network and distorting its shape (see Fig. 1b, c). On rice. 1 (g, d) shows the supply voltage during emergency outages, which can be attributed to long-term failures.
In reality, in practice, various combinations of the considered interference are possible.
Voltage dips are one of the most common types of interference causing computer malfunctions (data loss or, even worse, failure of its individual elements). Statistically most probable for Ukraine are failures lasting from 6 to 15 seconds (up to 50%) and longer, from 21 to 30 seconds (about 30%), and the depth of the most common failures ranges from 35% to 100%.
Another type of hazardous interference is high voltage voltage pulses. The cause of their occurrence is most often lightning discharges, static electricity discharges, an electric arc in switching devices. Sometimes, the source of pulsed high-voltage interference with an amplitude of up to 1000 V can be the currently widely used conventional choke fluorescent lamps.
The quality of the supply voltage, determined by the documents GOST 13109-97 and DSTU 3466, is best controlled by special automatic complexes for measuring voltage levels. Conventional AC voltmeters with an upper limit of 500 … 700 V (both dial and digital) can only record long voltage dips. Sometimes, in the absence of special measuring equipment, oscilloscopes connected to the network through a special voltage divider are used to observe periodic pulsed interference.
Depending on the cause of the interference, electromagnetic interference can be divided into external and internal. External interference includes atmospheric, space and industrial.
Atmospheric and cosmic interference are the result of natural processes occurring in nature: lightning discharges, solar radiation, cosmic radiation, magnetic storms, etc. The most significant interference may occur during lightning discharges, as Lightning creates a very strong electromagnetic field, leading to a significant change in voltage in power lines up to the violation of their insulation.
For computers, industrial interference is especially dangerous, which is created by arc and resistance welding equipment, power ballasts, electrical equipment, electromechanical devices, medical equipment, etc.
As already noted, from external causes, the most often encountered an unacceptable change or short-term loss of the input AC voltage of an industrial power supply network. This is due to unstable operation of the primary network or a violation of the rules for the operation of electrical installations by consumers working in non-stationary modes and eating together with computers from a common transformer substation.