Spare power supply

Need for UPS
Computer systems and computer systems play an increasingly important role in all fields of human activity, and it is inconceivable to imagine today’s world without them. For these systems to work, a power supply is required, however, which is affected by the impact of disturbances of natural or industrial origin.

The deflection of the power supply parameters from their nominal values ​​affects the operation of sensitive electrical devices and in some cases may lead to unintended consequences of loss of information, damage to data carriers or processing equipment, process mode violations, etc.
Statistics show that due to a break in the grid, 75% of the cases are losing information, and 65% of the electronic equipment itself.
Suddenly dropping your computer’s power supply (for whatever reason) may cause data loss in your operating and cache memory, possibly the FAT disk table. In the worst case, electronic components are damaged. Such may be the consequences of short-time “interruptions” of the supply voltage for parts of a second (Sags, or Brownout) and a “floating” (slowly but not periodically) reduction of the supply voltage (Rolling Brownout). Sometimes surges and surge boosts with amplitude of not less than 100% of the nominal (Spike) occur in the network, which may damage the computer’s impulse power sources.

Under the influence of strong electrical noises generated by the operation of Electro Magnetic Interference (EMI), Radio Frequency Interference (RFI), the sinusoidal shape of the supply voltage can be deformed resulting in an apparatus breakdown (Glitch) and errors in program execution.

Voltage fluctuation
According to National Observatory, taken from March 1990 in 235 randomly selected cities of the United States and Canada, there are on average about 2000 disturbances per year in a settlement. Interferences are classified according to the tolerances recommended by the Computerization and Business Equipments Manufac- turers Associa- tion (SBTEA). Out of the recommended granules for the average city, there are 443 interference annually, of which:

  • 36 are spiers (Spiques) lasting up to a few milliseconds (1/1000 part of the weekend);
  • 128 are Surges over a period of network voltage (20 milliseconds);
  • 264 are drops (Saggs), contrary to the surges, the voltage is less than normal;
  • 15 are interruptions (Bloscocs) of the power supply over 10 milliseconds.

The survey shows an increase in drops compared to data taken from the IBT in 1972 and AT & T in 1979. The surges increase by 150%, and in some regions they reach 2.8 in a month. Very often the interference is combined, in 17% of cases interruptions are preceded by more than a few period of network voltage drops.
In our country, disruptions in the delivery of electrical communications represent 37.7% of the average annual number of disturbances. The accuracy of the information processed affects broadband spectrum disturbances that have a diverse nature of occurrence. For small amplitudes, these disturbances are defined as noise and harmonic distortions are present in anomalous shape deviations and frequency of supply voltage from the ideal sinusoid at 50 Hz.

Impact on equipment
Unreliable power supply has a varied impact on the operation of electronic devices, but according to the output, two groups are formed:

  • leading to loss of information;
  • resulting in damage to equipment.

Loss of information
The first group covers all types of power failure interruptions of varying duration that lead to disruptions in the power supply of the devices but are generally not dangerous to the integrity of the components. The reduction of the amplitude of the supply voltage upon reaching the limit values ​​(the standard deviation to -15% and + 10% of the nominal voltage, which in Bulgaria is 220 V, ie the limits are from 187 to 242 V) leads to a proportional reduction of secondary voltages, supply circuits and thus disturbance of their work. The shape of the impulse signals is changed, the RAM forgets the recorded information, the transmission of signals between individual subscribers when operating on a computer network is disturbed.

Component failure
The second group refers to all incitements triggered by lightning strikes near power transmissions (with the current velocity increasing to several hundred thousand amps in milliseconds, and the induced voltages – ten thousand volts) or directly on them, as well as for power users with inductive load capacities, electric welding machines, power generators, and so on. At low energy levels, these impulse effects lead to reversible electrical breakthroughs that recover, but can cause a gradual change in the electronic components with subsequent degradation and refusal. At significant energy levels (over 50 joules), there is a risk of an irreversible electrical breakdown of semiconductors and passive components, and a general failure of the power packs of the devices with all the resulting consequences.
However, despite the fearsome sound, these considerations are not intended to intimidate naive customers but describe some of the real problems arising from the use of electronic equipment connected to the power supply network. Regardless of the quality and reputation of the manufacturer, the electronic devices work in a real environment and can not be completely isolated from its sometimes destructive influence. Lightning and thunderstorms on Earth have since the moment of the emergence of an atmosphere, and pessimists predict their existence long after the disappearance of human civilization

Means of protection
The simplest protection of computer power supply is overvoltage limiters. They protect computer assemblies from peaks and short drops in the power supply voltage of the network, as well as from RF noise. A higher level of protection ensures the normalization devices that filter the supply voltage and adjust it in a sufficiently wide range. The power supply of the computer with a ferro-resonant converter provides full galvanic separation by frequency and prevents the intrusion of high frequency noise into the payload circuit. The ferro-resonant transformer also protects against voltage drops, sharp drops, and peaks in the power supply. Much of the damage to system, modem and fax modems and network boards is a consequence of high-voltage pulses falling into the interface port not on the power supply network, but on the data cables.
To solve these major problems, a wide range of security features have been created, including various filters, stops, dischargers, stabilizers, and, ultimately, the UPS (Uninterruptible Power Supplies) hierarchy. Because of the wide range of harmful effects, UPS resolves the task of protection in various ways, including both the more elementary (filters, dischargers, varistors) and the more complex means (stabilizers) in a single complex.
There are two main UPS tasks:

  • protection against power supply instability and emerging disturbances with dangerous for the load parameters (amplitude of voltage, frequency, spark, energy);
  • securing autonomous operation of the user in case of a long interruption of the supply voltage from the mains.