Many computer and electronic equipment now in use in the intelligent building. Computers and other automation equipment, the prevalence of low dielectric strength, high quality of power supply requirements, over-voltage tolerance of poor weakness, making these highly sensitive electronic systems often due to the emergence of the power at runtime runtime error data errors, time errors, crashes, no reason to restart fault even use power equipment to the formation of permanent damage caused huge losses. To this end, in the intelligent building, research the quality of power supply to the implementation of effective protection measures are very necessary. 
 Power quality of the technical indicators 
 The technical indicators for measuring power quality including voltage fluctuations, frequency fluctuations, harmonics and unbalanced three-phase. The quality of power supply will be affected by many factors. Use of a large number of nonlinear loads, such as load changes, the impact of high harmonics, the input of the power factor compensation capacitors, and cut off, lightning and human failure, and public facilities. If the operation of motors, elevators, etc. will affect the quality of the power supply thereby reducing the quality of power supply. 
 Voltage fluctuations 
 The ideal supply voltage sinusoidal waveform is continuous, smooth, no distortion, and its amplitude and frequency is stable. When the load appear larger increase is especially large equipment near the system to start from time to time so that the amplitude of the power supply sine wave affected 
 The low voltage. Even make computers and sophisticated electronic equipment operator will make an error when the power supply voltage fluctuations exceed the allowable range of power failure detection circuit of the computer mistakenly believe that the power outage issued blackout signal processing??? Computer work properly. General computer allows the voltage fluctuation range for the supply AC380V, 220V ± 5%, the voltage is reduced to 70% of the rated voltage. Computer can be considered as broken. Voltage fluctuations, computer room design specifications "GB50174-93" hereinafter referred to as the "norm" clear that the voltage fluctuation is divided into A, B, C, three. 
 Frequency fluctuations 

 Frequency fluctuations in power supply caused due to changes in generator speed is mainly due to the power grid overload operation. External device of the computer most of the general computer frequency of the synchronous motor allows the fluctuation range is 50HZ ± 1%. Generate an error when the frequency of the power supply frequency fluctuations exceed the allowable range can make your computer information storage changes may even lead to information loss. "Norms" have a clearly defined frequency fluctuations, frequency fluctuations are divided into A, B, C, three 
 Waveform distortion 

 Generate the supply voltage waveform distortion, mainly due to an impact on the grid of nonlinear loads in particular some high-power controllable rectifier device would be the power supply voltage waveform. This waveform distortion, cause the computer to the DC power supply circuit of the filter capacitor current is significantly increased capacitor fever, but also because of the saw-like waveform of the emergence of the computer power failure detection circuit to mistakenly believe that a power outage and issued by the blackout signal processing, the impact of computer work properly. The technical indicators that measure the waveform distortion waveform distortion rate, the electrical equipment input AC voltage to all high-harmonic and fundamental Valid values ??for the ratio of the percentage. " 

 4 transient pulse 
 Transient pulse, also known as spikes or voltage flash change. Grid ideal sine wave superimposed on the narrow pulse in time is less than the grid half cycle. Peak voltage up to the 20000V duration profession in millionths of a second to thousandths of a second pulse voltage, it will not only cause electronic equipment malfunctions or cause electronic equipment susceptible to interference and data loss, or temporary paralysis in severe cases can cause component breakdown and the circuit board burned the whole system came to a standstill. Caused by the transient pulse of the many reasons, usually the main internal over-voltage and lightning over-voltage. 
 5 three-phase unbalance 
 Three-phase load current asymmetry due to the uneven distribution of three-phase load, the resulting three-phase negative sequence component. The degree of imbalance indicators to measure the three-phase load voltage imbalance, current imbalance, phase imbalance. Unbalanced three-phase to what extent will affect your computer's stability and reliability, there is no complete information. Reference vendors to ensure that the specific requirements of unbalanced three-phase computer and its normal equipment, stable operation of the general requirements for the three-phase unbalanced load is less than 20%. 
 6 momentary power failure 
 If the power grid instantaneous power failure occurs. Will directly affect the normal operation of the computer. Capacitor discharge by the host computer when the power interrupted within 1.5ms to maintain the computer continues to run the system. Memory commonly used CMOS circuit when power is interrupted more than 1.5ms, once outage time, the computer will lose their memory intensive computing process of data loss resulting computer operator error as well as downtime. Generally to maintain the normal operation of the computer's power failure in 1O ms within. Interruption duration for the moment. "Norms" on the quality of power supply requirements are divided into A, B, C, three. Class A: O ms 4 ms; Class B: 4ms 200ms; C-level: 200ms 1500ms above is a measure of the major technical indicators for power quality, good or bad of these technical indicators reflect the quality of power supply. Will directly affect the operation of the computer system. This should be to power the level of pollution as well as computer systems for power quality requirements, to take appropriate protective measures to prevent interference with other devices in the grid, and improve the quality of power supply, so that the computer system can be stable, reliable operation. 
 2 ways to improve the power quality 
 Factors affecting power quality is complicated when the power supply to be contaminated after its run in the supply of computers and sophisticated electronic equipment is extremely harmful. When the power supply grid power quality can not meet the requirements needed. Reasonable power supply system, as well as the necessary technical measures have targeted elimination of pollution in the power of computers and sophisticated electronic equipment. These measures include: the use of isolation transformers, filters, regulators, and uninterruptible power supply equipment. In order to filter out high frequency noise, stable voltage isolation with the city power grid to eliminate the deviation of the voltage and frequency, and to absorb the surge and other kinds of interference in order to obtain the desired power. Several computer power supply system has a direct power supply system. Isolation transformers, voltage regulators and filter combination system and uninterruptible power supply system. 
 2.1 Direct power supply system 
 Direct power supply system is mains (usually AC38OV, 50HZ) directly connected to the distribution cabinet and then distribute them to the computer equipment. The direct power supply system is only applicable to grid-quality technical indicators to meet the requirements of the computer, and not near the start of a larger load and braking, as well as a small electromagnetic interference. The advantages of direct power supply system: the power supply system is simple, less equipment, low investment, low operating costs, easy maintenance. The disadvantage is that the quality requirements on the grid power source pollution does not have any protection, vulnerable to grid load change impacts. 
 2.2 isolation transformers, voltage regulator and filter combination system 
 The isolation transformer 'voltage regulator and filter combination system is the use of a distribution system of the computer room. The system can eliminate the transient disturbance in the grid, starting and braking of the large load, voltage fluctuations and electromagnetic interference. The advantages of the system is inexpensive, reliable operation, easy maintenance, low running costs. The disadvantage is that a greater frequency in the power grid fluctuations and sudden loss of power protection. 
 2.3 Uninterruptible power supply 
 Uninterruptible power supply it is the power converter, energy storage (batteries) and switch into a power supply. Uninterruptible power supply with voltage regulation, frequency stabilization, anti-interference, to prevent surges and other features. Moreover, when a sudden power failure occurs, the uninterruptible power supply of electricity equipment can continue to supply power for some time, so the timely processing of memory in computers and other equipment, or to immediately start the standby power computers and other devices continue to work. 
 2,4 transient surge protection 
 Transient over-voltage is the most common form of interference in the distribution system lightning is only a main switch operation, the inputs and the removal of heavy duty equipment, reactive compensation capacitor and elevators, will have a transient overvoltage. Most of the over-voltage generated with random and repetitive, often accompanied by the occurrence of other disturbances in the grid. Above several power supply system including power supply and uninterruptible power supply can not eliminate the voltage power supply and uninterruptible power supply, fast pulse voltage can not be a timely response, and even will the power supply and uninterruptible power supply damage. Therefore must be transient surge protection to protect electronic equipment from transient over-voltage interference and abuse. To sum up with the intelligent construction of the continuous development of power quality requirements become more stringent. However, how to improve the quality of power supply to eliminate the hidden dangers in the electrical, to ensure the normal operation of computers and sophisticated electronic equipment, the engineering staff has been of concern. · 

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