Harmonic status of data center distribution system
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To meet the operational needs of large-scale data centers, data center power distribution systems in the UPS capacity increased dramatically. According to the survey, the main harmonic source equipment of low voltage distribution system in data center is UPS, switching power supply, inverter air conditioner, computer and server. Equipment manufacturers have different harmonic current content of the larger, but generally high, THDi (current total harmonic distortion rate) even more than 50%. 5 times, 7 times, 11th harmonic serious, and sometimes also contains a larger amount of the 3rd harmonic. And these harmonic source device displacement power factor is extremely high.
Harmonic characteristics of the main load in the data center are as follows:
● UPS power supply, stand-alone capacity, most of 6 pulse UPS uninterruptible power supply equipment (3 times,
5 times, 7 times, etc.)
● Switching power supply, mainly for computer and other office equipment power supply, a large number (3 times, 5 times, 7 times, etc.)
● inverter air conditioners, elevators, etc., frequency conversion drive equipment as the main source of harmonics (5 times, 7 times, etc.)
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Harm of Harmonic in Data Center Distribution System
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The harmonics in the data center distribution system will adversely affect the electrical equipment and distribution equipment, the main impact of the following points:
(1) Interference communication and data transmission:
Harmonics can cause interference to nearby communication systems, introduce noise, reduce communication quality, and even lose information in severe conditions, thus preventing the communication system from working normally and affecting the precision of electronic equipment while the UPS and other rectifying devices are generated during rectification and charging The harmonics will also affect the computer network, causing network downtime
Wrong
(2) Harmonic resonance caused by equipment damage or switch malfunction:
Under normal circumstances, the power system parameter design makes the resonant frequency of the circuit away from the fundamental frequency, but if the circuit in the resonant phenomenon, it will have serious consequences If the circuit in series resonance, the impedance of the line will suddenly decrease, the line Current close to the short-circuit current, which will cause the cable overheating burn, and then there is power failure such as system short-circuit switch trip; and appear parallel resonance, will show the line impedance suddenly increases, so the system harmonic voltage is amplified, which will Resulting in high voltage breakdown of the insulation of the electric equipment such as the line cables, distribution switches and compensation capacitors, and the system will have serious short circuit fault
(3) increase the load capacity of the transformer:
Transformer will be due to excessive harmonic current eddy current loss and hysteresis loss, which will cause the transformer core temperature rise too fast, resulting in lower efficiency of the equipment; the same time will make the insulation damage, or even cause short circuit fault In order to suppress the temperature rise (for the transformer, the temperature rise for each increase of 8, life expectancy will be reduced by 50%), the transformer derating use;
(4) destruction of the protection of the normal operation of the device:
Harmonic current will cause the relay device to increase the heat, which will result in thermal tripping circuit breaker and thermal relays rated tripping current is reduced, the electromagnetic circuit breaker due to eddy current tripping difficulties
(5) accelerate cable aging, shorten the service life:
Due to the harmonic current, the actual RMS current in the cable will be greater than the fundamental current; meanwhile, due to the skin effect, the harmonic resistance of the wire is increased, the line loss is increased, the transmission capacity of the circuit is reduced, Discharge, accelerate cable aging, shorten its service life
(6) caused by capacitor overload fever, increased breakdown breakdown:
Capacitor impedance characteristics on the one hand with its own capacity, on the other hand is also inversely proportional to the frequency of the power supply, which makes the capacitor is very easy to absorb harmonic currents caused by overheating, insulation media accelerated aging, severe, will be hit Wear or even explode. In addition, the harmonic current will also reduce the output capacity of the generator set meter and other measuring equipment measurement confusion, affecting the reliable operation of the distribution system, waste of energy, reduce power consumption efficiency and other issues
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The status of data center harmonic control
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Large-scale data center systems in the past have only taken some precautions to eliminate or suppress harmonic hazards. For example, when determining the rated capacity of power transformers according to the load, a margin should be taken into account for harmonic distortion; a line filter should be added to the equipment susceptible to interference Etc., can not fundamentally eliminate the harm of harmonics.
There are two ways to take the passive filter or active filter for harmonic control, the filter is no filter by the filter capacitor reactor and resistor appropriate combination of filter device, in parallel with the harmonic source, in addition to filtering The main disadvantage is that the compensation characteristic is affected by grid impedance and operating conditions, and the parallel resonance of the system is easy to occur. As a result, harmonics are amplified and the LC filter is overloaded or even burned. In addition, it can only compensate for the fixed frequency harmonics, the compensation effect is not very satisfactory.
The active filter is a harmonic compensation device composed of power electronic devices. Its basic working principle is as follows: detecting the voltage and the current of the object to be compensated, calculating a compensation current command signal by the command current calculation circuit, and compensating The current generating circuit amplifies and obtains the compensation current, the compensation current and the harmonic currents to be compensated in the load current, and the reactive current and so on, finally obtains the expected power supply current. Active filter with good filtering effect, the filtering effect is not affected by the system impedance, and can suppress the system of series resonance and parallel resonance and so on.
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solution
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LDAPF family of active filters
The LDAPF family of active power filters is a truly effective harmonic management solution that uses state-of-the-art active harmonic compensation to dynamically eliminate grid harmonics. LDAPF real-time detection of non-linear load current waveform generated, the separation of the harmonic part, and then through the IGBT inverter circuit output equivalent reverse harmonic current to offset the load harmonics to ensure that the current drawn from the grid sine wave, to achieve harmonic Wave filter function. In addition, LDAPF can provide advanced or lagging reactive current, used to improve the power factor of the grid, to achieve dynamic reactive power compensation.
