Modern commercial buildings pay more attention to intelligence and modernization, while making the power quality problems such as harmonics, voltage fluctuations, flicker, three-phase imbalances become even more serious. Especially for commercial buildings, hospitals and other modern buildings, a large number of fluorescent lamps, inverter elevators, dimming lights, inverter air conditioner, computer, charging equipment, UPS and power electronics access, greatly increased the harm of harmonics, while a large number of automation Control, higher requirements for grid compatibility, an urgent need for an efficient and comprehensive solution.
.
Harmonic Analysis of Shangjian Power Distribution System
.
With the ever-changing intelligent buildings, a large number of modern electrical equipment, most of them are non-linear load, summarized as follows: a), lighting lighting ballasts, dimming equipment (phase angle controller) ; B), computers, photocopiers, printers and other office automation equipment, single-phase load; c), UPS uninterruptible power supply, red batteries and by the switching power supply all kinds of modern electronic equipment; d), elevators, air conditioners, fans and other power (VFDs) commonly used in equipment; e) other electronic control devices with certain non-linear load characteristics, the internal devices of which adopt diodes, transistors and inductive loads to work with high-frequency working state to generate harmonics , The control loop builds the harmonic wave generated by adopting the bridge type filtering and finishing circuit, and the working characteristic of the IGBT such as the frequency conversion equipment itself also produces harmonics and harmonics, which leads to the distortion of the voltage and current waveforms, seriously affecting the safety of commercial building power supply system.
Based on the measured data and theoretical analysis of the commercial construction industry in the past, we can see that the average power factor of such a system is between 0.78 and 0.85, and the power factor is in a low state. Therefore, centralized reactive power compensation is needed to increase the system power Factors; Fluorescent lighting equipment generated mainly in the third harmonic harmonics, the current distortion rate of 16.5% to 46.8%; Rectifier class load, such as frequency converters, the current majority of 6-pulse, resulting in 5,7 , The 11th and 13th harmonics, the more serious the fifth current, the distortion rate of 21.8% -28.5%; harmonic current through the superposition of 0.4kV main bus in the system, the total harmonic current distortion rate is low, the general commercial power distribution Center 0.4kV bus harmonic current distortion rate of 10.3% to 17.9%.
.
Hazards Harmonic to Shangjian Power Distribution System
.
◇ Harmonic impact on the power supply line For the power supply line, due to skin effect and proximity
Effect, the line resistance increases rapidly with increasing frequency, there will be a great waste of energy in the line, in the commercial distribution system, due to the single-phase load, and the existence of the third harmonic, a large number of harmonic currents Flow through the N line, resulting in serious cable fever, soon damaged insulation, also caused serious failure. 3.2. Harmonic effects on power transformers
The existence of harmonic current increases the hysteresis loss, eddy current loss and copper loss of the power transformer, and will greatly increase the harmonic component of the exciting current for the transformer with the asymmetrical load. Harmonic currents, especially those three times (and multiples thereof), invade a delta-connected transformer, creating a circulating current in the windings that heat the windings. 3.3. Harmonic compensation capacitors
Since the impedance of the capacitor to the harmonics is small, the harmonic current superimposed on the fundamental current will greatly increase the current flowing through the power capacitor, causing the temperature rise of the power capacitor to increase, causing the capacitor to overcharge or even explode. At the same time, harmonics may also parallel resonance with the pure capacitor, the current doubled, serious harmonic amplification. 3.4 Harmonic impact on electrical equipment
Electric equipment control system, harmonic zero-trigger delay caused by the control system, reach the expected control requirements, resulting in poor overall reliability, easy to cause system failure or system failure to expand.
◇ Harmonic impact on the communication system In the power line flow through the odd magnitude of the larger low
Frequency harmonic current, through the electromagnetic coupling, will generate interference voltage in the communication line adjacent to the power line. Interfere with the normal operation of the communication line, make t call clarity reduced, and even cause damage to the communication line.
.
Determination of governance measures
.
Combining with the past research on the power supply system of commercial buildings and the actual situation of governance, in the commercial building distribution system, due to the existence of a large number of inductive loads, the power factor is low, thus increasing the PF value and increasing the PF value without suffering from the power supply bureau Fine, while raising the substation, the supply capacity of transmission equipment, reduce network losses, end pressure drop will not be low, thus improving the quality of power supply; due to the existence of nonlinear loads, the power network there is a certain degree of harmonics, harmonic elimination Waves can reduce electrical faults and extend the life of the equipment, so designing an integrated power management solution is needed.
To solve the power quality problems of commercial building power supply system, the key point is to solve the problem of harmonics. For the special and complicated system of the system, the solution of harmonics is the primary problem, mainly from two aspects: (1) The harmonic generated by the load passes Efficient APF active filter for effective elimination; (2), for easy harmonic amplification load, the use of more effective suppression method to prevent amplification; through a combination of the two, more effective solution to the various hazards caused by harmonics .
Commercial building distribution system easy to harmonically amplify the preparation of the main compensation device, compensation branch improper design will cause a certain degree of harmonic amplification, for this case generally have four kinds of design ideas, the first one is the pure compensation non-series reactance This situation is mainly for the absence of harmonic occasions, where there is a purely harmonic capacitive harmonic reactive harmonic resonance, harmonics are infinitely magnified, the industry is not desirable for this approach; the second way, 6% reactor in series, this method is mainly for the system to the 5th harmonic mainly used to suppress the 5th and above harmonics, but will be the third harmonic amplification; the third way, in series 13% reactor , This method is mainly for the system based on the 3rd harmonic, this square
It is better from the viewpoint of benefit because the suppression starts from the third harmonic and can be harmonized more than three times at the same time. However, the volume and capacity of 13% reactors are large, the voltage of the capacitor is high, and the overall cost is high. Way, series 13% and 6% reactors, this way combines the second and third ways to suppress harmonics 3 and above, in line with the harmonic load characteristics of commercial buildings, nor because of space and cost troubled users And designer
