The scientific instruments used in the experimental teaching process of colleges and universities contain a large number of harmonic source equipment. For the harmonic source test of science and engineering colleges, the harmonic characteristics of the university power system are analyzed and the influence of harmonics is predicted. . --- Harmonic test analysis and treatment plan for harmonic source equipment in colleges and universities
Jiangsu Ankerui Electric Manufacturing Co., Ltd. Jiangyin, Jiangsu 214405, China
Abstract: The scientific instruments used in the experimental teaching process of colleges and universities contain a large number of harmonic source equipment. For the harmonic source test of science and engineering colleges, the harmonic characteristics of the university power system are analyzed and the harmonics are predicted. The impact of the proposed harmonic management scheme, the scheme uses the active power filter products of Ankerui Electric Co., Ltd. to provide optimization solutions and reference basis for the building electrical design of colleges and universities. --- Harmonic test analysis and treatment plan for harmonic source equipment in colleges
Keywords: colleges and universities; harmonics; active power filter; building electrical
1 Introduction
In modern society, as more and more non-linear load devices are connected to the grid, a large amount of harmonic current is injected into the grid, causing the voltage of the common access point to be distorted, resulting in current distortion of the grid and deteriorating power quality. The existence of harmonics will inevitably increase the loss of the transformer, and it will also cause the capacitor of reactive power compensation to resonate, interfere with sensitive electronic equipment, cause motor vibration and relay malfunction. Now the harm caused by harmonics has begun to be paid more and more attention, and it is hoped that the corresponding measures can be taken to control the harmonics in the power grid [1-2].
When dealing with harmonics, it is necessary to determine the existence of harmonic sources and analyze their harmonic characteristics, which is the key to adopting a correct governance solution. The characteristics of common harmonic sources such as typical nonlinear loads are well known and can be targeted for suppression and governance. However, the harmonics appearing in the university building's experimental building and the teaching building power grid system are special. For example, many harmonic source devices and a large number of sensitive devices that are rarely encountered in ordinary civil buildings need to be “clean†(cannot contain harmonics). The power grid environment to ensure the normal operation of the system [3-4]. In view of the above reasons, this paper analyzes the harmonic characteristics of several typical laboratory equipments in a science and engineering university, and gives the harmonic control scheme and related products to control harmonics. This paper uses Ankerui Electric Co., Ltd. The model produced is the ANAPF50-400/B three-phase four-wire active power filter to control the harmonic load of a university.
2 Typical laboratory equipment harmonic characteristics
A science and engineering university laboratory includes the embedded system laboratory of the Department of Automation, the accelerator laboratory of the Department of Engineering Physics, the NMR spectrometer laboratory of the Department of Biomedicine, and the sintering laboratory of the materials department [5]. Typical harmonic waveforms for each laboratory are listed in Figure 1, Figure 2, Figure 3, and Figure 4 below. According to these four typical harmonic waveforms, you can know:
First, in the embedded system laboratory, the three-phase current waveform is the characteristic of the rectifier circuit, and the capacitor charging process has current and obvious distortion. It can be seen from the FFT that the THDi content of the 3rd, 5th and 7th harmonics is very high. The 3rd harmonic distortion rate is 78%, 5 times is 49%, 7 times is 28%, and the total harmonic distortion rate is as high as 95.6%, but the laboratory consumes less power, and the highest B-phase current is 16A, considering The building's power transformer has a large capacity and a small system impedance, so the voltage distortion rate is low and does not exceed the standard limit. Another phenomenon that needs attention is the neutral current. When there is only the fundamental current, the three-phase unbalanced current flows through the neutral line. The value of the fundamental wave current of each phase is definitely offset by the value of the largest phase. Phase fundamental current. However, the 3rd harmonic is a zero-order harmonic, which causes the harmonic current to be superimposed on the neutral line, with the current distortion rate of 78% as the reference. The current on the neutral line is more than twice the phase current, given the incoming circuit breaker. For the three-pole circuit breaker, the neutral current is not detected. Even if the neutral current exceeds the allowable current capacity of the conductor, the circuit breaker will not operate. This may cause the neutral line to over temperature, insulation aging, ground fault, and power supply interruption. There is even an electrical fire.
Second, in the accelerator laboratory, the peak coefficient (CF) of the current C phase is 4.74. Moreover, half-wave asymmetry leads to the occurrence of even harmonics and DC components. From the FFT of the current, it can be seen that the 3rd harmonic distortion rate is 59.5%, 5 times is 53%, 7 times is 47.1%, and the total harmonic distortion rate is as high as 99.2%. The accelerator has a large harmonic content and needs to be treated. The active filter of Ankerui Electric can be used to eliminate harmonic interference.
Third, in the NMR spectrometer laboratory, from the current waveform, it can be known that the device is connected only to the A phase, and the current waveform exhibits a nonlinear characteristic of magnetic saturation. By analyzing the current waveform, it can be known that the 3 and 5 harmonics are included. wave. The 3rd harmonic distortion rate is 30.8%, 5 times is 11.4%, 7 times is only 2.7%, and the total harmonic rate is 33.3%. Harmonics need to be treated.
4. In the sintering furnace laboratory, the grid system contains even harmonics and DC components. From the FFT of the current, it can be known that the current has 5th harmonic and a small number of even harmonics, and the third harmonic distortion rate is 7.6%. The second time is 20.9%, the 7th time is only 3.2%, the total harmonic distortion rate is 28.1%, the total harmonic current of the system is 13A, but the reactive power of the system is large, resulting in the system power factor is 0.33. section.
Figure 1 Embedded system laboratory harmonic test results
Figure 2 Accelerator Lab Current Harmonics
Figure 3 NMR spectrometer harmonics
Figure 4 Sintering laboratory harmonics
Aiming at the typical harmonic characteristics of the above-mentioned university laboratories, it can be concluded that the products of the active filter required have the functions of controlling harmonics, compensating for reactive power, and adjusting three-phase unbalance. According to the APF products on the market, the APF products produced by Ankerui Electric Co., Ltd. have the above three functions, which can perfectly solve the above problems of harmonic, reactive and three-phase unbalance.
3 University Laboratory Harmonic Treatment Program
A three-phase four-wire active power filter modeled by Ankerui's model ANAPF50-400/B is used to incorporate ANAPF into the power distribution cabinet of each laboratory using the local management method, as shown in Figure 5. Current sampling is performed at the feeder of each laboratory by where to pick up.
Figure 5 Ankerui's ANAPF local compensation plan
The main technical specifications of ANAPF (Active Power Filter) produced by Ankerui and the ANAPF active filter quotation and main component list are shown in Table 1 and Table 2.
Table 1 Main technical indicators of Ankerui ANAPF (active power filter)
Table 2 Ankerui ANAPF active filter offer and main components list
0 The university used Ancorui's ANAPF50-400/B three-phase four-wire active power filter to control the sintering laboratory in situ, and obtained a perfect sine wave as shown in Figure 6. The ABC three-phase THDi content is 2.9%, 2.8%, and 3.4% indicate that the treatment effect is satisfactory.
1 2 Figure 6 Current waveform after sintering laboratory treatment
4 Conclusion
In this paper, the causes and harmonic characteristics of harmonic currents in university laboratory power systems are analyzed by parameters such as waveform and distortion rate, and the treatment scheme for harmonic control is given. Although the experimental equipment in colleges and universities is diverse, harmonic generation and variation have great randomness and complexity. However, by analyzing its load characteristics, it is still possible to roughly judge its harmonic type, and then accurately analyze the harmonics by combining the measured spectral data. , give the corresponding governance measures. Actually, the use of Ankerui's ANAPF in the sintering laboratory shows that the harmonic effect is ideal and the harmonic problem is solved.
references
[1] Department of Construction Quality and Safety Supervision and Industry Development Department of the Ministry of Construction. Technical Measures for the Design of National Civil Engineering - Energy Savings Special [M]. China Planning Press, 2007.
[2] Ministry of Housing and Urban-Rural Development of the People's Republic of China. Electrical Design Code for Educational Buildings (Review) [S].2013.
[3] Chen Zhongli. Research on Harmonic Quality Technology of Shanghai Light Source Engineering[J]. Construction Electric, 2012(1) : 3-11.
[4] Xiang Chengjiang. Application of Tuned Filter Device [J]. Intelligent Building Electrical Technology, 2010 (3): 80-83.
[4] Wang Lei, Pan Min. Analysis of Harmonic Test of Experimental Equipment in Colleges and Universities[J]. Intelligent Building Electrical Technology, 2013(4): 16-19.
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