Harmonic Test Analysis and Treatment Scheme of Harmonic Source Equipment in Colleges and Universities

Xu Shuang

(Ankerui Electric Co., Ltd. Shanghai Jiading 201801)

Abstract : The scientific instruments used in the experimental teaching process in colleges and universities contain a large number of harmonic source equipments. According to the harmonic source test situation of the universities of science and engineering, the harmonic characteristics of the university power system are specifically analyzed and the harmonics are estimated. The impact of the proposed harmonic control program, the program uses Ankerui Electric Co., Ltd.'s active power filter products, for the university's architectural electrical design to provide optimization programs and reference.

Keywords: colleges and universities; harmonics; active power filter; building electrical

1 Introduction

In modern society, more and more non-linear load devices are connected to the power grid, and a large amount of harmonic current is injected into the power grid, which causes the voltage of the public access point to be distorted, resulting in distortion of the power grid current and deterioration of power quality. The existence of harmonics will inevitably increase the loss of the transformer, and will also cause the reactive compensation of the capacitor resonance, interference sensitive electronic equipment, causing motor vibration and relay malfunction. Now the harm caused by harmonics has gradually been paid attention to by people, and it is hoped that by taking corresponding measures to harness 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. This is the key to adopting a correct solution. The characteristics of common harmonic sources, such as typical non-linear loads, are well known and can be targeted for suppression and management. However, the harmonics appearing in the power grid systems of university lab buildings and teaching buildings are special. For example, many harmonic source devices and a large number of sensitive devices that are less frequently encountered in common civil buildings need to be “clean” (cannot contain harmonics Wave) grid environment to ensure the normal operation of the system [3-4]. In view of the above reasons, this article analyzes the harmonic characteristics of several typical laboratory equipments in a science and engineering university, and provides harmonic treatment solutions and related harmonic control products. This article uses Ankerui Electric Co., Ltd. The production model 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

The laboratory of a science and engineering university includes the embedded system laboratory of the automation department, the accelerator laboratory of the engineering physics department, the NMR spectrometer laboratory of the biomedical department, and the sintering laboratory of the materials department [5]. Figure 1, Figure 2, Figure 3, and Figure 4 below show typical harmonic waveforms for each laboratory. According to these four typical harmonic waveforms you can know:

First, in the embedded system laboratory, the three-phase current waveform is the characteristics of the rectifier circuit, the capacitor charging process has a current, there is a significant distortion. The THDi content of the 3rd, 5th, and 7th harmonics is high by FFT. Among them, the third 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%. However, the lab consumes lower power and the highest B phase current is 16A. The building's power transformer has a large capacity and the system impedance is small, 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, a three-phase unbalanced current will flow on the neutral line, and the value of the phase-wave currents of each phase canceling each other will definitely be smaller than the maximum phase. Phase fundamental current. However, the third harmonic is the zero-sequence harmonic, resulting in harmonic currents superimposed on the neutral line, with the current distortion rate being 78% as the reference, and the current on the neutral line is more than twice the phase current, considering the feeder circuit breaker For a three-pole circuit breaker, the neutral current is not detected. Even if the neutral current exceeds the allowable ampacity of the conductor, the circuit breaker will not act, which may cause over temperature of the neutral line, insulation aging, ground fault, and interruption of power supply. Even an electrical fire broke out.

Second, in the accelerator laboratory, the peak factor (CF) of the current C phase is 4.74. Moreover, half-wave asymmetry can lead to even harmonics and DC components. From the FFT of the current, it can be seen that the third harmonic distortion rate is 59.5%, 53 times for 5 times, 47.1% for 7 times, and the total harmonic distortion rate is as high as 99.2%. Accelerators have large harmonic content and need to be treated. Accor's active filters can be used to eliminate harmonic interference.

Third, in the NMR spectrometer laboratory, from the current waveform can be seen that the device is connected to the A phase only, the current waveform shows a magnetic saturation of nonlinear characteristics, through the FFT analysis of the current waveform can be known to contain 3rd and 5th harmonics wave. The 3rd harmonic distortion rate is 30.8%, 5 times is 11.4%, 7 times is only 2.7%, and the total harmonic ratio is 33.3%. Harmonics need to be treated.

Fourth, in the laboratory of the sintering furnace, the power grid system contains even harmonics and DC components. From the FFT of the current, it can be known that the current has a fifth harmonic and a few even harmonics, and the third harmonic distortion rate is 7.6%. 5 The time is 20.9%, 7 times is only 3.2%, the total harmonic distortion rate is 28.1%, the total harmonic current of the system is 13A, but the system's reactive power is relatively large, resulting in a system power factor of 0.33. At this time, compensation for reactive power is required. section.

Figure 1 Test results of laboratory harmonics in embedded systems

Figure 2 Accelerator Lab Current Harmonics

Figure 3 NMR spectrometer harmonics

Figure 4 Sintered laboratory harmonics

For the typical harmonic characteristics of the above-mentioned university laboratories, it can be concluded that the required active filter products have the functions of controlling harmonics, compensating for reactive power, and adjusting three-phase imbalance. According to APF products on the market, the APF products produced by Ankerui Electric Co., Ltd. have the above three functions and can perfectly solve the problems of harmonics, reactive power and three-phase imbalance described above.

3 Harmonic Solutions for University Labs

The use of three-phase four-wire active power filters of the Ancorr company type ANAPF50-400/B integrates ANAPF at the distribution cabinets of each laboratory using local control methods, as shown in Figure 5. Current sampling is performed at each laboratory's feeders, where the method is to make up where.

Figure 5 Ankerui's ANAPF Compensation Program in Place

The main technical specifications of ANAPF (active power filter) produced by Acrel and the ANAPF active filter quotation and main components list are shown in Table 1 and Table 2 below.

Table 1 Main Technical Specifications of Ankerui ANAPF (active power filter)

Table 2 Quark ANAPF active filter quotation and main components list

The university used Ankerui's ANAPF50-400/B three-phase four-wire active power filter to control the sintering laboratory on-site and obtained the perfect sine wave as shown in Figure 6. The ABC three-phase THDi content was 2.9%, 2.8%, and 3.4% indicate that the effect of governance is satisfactory.

Figure 6 Current waveform after sintering in a sintering laboratory

4 Conclusion

In this paper, the causes of harmonic currents and the characteristics of harmonics in the power system of university laboratories are analyzed through parameters such as waveform and distortion rate, and the treatment plan for harmonics is given. Although there are many kinds of experimental equipment in universities, there are great randomness and complexity in harmonic generation and changes. However, by analyzing the load characteristics, it is still possible to roughly judge the type of harmonics, and then combine the spectrum data obtained by the test to accurately analyze the harmonics. , give the corresponding governance measures. The fact that Ankeray's ANAPF is actually applied to 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 of the Ministry of Construction. National Civil Engineering Design Technical Measures - Energy Conservation Specialist Electrical [M]. China Planning Press, 2007.

[2] Ministry of Housing and Urban-Rural Development of the People's Republic of China. Specification for Electrical Design of Educational Buildings (Paper Review) [S].2013.

[3] Chen Zhongli. Study on Harmonic Quality Technology of Shanghai Light Source Engineering [J]. Building Electrical, 2012(1):3-11.

[4] Xiang Chengjiang. Application of Tuning Filter Device [J]. Intelligent Building Electrical Technology, 2010(3):80-83.

[4] Wang Lei, Pan Min. Harmonic test analysis of experimental equipment in universities [J]. Intelligent Building Electrical Technology, 2013(4): 16-19.

About the Author:

Xu Shuang, female, undergraduate, Ankerui Electric Co., Ltd., major research interests in power electronics and harmonics governance. Email: Mobile QQ