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关键词:Supply HarmonicsElectricity sinusoidal voltagesvoltages
harmonic that may be permitted anywhere on the system. Table 7.5 shows IEEE standard
519-1992 distortion limits at the various system voltages.
Table 7.5 IEEE Standard 519-1992 recommended voltage distortion limits
System Voltage Individual
Harmonics voltage
distortion
Total Harmonic
Distortion (THD)
69 kV and below 3.0% 5.0%
115 kV – 161 kV 1.5% 2.5%
Above 161 kV 1.0% 1.5%
Finally, there is IEC standard 61000 which not only limits the harmonic distortion levels
produced by electrical equipment but also deals with EMC compatibility and specifies that
electrical equipment should be robust enough to operate from supplies with voltage
distortions within stated limits.
Exercise 7.1
In Equation 7.2 can you suggest why we stop our summation at the 50th harmonic?
Turn to the end of the booklet for suggested answers.
S7: Supply Harmonics
116 EEE8044: Fundamentals
7.4 Harmonic Measurements
Site measurements of voltage and current harmonics are regularly carried out to assess
compliance with relevant standards, monitor the level of existing harmonics, help in the
planning and connection of new non-linear loads and for trouble shooting purposes in
situations where there is a harmonics related problem with the performance of electrical
equipment.
A range of measuring equipment is available for the analysis of nonsinusoidal voltages and
currents ranging from spectrum analysers that display the power distribution of a
nonsinusoidal signal as a function of frequency to specialised harmonic analysers that
measure the amplitude of a periodic function and gives the frequency spectrum of the
signal and even distortion analysers that give a direct reading of the THD.
Exercise 7.2
You need to perform some site harmonic measurements. Use the www to search for
possible suppliers of the three types of analysers and compare their specifications.
List the web sites that you visited below.
S7: Supply Harmonics
117 EEE8044: Fundamentals
7. 5 Harmonic Calculations
For most systems, the calculations of system harmonic distortion levels require the use of
some computer simulation software to aid the system planner in his analysis. However, for
simple distribution systems and some industrial supply networks, it is possible to perform
the analysis using simple manual calculations. This requires knowledge of the
characteristics of the harmonic generating non-linear load. For most power electronic
devices, it is possible to determine the harmonic spectrum analytically. For other types of
non-linear loads, such as arc furnaces, it is often necessary to use typical characteristics in
the absence of any better load information.
For purposes of analysis, most harmonic sources may be represented as ideal current
sources (at each harmonic frequency) with power flowing from the harmonic sources
through the network from the customer up into the higher voltage distribution system and
into other loads.
Hand calculations can be performed when the system under consideration can be
represented by one of the following circuits: a simple network with no power capacitors; 本论文由英语论文网提供整理,提供论文代写,英语论文代写,代写论文,代写英语论文,代写留学生论文,代写英文论文,留学生论文代写相关核心关键词搜索。