IEEE Standards are publications that provide acceptable design practice. IEEE Standards addressing power quality include those defining acceptable power quality (IEEE Standard 519) and another standard relating to the measurement of power-quality “events” (IEEE Standard 1159).
Both of these standards focus on AC systems and their harmonics (that is, multiples of the line frequency). IEEE Standard 519 [2.1] (denoted IEEE Std. 519-1992) is titled “IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems.”
The abstract of this standard notes that power conversion units are being used today in industrial and commercial facilities, and there are challenges associated with harmonics and reactive power control of such systems. The standard covers limits to the various disturbances recommended to the power distribution system.
The 1992 standard is a revision of an earlier IEEE work published in 1981 covering harmonic control. The basic themes of IEEE Standard 519 are twofold. First, the utility has the responsibility to produce good quality voltage sine waves.Secondly, end-use customers have the responsibility to limit the harmonic currents their circuits draw from the line.
Shown in Figure 2.1 is a utility system feeder serving two customers. The utility source has resistance R and line reactance jXs. The resistance and reactance model the impedances of the utility source, any transformers and switchgear, and power cabling.
Figure 2.1 Harmonic-generating load causing voltage distortion at the point of common coupling (PCC). The AC source is modeled as an ideal voltage source in series with a resistance Rs and a reactance jXs.
Customer #1 on the line draws harmonic current Ih, as shown, perhaps by operating adjustable speed drives, arc furnaces, or other harmonic-creating systems. The voltage Customer #2 sees at the service entrance is the voltage at the “point of common coupling,” often abbreviated as “PCC.” The harmonics drawn by Customer #1 cause voltage distortion at the PCC, due to the voltage drop in the line resistance and reactance due to the harmonic current.
The voltage harmonic distortion limits apply to the quality of the power the utility must deliver to the customer. For instance, for systems of less than 69 kV, IEEE 519 requires limits of 3 percent harmonic distortion for an individual frequency component and 5 percent for total harmonic.
The current harmonic distortion limits apply to limits of harmonics that loads should draw from the utility at the PCC. Note that the harmonic limits differ based on the ISC/IL rating, where ISC is the maximum short-circuit current at the PCC, and IL is the maximum demand load current at the PCC. IEEE Standard 1159 [2.2] is entitled “IEEE Recommended Practice for Monitoring Electric Power Quality,” and as its title suggests, this standard covers recommended methods of measuring power quality events.
Many different types of power-quality measurement devices exist and it is important for workers in different areas of power distribution, transmission, and processing to use the same language and measurement techniques. In future chapters, we draw extensively from IEEE Standards 519 and 1159. distortion.
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