Page 231 - Power Quality in Electrical Systems

Power Quality Measurements 213

Next, we’ll look at the power factor. The data acquisition system cal-
culated a power factor of 0.9, which means the angle between voltage
and current is
1
cos (0.9) 25.8
However, we know that the actual angle is 5 degrees more (due to the
error in phase shift from the CT). Therefore, the actual power factor is

PF cos( 30.8) 0.86

We now find the real power:

P (PF)(S) (0.86)(10 kVA) 8.6 kW
Next, we find the reactive power:

2
2
Q 5 2S 2 P 5 5.1 kVAr
The result is that a relatively small phase shift can result in large cal-
culation errors.

Summary
In this chapter, we have discussed some of the subtleties of power-qual-
ity measurement, including selection of the proper measurement equip-
ment. A successful power-quality measurement involves choosing the
proper measurement tool, and using it correctly.

References
[14.1] J. Williams and T. Owen, “Performance Verification of Low Noise, Low Dropout
Regulators,” Linear Technology Application Note 83, March 2000. Available on the
Web at http://www.linear.com/pc/downloadDocument.do?navId H0,C1,C1003,
C1040,D4172.
[14.2] IEEE, “IEEE Recommended Practices and Requirements for Harmonic Control in
Electrical Power Systems,” IEEE Std. 519-1992, revision of IEEE Std. 519–1981.
[14.3] Dranetz-BMI, The Dranetz-BMI Field Handbook for Power Quality Analysis, 1998
[14.4] B. Boulet, L. Karar, and J. Wikston, “Real-Time Compensation of Instrument
Transformer Dynamics Using Frequency-Domain Interpolation Techniques,” IEEE
Instrument and Measurement Technology Conference, May 19–21, 1997, pp. 285–290.
[14.5] V. Kumar, P. S. Kannan, T. D. Sudhakar, and B. A. Kumar, “Harmonics and
Interharmonics in the Distribution System of an Educational Institution—A Case
Study,” 2004 International Conference on Power System Technology (POWERCON
2004), November 21 and 24, 2004, pp. 150–154.
[14.6] IEEE, “IEEE Standard Conformance Test Procedures for Instrument Transformers,”
IEEE Standard C57.13.2-1991, published by the Institute of Electrical and
Electronics Engineers.
[14.7] ____, “IEEE Standard Requirements for Instrument Transformers,” IEEE Std.
C57-13-1993, published by the Institute of Electrical and Electronics Engineers.