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Harmonic Analysis
Approach to the study
Guidelines to Measurements
Features of the software
Related Documents
Sample SLD and Plots
Harmonic Analysis
Approach to the study
Guidelines to Measurements
Features of the software
Related Documents
Sample SLD and Plots
Harmonic Analysis
Approach to the study
Guidelines to Measurements
Features of the software
Related Documents
Sample SLD and Plots
Harmonic Analysis
Approach to the study
Guidelines to Measurements
Features of the software
Related Documents
Sample SLD and Plots
Harmonic Analysis
Approach to the study
Guidelines to Measurements
Features of the software
Related Documents
Sample SLD and Plots

Harmonic Measurements, Analysis and Filter Design


Harmonics in power systems can result in undesirable influence such as Capacitor heating/failure, Telephone interference, Rotating equipment heating, Relay misoperation, Transformer heating, Switchgear failure, Fuse blowing. The main sources of harmonics in power system are static power converters, arc furnaces, discharge lighting and any other load that requires non-sinusoidal current. In order to limit the harmonic current propagation in to the network, harmonic filters are placed close to the source of the harmonic currents. Harmonic filters provide low impedance paths to harmonic currents and thus prevent them from flowing into the power network. Harmonic analysis program computes indices such as total voltage harmonic distortion factor at system buses to evaluate the effect of the harmonic sources and to evaluate the effectiveness of the harmonic filters. Also, driving point impedance plots of the buses of interest are generated to identify whether series or parallel resonance phenomenon occurs at any harmonic frequency of interest.


Our Approach to Harmonic Analysis


We use 4 step approach as described in this section.

-       In the first step for existing and functional networks harmonic current measurements is performed at selected points to identify the harmonic currents injected into the network by the harmonic sources. These measurements reflect harmonic currents for one operating configuration and the loads prevailing at the time of measurements only. These may not represent conservative estimates of harmonic currents available.

-       In the second step, the measurement information of the first step will be used along with design data of harmonics where available from non-linear loads, generating harmonic currents. A computer network model will be prepared as per IEEE standards and the effect of various harmonic sources at various harmonic orders will be examined. Various harmonic distortion factors will be computed as outlined in relevant IEEE standards. The advantage of computer model and simulation is that it can take care of large number of operating configurations and conservative estimates of harmonic currents, which cannot be covered by field measurements. Field measurements of the first step, can however be used to validate the computer model developed.

-       In the third step, harmonic driving point impedances of all buses of interest will be generated at various harmonic orders and plots of the driving point impedances will be generated with respect to a range of harmonic orders [orders 1 through 50]. These plots indicate series and parallel resonance conditions in network.

-       In the fourth step, analysis of results of the first 3 steps will be carried out and solutions needed to solve any harmonic related problems will be obtained. These solutions are verified by using the computer model developed. The problems that might arise could be excessive harmonic distortion factors beyond relevant IEEE specified standards, existence of resonance conditions close to an exciting harmonic frequency. Where these problems are encountered, solutions will be provided by introduction of harmonic filters and its design will be verified again by using the computer model developed. Recommendations include specifications on sizing of individual components of the harmonic filters.


Our Guide Lines for Harmonic Measurements


  1. Case 1: In this case the power supply to individual loads are supplied by dedicated panels, with no other loads other than the specific non-linear load. The load size is significantly large enough to warrant a specic dedicated harmonic filter. The measurements will be taken for this load feeder
  2. Case 2: A single supply switch board supplies several non-linear loads. All loads are sufficiently small and nearly similar to each other. In this case dedicated harmonic filters for individual loads may not be necessary. A common filter may be provided at the incomer, provided the outgoing feeder loads are reasonably constant. The measurement will be done on the incomer of the switch board only.
  3. Case 3: A single switch board supplies several non-linear loads. The nature of the loads are significantly different from each other. The net switch board load is not constant or uniform making it difficult to arrive at a common filter at the incomer. In this case we take harmonic measurements at each outgoing feeder and design individual load filters.

Apart from the above cases for harmonic measurements for purpose of filter design, it may be necessary to carryout measurements at point of common power coupling at HV levels to ensure that statutory requirements are satisfied.

From the guidelines provided, it is fairly straightforward to examine the electrical network and to determine the number of measurement points. Measurements may have to be performed at different short circuit levels at the point of grid coupling as the electrical network characteristics changes with fault levels.


General Features of Harmonic Measurements, Filter Design and Analysis



Harmonic Analysis Related Documents

ValidationDocument_HarmonicAnalysis_IEEEStd399_1997
Typical Harmonic and Power Quality Measurements Report Extract

Sample Single Line Diagram and Driving Point Impedance Plot for Harmonic Analysis


Single Line Diagram and Harmonic Impedance Scan Plots


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