Know the Difference Between Harmonic Analysis and Harmonic Measurements

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One of the advantages to working with NEPSI is the experience that we have doing thorough and in-depth harmonic analysis. All too often, people will present us with a set of harmonic measurements from their facility, believing that this set of measurements is the harmonic analysis. They often misinterpret the measurements report and incorrectly ask for harmonic filters tuned to the most dominant harmonic current or lowest order harmonic current, or worse yet, ask for a capacitor bank when their measurements are within IEEE 519 distortion limits. This request, if not properly evaluated by the equipment supplier, leads to an improper purchase, equipment failure, and in fact a worsening of the facility’s power quality. Knowing the difference between a harmonic measurement report and full harmonic analysis is essential when determining the need for capacitor banks and harmonic filter banks. A good supplier of this equipment will challenge a request that is based exclusively on a measurements report, dig deeper, and perform a full analysis to determine customer needs.

Harmonic measurements are the measurements of harmonic current and harmonic voltage within an industrial facility or at its point of interconnection with its power supplier. The harmonic measurement report provides details of the harmonic current distortion and harmonic voltage distortion at the measurement location. If conducted at the main incomer or at the facility’s point of common coupling (PCC), the harmonic measurement report may also compare the facility’s distortion to the IEEE 519 or other similar standard. Other data in the harmonic report may include such things as power factor and reactive and active power flow, to name just a few possible data elements. The report may also include some recommendations, such as remedial action. Any recommendations from a measurement report alone, if too specific, should be followed with caution. You always need more information.

Harmonic Analysis utilizes power system software (e.g. ETAP, EasyPower, SKM) to predict or simulate the potential impact to a system given a particular change, whether that be the addition of a non-linear load or a capacitor bank, or a change in source characteristics. This analysis can be performed either during the planning stage of a new system or when evaluating changes to existing or growing systems. 

When working with an existing system, there are many reasons why a facility may need to add reactive power. They may be incurring power factor penalties, high KVA demand charges, or they may need to meet an interconnect requirement. The harmonic analysis uses various inputs (including data from a harmonic measurements report) to determine the form of that reactive power compensation best suited to the environment - a capacitor bank, a de-tuned capacitor bank, or a harmonic filter bank. 

A Hypothetical…

Consider a large manufacturing plant who calls and asks for a low tuned harmonic filter. They provide a measurements report which includes only harmonic data and the active and reactive power demand of the plant. That information alone, on the surface, may indeed point to the likely need for a low tuned harmonic filter. But without a thorough analysis, the customer is exposed to unnecessary risk; that low tuned harmonic filter may not actually work in their system. Harmonic analysis goes a step beyond simple measurements and incorporates elements of the system such as short circuit impedance of the network, existence and/or location of other capacitor banks and harmonic filter banks, unusual system configurations for contingency operation, anticipated future load growth, to name a few. Considering the multiple variables may lead to a very different end product for the plant. 

In our hypothetical case, the plant was connected to a utility medium voltage distribution system, where pole-mount capacitor banks are widely used. A low-tuned harmonic filter could cause resonance with those utility capacitor banks, ultimately causing more problems at the plant than it solved. Thus, the recommendation for the plant’s power factor correction solution was something other than what they had originally asked for based their limited measurements report. The full harmonic analysis identified potential undesired effects and allowed for the plant to make a more informed decision and mitigated their risk.

This is but one example of where a full harmonic analysis can steer you clear of the wrong solution.

Takeaway

When considering a harmonic filter supplier, it is important to understand your supplier’s analysis capabilities. Their experience. Ask them which software package they use. Make sure that it is an industry accepted analysis tool (SKM, EasyPower, CYME, ETAP). Due to the complexity of analysis, avoid working with suppliers that only utilize Excel spreadsheet tools, internally developed tools, or those who do not possess robust experience and knowledge. Ask for a biography of the analysis engineer or a sample of a previous study. Ask questions and demand expertise to ensure you are getting the product that best meets your needs. 

IEEE has several great resources to learn more about harmonics and harmonic analysis, including: IEEE Std 3002.8-2018 - Recommended Practice for Conducting Harmonic Studies and Analysis of Industrial and Commercial Power Systems, and IEEE Std 519-2014 – Recommended Practice and Requirements for Harmonic Control in Electric Power Systems. NEPSI takes these valuable resources a step further, providing robust analysis to recommend the best power factor correction solution for your needs.

About NEPSI

NEPSI is the world's leading supplier of medium-voltage metal-enclosed capacitor banks and harmonic filter banks. NEPSI’s inhouse power system engineers are licensed professional engineers having advanced power system engineering degrees and over 50 years of combined experienced. NEPSI’s equipment is used by industrial, commercial, and utility power system owners and operators with operating voltages from 2.4kV through 38kV to correct power factor and improve power quality. See NEPSI.COM to learn more.

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