Harmonic Studies

What are Harmonic Studies?

• Any devices with nonlinear voltage-current characteristics can generate harmonics. All harmonic sources can be referred to as non-linear loads because they draw non-sinusoidal current when sinusoidal voltage is applied to them. The non-sinusoidal current generation may be due to the inherent characteristic of the load (arc furnaces) or switching devices such as power converters.

• Since the non-linear loads are increasing in industrial and commercial electrical power distribution systems, harmonic studies are very important for the overall system design and operation.

• The harmonic studies are carried out to determine the effect of the harmonic contributions from nonlinear loads on the voltage and current response in the power system and to check whether the harmonics in the voltage and current are within acceptable limits.

• Harmonic studies can be used to calculate the harmonic bus voltage and current flows in the network (i.e., individual, and total harmonic distortion in the bus voltage and branch current), and to evaluate the resonance by plotting impedance vs frequency spectrum.

What is the Importance of Harmonic Studies?

The main purpose of harmonic studies is:

• To check whether the voltage and current distortion limits are within the acceptable limits specified by the standard at the point of common coupling (PCC) with the utility.

• To sizing and locating capacitors or passive filters for minimizing the effect of harmonics and optimizing system performance.

• To reduce the harmonic-related problems such as failure of power-factor compensation capacitors, losses and overheating with the equipment such as cables, lines, transformers, motors, etc., or maloperation of protective relays or control devices.

• To expand the power plant/system by adding a significant number of non-linear loads.

• To design a new system where load flow, power factor correction, and harmonic studies are considered as one study to determine how to meet the reactive power demands and harmonic performance limits.

How Do We Perform Harmonic Studies?

• Step-1: Data collection such as single line diagram (SLD), specific system configurations, voltage rating, short circuit MVA and impedance, X/R ratio at the utility point, shunt capacitors, transmission lines/cables, shunt reactors, load and harmonic filter type and characteristics, generators, transformers, voltage and current harmonic spectrum data, other non-linear devices, etc.

• Step-2: Modeling the study system/substation for the harmonic studies using PSCAD/EMTDC software.

• Step-3: Preparation of simulation case studies with the study scenarios specified by the IEEE Std 3002.8-2018 and accepted by the clients.

• Step-4: Preparation of technical report and submission to clients.

What Standards can be Referred for Harmonic Studies?

• IEEE Std 3002.8-2018 - IEEE Recommended Practice for Conducting Harmonic Studies and Analysis of Industrial and Commercial Power Systems.

• IEEE Std 519™-2014 - IEEE Recommended Practice and Requirements for Harmonic Control in Electric Power Systems.