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1. HARMONIC STUDY
&
ANALYSIS

2. Harmonics are electric voltages and currents on an
electric power system that can cause power quality
problems.
Because equipment and
machinery can malfunction or
fail in the presence of high
harmonic voltage and/or current
levels, harmonic distortion has
become a growing concern for
facility managers, users of
automation equipment,and
engineers.

3. Harmonics are AC Voltages and Currents with frequencies with
integral multiples of the fundamental frequency. Rapid
advancement of power electronics in the industrial applications
makes industrial load non-linear which generates harmonics.
Since the load is non – linear, the current will be distorted and
become non – sinusoidal.
Harmonics arise from inverters, VFDs, rectifiers, voltage
controllers, frequency controllers and other semiconductor
switching devices generators, transformers, welders and arc
furnaces.

4. Harmonics Can Cause:
•Circulating currents and high voltages caused by harmonic resonance
•Equipment malfunctions due to excessive voltage distortion
•Increased internal energy losses in connected equipment, causing
component failure and shortened life span
•False tripping of branch circuit breakers
•Metering errors
•Fires in wiring and distribution systems
•Generator failures
•Lower system power factor

5. Why is Harmonic Study & Analysis Necessary ?
Although the possibility of harmonic problems is narrow, the cases in which
they do appear can lead to reduction in power system reliability. Harmonics
degrade the level of power quality and its efficiency, particularly in a
commercial building or industrial facility. An insight of the potential effects
and causes can help avoid harmonic related problems at the design stage and
decrease the possibility of undesired effects happening on start-up.
IEEE Std. 519-1992, which is titled “IEEE Recommended Practices and
Requirements for Harmonic Control in Electric Power Systems”, Chapter 10
“Recommended Practices for Individual Consumers”, this section is written
from the perspective that harmonics must be within acceptable limits at the
point where the power system serves more than one customer.

6. It should be kept in mind that only when the non-linear loads become a
substantial portion of the total load, harmonic study and analysis is
recommended to predict harmonic levels and identify potential resonance
problems regardless of the rectifier pulse number.
Most buildings can withstand nonlinear loads of up to 16% of the total
electrical system capacity without concern. If the nonlinear loads exceed
16%, some non-apparent negative consequences can result.

7. Objective of Harmonic Analysis Study:
•Identification of harmonic sources
•Protecting the equipments from power related problems
•Safety against loss and interruptions

8. In the following cases Harmonic Study need to be performed:
•If in the design state of a project, if the measure of the nonlinear loads surpasses
25% of the total loads on a bus or a system, a harmonic analysis study is
necessary to verify the agreement with the predetermined harmonic limits.
•To solve harmonic-related problems such as failure of electrical equipment or
malfunction of protective relays.
•If present plant is expanding and a major amount of nonlinear loads is going to
be inserted, then a harmonic analysis study is necessary to check the plant
functioning after the addition of these loads.
•If a capacitor bank is added in any electrical system that comprise numerous
nonlinear loads, then a harmonic analysis is necessary to verify the probability of
resonance occurrence.

9. What is Done During Harmonic Study and Analysis?
Harmonic analysis or harmonic modelling is an arithmetical method of
foreseeing potential resonances and harmonic distortion levels depending on the
available power system data.
All but the simplest of systems will require a computer to perform this analysis.
A number of software packages are available specifically for this purpose.
Equipment like transformers, capacitors and utility system impedance are
considered and non-linear loads are represented by several frequency harmonic
current sources.
Such a modelling study will indicate if harmonic levels will fall within IEEE or
utility limits.

10. Two types of analysis are present in a harmonic analysis and study:
Current & Voltage Distortion Analysis
The discrete and whole current and voltage harmonic distortions are estimated
at several buses then the outcome are judged against the predetermined limits.
Impedance versus Frequency Analysis
A chart of the system impedance at different buses is plotted against the
frequency. This analysis is important in predicting the system resonances prior
to energizing the electrical system.
A rise in the impedance plot implies a parallel resonance while a depression in
the impedance plot denotes a series resonance.

11. If harmonic analysis denotes extreme harmonic levels or a potentially harmful
resonance condition, there are numerous substitute corrective actions that can
be performed.
•Implement a rectifier with a pulse number higher than 6.
•Relocate or disconnect a small amount of power factor correction capacitance
to shift a resonant frequency away from a characteristic harmonic.
•Harmonic filters can also be added to the system.
•Implementing a Pulse Width Modulated (PWM) rectifier.

12. How is Harmonic Study and Analysis Performed?
A harmonics analyser is the best equipment for conducting study and analysis of
power quality to find out the wave shapes of current and voltage on corresponding
frequency spectrums.
A harmonic analyser is also useful in instances where the lack of obvious
symptoms prevent you from determining if harmonics are a cause for concern. A
harmonics analyser is used to provide a detailed analysis of the suspect source.
Similar to other power systems studies the harmonics study consists of the
following steps:
•Definition of harmonic-producing equipment and determination of models for
their representation.
•Determination of the models to represent other components in the system
including external networks.
•Simulation of the system for various scenarios.

13. If a harmonic analysis study is required to be performed, the following steps
should be followed:
Step 1: Obtain the electrical system one-line diagram and highlight the available
nonlinear loads, capacitor banks and medium voltage cables of long length within
the industrial system.
Step 2: Focus the place of common coupling (PCC) which is the point that joins
the industrial network with the facility or with the adjacent plant.
Step 3: Highlight the in-plant system buses that are expected to be affected from
harmonic distortions.
Step 4: Gather the harmonics-related data of all nonlinear loads within the plant.
Step 5: From the utility company, get the important data of voltage and current
harmonics at the predetermined PCC including the highest and lowest short circuit
fault levels and the permitted limits on current and voltage harmonics because the
permitted harmonic limits differ from country to country.

14. Step 6: Mock-up the electrical network with the help of any of the accessible
software like electrical transient analyser program (ETAP).
Step 7: Perform the harmonic analysis for the electrical network at the various
possible operating scenarios.
Step 8: Verify whole and discrete levels of current and voltage distortion levels at
the concerned system buses and at the PCC.
Step 9: Check the harmonic frequency spectrum, which is a plot of each individual
harmonic value with respect to the fundamental value versus frequency.
Step 10: If the harmonic distortion outcome surpasses the permitted levels, chose a
suitable harmonic mitigation solution and the best insertion point for that solution.
Step 11: Re-perform the harmonic analysis study after adding the harmonic
mitigation technique to ensure compliance with the contractual / international
harmonic limits.

15. Application:
•To prevent Voltage and current harmonics as per IEEE 519:1992 and CEA
Regulations
•To limit Frequency variation
•To limit Voltage and Current Unbalance
•To Improve Power Factor Analysis and maintain close to Unity
•To limit Voltage fluctuations as per NFPA 70B
Advantages of Harmonic Study Analysis:
•Improved system efficiency
•Suppress the magnitude/frequency of power variations
•Add solution to mitigate the power quality problems
•Safety measures against harmonics
•Decrease the liability of failure of electrical equipments
•Avoids line loading and losses.