*2.9.1. Harmonics sources*

take place and it may take a long time to restore the electrical supply. This may be long inter-

According to IEEE 1250 [16], the electrical interruptions can be categorized into four types

Momentary interruptions may cause a complete loss of voltage, while sustained interruptions

The fundamental frequency varies from its rated (50 or 60 Hz) value. This frequency deviation is infrequent in stable and stiff interconnected power system networks. However, it can be noticed in weak power systems fed from local generators especially during sudden load application or rejection conditions.The operating frequency range should be kept within ±1% the rated frequency for 95% of week and -6%/+4% for 100% of week [15, 16]. The ratio of fre-

> *<sup>m</sup>* <sup>−</sup> *<sup>f</sup>* \_\_\_\_\_*r*<sup>|</sup> *f r*

Most of today's power system waves are distorted. By definition, "any periodically distorted waveform can be represented as a sum of pure sine waves in which the frequency of each sinusoid is an integer multiple of the fundamental frequency of the distorted wave. This multiple is called the harmonic of the fundamental." The sum of sinusoids is referred to as a

In the last years, all have focused on power system harmonic distortion, because it has adverse impacts on both the utility and consumers, alike. Sometimes, when the terminology of power

*<sup>m</sup>* is the measured frequency which is time-varying quantity and *f*

**Type of interruption Duration starts at Duration ends at**

Instantaneous 0.5 cycles 30 cycles Momentary 30 cycles 2 s Temporary 2 s 2 min

× 100 (4)

*r*

is the rated system

ruption or short interruption based on the fault.

**2.8. Frequency deviation**

where *f*

frequency.

"Fourier series."

**2.9. Power system harmonics**

**B.** Classification according to interruption duration

quency deviation (RFD) can be defined as follows:

*RFD* <sup>=</sup> <sup>|</sup>*<sup>f</sup>*

Sustained Longer than 2 min

**Table 1.** Electrical interruptions categorized based on their durations.

according to the duration of the interruption as present in **Table 1**.

6 Power System Harmonics - Analysis, Effects and Mitigation Solutions for Power Quality Improvement

are generally noticed in case of permanent short-circuit faults.

At present, as a consequence of the extensive use of power electronic-based components in all power system applications, most of today's loads are nonlinear. To generalize, three categories can be recognized as primary sources of harmonics in power systems [6]. They are given as follows:


On one hand, if the power system is characterized by series and shunt elements; thus, the nonlinearities exist in the system are mainly introduced by the shunt elements, such as loads. On the other hand, a series impedance of the power delivery system (impedance between the source and the load) is particularly linear, that is, short circuit or Thevenin impedance of a system. Even within a power transformer, the shunt branch (magnetizing impedance) of the standard T model is the source of harmonics, while the series leakage impedance is considered as a linear element.

Today, the most prevailing harmonic sources are:


• Static power converters using thyristor to control speed and torque of variable speed drives.

**3. Solutions**

A thorough understanding of electrical system related problems is helpful to implement good power conditioners and custom power devices to enhance the power quality. Today, it is assumed that the most of our electrical loads become nonlinear in nature. Generally, power factor improvement and other power quality-based equipment are the two main groups of

Introductory Chapter: Power System Harmonics—Analysis, Effects, and Mitigation Solutions…

http://dx.doi.org/10.5772/intechopen.76628

9

These solutions certainly guarantee energy bill savings from reduction of low power factor

solutions that can enhance the power quality performance in a system, thus:

These solutions can enhance the power quality but with no real savings [24].

Each power quality solution has its own merits and drawbacks at different circumstances. Consequently, selection of a precise solution to solve a power quality problem necessitates familiarity with the different technologies to ensure that it is the proper techno-economic

Besides, as the grids transition toward low-carbon technologies, the use of power electronics becomes widespread. Also, renewable sources may introduce harmonic distortions which may adversely affect consumer equipment, but also monitoring and controlling devices that

**A.** Power factor improvement equipment [17–24]

• Power factor correction capacitors.

• Inline reactors or chokes.

• Neutral blocking filter.

• Surge protection.

• Zigzag reactors.

• Soft starters.

• Harmonic filters, especially passive filters.

penalties, not power or energy savings [24].

• Negative sequence current reduction.

• Passive, active, and hybrid filters.

• Conservation voltage reduction.

• Multiple pulse converters.

solution for an application.

• Green plug filters, FACTS, and D-FACTS.

**B.** Other power quality-based equipment [17, 24–27]

• Harmonic mitigating and K-factor transformers.


#### *2.9.2. Harmonics effects*

Impact on harmonics can range from degradation of performance of equipment to its serious failure. The effects of power system harmonics can be clustered into two broad groups: as effects on power system networks and equipment and effects on telecommunication systems.

The most common consequences on the different sectors of an electrical system are summarized below [17].

