**2.1. Over voltages and under voltages**

On one side, voltage quality focuses on variations of voltage from its ideal waveform (i.e., characterized by a sine wave of constant magnitude and frequency), while current quality is concerned with the deviation of the current from the ideal sinusoidal waveform. On the other side, discrimination of power quality as a voltage quality or current quality is an ambiguous way of thinking as a deviation in voltage can result in a deviation in current and vice versa. Thus, in order to keep generality, and as the power is mathematically the voltage times current, power quality should be the combination of both voltage and current qualities [3] and is signified by a set of electrical limitations (reference boundaries/margins) that enable an equipment to operate in its planned manner without major operating losses [4, 5] to long live

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

All electrical equipment may fail or malfunction when come across power quality disturbances, depending on the severity of the disturbance. It is essential for engineers, technicians, manufacturers, and power system operators to well understand and face the several power

Power quality issues include voltage variations (dips, interruptions, flicker, etc.), transients (surges, lightning, and switching events), and grounding issues. **Figure 1** summarizes the

as possible.

**2. Disturbances**

quality disturbances.

common power quality problems.

**Figure 1.** The common power quality problems.

Over voltages are defined as any voltage greater than the equipment nominal operating voltage when the equipment is specified to operate at for a time period that exceeds 1 min. While, the under voltage can be defined as any voltage below the nominal operating voltage of the equipment for a time period that exceeds 1 min.

Over-voltage phenomenon has many causes in power system networks such as sudden changes in the system operating settings, abrupt load rejection, series/parallel harmonic resonance cases, sudden line-to-ground faults, improper earthing schemes, poor voltage regulation throughout the system, and overcompensation of the reactive power support provided by capacitor banks. Under voltages can result from improper power cables sizing, long feeder routes with high loading capacities, and large motor starting conditions.

Over voltage has a serious impact on electrical equipment and power systems as it stresses the equipment's insulation and may damage it, in addition to protective devices tripping because of dielectric failure. Also, over voltage may lead to flashover between line and ground at the weakest point in the system and can cause breakdown of the equipment insulation. On the other hand, under voltage causes an increase in the system losses and results in voltage stability problems. Also, different operational problems may arise due to under voltages such as motor starting problems and protection relay tripping [7].
