Problems Caused by Harmonics in Electrical Plants
Harmonics are popular power quality distortion of recent years that is being spoken more and more everyday and has different distorting impacts in many different facilities. Within scope of this article, distortion affects caused by harmonics on various basic electrical equipments shall be examined.
Harmonics are not available in an electrical system having linear elements fed by a source having purse sinusoidal wave shape at fixed amplitude and frequency. However, non-linear loads such as power electronic elements increasing parallel to advanced technology withdraw harmonic currents over the source and pollute the source. Electrical systems with intense harmonics experience various problems arising from harmonics.
- Source voltage wave shape distortion
- Efficiency loss in transmission and distribution depending on RMS current increase on lines
- Failures in compensation systems
- Overheating in electrical engines and transformers
- Failures in sensitive electronic devices, PLC and CNC devices
- Difficulties and abrasions in insulation levels of equipments
- Increased losses in the system
- Having faulty works in protection and control systems
- Increased voltage reductions
- Resonance risks at high frequencies in systems
Failure Analysis Based on Equipment Type
1 – Condensers
2 – Engine and Generators
3 – Transformers
Harmonics cause noise, abrasion and mechanic difficulties on transformers.
When magnetic core of transformers reaches saturation, they also generate harmonic. Thus, transformers are indicated as harmonic sources in the literature.
4 – Switching Elements and Fuses
RMS currents increasing with availability of harmonic currents cause faulty operations on switching elements. Failures may occur in operation of electromagnetic induction coil used by circuit breakers while performing arc extinguishing function due to high frequency components. Faulty operations in the coil affect operation of the breaker. Heat increase arising from harmonics also negatively affects life of switching elements.
5 – Electronic – Sensitive Devices
Electronic control devices operating in systems with harmonics sometimes cause faulty operations. Harmonics distort wave shape of the voltage as well as change and shift zero pass points. Zero pass point is an important reference point in electronic control devices such as PLC and any change in this reference affects operation of entire system.
6 – Cable and Busbar
Harmonic components are high frequency and create the impact called as skin-effect in the literature. Resistance of a conductor at alternative current is higher than the resistance at the direct current. This resistance increases more for harmonic components.
>While high frequency harmonic currents pass through the conductor, they shall commonly prefer the outer surface of the conductor and that shall cause reduction of the section used by current for flowing and increase of resistance. Conductor losses increase due to skin effect and conductors expose to mechanic difficulties and vibrations. Overheating is one of the negative results of harmonic sourced skin effect on conductors.
In addition to above written issues, many electrical items such as relays, illumination items, transmission and distribution lines are getting affected from harmonics. Through purification of electrical systems from harmonics, commercial revenues acquired for facilities and all system elements can operate for a longer period and without any problems through improvement of facility regarding power quality.