Power Quality And Harmonics Essay

Questions:

1.What is Power Quality?
2.What are Some Power Quality Concerns?
3.What are Harmonics and what Causes them?
4.What is the Effect of Harmonics Distortion?
5.What are the Process for ttenuation of Harmonic Distortions?

Answers:

1.The grid’s ability or electricals’ network provide a stable and clean power supply is known as Power Quality. A perfect power supply which is always available, creates power supply. It has a shape of pure sinusoidal wave and it always within frequency tolerance and voltage (Ortega, Hernandez & Garcia, 2013).

As per IEC what are the general classes of Power Quality problem?

  • Conducted low –frequency phenomena
  • Voltage fluctuation (flicker)
  • Signal system (power line carrier)
  • Voltage imbalance (unbalance)
  • Voltage dips and interruption
  • Induced low frequency voltage
  • Power frequency variation
  • DC in AC network (Das, 2016)
  • Harmonics and inter-harmonics
  • Radiated low frequency phenomena
  • Magnetic and Electric field

2.The significant sign of a power-quality issue may be an anamorphic sine wave of the sources of power. Problems may persists in the amplitude form either till a certain level. At certain cases the power-quality may be completely interrupted due to the problem. The aggravation would by and large initiated by harmonics in the supply system of the main voltage or in the current or in both. Several industries from offshore oil rigs to even high profile data centres, throughout the globe suffers as a consequence of poor quality of power (Satyanarayana et. Al, 2013). Low quality of power leads to increasing cost of energy production and high usage of energy. This rising energy and disturbances in the production can be very problematic especially when people are using modern equipment with high level of sensitivity. Ironically, it has been observed that the disturbance occurs from the equipment itself.

3.Harmonic Distortion

The summation of integral multiples of some basic frequency that generates distorted wave-form is known as Harmonics (Ebenezer, Ramachandrala, Pillai Sarasamma, 2015).

The situation where there is disturbance caused by the frequency multiples of sine waves in the AC power signal is termed as Harmonic Distortion.

Total Harmonic Distortion (TDH) is the measurement of the aggregate amount of Harmonic distortion within a system. TDH is mathematically represented as the ratio of power supply due to harmonics and power of the rudimental supply.

Causes of Harmonic Distortion

The non-linear loads within any power system causes the formation of Harmonics within the same. The non-linear load is incapable of drawing proportionate amount of current with the sinusoidal waveform of 60 Hertz voltage. In other words, the equipment does not take into current in a smooth fashion but gulps it from the supply point (Kalbat, 2013).

There are several devices with power electronics that produces harmonics with non-linear loads. They are as follows:

  • Consumer electronics
  • Electronic lighting ballasts
  • Computer equipmen
  • Welders and battery charges
  • Adjustable speed motor drives (ASDs)+

In order to control the circuits, the modern electrical system uses power electronics. All these power electronics namely different types of domestic electronic gadgets like computer, television and others requires the supply of DC power to function and operate (Castilla et. Al, 2013). The 3-Phase AC supply in a utility supply has been shown below:

Figure 1: Three Phase Altering Voltage

Source: Created by the Author

A perfect sine wave has been portrayed here with a frequency of 50 Hz. Keeping things simple and for ease of calculation the amplitude has been kept at 1that is it has been normalised. The waveform shown here is a perfect sine wave at a frequency of 50Hz. For simplicity the amplitude is normalised to 1.

Figure 2:

Source: Created by the author

Here, f(x) = sin (x) and f(x) =

The resulting wave shows a strong departure from the smooth waves comprising it:

Figure 3

Source: Created by the Author

Figure 4

Source: Created by the Author

In reality a sine wave and some harmonics of the same can help in creating any function.

Symptoms of harmonics

Harmonics has little concern, in a small quantities. In your facility too much non-linear loads can make power quality problems (Aye & Naing, 2014).

How do you know the harmonics present in your electrical system?

There are few symptom to be aware of:

  • Overheated motors and transformers
  • Over-loaded neutral conductors
  • Timing errors in sensitive electronic equipment
  • Failure of power factor correction capacitors
  • Blown fuses or breakers tripping repeatedly

4.Distortion Effect:

The waveform of multiple frequency of the fundamental input signal is known as Harmonics. Harmonics effect (high frequency sine wave) can be explained by studying the fundamental frequency sine wave with the relationship of Harmonics. To increase the current in the system is one of the main effect of power system harmonics. This is basically the case of third harmonics which causes the incrementing zero sequence current and this causes the increment of current in nuclear conductor (Ruiz-Cortes et. Al, 2015). In order the non-liner load to the design of the electric system, this effected special consideration

5.Attenuation of Harmonics

Inductive Reactance

Method:To attenuate harmonics we need to add a line reactor or isolation transformer.

Benefits: Technically simple and low cost.

Concern: In high order harmonics the reduction is done due to which a little effect occurs on 5th and 7th harmonics which cause a drop of associated voltage, the added amount of reactance are limited (Castilla et. Al 2013).

Passive Filters:

Method: It provide a path of low impedance to the ground for harmonic frequencies

Benefits: Passive filters helps to tune frequency between two harmonics so as to abate both of them.

Disadvantage: The filter needs tuning which indulges labour intensive techniques. They offer gateway to harmonics and hence are difficult to size. In addition, they are sensitive to future changes.

Active Filters:

Method: The active filter cancels those harmonics generated within the equipment by injecting opposite yet equal harmonics within the power system.

Benefit: The main benefit of this filter is that it has helps in reducing the harmonics below the required level (Kalbat, 2013).


Disadvantages: The high performing inverter which helps in injection of harmonics very costly. Reliability is a problem for the power transistors which are exposed to the conditions of the line.

12-pulse Rectifiers

Method: A single DC bus is used to separate two rectifier. From the phase shifted supplies, the two bridges are faded.

Benefits: It is very effective to eliminate 5th and 7th harmonics. It stops harmonics from the source. It is insensitive to change the future system.

Concerns: A little attenuation is done to the 11th and 13th harmonics. In every case it may not meet the IEEE standard (Das, 2016).

18-Pulse Rectifiers

Method: This is an integration of rectifier and phase shift transformer which can draw sinusoidal wave directly from the source of generation.

Benefit: The most important thing about this rectifier is that it meets the criterion set by IEEE. It is insensitive in nature with the future changes and stops the harmonics right at the source. In addition, it attenuates them up to 35th step.

Concern: The main concern it that this rectifier can be expensive especially at smaller level of HP’s.

Figure 5

Eliminating harmonics

There are umpteen tools available for workers which are designed to deal with harmonics. There is a need for proper analysis of the different tools available in the market to eliminate any problem associated with the application. The usage of active filters and passive filters depends on the specific situation where it is being used. The active filters is the latest technology in the market which expects to rule the market and gain large volume of market share (Aye & Naing, 2014). It can be possible as soon as the initial cost of establishment becomes competitive with the existing passive filter. The passive filter on other hand is the one which is mostly used at present in the market. It has the upper-hand of being custom designed as per the requirement of application and site

Reference:

Aye, T. M., & Naing, S. (2014). Analysis of Harmonic Reduction by Using Passive Harmonic Filters.

Castilla, M., Miret, J., Camacho, A., Matas, J., & de Vicu?a, L. G. (2013). Reduction of current harmonic distortion in three-phase grid-connected photovoltaic inverters via resonant current control. IEEE transactions on industrial electronics, 60(4), 1464-1472.

Das, J. C. (2016). Power system analysis: short-circuit load flow and harmonics. CRC press.

Ebenezer, M., Ramachandralal, R. M., & Pillai Sarasamma, C. N. P. (2015). Study and Analysis of the Effect of Harmonics on the Hot Spot Temperature of a Distribution Transformer Using Finite-Volume Method. Electric Power Components and Systems, 43(20), 2251-2261.

Kalbat, A. (2013, October). PSCAD simulation of grid-tied photovoltaic systems and Total Harmonic Distortion analysis. In Electric Power and Energy Conversion Systems (EPECS), 2013 3rd International Conference on (pp. 1-6). IEEE.

Ortega, M. J., Hern?ndez, J. C., & Garc?a, O. G. (2013). Measurement and assessment of power quality characteristics for photovoltaic systems: harmonics, flicker, unbalance, and slow voltage variations. Electric Power Systems Research, 96, 23-35.

Ruiz-Cort?s, M., Milan?s-Montero, M. I., Barrero-Gonz?lez, F., & Romero-Cadaval, E. (2015, April). Analysis of Causes and Effects of Harmonic Distortion in Electric Power Systems and Solutions to Comply with International Standards Regarding Power Quality. In Doctoral Conference on Computing, Electrical and Industrial Systems (pp. 357-364). Springer International Publishing.

Satyanarayana, G., Prasad, K. N. V., Kumar, G. R., & Ganesh, K. L. (2013, April). Improvement of power quality by using hybrid fuzzy controlled based IPQC at various load conditions. In Energy Efficient Technologies for Sustainability (ICEETS), 2013 International Conference on (pp. 1243-1250). IEEE.

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