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Power Quality

Power quality refers to the ability of electrical equipment to consume the energy being supplied to it. A number of power quality issues including electrical harmonics, poor power factor, voltage instability and imbalance impact on the efficiency of electrical equipment.

What are harmonics?

Harmonic is a component of a periodic wave having a frequency  that is an integral multiple of the fundamental power line frequency of 50 Hz.  For example, 150 Hx (3 x 50 Hz) and 250 Hz (5 x 50 Hz) is a 3rd and 5th order harmonic of the fundamental frequency. The result is harmonic distortion of the power waveform when the fundamental with 3rd and 5th harmonic are combined. Harmonics are a steady-state phenomenon and should not be  confused with short-term phenomena that last less than a few cycles.

Consequences of high harmonic distortion level?

Harmonics can cause several problems such as 

  1. Transformers vibrations & getting overheated 
  2. Significant Transient activity in supply system and damage power systems
  3. Decreasing distribution capacity due to hot cables
  4. Neutral conductors in 3-Phase balanced circuits getting overheated and / or burnt
  5. Circuit breakers false tripping for no apparent reason
  6. Failure of PF improvement capacitors
  7. Interference in telecommunication equipments
  8. Generator Hunting
  9. Supply Voltage distortion and lagging power factor

How are harmonics generated?

Harmonics are generated by nonlinear loads. A nonlinear load is a  circuit element that draws current in a nonsinusoidal manner. Until recently, most factory loads were primarily linear, with current waveform closely matching the sinusoidal voltage waveform and changing in proportion to the load. More recently, however, factory loads with major nonlinear components have increased dramatically

Examples of Linear and Nonlinear Devices
Linear:
- Some motors 
- Incandescent lighting 
- Heating loads

Non-Linear:
- DC drives
- Variable frequency drives 
- Programmable controllers 
- Induction furnaces 
- Solid-state uninterruptible power supplies (UPSs) 
- Arc furnaces 
- Arc welders

Nonlinear devices that cause the most problems can generally  be grouped into two categories—electronic power converters  and arcing devices.

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Transients, electrical disturbances, overvoltage surges, and  undervoltage sags in the supplied voltage are not harmonics. Some of these short-term disturbances in voltage or current can be mitigated by transient voltage surge suppressors, line reactors, or isolation transformers.

However, these devices usually have little,  if any, effect on harmonic currents or voltages. The level of voltage or current harmonic distortion existing at any one point on a power system can be expressed in terms of the total harmonic distortion (THD) of the current or voltage waveform. The 

THD (for a voltage waveform) is given by the following formula:

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IEEE Standard 519-1992, IEEE Recommended Practices and  Requirements for Harmonic Control in Electrical Power Systems, represents the most recent effort to establish a standard level of  acceptable harmonic distortion levels on a power system.  

Note: The current distortion limits are dependent upon the size of the  
customer’s load relative to the available short-circuit capacity of the utility (stiffness). In this way, customers whose loads potentially have more effect on the utility system and neighboring customers are held to the tighter limits.

UK G5/4, published in March 2001 seeks to limit harmonic voltage distortion levels on public networks at the time of connection of new non-linear loads to ensure compatability of all connected equipment. G5/4 defines planning levels of 5% and introduces compatibility levels of 8% for individual harmonics and THD over the voltage range from 400V to 400kV.  

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Solutions to Power Quality Issues: 

One device, Multiple Solutions!

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Hybrid Var Compensator combine the technical advantages of AHF, ALB and SVG with the cost-effectiveness of conventional contactor or thyristor switched detuned filter capacitor banks to form an economical stepless real-time compensator with a single controller compared to a full SVG solutions.



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Using single-phase loads on a three-phase electric power system (connected phase-to-phase or phase-to-neutral) results in unbalanced load conditions in the system. Unbalanced load currents result in unbalanced voltages and affect other loads connected at the point of common coupling. Unbalanced load conditions also cause excessive neutral current, resulting in overheating motors and transformers, power losses and lower system efficiencies. Load balancing is necessary to improve the power quality and efficiency of the system. 
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SVGs deliver real-time inductive or capacitive reactive power compensation. Rapid response time provides stable and accurate power factor correction without the drawbacks of conventional solutions like capacitor banks and reactor banks.



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Power Quality Solution

Solving power quality problems with ELCO Power