Harmonics
With the increasing use of power electronics and non-linear loads such as variable-speed drives, computers and other IT equipment, uninterruptable power supplies, or arc welding for example, the power system is getting more and more polluted. This is causing power quality problems such as harmonic distortion, low power factor, unbalance and flicker among other disturbances. The focus of this article is harmonic distortion.
Power electronic and non-linear loads draw distorted currents due to the switching nature of the equipment. The distorted current is composed of a fundamental current component (50Hz) and its multiples (150Hz, 250Hz, 350Hz, etc…). These current multiples are termed harmonics and their values depend on the load characteristics. Figures 1-3 show typical current waveforms for standard equipment.
Figure 1: Personal Computer current and its harmonics
Figure 2: Microwave Oven current and its harmonics
Figure 3: Three phase adjustable speed drive current and its harmonics
The effects:
- Increases the total RMS current drawn from the grid and can lead to overload of system equipment such as cables, transformers, Distribution Boards, etc…
- Higher energy costs
- Abnormal tripping of protection switch gear
- Increased ageing of equipment particularly in motors due to added vibration
- Measurement errors
- Permanent damage to sensitive equipment as for example Power Factor Correction capacitors
- Reduced precision in production processes – Robots, PLC, Data acquisition, etc… This can lead to deterioration in quality of the products being produced. Particularly important in hospitals!
Why should one invest in an equipment to remove Harmonics?
- There are standards such as IEEE Std. 519 and EN61000-3-2 that establishes the maximum permitted levels of harmonics for the voltage and current in an electrical system. (Voltage harmonics are caused by voltage distortion developed across the line impedance due to the harmonic currents by the connected loads.)
- Removing unnecessary losses from cables and other equipment
- Improving the lifetime of equipment
- Increasing the efficiency of energy consumption
- Reduce risk of damaging equipment such as a power factor correction devices
- Ensuring correct operation of equipment
- In certain cases the warranty of sensitive equipment is void if operated in a polluted supply environment. This type of equipment normally monitors and logs internally the electrical grid quality. Harmonic filtering is one of the best ways to avoid warranty issues with such equipment.
Where is Harmonic Filtering recommended?
- All manufacturing industries particularly those with automated production lines
- Steel and Iron works
- Large cranes and hoists
- Large pumps (Water, Sewage, Water treatment, etc…)
- Solar Farms
- Data Centres
- Hospitals
- Large offices and commercial buildings
- Industrial Plants
If you want to know more about your power quality and how to improve it, we encourage you to contact us.