The Power Quality issue is becoming increasingly important to electrical utilities as well as to individual customers. Energy conservation efforts and the need for continuous control of certain industrial processes have led to an increase of electronic equipment and motor drives. Process automation involving the extensive use of electronic and digital control systems has become common in modem industrial plants. Poor voltage waveforms, due for instance to harmonics or transients can lead to unnecessary and costly disruptions in production and equipment failure.

What are harmonics?

The technical definition of a harmonic is "the sinusoidal component of a periodic wave or quantity having a frequency that is an integral multiple of the fundamental frequency." In music, harmonics are the overtones that distinguish the sound of one string or woodwind instrument from another by producing complex sounds. Similarly, electrical harmonic currents produce waveforms that may be broken into components. When a current sine wave is not proportional to the electrical systems' voltage, harmonics are present. Harmonic frequencies are integral multiples of the fundamental frequency.

Ideally, power systems only supply pure sine wave. The frequency is only 50Hz or 60Hz, but the equipment of present industry and information system are non-linear loads that are harmonic sources. We can analyze many components which are integer multiple of fundamental frequency from distorted waves. This AC sine wave drawn out fundamental component is called harmonic. The component of n multiple fundamental frequency called n order harmonic. For e.g., 250Hz is 5th order harmonic.

Why do harmonics damage electrically powered equipment?

Harmonic currents travel from the load through the electrical system and onto the power source. The amount of harmonic voltage an current that a system will tolerate is dependent upon both the load and the source. The continuing proliferation of single-phase nonlinear power electronic loads guarantees that damaging harmonic disturbances will only increase as equipment operation becomes faster and more sophisticated.

What problems do harmonic disturbances cause?

Resulting problems from harmonics can be varied, but typically relate to performance, safety and overheating. One of the best-known and most frequent harmonic disturbances is the overheating that can develop from large quantities of single-phase non-linear loads producing current magnitudes of potentially 1.7 times the phase current ampacity on shared neutral conductors. (Some experts claim that magnitudes of up to 300% can be achieved.) In facilities where neutral conductors have been cle-rated as permitted by the National Electrical Code, "skin effect" causes the conductor to operate at temperatures higher than expected. This overheating may also be found in the upstream WYE transformer, where fire may be the ultimate consequence.

Power distribution network polluted by harmonic can lead to:

• Over voltage/current in the distribution network.
  
• Over heating in distribution systems due to skin effect; and copper and iron loss in transformers, motors and generators.
  
• Nuisance tripping in circuit breakers and protection relays.
  
• Malfunction of automatic control systems.
  
• Damage to capacitor due to resonance.
  
• Inaccuracy of instrument measurement
  
• Interference in telecommunication systems
  
• Voltage distortion and lagging in power factor
  

Typical Harmonic Generators are:

• Uninterruptible Power Supply (UPS)
  
• DC Power Systems
  
• Frequency converters
  
• AC/DC variable speed drives
  
• Fluorescent lamps
  
• Welding machines
  
• Computers and peripherals
  
• High Frequency induction furnaces
  
• AC/DC furnaces

Other Power Quality problems:

Voltage sags, Voltage swell, and surges are all Power Quality problems and can lead to damaging effects within a facility.

NEC, your Power Quality Solution provider:

NEC has the expertise to undertake an in depth Power Quality audit using the latest start of the art instrumentations.

The final report will point out the problems and we will provide complete turnkey solutions from surge suppressors to passive filters, and active filters.

We team up with the best manufacturer to provide tailor made products and solutions.

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