Harmonic symptoms - Effects of harmonics on a power system

  Equipment failure and misoperation

The following symptoms are examples of equipment failure and misoperation associated with harmonics on a power system:  

• Overheating (motors, cables, transformers, neutrals)
• Motor vibrations
• Audible noise in transformers and rotating machines 
• Nuisance circuit breaker operation
• Electrical fires 
• Voltage notching
• Erratic electronic equipment operation
• Computer and/or PLC lockups
• Voltage regulator malfunctioning
• Timing or digital clock errors
• Generator regulator malfunctioning
• LED lights flickering

  Economic considerations

The following are economic considerations that should be evaluated with regard to harmonics:

• Losses/inefficiency (motors)
• kW losses in cables and transformers
• Low total power factor 
• Generator sizing 
• UPS sizing 
• Capacity concerns (transformers, cables)
• Utility imposed penalties

  Power factor correction capacitors

Applying power factor correction capacitors requires special considerations with regard to harmonics:

• Capacitor failures 
• Fuse or breaker (feeding capacitors) nuisance tripping
• Calculated or measured harmonic resonance conditions (series or parallel resonance)

  Other significant issues

Other significant issues are typically raised with regard to harmonics.  Interestingly, these issues are often not real problems but rather hype created by a lack of understanding of harmonics.  Many “harmonic problems” are specification issues rather than real problems.

• Metering – do you really have a problem or did you just install a new permanent or temporary meter that can show you the waveform and it “looks like” you should have a problem?
• Marketing hype based upon a product spec – do you even have a problem or is somebody scaring you into believing that a problem exists so you buy their product?
• Specmanship – “Thou shall follow IEEE-519…”.  While IEEE519 is a recommended practice (note that the key word is “RECOMMENDED”), some thought must be given to the practical side of the standard.  In addition, applying the IEEE519 limits at other locations in the power system, other than the point-of-common-coupling (PCC) is typically overkill and often costly or problematic.

Depending on your electrical power system, there are a lot of places where harmonics can cause inefficiencies.

In a manufacturing setting, unmanaged harmonics can increase motor temperatures by 10 degrees to maintain output. This side effect can reduce the life of a motor by 50%. Distribution transformers can lose a full +1% of efficiency when carrying 100% harmonic current, and motors lose 0.1% efficiency with each 1% of harmonic voltage distortion. These losses can cause a dramatic decrease in the lifespan of fan and pump motors due to extra heating in the motor stator.

In a hospital setting, a large HVAC system with a 500 horsepower fan and pump load, running at 5% voltage distortion instead of 1%, can cost $15,000 per year at 10 cents per kwh. This is in addition to the costs of the reduced lifespan of the motors caused by the heating effects of the harmonic currents.

Learn and understand if you should expect harmonics on your power systems based on your loads and systems of harmonics.

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