Effects of harmonics - Economic impact
Harmonics cause additional losses (Joule effect) in conductors and equipment.
Higher subscription costs
The presence of harmonic currents can require a higher subscribed power level and consequently higher costs. What is more, Utilities will be increasingly inclined to charge customers for major sources of harmonics.
Oversizing of equipment
- Derating of power sources (generators, transformers and UPSs) means they must be oversized
- Conductors must be sized taking into account the flow of harmonic currents. In addition, due the skin effect, the resistance of these conductors increases with frequency. To avoid excessive losses due to the Joule effect, it is necessary to oversize conductors
- Flow of harmonics in the neutral conductor means that it must be oversized as well
Reduced service life of equipment
When the level of distortion THDu of the supply voltage reaches 10%, the duration of service life of equipment is significantly reduced. The reduction has been estimated at:
- 32.5% for single-phase machines
- 18% for three-phase machines
- 5% for transformers
To maintain the service lives corresponding to the rated load, equipment must be oversized.
Nuisance tripping and installation shutdown
Circuit-breakers in the installation are subjected to current peaks caused by harmonics. These current peaks may cause nuisance tripping of old technology units, with the resulting production losses, as well as the costs corresponding to the time required to start the installation up again.
Given the economic consequences for the installations mentioned below, it was necessary to install harmonic filters.
Computer centre for an insurance company
In this centre, nuisance tripping of a circuit-breaker was calculated to have cost 100 k€ per hour of down time.
Harmonics caused the failure of a generator set and the interruption of a long duration test on a new medication. The consequences were a loss estimated at 17 M€.
A set of induction furnaces caused the overload and destruction of three transformers ranging from 1500 to 2500 kVA over a single year. The cost of the interruptions in production were estimated at 20 k€ per hour.
Factory producing garden furniture
The failure of variable-speed drives resulted in production shutdowns estimated at 10 k€ per hour.