Types of PQ Issues
A good knowledge of the varying power quality issues is essential to the identification of the cause and effective solutions for the power quality issue. The various power quality issues are as follows:
Sustained undervoltage – most evident in the home with slow cooking or in businesses with motors not having enough torque to start or overheating and burning out.
- Sustained overvoltage – this results in the shortening of the life of equipment, especially capacitors and electronics.
- Voltage variations resulting in flicker – the redundancy of incandescent and halogen lamps has helped to reduce this issue.
- Waveform distortion/harmonics – this was expected to be the merging power quality issues in the late 90’s but this has not been realised because of ‘good’ equipment design standards. Many electrical workers have little or no understanding of harmonics or other forms of waveform distortion.
- Voltage unbalance – this is often caused by unbalanced single phase loads on the low or medium voltage networks or unbalance network impedances. Voltage unbalance results in additional three-phase motor heating and loss of motor life.
- Oscillatory transients – these are caused by capacitor switching with impacts mainly experienced by variable speed drives dropping off line.
- Impulsive transients – the causes are lightning and load switching. The effects of these can vary from low level to totally destructive. Protection is essential to prevent disruptions.
- Electromagnetic Interference – there are various sources of electromagnetic interference (EMI) from other pieces of electrical equipment to powerline problems and many other sources.
- Poor power factor – this is not regarded as a power quality issue but can affect power quality by the increased reactive current and the associated voltage drop.
- Supply interruption – whilst the total lack of the electricity supply is also not a power quality issue as such, this can have devastating consequences for businesses or for individuals.
- Electromagnetic fields – this is also not a power quality issue but often managed by power quality technicians.
- Neutral earth voltages – the multiple earth neutral (MEN) system is not perfect and so voltage drop across the neutral will be transferred on the earthing system at installations and can result in electric shock incidents.
- Frequency variations – this is not often an issue with the grid but more so with isolated systems or portable generators.
- High voltage and low voltage intermixes – these are generally associated with overhead networks and high or medium voltage wires coming into contact with low voltage mains.
Effects of Poor PQ
The effects of poor power quality vary from inconvenience to reduced plant and equipment life, some equipment might not work properly or trip off, equipment could be damaged, and there could be lost production or temporary loss of product quality, blocked production lines, increased costs, loss of contracts or the demise of struggling businesses.