Electrical breakdowns are a leading cause of equipment failure, often involving large income losses and business interruptions. Many facilities discover this the hard way, left searching for the underlying cause because they were unaware of an impending breakdown or overload. This expensive trend makes Power Quality Analysis (PQA) of electrical systems crucial for maintaining reliable and efficient power.
To most, power quality refers to how often the lights go out due to power interruptions. However, due to major technological advances in consumer electronics, as well as commercial and industrial applications of solid state electronics, our understanding of power quality has been expanded to include:
Harmonic pollution - Distortions cause extra stress on networks, and negatively impact installation efficiency
Reactive power - Loads up supply systems unnecessarily, and also negatively impacts installation efficiency
Load imbalance - Particularly prevalent in office building applications. Unbalanced loads can lead to excessive voltage imbalances causing stress on other loads connected to the same network. This can cause an increase of neutral current and neutral-to-earth voltage build-up
Fast voltage transients - Sags and swells, surges, and reductions that lead to flicker
The benefits of the boom have, however, come at great cost to rail infrastructure. Bulk freight loads, overloaded by massive iron ore, coal and container transit loads, have exacerbated rail wear and fatigue, leading to a rise in track-failure incidents and a significant reduction in the lifespan of rail infrastructure.
The above lead to system inefficiency and more seriously, can result in transformers overheating, circuit breakers tripping, or electronically controlled variable speed motor controllers dropping off-line. Of particular concern is harmonic distortion.
Typical Problems & Potential Consequences
Much of the equipment we use today (computers, automated process control equipment, variable speed drives, solid state power conversion equipment) contains circuits that convert alternating current (ac) to direct current (dc). When energised, these power conversion circuits (themselves very sensitive to power fluctuations and abnormalities) create harmonics that can severely distort the power supply and cause problems for others connected to the same source.
Most circuits in Australia are designed to operate at a frequency of 50 Hz. The frequency of a harmonic current or voltage is a multiple of the original frequency. For example, in a 50 Hz system, the second harmonic would be 100 Hz; the third harmonic would be 150 Hz and so on. Harmonics add to the fundamental frequency in magnitude and can produce peak voltages greater than the line voltage. These voltages can become a problem when they exceed the design voltage of electrical devices.
It once was extremely difficult and very time consuming to identify the presence of harmonics in a power system. Most electrical measuring instruments didn’t have the response time required to detect harmonics. Today, high speed analysers are available to identify and record the various frequencies present in a power system. Software also helps to simplify the process of identifying each discrete frequency. These instruments provide an efficient and user-friendly method of identifying troublesome harmonics. Once identified, a range of solutions can be implemented to reduce or eliminate the effects of unwanted harmonic frequencies:
Whenever changes are planned in an electrical power system it’s important to investigate the susceptibility of the power system to harmonic distortion. These investigations should be made in conjunction with any normal power system studies performed when modifications to an electrical system are anticipated.
Problems with power quality are not, and should not remain, mysteries. Although issues are not always easy to identify, and sometimes require intensive investigation, doing so can ensure optimal reliability and efficiency for your electrical supply.
Contact TechRentals today to enquire about our PQA inventory, and discuss how you can best identify harmonics, voltage swings, flicker, power outages and surges in your power system. Also available, our range of power demand analysers suitable for energy auditing.