Poor power quality can stop production, cause disruption to operations and have serious financial impacts on businesses.
Efforts to prevent problems can include planning where to site and connect a new business to the grid, specifying requirements for new equipment, carrying out condition based monitoring and scheduling any identified maintenance, having emergency plans in place, conducting power quality investigations should things go wrong, and implementing cost effective solutions.
Planning
The considerations with regard to electricity should start from the onset when deciding where to site and connect the new business to the grid. The location of connection to the electricity grid can have a dramatic impact on the reliability and quality of the supply to the new premise. Those connected to a long rural or remote power line can expect more power problems than those connected in the CBD of a major city, even though the cost of electric energy may be higher in rural areas.
An application will need to be submitted to the power company to have the supply connected or if increasing electrical load. Conditions may be imposed on the business by the network business before approval is granted to upgrade or connect to the grid. A suitably qualified consultant is generally needed to assist with this process, particularly if in-house electrical engineering staff are not employed by the business.
Existing businesses will have a reasonable idea about how often power problems are causing disruptions to operations and how much this is costing but even so, power problems should be factored into emergency planning.
Regardless of whether the business is new or there is additional equipment being installed as part of a retrofit or expansion, it will be necessary to purchase equipment that will operate satisfactorily and is compatible with the grid supply. There are many technical aspects to the power supply that may need to be considered when planning or purchasing equipment, such as:
- The loss of the electricity supply – it may pay to have automatic backup generators, or at least connection points for portable generators, uninterruptible power supplies for critical equipment or processes, and so on.
- The nominal supply voltage – normally 230 volts in Australia.
- The range of supply voltage – 230 volt rated equipment should be able to cope with at least a range from 195 to 253 volts.
- The level harmonic current drawn – this will add to background levels of voltage harmonics and may cause unexplained disruptions, loss of supply or cause severe damage to equipment.
- Voltage sags or swells – these occur when there are faults on other parts of the grid or when large loads are turned on or off, particularly within the premise or in neighbouring premises.
- The level of voltage unbalance – can increase motor losses and cause current unbalance protection to operate, particularly if the motor is lightly loaded.
- Voltage fluctuations and flicker – these are often caused by heavy industrial equipment, particularly within the premise. Fluctuation in the light output from luminaries is generally the only effect and less of an issue these days.
- Transients – these occur when lightning occurs nearby, when lightning hits the power system or when switching large electrical equipment and/or loads, either on the network or within premises. These are very short events, typically a fraction of a second but can damage or destroy almost any electrical equipment depending on the parameters of the transient.
- Momentary loss of supply from the network business can occur for periods up to 10 seconds. Some equipment is especially designed to cope with minor events.
Most network businesses or state based legislation have requirements for electricity users not to cause interference to the power system such that the power quality to other customers is not affected. One way to stop such problems is to specify equipment that meets all relevant Australian Standards. Imported products may not comply with the relevant Australian Standards and so care is needed.
Protecting equipment
Specifying the requirements for equipment is one thing, but protecting equipment from foreseeable conditions or events is another.
Surge/transient protection is essential for sensitive and critical equipment, especially where the grid is an extensive overhead network.
Under and over voltage protection is always a good idea as things can go wrong with the grid supply or within the plant or business. AS/NZS3000 Wiring Rules require undervoltage protection unless the “potential damage to electrical equipment is considered an acceptable risk”. Phase fail/undervoltage protection is recognised as essential for large and expensive motors.
Motor protection relays now offer much better protection of motors than provided by more archaic/traditional methods of motor protection. Motor protection in rural areas offers some challenges with current unbalance if the grid supply has a high level of voltage unbalance and the motor is lightly loaded. Motor warranty can be voided if current unbalance protection is disabled.
Excessive levels of harmonics may require the use of passive or reactive filters. Tight specifications and compliance with Australian Standards for new equipment is likely to negate the need for retrofitting such equipment.
Maintenance
Some businesses might take the approach of minimising maintenance and carrying out repairs once equipment has broken down. This is generally a much more expensive and stressful approach than implementing a condition based maintenance regime.
Condition based maintenance programs are now well established in many businesses and allows critical maintenance to be carried out without disrupting operations and/or production.
Condition based maintenance programs can include power quality monitoring, energy monitoring, thermography for gearboxes and bearings, vibration analysis and alignment of motors and gearboxes, and condition monitoring of motors, cables, high voltage equipment and transformers.
When problems occur…..
Proper planning is of course the best solution to prevent problems but when things go wrong it pays to have a contingency plan in place. Being prepared for loss of supply is sensible, having spare parts for critical equipment is essential and replacing old equipment where spares are not available are just some planning options that will need to be considered.
In some cases it will be obvious that a power problem has caused the business, plant or part of a plant to shut down. At other times, the cause will not be identified and it will be important to have technical electrical staff in-house or a power quality consultant available.
Sophisticated monitoring equipment is likely to assist in identifying the cause of problems. Careful analysis of logged results will be especially important to ensure the necessary solutions are implemented.
For events that might occur rarely, some assumptions may need to be made based on hearsay evidence of previous events and solutions implemented in an effort to minimise disruptions in the future.
Solutions to overcome electricity reliability or power quality problems will need to be cost justified. The cost of the solution will need to be offset against the cost of lost production, downtime to unclog production lines, damage to equipment, contract penalties for not meeting delivery deadlines.
Conclusions
The electricity supply to an installation should be considered in the initial planning process. The siting of a business can be essential in ensuring a high quality and reliable electricity supply.
Specifications for new electrical equipment should include requirements to ensure compatibility with the grid and trouble free operations. Specifying that equipment must meet relevant Australian Standard is one important way of achieving this.
Having a condition based maintenance program, including power quality monitoring, can also assist in this process by correcting power problems and ensuring that critical maintenance is carried out before equipment fails. Any necessary maintenance can be scheduled to prevent excessive disruption to operations.
Contingency plans can assist when a power problem occurs to ensure production is resumed as soon as possible. Sophisticated power quality monitoring equipment may need to be installed as part of the power quality investigation and analysis of the results will be required. Solutions for power quality problems are always available and may be quite costly, a cost-benefit-analysis is therefore important.
Trained electrical staff that can investigate power quality and power quality incidents will be important. PowerLogic offers, arguably, the best Power Quality Investigation Training Course in Australia. Check it out at https://www.powerlogic.com.au/product/power-quality-investigations/
