Problems with Power Quality at Electrical Installations
7 July, 2020 | Blog
To varying degrees, there are many types of disturbances that can affect the electrical power supply of customers that are connected to a public power distribution system. These can include transient overvoltages, voltage dips, harmonics issues, voltage flicker or fluctuations, or unexpected but short-lived interruptions. Power quality issues can arise from both the distributor system and from client installations. In addition to disturbing the plant’s power system, the client’s perturbating equipment is likely to affect the distribution system and cause cross-disturbances with other clients, hence the reason for emission limits imposed by the distributor on clients.
Consequences from poor power quality can vary depending on the type of industry. Here are some examples:
- Agri-food industry: inadequate cooking times, even causing products to overcook when they cannot be removed from the oven in time. This issue very often leads to data loss in terms of sanitization parameters, forcing the company to reject the batch in production and to carry out a major cleaning before resuming operations.
- Plastic extrusion and injection: unexpected production line shutdowns, followed by an accumulation of plastic that needs extensive cleaning before restarting and gradually resuming production. The same type of issue exists in the glass industry.
- Machined products: desynchronization of a rolling mill, causing material production losses, followed by a cleaning of the production lines, which can last a few hours.
- Semiconductor manufacturing: rejection of high value-added products during processing.
- Chemical processes: processes that involve risks of explosion and fire in the event of an unexpected and unscheduled shutdown.
In general, there are improvements that both power distributors and clients can implement. In fact, clients can often prevent this type of issue by purchasing less sensitive equipment and implementing appropriate mitigation measures on their overall power supply or only in problem areas.
Investigation and analysis
The following activities must first be performed to improve electrical power quality at a client site:
- A comprehensive review of potentially disruptive equipment, such as variable frequency drives (VFDs), capacitor banks and harmonic filters, and any other highly disruptive processes (e.g., arc furnaces, welding machines, reciprocating compressors, crushers or shredders).
- A campaign of continuous power quality measurements performed over a period of two to four weeks. Continuous power supply monitoring to detect any potential problem of presumed incompatibility between client and distributor systems, such as power system disturbances. Continuous power supply monitoring helps detect incompatibility issues between the client and distributor systems, such as disturbances outside acceptable criteria, including voltage dips, voltage variations, transient overvoltages, frequency variations, harmonic currents and voltages, and flicker. All including the date and time of each of these events.
- Spot-check measurements in various strategic locations within the client distribution system to determine the quality of the system’s power supply and the way the loads themselves behave to ensure there are no cases of self-pollution within the plant, for example, excessive harmonic distortion, operation voltage that is too low or too high, protection settings that are too sensitive, etc.
- The client compilation (date and time) for each incident that affected production, along with a brief description of the issues observed and, more specifically, where possible, the identification of production equipment that was affected during each incident.
Analyzing resulting measurements helps identify and quantify the type of disturbance related to the power quality. Further analysis also helps separate the respective responsibilities of the client and the distributor, especially when the disturbance can be attributed to a neighboring client, for example. This rigorous approach is critical to clearly identifying the issue and implementing appropriate mitigation measures.
Selecting the right mitigation
In many cases, a significant portion of production losses can be prevented by using low-cost solutions in an initial mitigation effort. Sometimes, clients unnecessarily add costly or inappropriate mitigation measures to address the current issue. This may occur when the issue is analyzed by a supplier that is promoting its own solutions to the detriment of other more effective and sometimes less costly options. Within this context, dealing with an expert who does not have any commercial ties with suppliers can be an excellent practice.
During the mitigation study, it is important to assess with the client possible mitigation solutions that are based on the cost of preventable production losses. In fact, the payback period for each solution generally varies quite a bit, i.e., very short-term for the initial mitigation stages, and less and less profitable as we apply more expensive mitigation solutions. However, in addition to economic losses, the impact on the company’s reputation must also be considered, especially when the company operates in the just-in-time production market, where each production shut down leads to delays in delivery or the resumption of the part being processed.
With over 250 power quality studies under its belt, BBA has the right equipment and highly qualified resources to use measuring instruments and to compile and interpret results. BBA also has a team of experienced designers who are present from project start to finish, to continue, where required, with engineering the proposed mitigation measures, monitoring construction and commissioning, and assessing performance.
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