Among the most frequent disturbances, voltage dips and short interruptions are at the top of the list and they may interfere with proper operation of a large number of electric, electronic equipment and even entire processes. Thus, residential, commercial and industrial loads may be more sensitive to common network disturbances if precautions are not taken in the design stage. This technique can be used to solve issues with loads being affected by any type of Power Quality disturbances, coming from the supply or generated by other loads. An article on how to correct Power Quality problems generated by loads will come soon.
Depending on the type of equipment malfunctions or failures, different protection devices or ride through techniques can be used to economically increase immunization to disturbances at acceptable levels.
Several steps are needed to determine whether the implementation of a solution is required. The next figure illustrates an effective step-by-step Power Quality problem solving technique for large commercial or industrial loads affected by disturbances. Consequently, the problem solving process is a lot simpler for smaller loads. For now we will concentrate our efforts on larger loads.
Step 1 – Collect Data
Data is needed to determine what is the problem and the consequences. An efficient way to collect data is the use of an event log where the following information is recorded:
- time that the event occurred,
- outside environmental conditions (temperature, lightning, snow, tropical storm …),
- identification of disturbed loads,
- disturbance description (was is a sag, outage or not identified), contact your electric utility to help associate the disturbance with fault occurrences on the network,
- list of alarms,
- total downtime,
- list of scrap material the consequences,
- list of personnel affected,
- and other useful information to determine the cost of event.
To have a better idea of what is going on and to determine if the supply is according to standards, it is necessary to install a monitoring instrument. If you have a doubt concerning the possible non respect of the electrical supply to standards, it is necessary to use a calibrated monitoring instrument that is built according to international monitoring standards (ex. IEC). Also it is required to monitor for a period of at least 1 week to a maximum of 1 month or even for a longer period until the disturbance of interest is recorded. I will soon write an article to indicate you what would be the best things to measure and how to use the data.
Step 2 – Evaluate losses
Step 2 requires to evaluate the losses associated with the equipment malfunction or failure, or more specifically: materials (scrap, second quality products and cost rework), labor (downtime, cleaning, restarting the equipment needed overtime to catch up), the losses sales, equipment condition (damage, repair and replacement) and risks (loss of contracts, litigation, just in time delivery and penalties) incurred. To estimate annual production losses from the data collected, it is possible to calculate these losses by multiplying the cost by the estimated yearly number of disturbance. If the losses are relatively low, it is not justified to install protection devices because it would not be economically viable.
Step 3 – Evaluate and Compare Solutions
The most important part in Power Quality is finding the best solution or even better the more feasible one. Do do so, try to find at least 3 to 4 solutions to correct or mitigate the Power Quality Problem that applies to the specific disturbance. Like for example, you have problems with a tripping variable speed drive cause by capacitor switching, different solutions could be to add a choke inductor or add an DC voltage maintaining (booster) device or a dynamic voltage regulator (DVR) or even a capacitor current inrush limiting device. Each solution have its own advantages and disadvantages that can be compared.
To compare solutions it is necessary to evaluate the acquisition cost, commissioning, auxiliary services additional to annual maintenance and the degree of effectiveness of the solution in terms of disturbance correction in order to compare solutions. . To determine the level of effectiveness of a solution and to demonstrate its feasibility, it is often necessary to resort to digital simulation.
These data are used to calculate the return on investment (ROI). Select the most feasible solution and verify if the ROI is acceptable.
Step 4 – Apply Power Quality Mitigation Solution
The last step is to apply or install the Power Quality Solution to correct or mitigate the equipment malfunctions or failures.
At this step it could be interesting to measure how well the Power Quality Mitigation is doing its job with a monitoring instrument. The results can be used to fine tune the installation. Log sheets could also be completed for a period of several months.
We have seen that by following an easy step-by-step solution technique that it is possible to overcome Power Quality problems related to electrical equipment affected by disturbances.
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Denis Ruest P.Eng.[ratings]
November 2012 .Please read my Bio.