Power Quality Events
Power quality is a well-known term in the electrical industry. For those who don’t know, power quality refers to the ability of the electrical system to maintain consistent and smooth voltage that is consistent and true to the predicted values. Power quality plays a significant role in the performance and cost of a power system. In short, power quality events are the electrical grid’s response to events occurring throughout the day. So, what are these events, and how do they affect us? Let’s dig in…
Outages
A blackout or outage is a voltage loss delivered to your facility or home by the utility company. In most cases, they result from things interfering with power lines in our distribution and transmission systems. For example, a car may knock down a pole, or a tree may fall over the distribution lines in your neighborhood. Although outages are nothing new, let’s review them nonetheless.
An outage occurs when the utility-supplied voltage waveform drops below zero volts on the service entrance for ten seconds or longer. Below is an illustration of how the waveform plot looks during an outage:
3 Most Common Power Quality Events
1.Transients
Transients are short-duration voltage variations of greater magnitude than standard voltage. Due to their short duration, they cannot provide sufficient energy. Transients typically last less than one cycle. For example, one cycle in a system such as North America is 0.01666 of a second or about 20 milliseconds.
Utilities use large power factor correction capacitors to maintain grids as close to unity (100%) as possible. These pole-mounted or substation capacitors switch on and off automatically during a power outage. Typically, these switching transients have little to no effect, but they occur regularly every morning and evening.
2. Sags & Swells
Sags and Swells are slightly longer voltage changes with less magnitude change.
- Swells are a higher than normal voltage excursion that lasts between 20 milliseconds and 10 seconds.
- Sags are lower than normal voltage excursion that lasts between 20 milliseconds and 10 seconds. Of the two, sags are more prevalent and typically cause the most impacts to sensitive loads connected to the grid.
Typically, voltage sags and swells result from an outage elsewhere in the network, not directly between your facility or home and the fault causing the outage. Most sags result from short-duration contact with a power line, such as a bird or squirrel electrocution. When the victim clears the power line, the voltage returns to normal.
3. Over & Under Voltages
Over and under voltages are long-term voltage changes (more than 60 seconds) with a slight magnitude shift.
- Over-voltage is a higher than normal voltage excursion (typically 110% – 120% of nominal) for a duration longer than 1 minute.
- Under-voltage is a lower than normal voltage excursion (typically 80% – 90% of nominal) for a duration longer than 1 minute.
Maloperation of the Load Tap Changer is typically responsible for over and under voltage events. In short, it follows the load on your local distribution transformer and maintains the voltage within plus or minus 10% of the nominal value (120V). As a result of their failure, many become stuck in one position and overvolt for several hours.rs.
APT 4 Power Quality
When you fail to prioritize reliability, the effects on your business are significant and prevent you from attaining optimal grid performance. APT’s business focuses on helping customers work with their utility suppliers to understand the expected “quality of service” the electric utility will provide. This defines how to size generators, transfer switches, and Uninterruptible Power Supplies (UPS) to ride through interruptions and other deviations in service quality.
Furthermore, APT specializes in helping customers reduce costs and, in many cases, prevent impact to critical loads. Our twenty-five-year history as a service provider allows us to provide a unique and valuable service for customers concerned about their electric power quality of service and its impact on their operations.
Interested in measuring Power Quality at your business?
Contact APT. We specialize in the measurement and analysis of Power Quality. We design solutions to save you money and maximize your reliability.
Andy Taylor PE, APT Chief Executive Officer
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