Abstract
Here’s our quick list of 7 common utility distribution challenges. These shouldn’t come as a surprise to anyone in the industry as utility companies are experiencing more challenges than ever. And finding ways to quickly identify, manage, analyze, and resolve problems is a pressing issue.
In addition to identification of the issues we also discuss how you can utilize PMI’s Boomerang hardware coupled with Canvass software to rapidly identify and address issues. The wireless cell-based Boomerang voltage/current sensor, coupled with the cloud-based Canvass data collection and analysis system, lets you visualize what’s happening in your distribution network with unprecedented resolution and ease. Boomerangs at substations, end of lines, at cap banks, in Form 2S meter bases, or even at a 120V receptacle automatically stream voltage, current, and power data to PMI’s cloud-based Canvass system. Generate graphs and reports in a web browser, receive instant email and SMS alerts on system activity, and export high-resolution data for detailed engineering analysis without the hassle of SCADA historian report writing, installing PC software or installing cumbersome multi-product solutions.
1. Storm Analysis
During intense storms like hurricanes it’s important to have rapid awareness and response to interruptions, faults, recloser operations and more. PMI’s Boomerangs can be leveraged during these types of events to provide insight into interruptions as substation breakers and reclosers operate. In addition, the effects of neighboring feeders, upstream events, and faults on other phases may be seen as the distribution voltage experiences deep sags between interruptions. Islanding due to local generation may also be detected. The Canvass data, with second-by-second voltage monitoring, can also be used to verify correction operation of substation breakers and system protection strategies.
2. Cold Load Pickup
Load diversity is lost after an extended outage. After an interruption of several hours, water heaters, HVAC systems, etc. are energized simultaneously. This abnormally high current causes a low voltage condition known as cold load pickup. Boomerangs, (especially in a Form 2S configuration) at the point of common coupling or at the end of a feeder, provide the data needed to quantify cold load pickup problems. As seen in the image above, voltage is restored after a multi-hour interruption at around 7 AM. The voltage is 7% low for at least 30 minutes. As load diversity increased, the voltage crept back to its nominal value almost 2 hours later. The 7% undervoltage during cold load pickup may indicate a system weakness during peak demand or a need to adjust (or install) a voltage regulator. Since extended outages are usually a surprise, continuous monitoring is needed to capture this data. This data is important for future planning, system reliability, and recovery.
3. Voltage Unbalance
Voltage unbalance is especially important during times of peak load or voltage optimization/reduction programs. Any separation in phase voltages reduces the range of reduction possible. Rebalancing loads, adjusting regulators, and possibly correcting for PT errors allows for maximum voltage reduction across phases without falling below regulatory minimums.
A Boomerang at a substation or inter-tie point can reveal unbalance from upstream, or due to a malfunctioning substation regulator. The 3-phase Boomerang can be used directly for voltage unbalance tracking. Single phase Boomerangs may be grouped as a virtual 3-phase device in Canvass, if strategically placed on different (but electrically “close”) phases. Here, phase C (blue trace) was 8% low due to a bad motor on that phase’s tap changer. This was fixed, and the regulator re-adjusted, as seen when the voltages come back in line on the left side of the graph.
A local unbalance situation is displayed in the image on the right. The unbalance is around 4% during the day at peak load and well under 1% at night. This data is key to improving the situation with proper load balancing along the feeder.
4. Discovering Equipment Failures
Continuous one-second resolution data allows for discovery of intermittent or brief fluctuations that precede equipment failure. In the figure to the right, a 120V single-phase Boomerang was installed at a residential location. Many one second excursions below 115V and above 130V were measured. These were not noticed by the customer but indicated arcing and possible insulation failure. The underground service drop to this customer was replaced and the voltage afterward shows a steady 120V. Without replacement, the underground cable would have failed, causing a more serious, unplanned event with a much more costly fix.
5. Photovoltaic Tracking
Understanding power flow and voltage changes from photovoltaic generation are crucial to maintaining a reliable distribution system when a significant portion of the power is supplied by customers. A key issue is voltage regulation. As DER (distributed energy resources) supply power, the overall system voltage is increased. Unlike traditional 24-hour load models, this DER power is not as predictable, and can change on a minute-by-minute basis (e.g. clouds cover an entire neighborhood, then blow past).
“Sentinel” Boomerangs at representative PV locations can help track these patterns. In the figure below, local PV generation (bottom plot) is graphed along with RMS voltage (top plot). As clouds clear up, the PV output increases, along with the RMS voltage. The RMS voltage change depends on local loading and generation, system impedances, and voltage regulator settings. With enough PV in the system, extra regulators may need to be installed so that voltage can be kept within limits.
6. Distribution Responses to Upstream Events
By placing Boomerangs at multiple substations (or downstream from different substations), it becomes possible to separate distribution from transmission voltage excursions. Voltage changes from upstream transmission will be seen by all downstream devices. More localized RMS voltage changes, with a root cause at the distribution feeder or customer level, will typically only be seen on a single feeder. Overlaying multiple Boomerangs on a single graph in Canvass brings out these patterns making it easy classify these events visually. In the figure, a voltage phase from three Boomerangs are shown (green, red, blue traces). These Boomerangs are fed from different substations, but share the same 230 kV transmission source. At point 1, all devices experienced a 1% voltage increase, followed a few minutes later by a reduction back to the previous level. One feeder did not respond to the change, but two others quickly reacted both to the increase and subsequent voltage decrease. Similar patterns occur later in the data. These two regulators are adjusting too quickly to upstream adjustments and should be re-programmed to avoid causing unneeded voltage fluctuations.
7. Voltage Reduction Tracking
A mid-sized co-op (92,000 meters) implemented a voluntary peak demand load-shaving program called “Beat the Peak.” With this program, co-op members get email or text alerts during times of peak power demand. Adjusting thermostats, delaying appliance usage, and turning off extra lighting are some of the co-op suggestions for reducing demand during these times. In parallel, substation regulators implement a voltage reduction mode to lower distribution voltage.
Canvass data collected from Boomerangs at key locations (end of line, substation, and mid-feeder cap banks) provides essential data to monitor and fine-tune these programs. As seen in the figure to the right, a 2-4 volt reductions are seen at this residential location. The lowered RMS voltage is still fairly high — over 118V. This indicates further savings can be made by more aggressive voltage reduction.
Conclusion
The fine-grained voltage, current and power data from Boomerangs, coupled with the automatic data collection and easy cloud-based Canvass analysis system, provides tools for visualizing what’s happening in real time on the distribution network. By setting thresholds on voltage, current, and other key parameters, email or SMS notifications give engineers warnings prior to equipment failure or customer complaints. The data analysis capabilities give engineers the tools needed to stay ahead of problems, plan for distribution changes, and understand the effects of more complex loads and DERs.
