This fall, Midland Power will begin testing a new defense against power blinks and outages.
The co-op will be among the first electric cooperatives in Iowa to test Hubbell LineDefenders, electronic single-phase reclosers designed to replace conventional oil circuit reclosers (OCRs) on distribution lines.
Midland will deploy 15 LineDefenders across several main distribution lines, prioritizing areas with a disproportionate history of “blinks” — brief service interruptions that may cause lights to flicker or microwave and oven clocks to reset.
The LineDefenders will be monitored over the following nine to 12 months to verify their reliability and allow Midland’s lineworkers to operate them under various weather conditions.
Although blinks may seem like simple annoyances, Midland Power Utility Engineering Manager Johanna James said they are actually a sign that the distribution system is working as intended.
“If you’ve ever been at home and experienced a blink, that’s typically a recloser operating,” James said. “If Midland did not have the system designed the way it is with these reclosers — and if we eliminated the possibility of a blink — then every time there was a squirrel, lightning, a tree branch, high winds, or ice on the line, it would result in an outage, and a crew would have to come out and close in the line.”
Reclosers help sectionalize Midland’s distribution system and limit the number of members affected by a fault. When a temporary fault occurs, a recloser briefly interrupts the flow of electricity and then
automatically tests the line by closing again. If the fault has cleared, power remains on. If the fault persists, the recloser operates again and may remain open, isolating the affected section until crews can make repairs.
Limiting blinks
LineDefenders are designed to minimize unnecessary blinks and help shorten outage durations.
Unlike hydraulic OCRs, LineDefenders are not subject to operating variations caused by temperature fluctuations. They can also be programmed to account for changing conditions on the line and recognize when a downstream recloser is attempting to clear a fault.
Because conventional OCRs operate hydraulically and mechanically, they cannot be programmed to account for those variables. Consequently, upstream OCRs may also operate when a downstream device is already addressing the fault, causing members outside the affected area to experience unnecessary blinks.
Electronic reclosers can be programmed to coordinate more precisely, limiting the number of members who experience blinks while helping crews restore service more quickly and safely.
Another major advantage, James said, is giving lineworkers an alternative to manually closing a recloser with a hot stick — an insulated fiberglass pole that can extend about 30 feet.
“Last year, during the big winter storms, we had a substantial amount of snow in a short period of time. If visibility is very low and winds are high, the handle is extremely hard to control,” James said. “That operation can take 15 to 20 minutes. With the LineDefenders, they don’t have to get out [of their truck]. They can operate the recloser and close the line back in with their iPad. So now we’re talking something that takes less than a minute.”
Long-term savings
Midland currently has more than 1,300 conventional OCRs on its system. The units must be maintained at least every five years, requiring lineworkers to remove, lower, inspect, and service them.
Although LineDefenders cost more initially, the electronic units are designed to last more than 30 years without the routine maintenance required by hydraulic OCRs. That could reduce long-term maintenance costs while freeing crews to complete other reliability work across Midland’s system.
“If the testing phase goes well, then we’ll start phasing out the hydraulic OCRs as we go through our five-year maintenance rotation,” James said. “When we bring them down, instead of putting another set of hydraulics up, we would replace them with LineDefenders.”