Each year, We Energies (WE) reviews data from its Customer Outage Reporting System (CORS) to determine problem areas and patterns that may reveal overall system weaknesses. Once a recurring problem source is identified, a task force is assigned to investigate the problem, do field inspection of the trouble area and find a solution.

WE's “Top 100 Feeder Program,” in place since 1995, is designed to identify and prioritize distribution feeders in need of reliability improvements. Each year, circuits are selected for review using different selection criteria, including SAIFI, SAIDI and number of customer complaints, along with operating, customer service and area input. Since 1988, these programs have received added emphasis and expansion through increased funding for feeder protection remediation.

Customer Demand

We Energies (Milwaukee, Wisconsin) has seen an increase of customers wanting to know specific details, including what happened and what the company is doing to prevent future outages. With more than one million customers in the Fox Valley and Southeastern Wisconsin and Iron Range (Michigan), WE's Electric Distribution Group has many outage inquiries.

Lightning Strikes

One of the first major initiatives after the establishment of WE's Top 100 Feeder Program involved addressing lightning and recurring momen-taries. The utility's distribution system is composed of more than 1800 feeders (28,000 circuit miles), of which there are 18,000 miles of overhead conductor. The reliability team determined that feeder momentaries (recloser or breaker operations) and outages (recloser/breaker lockouts or blown fuses) were being caused by lightning-induced flashovers. To reduce the lightning impact on the system, the reliability group installed single- and three-phase arrester protection on the problem feeders.

WE knew the arrester protection would not eliminate all lightning-induced flashovers. However, it assumed the addition of lightning arresters would positively impact reliability by minimizing the probability of phase conductor flashover (outages) and by helping protect utility and customer equipment. Although it was difficult to quantify whether the arrester protection was working, a general improvement in lightning performance during storms was realized.

After several years of adding enhanced lightning protection to feeders that had poor storm performance, WE saw an increase in the number of feeder momentaries on non-storm days. Cursory feeder patrols yielded no answers as to what was causing the breaker and recloser operations. Speculation arose that the outages were caused by wildlife, but finding evidence to support this theory proved difficult.

A bigger issue that needed to be addressed was how these “clear sky” momentaries were affecting customers. Not only is a momentary disruption annoying, it is costly to customers in terms of lost productivity. The voltage sag on the substation bus, due to the fault, also can affect customers on other feeders connected to that same bus section.

The Cost to Customers

A recent outage illustrates the cost to both the utility and the customer. A single transformer 138-kV/24.9-kV substation serving more than 3000 customers was experiencing a rash of unexplained feeder breaker operations. Several large industrial/commercial customers, along with a data processing facility, were fed from this substation. Not only was the substation breaker operation on the faulted feeder a major problem for customers connected to that feeder, it also was a problem for customers fed from the three other feeders attached to the same substation bus. The substation relays had recorded bus voltage sags down to as low as 45% of nominal voltage.

WE's outage reporting system indicated that 19 unknown substation feeder breaker operations had occurred between 1999 and 2003. Of the 19 operations, nine occurred in 2001. A detailed patrol on each feeder revealed that at least six three-phase lightning arrester assemblies had previously flashed over due to wildlife contact. The problem was further compounded by the fact that two of the substation feeders run adjacent to a landfill that attracts many birds and birds of prey.

Wildlife Momentaries

Most electric utility engineers know that once the outage problem is discovered, the solution is usually simple — provided resources and money are available to correct the problem. However, sometimes locating a fault on a feeder is like finding a needle in a haystack. The good news for WE was that the reliability team that addressed the lighting outage problems was already in place and ready to take on round two — “clear sky” momentaries.

The reliability team gathered relevant information, including customer complaints, outage locations and system configurations associated with the locations and repair reports from the area in question. Feeder patrols conducted field evaluations of the equipment, the environment and vegetation in the area. They concluded that wildlife encroachments were a significant cause of the feeder momentaries. But because it is difficult to track momen-taries (other than by tracking recloser and breaker counts), it is hard to know exactly how many momentaries are wildlife induced.

As for verified wildlife-induced outages, in 2003, 16% of the 9000 total outages were attributed to wildlife; six percent of the outages were classified as unknown. An estimated two-thirds, or 4%, of these unknown were due to wildlife. Therefore, wildlife contributes as high as 20% of the total outages (1800 outages).

Determining Total Cost

Total cost was estimated to be $300 per outage, which included approximately 2 hours of troubleshooting at $150/hour. Total cost for the year was estimated at $540,000. Further investigation found that between January 2004 and June 2004, 92 outages on transformers out of a total of 809 transformer outages were attributable to wildlife contact. Using the same troubleshooter cost listed above brings the transformer cost to $27,600. Countless momentaries on 24.9-kV feeders have been attributed to wildlife. And because these 24.9-kV distribution feeders typically are longer, they have more exposure to wildlife.

Feeder Patrol

Some of these distribution feeders are more than 25 miles long after the protective device, which further complicates trying to patrol the feeder and identify the outage problems. After a utility worker performs several feeder patrols, he begins to see a pattern develop. WE began to see arresters on three-phase installations that had flashed over externally without blowing the isolator at the bottom of the arrester. Since the arresters were holding voltage (energized), the cause of the flashovers could not be determined. Initially, WE ruled out wildlife because, in many cases, no “body” could be found.

The initial thought was that the arresters were flashing over externally because of the voltage developed across the outside of the arrester due to a high magnitude lightning current discharge. WE didn't know if there was something unusual about its mounting configuration (grounded brackets mounted with the “L” down) or if there was something wrong with the lightning arresters themselves.

WE completed an investigation at one of its arrester manufacturer's test facilities to try to understand the problem. Tests were completed on both new and previously flashed over arresters in various mounting configurations. WE also tested arresters from alternate suppliers. All of the arresters tested were within the manu-facturer's specifications. It also was found that the mounting configuration did not have an adverse affect on lightning discharge current performance. At this point, the utility found itself “scratching its head.”

As the momentaries on the 24.9-kV feeders continued, troubleshooters began to focus on the three-phase arrester assembly as the likely source. WE found evidence that various animals (squirrels, birds and raccoons) were initiating the flashovers. In many cases, the wildlife was not found because it was either not killed or another animal had carried away its body.

Flashover Tests

It became obvious that the wildlife cap provided with the arrester in combination with the close proximity ground plane was the culprit. WE performed a number of in-house tests that showed the wildlife caps provided by the arrester manufacturer do not provide adequate protection on 25-kV systems (14.4 kV to ground). Another problem was the attachment mechanism from the wildlife cap to the stud on the arrester. In some cases, linemen were using vinyl tape to secure the caps and keep the wind from blowing them off.

Problem Isolated, Remediation Began

Now knowing what the actual problem was, WE was able to incorporate design changes to remedy the situation. The goal was to improve the wildlife performance without increasing the overall cost of the arrester assembly. The first action WE took was to flip the “L” brackets upward and increase the electrical strike distance to ground. The second change was to unground the “L” bracket, reducing the probability of flashover between the arrester termination and the “L” bracket. The third solution was to install an aftermarket wildlife guard to provide adequate protection for both phase-to-ground voltage and phase-to-phase voltage.

WE incorporated these design changes on several problem feeders over the past couple of years. Dramatic reliability improvement has been realized when it comes to wildlife-induced outages. The only remaining issue was the cost to implement the aftermarket wildlife guard on both a retrofit and a new production basis.

In an attempt to find a more cost-effective wildlife guard design, WE performed in-house development work on the wildlife guard to determine what electrical parameters are necessary for operating at 25 kV (14.4-kV ground). A foolproof solution was developed, and a patent is pending.

In the mean time, bids were solicited from several manufacturers. The cost target was $5. Currently, WE is working with a supplier to manufacture a more reliable and cost-effective wildlife guard for arresters. The utility is using what it learned on the arrester project to improve the wildlife performance of transformer bushings and cable riser terminations.

Results

The first arrester retrofits with expensive aftermarket wildlife guards were completed in the fall of 2003. To date, only a few unexplained momentaries have occurred on these feeders, and the situation will continue to be monitored. More importantly, WE has made a significant improvement in the reliability of the feeders fed from this substation, which will result in fewer customer dollars being spent on lost productivity and downtime. Ultimately, this will mean better customer satisfaction.

Once developed, the plan is to install 5000 of the new arrester wildlife guards per year. WE has made a commitment to purchase a minimum of 15,000 (5000/year for three years) of the new wildlife guards from a supplier at $5 each. This will allow the supplier to amortize the tooling cost over the 15,000 parts. In addition, it will allow WE to evaluate the performance of the new wildlife guards.

Conclusion

The process of addressing momentary outages is a classic example of solving one problem and creating another. WE attempted to address the lightning-related issues but ended up experiencing more problems on “clear sky” days. As WE discovered during its investigation, wildlife-related reliability issues can be solved by paying close attention to the proximity of ground planes and by using properly designed wildlife guards for system voltage. WE is optimistic that this improved, cost-effective wildlife guard will eliminate many of the “clear sky” outages and thus improve customer satisfaction.

Joe Kysely is senior application engineer at We Energies, where he is responsible for the design and maintenance of electric distribution facilities. He has a BSEE degree from Marquette University and an MEEE degree in electric power engineering from Rensselaer Polytechnic University. He has 15 years experience as an electric power engineer, having worked as a design engineer on high-voltage switching equipment at S&C Electric Co. (Chicago) and as a senior design engineer doing development work on distribution transformers at Cooper Power Systems. He is a member of IEEE and a registered professional engineer in Wisconsin.
joe.kysely@we-energies.com

We Energies Wildlife Protective Guard Cost Study

Reliability Improvement Costs: Approximately 160 three-phase line arrester locations, fed out of one particular substation, were identified and retrofitted with aftermarket wildlife guards at a cost of $27 per guard. This equated to a material cost of:

160 locations × three guards/location × $27/guard = $12,960

It took a three-man line crew and truck two weeks to install the guards. At $160/hour for the crew, the labor was:

2 weeks × 40 hours/week × $160/hour = $12,800

Total project cost = 12,960 + 12,800 = $25,760

New Wildlife Guard Design

By Joe Kysely, We Energies

To find a more cost-effective wildlife guard design, WE developed a new wildlife guard to operate at 25 kV (14.4-kV ground). The electrical strike distances on the wildlife guard had to be increased dramatically over the manufacturer-supplied caps in order to better withstand moist and contaminated environments. WE found that insulated 600-V lead wire was excellent for intermittent wildlife contact.

WE also developed a better mechanical attachment to the arrester, which required keeping the wildlife guard material clear of the leakage current path on the arrester and not encompassing its first skirt. Leakage current across insulator skirts erodes polymer wildlife guard materials over time, especially if they are not designed for high-voltage applications.

WE's patent-pending design keeps the wildlife guard centered and out of the leakage current path for both new and retrofit applications. WE used a hex-coupling nut threaded onto the top of the arrester stud to provide a common standard attachment mechanism that could be used on arresters from different manufacturers. A tapered friction fit between the boss on the inside of the cap and the coupling nut provides a foolproof attachment mechanism. The improved attachment eliminates any need for linemen to tape the wildlife guard.

Retrofitting has always been an issue because lead wires must be disconnected to install new devices. Because WE installs 10,000 new arresters each year versus retrofitting around 1000, it did not want to sacrifice performance and cost in exchange for ease of retrofit. With the new design, no outages to customers are necessary, as most of the arresters that are retrofitted are line and riser arresters connected to the system with a separate jumper. Currently, WE is pursuing a wildlife guard design for its transformer bushings and polymer risers.