Kansas City Power & Light (KCP&L; Kansas City, Missouri) has been upgrading its system to meet the increased demand for capacity and to ensure maximum reliability. A major equipment consideration in the upgrades has been with transformers. From a field-maintenance perspective, working around transformers is an everyday occurrence, but the risks are multiplied when the transformers on an entire circuit need to be replaced.
This past summer, a line-maintenance crew working out of the Johnson County Service Center in Lenexa, Kansas, was assigned to replace an entire section of pole-top transformers in Leawood, Kansas. The Leawood project was located predominately in residential neighborhoods.
In my 21 years as a distribution lineman, 85% of my time has been spent in someone's backyard: responding to trouble calls, repairing lines, replacing poles and upgrading equipment. This was definitely the case on the Leawood project, where our line runs along the rear easement of large yards with mature tree lines. Several crews worked on this project, but my crew had primary responsibility for changing out the transformers and upgrading the circuit.
Some linemen call these types of work areas “the jungle,” because of the wood fences, flower beds with walking paths barely wide enough to walk through, and hills or landscaped slopes. When it rains, these artificial mounds of dirt become a slippery slope, which adds to the challenge.
But the real jungle effect comes from the trees that often appear to be encroaching on overhead lines. The KCP&L vegetation-management division does a good job, but trees can still be in the way when it comes to accessing transformers and power lines. From the street, our lines appear to thread through the tree lines in many customers' backyards. In some cases, it looks like you are going into a jungle, and to get there you have to go through a 36-inch garden gate.
To address the growing work demand in backyards with limited access, KCP&L has field-tested several mini-digger derricks. The main benefit of these compact units is their ability to perform all of the functions — installing new poles, accessing and replacing pole-top equipment and lines, and performing other emergency and routine maintenance on poles and overhead lines — of a full-sized truck-mounted digger derrick. A unique feature about mini-digger derricks is they can do all of these procedures from a small self-contained chassis, narrow enough to travel self-propelled through a customer's 36-inch gate.
KCP&L has tried out several types of backyard machines, including both rubber-tire and track-mounted units. Some of them would get stuck more easily, and others would turn over on some of our steep inclines. We finally settled on purchasing several track-mounted units from Altec (Birmingham, Alabama), mostly because of their stability and some of the well-thought-out features that help us do our job more efficiently.
On the Leawood project, we had a total of 22 transformers that needed to be replaced. Handling transformers is a common occurrence for KCP&L linemen. Every day our crews are involved in changing out a faulty, underloaded or overloaded transformer, or in returning a refurbished transformer to service. We are also retrofitting some of our older transformers with newer protective features. As with any job with these kinds of challenges, safety was the first priority.
At the top of the safety checklist is knowing what to look for on a faulty transformer. KCP&L linemen are taught to conduct a thorough inspection of the transformer and the surrounding area. We look for such indicators as bulging tanks or covers, discoloration, oil leaks, the smell of burning oil, damaged bushings, and frayed or burned wrappings on wires.
Some of the specific hazards we look for when working around older transformers include the potential exposure to hot oil and getting burned. Bad seals and arc temperatures also can be a problem. Transformers damaged by lightning can become dangerous, but such hazards are normally visible. The real risk comes from transformers that are not visibly damaged. These pots can explode at the seams after closing a nearby open fuse. In some applications, a crew will use a fault device to check the quality of a transformer.
To anticipate these types of dangers, well-defined safety procedures are followed: wearing appropriate personal protective equipment; applying wraps and blankets to the work area; keeping a safe distance during refusing; using only appropriate tools and equipment; and, when possible, de-energizing the conductor before repairing or replacing the unit.
Special precautions are taken when working with transformers around adjoining energized conductors. Backfeed through the transformer can deliver unexpected high voltages from the secondary winding. There is also the risk of faulty insulation with the way some of our transformers are configured. The primary and secondary windings are placed in close proximity and can short across if the insulation has deteriorated.
Experience has shown that the best way to prevent accidents is to remain current on best practices and the skills needed to safely handle transformers. KCP&L covers these and other best practices in ongoing training and tailgate safety meetings.
The surprising thing KCP&L discovered about the mini-digger derricks on the transformer-replacement project was the significant amount of time the machines saved our crews on a daily basis. They were purchased to access backyard easements, but when we began changing out the 22 transformers, we realized additional benefits of the backyard machine.
Most of the pots we installed were either 75-kVA or 100-kVA at an average weight of 950 lbs to 1100 lbs each. There were also some new poles to install. In the past, it would take us seven to eight hours to set a new pole in a rear-lot line. Digging was done by hand, and the pole had to be hand-carted to the back lot.
Altec's model DB-35 digger derrick comes with a detachable 18-inch auger assembly. There is also a pole-claw attachment. After a hole has been dug and the pole has been set, the auger assembly can quickly be detached and replaced with two full-capacity work platforms (buckets).
Being able to access pole tops from a bucket has significantly changed the way we do field maintenance. Not only do these work platforms save us valuable time and energy, they also afford us the ability to rubber glove, which is faster and more efficient. When working from a pole, which is the normal way we service all poles inaccessible by a bucket truck, KCP&L guidelines require line workers to hot stick and attach grounding clamps on energized conductors. But when working from a bucket, a lineman may choose to rubber glove. This is much faster than sticking or waiting to de-energize a line.
We still climb the poles to hang transformers and transfer secondaries, but most of the time we deploy the mini-digger derrick when available. For one thing, the 3000-lb rated boom on the digger derrick helps us transport and set a 1000-lb transformer on a pole. It also can set up wood poles that are up to 50-ft tall. The unit's tracks are retractable to fit through a garden gate and expand for stability when the boom is being operated. The 42-ft boom is further stabilized by large outriggers that drop down hydraulically on all four sides of the unit, creating a remarkably stable footprint.
Most backyards have well-groomed and manicured lawns, so we lay protective rubber mats down on the lawn before we tram the self-propelled unit across the yard. If we need to install a new pole, we dolly it into the yard attached to the rear of the mini-digger derrick.
The top 8 ft of the three-section telescopic and articulating boom is made of fiberglass. This section is always extended first to ensure maximum isolation from the energized conductor. A wireless remote-control box allows the operator to move around to the best vantage point to see what is going on. For close-up work, such as setting the pot in a tight place, the operator usually prefers to have his hands on the actual control levers, mounted at the back of the machine.
Labor Cut In Half
Being able to glove and not having to manhandle poles and equipment are just a few of the changes that have come about since KCP&L began using Altec's mini-digger derricks. Compared to a similar upgrade project we did in 2006, the mini-digger derricks have cut our daily completion time in half.
There are still applications where we need to climb — in fact, we still climb on just about every backyard assignment — but much of the heavy work of dragging poles, hand-digging holes and winching the transformers up to the pole top has been eliminated. And on hot days, when temperatures are close to or above 100°F, the extra muscle of the mini-digger derrick has been very helpful in backyards.
Glen Maughmer is a lead journeyman lineman at Kansas City Power & Light. He has worked for the utility for 21 years.