By William Atkinson, Electrical T&D World,
March/April 2001, Vol. 215 No. 2

Typically, when lineworkers are clearing lines or pieces of equipment, the source of energy is obvious. "The distribution feeder is supplied through transformation from a transmission line, which is applied from a generation source," explains Alan Drew, vice president of Northwest Lineman College, Meridian, Idaho. The power on the distribution feeder flows from the substation to the load in one direction. In the past, when work was needed on the circuit, linemen opened it at the desired device and took appropriate precaution. "Protection on distribution circuits was designed with the power flow in one direction, and it was intended to distinguish between temporary and permanent faults," continues Drew.

In the old days, customers were accustomed to power outages, and in certain rural areas, it was understood that the power might be off for several days following widespread storm damage. "As such, customers did the best they could under the circumstances," adds Drew.

Hospitals and other facilities with critical loads use standby generators, but these are not operated in parallel with the distribution circuit. "The locations of these generators are known and, in most cases, shown on utility circuit maps," states Drew. In addition, the interconnection of these generators is approved by the serving utility in most cases. Lineworkers are made aware of their existence, and if the line supplying the facility is de-energized for work, the lineworkers take appropriate precautions.

Along the same lines, residential customers with home life-support systems typically have generators, most of which are properly installed for safety purposes.

Outage fear fuels problem

As a result of Y2K concerns and growing dependence on electric power, thousands of regular residential customers recently purchased portable generators. "During the recent ice storms in Arkansas, for example, there were a large number of generators purchased and installed," states Drew. Adding to their popularity has been the recent wave of rolling blackouts in California. And, since customers now have the generators, they will certainly use them whenever there is an outage of significant duration. This increases the chance that a lineworker will experience a close call, injury, or fatality.

Drew cites an example: A line crew was dispatched at night to restore power to a small restaurant in a mountainous area. The restaurant was served by a 3-phase, 12.47-kV, tapline, three spans in length. "The crew found that tree limbs had fallen into a corner pole (one span from the restaurant) short-circuiting the line and blowing the fuses back at the tap pole. They also discovered that the restaurant was using a generator to maintain service."

The foreman confirmed that the main breaker at the restaurant was open, isolating the utility service. The crew tested and grounded the line and the tap pole and began repairs. When one lineman climbed the corner pole to remove limbs, he discovered that the jumpers and connectors were damaged and decided to replace them. "When he removed the jumpers, he was positioned in such a way that he was in contact with the under grounded portion of the line," continues Drew. For some reason, the restaurant owner was checking the generator and inadvertently closed the main breaker, backing power through the transformer bank and energizing the line up to the open jumpers. The lineman received a severe shock and died.

The hazard of generator back feed seems to be greatest when lineworkers are working on a single transformer or a small section of line. "Portable generators and motors are usually not powerful enough to supply large utility loads, and the voltage will tend to collapse under those circumstances," explains Drew.

In light of the problems associated with generators, Drew offers some general recommendations.

Safety on the customer side:

• Continue to educate the public on the proper connections and use of portable generators.
• Establish relationships with portable generator distributors, making sure they promote code-approved installations.
• When notifying customers of planned outages, include a warning on generator use with the notification document.

Safety on the utility side:

• Establish clearly understood precautions for employees to follow. Then, include generator backfeed as a specific topic at safety meetings on a periodic basis.
• Always consider the possibility of back feed when working on de-energized lines, and consider from which direction the power could flow. "This should be discussed during each job briefing session," Drew emphasizes.
• Listen for generators running in the area, and investigate as necessary.
• Use properly installed personal protective grounding.
• Provide a visually open point that isolates the potential source by removing the customer’s meter. "This will work with self-contained metering," he notes. "However, it will not work with transformer-rated metering." In the case of transformer-rated metering, provide a visually open point that isolates the potential source by removing the lead wires at the service connections or secondary transformer connections.
• Apply an easily observed, approved tag to any open points.

In the restaurant example, Drew offers some even more specific recommendations. "Installing another set of personal protective grounds on the generator side of the pole, installing temporary jumpers across the open point created by removing the permanent jumpers, opening the fuses on the transformer bank, and installing an approved tag on the main breaker could have prevented that [tragedy]."

Encouraging your customers to purchase generators specifically designed to prevent backfeed is another way to protect your linemen. One such model is offered by Pepco Technologies, Washington, DC, a subsidiary of the electric utility, Pepco. "We have been unable to find hard numbers on the number of linemen killed or injured as a result of generator backfeed, but all of the utilities we talk with say it is a huge problem and growing all the time," states Bradley Johnson, president of Pepco Technologies.

Pepco’s product, called GenerLink, functions like a transfer switch. "We package two interlocking relays," Johnson states. "The first is a 200-amp rated relay. As soon as the unit senses voltage, this relay disconnects the home from the grid.

The unit then waits a couple of seconds and closes a second relay that allows the generator to connect directly to the household wiring system," continues Johnson, "There are also multiple redundant systems in place to ensure that the two relays can never be closed at the same time. This ensures that there will never be backfeed."

The unit can be installed in about 15 minutes by unplugging the meter, installing a special collar, and reinstalling the meter. "In addition, because the unit has a 200-amp rated relay, the homeowner can keep his existing 200-amp panel connected, without installing a sub panel," adds Johnson. The homeowner can then manage his household load to the capacity of the generator by flipping breakers on and off.