Feeling lucky? Would you tempt fate by climbing a metal ladder hooked to an energized 34.5 kV cable?
You would if you were a maintenance technician at a wind turbine farm. It is common practice to send 34.5 kV power generated in a utility-scale wind turbine nacelle down to a transformer at the base of the turbine tower through a cable. The cable is usually attached by strain reliefs to the ladder technicians climb to get into the nacelle.
The unsettling thing about this situation is that the strain reliefs might well not meet National Electrical Code requirements. So points out Redwood Kardon, a consultant who does safety inspections and training for Praxis Corp. in Granbury, Tex. Kardon explains that wind turbines installed in the U.S. are often designed overseas by engineers who have no knowledge of U.S. electrical safety practices. “They don't have the same stringent standards we have in the U.S.,” he says. “Anything installed in the U.S. must be tested to a standard for safety. That's not the case for Europe or China.”
Adding to the problem is that for a variety of reasons, many wind farms never go through rigorous inspections for electrical safety. Kardon says he's seen numerous instances in which wind farm operators didn't know what government agency was responsible for checking whether their installations adhered to the NEC. Even when inspections do take place, turbines are difficult to inspect because they defy easy categorization in NEC and IEEE standards, he says.
Even the most fundamental electrical troubleshooting on a wind turbine is risky, says Kardon. One reason is that enforcement of safety standards on turbines can be lax. Some of the most shocking lapses prevent technicians from escaping the tower in emergencies. Kardon says in one case he saw 17 turbines on a farm where the doors to the main electrical panel in the base of the turbine were hinged to open across the towers' exit doors. With the panel door blocking the exit door, technicians would be trapped inside in the event of an arc flash.
That's particularly bad because the main safety problem with wind turbine installations is the potential for lethal arc flashes. Most arc flash accidents happen at pad-mounted transformers or at the main electrical panels inside the towers. “The line side of the first main breaker has an extremely high potential for arc flash. We are calculating incident energy levels at some installations that are off the charts. We've just never seen them that high before,” he says.
Such conditions can have tragic consequences. In one case, a turbine tech working on a 2-MVA transformer created a plasma blast when he mistook a tap changer, which adjusts the voltage of large transformers, for a load-break switch, a device that can be safely de-energized when under power. “What happened was described as a laser of energy coming out of the transformer that almost cut the poor man in half,” says Kardon.
Unfortunately, indications are that this wasn't an isolated incident. Says Kardon, “I teach classes on electrical safety and in three or four of them that I have held for wind farm technicians, there has been an empty chair that would have been occupied by someone who was in the hospital with arc flash burns.”