What: Power Lines – Radio Frequency Interference Issues
When: November 18, 2003 7:00 PM

Last month, we had Michael Martin of Potomac Electric Power Company (PEPCO).  Mr. Martin is considered to be the most experienced power line interference investigator in the country. He had the foresight to create the nation's most experienced power line interference investigation department at PEPCO at a time when the power company did not consider interference very important and had rotating personel which did not benefit from previous experience.

Most customer complaints of RFI come not from power company equipment, but from internal causes in the home or business. The number one RFI generator in the home is the common doorbell transformer. They have an internal thermal cutout that causes RFI when they fail. Sometimes a loose wiring connnection in the premises is the cause. Of course these bad wire connections can cause a fire if left unrepaired.

The number one source of RFI caused by power company equipment is loose hardware on power company wooden poles. The wood dries out and shrinks and the metal hardware on a pole loosens up over time, and because of the high electric fields, differenting potentials between the hardware causes small arcs to form. Objects on the line like tree branches and metal will also generate noise.

Mr. Martin uses a special receiver designed to seek out RFI sources. It was pointed out to Mr. Martin that the receiver did not have the capacity to receive on the AM broadcast band. He said that the band which is monitored was not very important since power line interference is very wide band and if the interference is affecting AM, then it is also affecting higher frequencies. Mr. Martin uses the receiver to determine the pattern of the interference that is affecting the customer and then after determining that the interference is not originating in the customer's premises, he goes out to locate the source. Sometimes the RFI source is in a neighbor's house, other times it is a problem with power company equipment that is in the neighorhood. Once in a while, the problem may be miles from the customer's location and involves a lot of driving while monitoring the receiver. After a noise source is locatized to a group of poles, Mr. Martin uses another instrument to locate the offending pole. The method used in the old days was to hit the suspect pole with a big hammer and see if the noise source changes, but this is a very dangerous practice that is no longer used. Equipment with damaged connnections can fail and cause a big fireball, or loose hardware can fall off poles. Mr. Martin stopped this practice after a bolt fell off a pole ended up going partway through his hardhat.

A question was raised about broadband over power lines and the potential for causing interference to broadcast services. Mr. Martin could not get into detail about this subject, but he does not believe it will have a great impact. In fact he believes that if this service is rolled out nationwide it will actually help broadcast services. If a power line has an RFI problem that affects customers, it will affect the data service more and the power companies will have to spend more time repairing noise sources in order to maintain the broadband service. Mr. Martin has been involved in field testing of broadband over power lines and he sees no more interference to broadcast services in the testing locations than locations where testing is not taking place. He says that the injection level into the powerline is much less than any noise source that is found on power lines.