Persistence Needed to Track TV/Radio Interference

By Michael Caruso, Field Planner
New  York State Gas & Electric Corp, Binghamton, NY

photo7.jpg (16694 bytes)When a customer calls in with a loss-of-power problem the utility sends out a line crew. But when the complaint is about TV interference or the inability to get a specific radio channel, a specialist must be assigned to the case.  TV or radio interference may be caused by many different things--even at atmospheric change-but one of the first suspected causes is electric utility equipment. To correct such problems, New York State Electric & Gas Corp (NYSEG) relies heavily on ultrasonic technology but creativity, persistence, and experience are also essential.

Recently, NYSEG received a call from a cable company complaining that it had lost VHF channels 3 and 4. These channels are picked up from Syracuse, NY, and transmitted through the company's cables.

A visit through the facility determined that there was electrical interference-an arc occurring somewhere in the area.  The engineer drove up and down the roads in all directions, checking things out, and finally located the problem pole, about a mile away, in the opposite direction from the cable company's directional antenna.

The general area of the arcing was found with a Model 610 locator, manufactured by Sprague Micro Tech Manufacturing Inc, Worcester, Mass. This is essentially a radio with a directional antenna. In this case, it signaled a strong emission, but was not precise enough to show the exact location of the source from the ground.  The engineer then picked up an ultrasonic instrument known as the Ultra-probe 2000, manufactured by UE Systems Inc, Elmsford, NY By pointing the instrument and listening for ultrasound from about 35 feet away, he zeroed in on a horizontal pin insulator. There had been a windstorm the previous weekend that had broken some of the tie wire just enough slip the 4800-V primary to the bolt, but not enough to be visible from the ground. A line crew was called and the problem corrected within an hour. Without the ultrasonic probe, this type of needle-in-a-haystack situation could take days to solve.

User's equipment often at fault

About half the times that utility troubleshooters visit a facility, it's the customer's own equipment that's causing the interference-for example, poor wiring, arcing or a doorbell or furnace transformer. Sometimes, the problem is intermittent and more challenging to solve.  It's important to know what to look for.

At NYSEG, if the problem can't be found from obvious causes or audible noises at the site, a triangular search is conducted using the Sprague locator.   Different types of arcs produce interference in different radio bands. Complaints may come from users of cable TV, AM or FM radio, land mobile radio, ham radio operators, marine radio, etc.  The directional capabilities of the Sprague locator are very dependent on the frequency.  Below 88 MHz, it has almost no directional capability, but it becomes more and more precise as the frequency increases.

When the arc location has been narrowed down as much as possible, troubleshooters start an ultrasonic search using the Ultraprobe 2000.  The instrument has a parabolic dish, giving it extremely precise directional capabilities.  It offers considerable benefits over older ultrasonic detectors that could only be used with a hotstick from a bucket truck, which required that a line crew be available.

An ultrasonic detector equipped with a parabolic reflector can pinpoint problem areas at distances greater than 300 ft.  Low-level ultrasonic signals generated by electrical arcs hit the reflector dish and are concentrated on a sensitive transducer at the focal point.  Background noise from a wide area is minimized.

The Ultraprobe is pistol-shaped and battery-powered so that users can easily move about while searching for arcs.  Turning capabilities enable the user to listen to the signals through headphones to gage their intensity.  An analog meter on the probe may also be used.

Recently, a ham-radio operator called NYSEG about a gross interference problem.  In this case, the feedback was too garbled and faint to use a Sprague locator, so the engineer walked from pole to pole checking the primary connections with the Ultrasonic probe.  All of these were clean.  On the way back, he inspected the neutral and secondary connections and found a loose 120-V secondary connector going to a streetlight.   The problem was corrected within an hour.

In another case, several customers, including car drivers, complained about AM radio interference along a particular road.  In this case, the ultrasonic probe showed every pole to be quiet. The Sprague locator had no directional capability at this frequency, but the engineer did notice a 5-dB increase in emissions as he walked under one particular pole.   A recheck with the Ultraprobe showed the pole to be quiet, so the engineer concluded it could be a micro-arc inside the poletop transformer, where it could not emit ultrasound.  The transformer was replaced and the problem disappeared.

The cause of interference in this unusual case was a common bond between the transformer and TV-cable grounds. This is compulsory in New York State.  Result was that the cable acted as an antenna for the emissions generated inside the transformer and caused interference on AM radios down 2 miles of road and 200 ft on either side of the line.

When responding to complaints of interference, NYSEG's policy is to check out its facilities close to the customer's site.  But the cause of interference may be 5 miles or more away and be out of the utility's control.  Once it has been determined that no NYSEG equipment is at fault, the customer is advised to call an electrician or consulting engineer.