Con Edison technicians patrol the streets of New York as part of the utility's aggressive program to prevent, detect and fix contact or stray voltage. Five nights a week, 14 trucks are out on patrol, testing everything from manhole covers to light poles for contact voltage. The utility monitors more than 60,000 miles of roadway each year and has reduced shocks by 79% as a result.
For many years, Con Edison's technicians and engineers measured contact voltage with a voltmeter. Seven years ago, however, the utility led the charge to develop a suite of more efficient ways to detect contact voltage. The utility partnered with the Electric Power Research Institute (EPRI) on a project to help field crews more quickly detect energized objects.
In 2005, Con Edison asked EPRI to help develop technology to assist the utility with its contact voltage program. The utility first shared some design specifications and objectives with EPRI. For example, the utility was looking for a device that was low cost, directional and non-contact.
EPRI researched the types of electric field sensors on the market. After careful review, it determined that none would be suitable without major modifications. EPRI then enlisted some of its research and development staff who had expertise in sensors and power electronics to conduct a series of tests on different sensors and antennas.
The device EPRI developed relies on mature off-the-shelf technology. The sensor is a standard scanner antenna available at electronics stores. EPRI's researchers integrated circuitry into the device that can amplify a signal and enable it to be directional.
After EPRI introduced the first-generation voltage detector, Con Edison crews were among the first to test it in the field. The engineering organization began beta testing the initial device, and then the distribution engineers worked with field crews to solicit feedback and offer suggestions for modifications. For example, the original prototype was operable but bulky. However, the design that was commercialized is lightweight and portable.
Another concern field crews had with the original prototype was it ran only on a rechargeable battery. Crews said they did not want to rely on rechargeable batteries, because they are never charged when they need them. The second-generation device runs on either a 9-V alkaline or a rechargeable lithium battery. No matter which battery users choose, they usually get a week's worth of test performance between recharge or replacement.
The troubleshooters also found the first-generation unit was prone to breakage. The new version is protected by a rugged case that has an option to attach a wrist strap. Even if a user drops it in the field, its operability will not be affected.
Con Edison's technicians also mentioned the prototype's analog meter with backlight was difficult to read, especially at night when they often do testing. In response, EPRI integrated red light-emitting diodes (LEDs) into the next generation of the device.
Out on the Market
It took about a year and a half from the beginning of the field trials to when the product was commercialized and available on the market. Con Edison's team dynamic and the collaborative effort between the engineers and troubleshooters helped get the product to market quickly.
Now two companies, Walker Engineering and ETI, are licensed by EPRI to produce the device. Walker Engineering, a small engineering and construction firm, now markets the device as the Handheld Contact Voltage Detector. The device detects the presence of voltages on supposedly voltage-free structures such as light poles, fences and doors. When a user holds the device in the vicinity of a voltage potential, the instrument indicates the relative field strength of the surrounding electric field.
The Canadian Electrical Safety Authority (ESA) has recognized Walker Engineering as a partner in the fight against potentially fatal contact voltage. ESA highlighted the device as “an ideal tool for verifying a reference (street pole) is not energized, indicating zero electric field.” ESA wrote the guidelines in response to the condition of low-voltage electrical distribution systems and the associated high-profile reports of electrical shocks and fatalities.
Product in Action
Since the product launch in early 2011, Walker Engineering has already shipped units to Con Edison and several other major utilities. Technicians are now using the tool to determine the safety of the environment or the validity of a true ground, according to Walker Engineering.
Now that Con Edison is using the product out in the field, the utility has discovered that the device saves a lot of time for its troubleshooters, both during routine patrols and when performing investigations. The contact voltage inspection crews and underground troubleshooters are now carrying the handheld devices to determine whether contact voltage is on the neutral or phase conductor. By finding the location sooner, Con Edison can make repairs faster, removing a hazard.
Before they began using the detector, troubleshooters had to walk around with a voltmeter and measure every conductive surface to determine which objects were energized. The users still have to make a measurement with a voltmeter if they want to know the exact voltage, but by using the EPRI-designed device, they can identify what is and is not energized. In some cases, they can even use the device to find energized objects, like a steel conduit under a sidewalk, that were previously undetectable using a voltmeter.
The device features an antenna that picks up the charge from any electric field. Users walk with the unit in their hands until some of the LEDs light up. Then they can sweep it from side to side and up and down. As they get closer to the source of the electric field, more LEDs light up. Because the device is highly directional, more LEDs light up when the tip of the antenna is pointed directly at an energized object. They can then use a voltmeter to check the voltage on a particular object.
After they find energized objects, the crew passes that information to the control center. When they call the information in, they often give the specific address, a description of the energized object and the voltage. In the future, EPRI hopes to offer a handheld version of the sensor that will synch to a smart phone and record the GPS location.
Some cases are simple to resolve. If a streetlight is energized, the contact voltage often will dissipate once a technician cuts the service. Other cases, however, can be more complicated, and the field crews work with the distribution engineering department to find the source of the contact voltage.
Con Edison's engineers routinely go into the field to work with the crews. The engineers share their analysis of events with the technicians and teach them to use the device. By soliciting feedback from the field, the engineers can identify the troubleshooters' challenges and work to resolve them.
Con Edison is deploying about 100 of the devices in the field and believes they will improve productivity. The utility is continuing to work on improving the device, and EPRI is developing the third-generation unit. EPRI has fabricated more advanced devices in its lab and is running field tests with a consortium of utilities, including Con Edison.
EPRI is now working on understanding the harmonic content of the contact voltage and using that information to identify the source. The third-generation device will indicate whether the source is an electrical fault or one of the many typical E-Field sources like a neon sign or voltage drops on return conductors.
Another future application is an enhanced mobile scanning technique with a variation of the handheld device. Con Edison has equipped 15 of its work trucks with mobile E-Field scanners, which alert the troubleshooters if an object is energized within 30 ft of the back of the truck. When the workers hear the signal, they can stop their vehicles, get out and pinpoint the energized object with the handheld device. In the future, the utility will integrate the harmonics knowledge and other signal-processing algorithms to make the mobile scanning and detection of contact voltage even more efficient.
EPRI also plans to come up with wearable versions of the voltage detector that would sound an alarm if the user came close to an energized field. Instead of using the antenna, EPRI envisions hooking up these devices to a vest with some woven metal fabric, or even outfitting a hard hat with a small sensing plate so the device is more hands-free. EPRI is considering moving off the hardware platform to a software platform for a portable device.
Con Edison recognizes that contact voltage detection improves public safety by reducing the potential for shock. The utility also learned that by ramping up its contact voltage program, it could actually improve system performance. As the utility eliminated cable with damaged insulation, it was able to improve reliability and reduce related power-quality concerns like flickering lights and customer outages. Through a partnership with EPRI, Con Edison has been able to minimize contact voltage, improve the reliability of its system and, most importantly, protect the public.
Stuart Hanebuth (firstname.lastname@example.org) is the department manager of secondary system analysis and has been with Con Edison for 13 years. He won a Technology Transfer Award from the Electric Power Research Institute for his work on the voltage detector along with his fellow researchers Graciela Varela-Maloney, engineer in distribution engineering, John Publik, senior specialist in distribution engineering, and Frank Doherty, project manager in research and development.
Doug Dorr (email@example.com) is a senior project manager for the Electric Power Research Institute. He is responsible for managing all of EPRI's contact voltage research. He has worked for EPRI for 20 years and works in the advanced monitoring applications group.
Con Edison's Shock Reports Decline
Contact voltage, also known as stray voltage, occurs when defective wires or cables energize objects such as manhole covers, lampposts, metal scaffolding or fencing. Wet conditions and road salt make it more likely for these objects to conduct electricity.
The number of reported electric shocks plunged for Con Edison as a result of its aggressive contact voltage-detection program.
Here are some of Con Edison's findings from 2010:
- Fifty-nine shocks were reported last year, which was a 30% drop from the 84 reported in 2009.
- Last year's number was 79% lower than the 285 shocks reported in 2004, which was the first year of the utility's program to detect and fix energized objects.
- The number of shocks has decreased six straight years, or every year since the program began.
- The number of shocks reported from Con Edison's equipment has declined even more. Fifteen shocks were reported from the utility's equipment last year, compared with 24 a year earlier and 210 in 2004.
- Con Edison tests nearly 750,000 structures, including manholes, service boxes, underground transformers, and city or municipally owned street and traffic lights.
- The utility found and made safe 2,099 pieces of equipment in 2004. By 2009, that number reached 6,267 before dropping back to 4,717 last year. More than 60% of the contact voltage conditions the utility found last year were due to failures on non-utility equipment.
- The number of energized objects has dropped as Con Edison has performed more scans. The utility scanned more than 60,000 miles of city streets last year.
Editor's note: For more information, view the utility's annual filing with the New York State Public Service Commission at www.coned.com/2010AnnualTestingProgram, or view a video at http://www.youtube.com/watch?v=i2j0HcJEWSM.
Con Edison www.coned.com
Electric Power Research Institute www.epri.com
Electrical Safety Authority www.esasafe.com
Electronic Technology Inc. www.eti-nj.com
Walker Engineering Inc. www.walker-us.com