Quick decision by a contractor’s field engineer paid off on several counts for a municipal water operation.
When it comes to electrical systems, most failures can be attributed, in large part, to installation problems, water damage, insulation issues, or poor workmanship. Such failures pose a serious safety threat and have the ability to shut down operations entirely. Ultrasound technology is a proven way to deal with them. In short, this easily deployed predictive tool offers sites a means of identifying and, thus minimizing the impact of these problems.
According to Doral, FL-based Ludeca Inc. (ludeca.com), ultrasound solutions can reveal electrical-fault conditions such as partial discharge (corona), partial arcing (tracking), and arcing discharge inside metal-clad switchgear, around substations, and in overhead transmission and distribution lines. Those types of electrical faults emit ultrasound signals at the site of the failure, often without generating any heat. Specific benefits of this technology include, among other things, being able to:
• detect partial discharge in its infancy, before it advances to an arcing or tracking condition
• safely inspect metal-clad switchgear prior to opening panels for infrared inspections.
A case in point
JetTech Mechanical, Goodyear, AZ, was recently contracted to conduct the startup and commissioning of two 1,250-hp, 4160-V, 900-rpm motors that drive a vertical-turbine pump for a major water municipality. The task involved collecting vibration data at multiple points on the motor and the pump, and ensuring Level III vibration analysis and reporting were complete, according to ISO and Hydraulic Institute (HI) standards.
Once the pump began running, JetTech’s field-service engineer waited for it to settle out, purge all air from the system, and reach its normal operating condition. As he recalled, it was around this time that he knew “something was just not right.”
Granted, vertical-turbine pumps are loud. Still, the engineer thought he heard what might have been electrical arcing in one of the motors. He couldn’t, however, pinpoint where that noise was originating. That’s when he put down his vibration analyzer and pulled out his SDT270 ultrasound system.
Donning a headset, the engineer scanned the motor in question with the airborne-ultrasound equipment and found that the electrical noise was originating in the unit’s termination junction box (where the motor leads connect to the main power feeding the unit from a breaker, VFD, or soft start). He swapped the instrument’s airborne sensor for a threaded contact-ultrasound sensor with magnet setup. Mounting the contact sensor on the junction box, he confirmed that severe electrical arcing was occurring. When the job-site supervisor was called over to the equipment, he heard the electrical arcing for himself. At that point, the unit was shut down and a LOTO (Lockout/Tagout) placed on it.
Electricians were brought in to remove the junction-box door. As soon as the door was removed, the cause of the arcing became clear: The motor’s electrical termination had been performed incorrectly. Instead of working with a proper termination kit, the electrical contractor had used CPVC pipe and standard black vinyl electrical tape.
The JetTech engineer’s use of ultrasound technology to determine the exact location of the electrical arcing (something that his vibration analyzer couldn’t do) was a life-saver in more ways than one. His decision to perform an ultrasound analysis not only helped to prevent costly damage and downtime associated with the recently refurbished motor and the vertical-turbine pump it drives, it may also have prevented a serious arc-flash injury (or worse) among the 15 people who work around the pumping system. MT
For more information on ultrasound technology, including the SDT270 system referenced in this article, visit ludeca.com.
Safely ‘Hear’ Problems Before They Shut You Down
Ludeca offers these tips for finding electrical faults with ultrasound:
• Most electrical cabinets are not hermetically sealed. Scan your ultrasound detector around the panel sides and vent holes to detect discharges such as arcing, tracking, and corona.
• Not all electrical-discharge faults produce heat. Use ultrasound to hear what your infrared camera cannot see.
• Electrical-discharge activity is amplified by high humidity. When performing ultrasonic scans at substations, make note of the date and weather conditions.
• Unlike audible sound, ultrasound travels directionally through air. Therefore, when scanning from a distance, it’s important to inspect electrical systems from all sides.
• Since corona discharge produces no heat on electrical systems below 240 kV, don’t rely entirely on infrared to find problems.