No-Outage Testing and NFPA 70E

Only a few years ago electrical testing companies were very concerned about how the NFPA 70E Standard would affect or even prevent energized equipment inspections from being performed. Since then, many changes have been introduced into the workplace so that field technicians are much better protected against injury and are still able to perform valuable no-outage inspections in order to maintain reliability.

This column discusses some of the most noteworthy safety evolutions for nooutage inspections that have taken place over recent years.

Handheld Partial Discharge Detector - This instrument, shown in Figure 1, was discussed in detail in the last NETA World. Used today primarily as a mediumvoltage insulation partial discharge detector to identify potential insulation defects, this device was originally developed overseas for safety purposes.

Tragically, several years ago two utility electricians were fatally injured while standing near a switchgear section that had partial discharge damage while an adjacent breaker was being switched out for maintenance. The mechanical vibration that occurred from the breaker operation was all that it took to disturb the latent insulation problem and trigger a fault that caused the incident.

Wanting to make sure that such an event never occurred again, utility management sought out a research company to develop an easy to use handheld device that could detect insulation defects in medium-voltage switchgear while the equipment remained in service. This led to the creation of the TEV or transient earth voltage detector which detects electromagnetic signals associated with insulation breakdown by placing the instrument against the outer metal clad switchgear cover. As mentioned earlier, the instrument is widely used today for both safety and equipment condition assessment. The instrument has evolved to include an ultrasonic sensor to supplement the TEV sensor.

Access Ports - Many different types of accessories have evolved that allow visible or line of sight access to internal components by modifying the switchgear covers. These modifications generally require creating an opening in the cover. The opening may be a simple hole that is closed or covered after the inspection or may consist of a special lens material covering the hole that allows infrared and ultraviolet wave transmission (see Figure 2). The lenses that allow ultraviolet transmission are desirable for medium-voltage equipment inspection as corona and surface partial discharge activity create ultraviolet emissions. Some lenses have been designed to be arc-flash resistant which allows protection during inspections, even though the exposures during inspections are minimal.

Some other novel switchgear modifications have been developed for medium-voltage switchgear to allow safer no-outage inspections to be conducted. One such innovation consists of a simple ultrasonic inspection port which allows temporary removal of a threaded fitting installed in the switchgear cover (see Figure 3). The plug is temporarily removed to allow an ultrasonic sensor to be placed into the opening and the signal to be measured. A few other additional modifications have been made to allow no-outage, medium-voltage cable inspections to be performed in a safer manner. Typically, these tests require switchgear cover removal to allow sensors to be placed on the cable shield and some innovations include installing hinges on the covers or creating smaller secondary hinged openings that allow shield access. Still other modifications involve rerouting the shields through the cover to a small externally mounted box that call be opened to allow shield access. Other solutions include installing permanent shield sensors and routing the output to externally mounted boxes.

Permanent Monitors - Several advances have made over the last few years in monitoring technologies that provide continuous protection of assets. These monitors do not require switchgear cover removal to obtain equipment condition. Not only is safety improved but these monitors also provide a much higher level of reliability over annual spot surveys and can track equipment condition over changes in load or atmospheric conditions. For critical equipment, the economical decision to install monitors may be especially favorable.

For medium-voltage switchgear a relatively new monitor has been designed that consists of multiple TEV sensors that are applied to the outside of the enclosure using magnetic sensor holders (see Figure 4). This monitor has the great advantage of being installed completely without an outage. A more advanced version of the monitor is also available that provides cable condition coverage by incorporating cable shield sensors in the package. Internal thermal switchgear condition can be trended through the use of continuous infrared monitors that employ infrared sensors shown in Figure 5 that mount through the switchgear cover. These sensors can also be installed in areas of the switchgear that would be impossible to access while energized.

A few types of arc-detection monitors (Figure 6) have been developed that utilize fiber optics routed through the switchgear to detect the flash of light created by the arc to send a signal to a relay that trips the main breaker. Unlike the partial discharge monitors that detect symptoms of medium-voltage insulation breakdown well in advance of complete failure, the arc detection monitor only detects the ultimate complete breakdown but does reduce equipment damage. This equipment is not really monitoring condition but is acting more like a traditional relay that minimizes fault damage. Therefore, this technology may be better suited for low-voltage applications while the partial discharge monitor would be better suited for medium-voltage applications.

Remote Breaker Operating Devices - Although the act of operating or removing and inserting a circuit breaker onto a bus is related to an outage and, therefore, is not truly a no-outage technology, these recent NFPA 70E- spawned innovations created for remote breaker operation and racking are certainly worth mentioning. These devices, shown in Figure 7, allow technicians to remain safely outside of the arc-flash exposure zone when operating breakers. Recently, a major incident was avoided at an eastern U.S. power plant by using a remote breaker racking device. A technician was racking a circuit breaker onto an energized switchgear bus and was positioned in an adjacent room far away from the breaker, viewing the process with the device’s remote camera. A massive flash was seen on the camera and the technician went out to investigate the damage. Apparently the breaker was in the closed position but the safety interlock was faulty and did not trip the breaker. This caused immediate current flow through the breaker fingers, which were not fully engaged on the bus, resulting in a flashover which caused severe damage to the breaker as seen in Figure 8 and the associated arc flash which was visible on the camera. Fortunately, the technician was protected from serious injury by using the remote device.

Conclusion - No-outage inspections are a very valuable tool for the assessment of electrical equipment condition, but these tests may place the technician in areas where the incident energy requires significant PPE. Other alternatives to opening covers have been developed that greatly minimize exposure, and we can be certain that additional technologies will evolve to maximize personnel safety while still allowing no-outage technologies to be performed.