Case Study 4

Middle School Electronic Emergency Lighting Fixtures Damaged by Voltage Transients from Sewage Lift Stations

Public & private schools like many other commercial & industrial facilities undergo lighting upgrades to achieve better illumination, energy savings & lighting control. The lighting in this middle school was upgraded to full electronic fluorescent lighting. All lighting in all rooms including the emergency lighting was upgraded to electronic lighting from traditional magnetic & incandescent lighting.

Shortly after the upgrade, the emergency lighting fixtures began to fail. Emergency lighting fixtures contain additional circuitry that allows the end users to test the emergency lighting capabilities. Each fixture has a separate power supply that charges a battery dedicated to power an electronic ballast that power the fluorescent lamps. When a momentary or temporary interruption or outage occurs, the power supply senses the power quality problem & switches the battery into the circuit, so it can power the ballast from the battery power until the power is restored.

These emergency lighting fixtures must be tested periodically on a regular basis to ensure they are in working order. Upon one test, many of the fixtures failed the test—that is, they did not illuminate the lamps when the test button was depressed. The test button simulates an interruption or outage & engages the battery in the circuit to ensure the battery is good & that the emergency lighting circuitry is working. This is a requirement by the local city code as well as the state code.

When the school discovered the emergency lighting fixtures were failing, they requested replacements from the manufacturer. The manufacturer gladly replaced the fixtures as they were under warranty. However, shortly after the fixtures were replaced, they began to fail again after a few weeks. This situation became a problem for the school system as they were not able to guarantee the emergency lighting fixtures would be operational when needed. When this happens, the school could be left in the dark when an interruption or outage occurs. This is a safety hazard for the occupants in the school.

The engineering manager for the school system contained PBE Engineers for assistance. An engineer from PBE discussed the problem with the engineering manager as well as the school maintenance manager and one of the associates from that school. These people were brought into the conference call to ensure PBE had all of & the correct information about the lighting problem that was occurring at the school.

The engineer from PBE requested that the maintenance manager send him three of the failed electronic power supplies removed from three different emergency lighting fixtures in the school. Upon receipt of the failed power supplies, PBE opened them up & examined the circuit board in each one. PBE found evidence of component failure likely caused by voltage transients. Upon this discovery, the engineering manager with the school system requested that PBE provide a proposal to visit the school & conduct a power quality investigation at the school. The PBE engineer explained that the investigation would include power quality monitoring as well as a detailed evaluation of the school’s electrical system including evaluation of the grounding and bonding system as well as a detailed evaluation of the switchgear, power distribution panels, dry-type transformers & branch circuit subpanels. The investigation also included evaluation of several of the emergency lighting fixtures.

PBE prepared the proposal & presented it to the engineering manager. The manager reviewed the proposal & secure approval for the work. When PBE visited the school, two temporary power quality monitors were installed in the school’s electrical system. The purpose of installing the monitors was to start recording the voltage & current behavior while the PBE engineer was conducting the detailed evaluation of the school’s electrical system.

After the monitors were installed, the PBE engineer began evaluating the school’s electrical system. The engineer discovered several electrical problems that needed to be corrected to ensure the power quality inside the school could be improved. Some of the problems discovered were ones that would magnify voltage transients when they occurred on the school’s electrical system. The PBE engineer didn’t find any sources of transients inside the school. However, reviewing the monitoring data revealed that some voltage transients were coming in on the main feeder to the school. None of the transients lined up with any of the voltage disturbances that could be caused by the local power company.

This discovery warranted further investigation as to what was generating the voltage transients that were coming into the school’s electrical system & causing damage to the power supplies inside the emergency lighting fixtures.

The PBE engineer drove around the community looking for any obvious signs of equipment or electrical systems that could be generating voltage transients. Since the transients had the shape of those caused by contactors, the PBE engineer was focused on source of transients that could include contactors turning a piece of equipment ON when needed.

Since the school was in a residential area where no industrial customers were located, the PBE engineer focused on electrical equipment in the area that could be generated such transients. The PBE engineer discovered that there were several sewage lift stations in the area that were several blocks from the school. The PBE engineer stopped to watch the operation of several of the lift stations to discover that they were working as intended. He recorded the typical time between lift station operations & found they would operate several times a day with a few hours between starts.

The PBE engineer went back to the monitoring data & discovered the time between transients matched up with the observed turn ON times for several of the lift stations near the school. The PBE engineer contacted engineering manager for the school system, so the owner of the lift stations could be contacted to inquire further about their operation.

A contact in the local county that managed the lift stations was identified & contacted for discussion. Once the contact was identified, he met the PBE engineer at a few of the lift stations. The PBE engineer examined the controls for the lift stations & discovered that the contactors used in the lift stations had no surge protection. When contacts operate, voltage transients are typically generated & can travel outwards on the local power distribution system. It was determined in this case that a few of the lift stations nearest the school were close enough to the school’s utility transformer to generate transients that would enter the school. These transients were magnified by some of the wiring & grounding problems found in the school.

The county agreed to have the right type of surge protection installed on the contactors that were operating the lift stations. In addition, the school system’s engineering manager agreed to have surge protection installed on the school’s main switchgear as well as on the lighting panels that powered the emergency lighting fixtures. These modifications were made along with another replacement set of power supplies installed in the lighting fixtures. Once these modifications were made, no additional failures of the power supplies occurred in the emergency lighting fixtures. The school system was pleased PBE’s power quality engineering work.