An Alabama hospital’s new addition mitigates arc-flash hazards while improving maintenance workers’ productivity with new, systemwide switchgear.

By Don Talend

The dangers of arc flash have been getting increased attention from regulators and from the electrician community in recent years. Safety recommendations such as the use of personal protective equipment (PPE) and setting work boundaries relative to electrical equipment have been developed to protect electrical maintenance workers from arc-flash incidents. However, these precautions can dramatically reduce workers’ productivity.

In Birmingham, AL, electrical workers at St. Vincent’s Medical Center—which underwent a major expansion in the period from 2000 through 2006—were facing productivity-restricting arc-flash precautions when performing maintenance in the additions.

The electrical infrastructure provider for a new six-story emergency room and 90-bed south tower, Birmingham-based Marathon Electrical Contractors Inc. addressed the owner’s concerns by incorporating new low-voltage switchgear into the project. The addition of the switchgear promises to give building owners a new approach to solving the arc-flash problem.

A Dangerous Event
Arc flash is a highly dangerous event that occurs when electrical insulation or isolation between conductors is broken or can no longer withstand the applied voltage. The release of energy from a fault in switchgear can result in an explosion that releases heat up to four times higher than the surface temperature of the sun. Aside from the release of heat, arc flash can turn metal molten and spray shrapnel over a wide area, causing serious injuries or even fatalities.

There are many reasons behind the increased focus on this hazard by the Occupational Safety and Health Administration (OSHA) and the electrician community. Estimates vary, but arc flash is thought to account for about 2,000 serious injuries in the United States annually. Increasing worker health care costs and the threat of litigation play a role. With globalization comes increased competition and greater profitability pressures in many industries, inspiring a drive for minimizing equipment downtime and having workers operate around energized equipment. Steady economic growth has often caused expansion of facilities and their electrical systems as well as higher electrical loading without a corresponding increase in overload protection. Last but not least, much of the nation’s electrical systems are aging, as is its overall infrastructure, increasing the potential for arc-flash incidents.

The electrician community has provided specific recommendations to address OSHA regulations relating to arc flash. OSHA regulations stipulate only that employees potentially exposed to arc flash not wear clothing that could increase its adverse effects, that these employees be protected against failures by shields or other devices installed to contain arc flash, and that these employees wear appropriate PPE. In the 1990s, the International Engineering Consortium emphasized in its IEC 60298 the importance of making switchgear enclosures safer for workers by having tests ensure that explosive pressure inside of enclosures be either confined or vented.

In 2002, the Institute of Electrical and Electronics Engineers published IEEE 1584, “Guide for Performing Arc-Flash Hazard Calculations,” which recommends several steps for arc-flash prevention. Among these steps is calculating incident energy for all of a building’s electrical equipment and setting a “flash protection boundary.” These recommendations coincide with similar ones relating to boundaries and personal protective equipment in the National Fire Protection Association’s NFPA-70E, “Standard for Electrical Safety in the Workplace.”

By mid-2007, OSHA is expected to finalize a proposed CFR 1910.269 revision to its Electric Power Transmission and Distribution standard. In 2006, the Edison Electric Institute (EEI) submitted language developed with the help of the International Brotherhood of Electrical Workers and OSHA that would give utilities greater flexibility in protecting workers during day-to-day work activities than NFPA-70E does.

Addressing Safety and Productivity
Better electrical system monitoring shows promise as a better way to prevent arc flash. Demonstrating this, Marathon Electrical Contractors addressed both arc flash and worker productivity at St. Vincent’s by giving the ownership remote diagnostic and maintenance capabilities while meeting OSHA standards. Marathon installed new GE Entellisys low-voltage switchgear that allows workers to perform maintenance on electrical systems remotely.

It was the first time that Marathon had used the new-generation switchgear, which makes it possible for electrical maintenance workers to have central control, monitoring, and diagnostics for an entire electrical system. “This [switch]board that we put in, it’s the first one we’ve ever seen that has a panel that operates every breaker in it,” notes Tommy Godwin, senior project manager at Marathon and a 45-year veteran of the electrical profession. “You don’t even have to be in the room with the breaker—we can operate the breaker from outside the room. We can tell it to open, close, whatever. But we’ve eliminated the dangerous part if something happens in that breaker—if it blows up, faults, whatever.”

Over the years, low-voltage switchgear has improved in reliability through the use of increasingly sophisticated breakers but at the cost of creating breaker-centered “information silos.” Unlike increasingly sophisticated fuses and trips that control each breaker based on the current in its respective conductor, the new St. Vincent’s switchgear monitors all breakers in the system and controls them based, essentially, on real-time data representing changing conditions throughout the system. The switchgear achieves its single-processor technology by taking system intelligence out of the breakers and putting it into one or more central processing units (CPUs).

The increased intelligence is particularly beneficial to both Marathon and the St. Vincent’s electrical maintenance staff because the project involved the installation of double mains, which resulted in increased monitoring requirements. “Not all buildings have double mains in them,” notes Godwin. “Most buildings have one main in them, but in hospitals, we use two mains and they feed off of two transformers, so if they lose a transformer outside we have a main tie breaker, which we can actually use to tie those two breakers together inside this board. So in case a power company transformer goes down, we can isolate that transformer and get everything back online through a main tie breaker.”

The switchgear system that Marathon installed uses a structured hardware configuration that consists of the CPU, a digital communication network, current sensors, device electronics for the circuit breaker, control power, voltage transformers, and a human-machine interface (HMI). The digital communication network uses a GE EntelliGuard Messenger that converts voltage and current signals from analog to digital signals at the breaker and transmits the signals to the CPU.

The Messenger also receives instructions from the CPU via a commercially available Ethernet switch and carries out the instructions at the EntelliGuard Breaker, a unit which, unlike conventional breakers, is not equipped with internal current sensors or an internal trip unit. The CPU, not internal breaker intelligence, controls the breaker. However, the circuit breakers are fused to limit current and protect the breakers at high fault values. Additionally, the breakers are compartmentalized with grounded separation panels between the breakers and barriers between the front breaker cubicles and the rear bus and cable compartments, reducing the chance of arc-fault transmission from one equipment area to another.

The HMI gives workers touchscreen viewing of myriad switchgear functions, including the status of switchgear itself, breaker status, protective settings (overcurrent protection and protective relays) for each circuit breaker, alarm settings and status, a sequence-of-events log, and captured waveforms. Access to the system is password-protected for security, and users can be given varying access levels from guests who can view operating data to administrators who can change breaker operation and protection settings. The standard HMI is set up in an auxiliary cubicle within the switchgear lineup.

Alternatively, the most significant facilitator of worker safety and productivity is the Near-Gear HMI, which uses networked desktops and laptops and can be placed up to 250 feet from the lineup—usually far outside of the flash-protection boundary. The Near-Gear consists of a stand-alone stack or wall-mounted enclosure with a touchscreen and remote software providing secure access to the system.

Remote HMI software is available that can be installed on individual personal computers or a local area network (LAN) that allows up to eight computers to communicate with the switchgear. Four local computers can be interfaced with the CPU and HMI using the Ethernet connection and four more can be supported by the LAN. The system has the ability to communicate with other information systems in a building, such as distributed control systems, power management systems, or building automation systems.

Additionally, the switchgear can communicate with remote computers located anywhere in the world via the secure communication link at the Ethernet switch. Four remote communication options are possible. Multiple near-gear HMIs can be located within 250 feet of the switchgear. Entellisys Remote View-Only Software can be loaded onto a desktop or laptop computer.

Entellisys Remote Interactive Software can also be loaded onto a desktop or laptop computer and gives the user the same ability to control electrical system functions as at a local HMI.

Finally, the system can communicate with a building’s other information systems through its compatibility with the open protocol of Modicon Modbus RTU and its availability over Ethernet via Modbus/TCP.

Godwin reports that the switchgear’s remote operating capabilities allow maintenance workers at St. Vincent’s to wear less-restrictive level-2 PPE when operating the switchboard, compared with level-4 PPE that would otherwise be required. This boosts worker productivity, he notes. “It’s worse than a welder’s outfit,” he says of the level-4 PPE. “You’re looking out of a visor. It probably takes 30 minutes to put the suit on so you can go in there and operate one breaker. With this board, you can go outside and hit a button and do the same thing. Labor savings is a big issue.”

Another safety-enhancing feature of the switchgear is a remote racking device, which mitigates arc-flash hazards in tasks that are among the most dangerous in system maintenance: breaker rack-in and rack-out from a live bus. Maintenance workers can open breakers using the HMI prior to attaching the racking device and then operate the device from up to 30 feet away, notes Godwin. “It racks in and pulls itself in, so that when that breaker goes in, you’re ready to roll,” he says. “Before, we had to take a little crank and crank them in and out. With these particular breakers, you don’t even have to be in the room. With this, when we rack it in, we can be outside the room and tell it to close the breaker, and if it blows up it’s not going to hurt. You’re not in the room, so you don’t have to wear this suit.” With conventional switchgear, he says, “we’d have to work everything dead, so we’d have to go in there and put the suit on to open up the breaker.”

Arc-Flash Mitigation
The hospital’s new switchgear also has diagnostic features that address the causes of arc flash as well as its symptoms.

When St. Vincent's Medical Center underwent a period of expansion, the owners sought to minimize arc flash by using low-voltage switchgear.

The first bus differential used cost-effectively on low-voltage switchgear provides zone-based protection. Use of bus differential is possible because the switchgear’s nonmechanical functions are software-based, minimizing the amount of components found in the switchgear’s central architecture.

The switchgear also has fast-protection capability that quickly customizes settings to minimize arc-flash energy. In contrast to conventional switchgear that captures waveforms by each individual breaker and keeps the information in a silo, the new switchgear at St. Vincent’s performs fully synchronized waveform captures of readings from every circuit in the system simultaneously. “They can go in there and they can check a breaker and see the amperage on it,” Godwin says of the hospital’s maintenance staff. “The board monitors the amperage on the breaker, and they can put limits on the breaker. If they’ve got air-handling units with filters in them, they can actually put a limit on the amperage on those units, and when the filters start getting dirty the amperage climbs and the board will actually tell them that they’ve got to change their filters. The computer tells them a lot of things that a normal board can’t.”

The switchgear also uses algorithms to analyze potential arc-flash energy based on short-circuit current where a fault occurs, the system impedance and voltage, and the length of time during which the fault persists. Based on this data, the switchgear runs diagnostic algorithms to identify the appropriate breaker and then to shut it down immediately.

Similar to automobile diagnostic systems that mechanics rely on to detect engine fault codes, the switchgear also records fault data for maintenance personnel to use for system operating analyses. All system protection and control function–related events are time-stamped and logged to provide a detailed chronology of these events in a sequence of events record.

“The [current transformers] in that Entellisys panel are monitoring the buses as far as balance,” notes David Jones, job manager for Marathon, who supervised as many as 10 workers on the St. Vincent’s project. “If you have a fault incident in the building, it’ll record it. It shows up, and I go into the system and track it down instantly.”

The software provides a high-level status report in a System Health Summary window. This report displays the functional status of each of the Messengers and CPUs in the system. Clicking on indicator lights both for the CPUs and for circuit breakers associated with each Messenger provides maintenance workers with greater detail about the status of these components.

The electrical maintenance staff at St. Vincent’s has the ability to use the system’s alarm function to alert it to conditions that warrant immediate attention, such as current that is too high or too low on a given feeder. The system has the ability to send alarms and reports to users via e-mail or PDAs or other digital devices.

After the project was completed, Godwin notes, the ownership and the maintenance staff at St. Vincent’s were excited about the new monitoring and diagnostic capabilities at their disposal. Those capabilities are in stark contrast to the conventional method of electrical system “monitoring,” which consists of resetting a tripped breaker with no real idea of why the trip occurred.

“A lot of times with a normal board we’ll get a blanker trip and we don’t know what happened, when it happened, what caused it, or whatever,” says Godwin. “The only thing we can do is reset the breaker and turn it on. If that’s a dead short, it’s going to come back on us and arc flash on us again. But this new board is a diagnostic tool deluxe.”

Writer Don Talend is a communications specialist based in West Dundee, IL.

DE - May/June 2007