Ideal Reliability

By Douglas E. Stover, P.E., Principal, Director of Electrical Engineering, FreemanWhite, Inc., Charlotte, N.C. July 1, 2005

Electricity is the lifeblood of a hospital. Naturally, patients’ lives depend on sophisticated medical equipment and highly skilled medical professionals, but people and equipment depend, in turn, on a hospital’s electrical “circulatory system.” Without power, lighting would be inadequate, temperature control would be difficult, and most critically, certain types of life support and diagnostic equipment would be impossible to use.

Consequently, reliability is the watchword for hospital power systems. But what degree of reliability can be considered adequate for a health-care facility?

While preventing system failure is the ultimate goal, after code requirements have been met, the level of reliability for a hospital’s electrical power system is in the eye—and budget—of the beholder. While there are numerous and assorted equipment combinations that can achieve the desired tier of reliability, ultimately, reliability rests on quality of equipment, redundancy in design and scheduled maintenance.

There are many different approaches to enhancing reliability and reducing the probability of electrical failure, ranging from a utility substation to a 120-volt receptacle in the wall of the patient’s room. In any case, the following discussion concentrates on some of the most common methods used to achieve power reliability, many of which are currently used in optimal electrical system designs for some of the nation’s largest hospitals.

A utility point of view

The good news for health-care facilities is that due to their community service and the critical nature of their business, hospitals are often given precedence by the utilities. “As a public utility we are charged to serve the public good,” explains Paul Basha, CEO of York Electrical Co-op, York, S.C. “An integral part of that service is public safety and the heart of a community’s public safety is its health-care facilities. We place these facilities at the top of our customer list for priority service. This means that we will allocate appropriate resources to get them back online and keep them online.”

While utilities generally have decent track records for reliability, there are, of course, occasional outages. “Over the past seven years, I’ve experienced a handful of occurrences,” relates Philip Stephens, director of facility management services, Northeast Medical Center, Concord, N.C. “One was due to an ice storm, another to a substation failure, and several were due to contractors cutting the lines during construction projects. However, in general, I’d have to say that our utility provides excellent service.”

But there are measures that the end user can take to increase utility reliability. Two good options are dual feeds from separate substations and utility switching between different utility circuits. However, because there can be substantial expense involved in obtaining a second service, these options may only be practical for hospitals with 300 or more beds.

In addition, campus systems can be better protected from construction outages by encasing underground conduits in concrete (but not under buildings); keeping accurate records of underground utilities; and including locator services in the specifications and budgets for new construction projects. But guaranteeing consistent power doesn’t just depend on the reliability of the utility and equipment outside the facility. Just as important—if not more so—are the systems inside the facility.

Optimizing circuit breakers

Naturally, the main service entrance electrical equipment is critical to a hospital’s power distribution system. One of the best ways to improve overall system reliability is to have service entrance switchgear with a main-tie-main configuration and draw-out circuit breakers or low-voltage-power circuit breakers (LVPCBs), providing multiple levels of reliability to the facility through both the switchgear and the LVPCBs.

It would be helpful to provide a little background here. Switchgear with LVPCBs were developed for industrial and institutional use. As a result, they are built to higher standards than the switchboard with molded-case, thermal-trip circuit breakers that are commonly found in commercial buildings. While the latter are still in common use in health-care facilities, switchgear with an LVPCB combination have a number of features that definitely increase a system’s reliability:

  • Individual compartments in the switchgear prevent damage to adjacent breakers if failure occurs.

  • Long service life, when comparing an 800-amp LVPCB to an 800-amp molded-case thermal-trip device; the former is rated at 1,250 more operations at load prior to maintenance.

  • Parts are replaceable in the field for repairing a circuit breaker on site instead of sending it to the factory or installing a replacement circuit breaker.

  • Adjustable trip settings allow the switchgear main circuit breaker and distribution circuit breakers to be coordinated so that a fault on a distribution feeder does not affect the main circuit breaker.

Preventive maintenance and testing of the main and distribution circuit breakers can also be accomplished with minimum disruption because switchgear with LVPCBs have a redundant component built in. As a result, in-house staff can move the load on all switchgear onto one main by opening the second main and closing the tie breaker. The resulting amount of redundancy depends on whether or not the load on the entire switchgear configuration is less than the size of one main. But even in a situation where the load is greater than the single main capacity, redundancy can be obtained by running the emergency power system generators.

Ed Kinzer, past president of the North Carolina Healthcare Engineers Assn. and chief engineer of Halifax Regional Medical Center, Roanoke Rapids, N.C., confirms that reliability is clearly tied to maintenance. “Our switchgear with its main-tie-main configuration and draw-out circuit breakers has allowed us to perform a rigorous maintenance program,” he says. “This has provided us with peace of mind for our service entrance equipment.”

Comes down to code

However, no matter how high the quality and how frequent the maintenance, it is still probable that a hospital’s electrical system, or a part of it, will fail at some point. This probability of failure, when attached to human lives, means health-care facilities are required by code to have emergency power systems. And while these systems can vary, ultimately, the codes dictate what is required.

The National Electrical Code (NFPA 70) and the Health Care Facilities Code (NFPA 99) require that an emergency power system be provided in all hospitals. Article 517 of NFPA 70 divides these emergency power systems into three branches—life safety, critical and equipment—with the function of each branch as follows:

  • The life safety branch is the most exclusive branch and is limited to egress lighting, alarm systems and a few other items. This branch must be restored within 10 seconds if normal power ceases.

  • The critical branch is a broader branch serving lighting, receptacles, equipment and special circuits relating to patient care areas and the operation of the hospital. As with the life safety branch, this branch must be restored in 10 seconds if the normal system fails.

  • The equipment branch serves major equipment that is essential for the operation of the hospital, e.g., air-handling systems, elevators and compressed air and suction systems. However, because the latter two systems support patient lives, it is desirable to have them placed on the critical branch, which has a higher priority and reliability than this branch.

The codes mentioned above, along with NFPA 110, Standard for Emergency and Standby Power Systems, dictate certain design considerations that increase a system’s reliability—for example, the codes require the following:

  • Emergency generators have to be protected from flooding and other similar disasters.

  • Emergency generators and automatic transfer switches (ATS) are required to be located in a separate room from the normal service entrance switchgear.

  • Emergency power system wiring serving patient-care areas must be installed in rigid metal conduit to help protect it from physical damage.

Beyond basic code issues, one of the major infrastructure considerations in hospital renovations is whether to install separate generators or a central generator plant. This is a significant and often difficult decision for hospital administrators.

Van Hauser, director of engineering, Forsyth Medical Center, Winston-Salem, N.C., was recently involved in this process. He offers the following observation: “After a thorough evaluation of our campus and where we are going in the next 15 to 20 years, we made the decision to create a central generator plant that should serve us well for the next 20 to 30 years. This decision will help us increase the reliability of our emergency power system.”

The separate generator option offers a large financial advantage during construction, mainly because hospitals don’t have to build a generator plant with built-in flexibility for future expansions. On the other hand, a central generator plant, with its much higher price tag, has a far greater number of reliability advantages, including the following:

  • Less maintenance, because fuel tanks are shared and access is centralized.

  • Fewer staff is needed for maintenance, monitoring and outage problems.

  • Centralized testing of equipment.

  • Fewer spare generator parts if the same manufacturer and model number are used.

  • Ability to consolidate required emergency stop switches.

  • Common paralleling switchgear is allowed.

Multiple generators grouped in a plant allow the facility to consider using the redundant capacity to supply part of the chiller plant. If a generator fails, the chiller plant would be shed from the system.

Though typically reliable, generators can also fail. Consequently, one full generator needs to be held in reserve. When looked at in terms of reliability percentage, the difference between 98.2% and 99.97% reliability may not seem like a lot, but over the potential 30-year life of the generators, at approximately 20 starts per year, 11 failures would occur with a single-generator system vs. less than one on a system with a redundant generator.

When two or more generators are used together, they are operated through paralleling switchgear that use PLC controls to start and synchronize the generators. The distribution portion of the switchgear then feeds multiple transfer switches throughout the facility. The ability to parallel generators together makes it easy to have a redundant generator start and come online in the event that one of the other generators fails.

Yet another important component, the ATS, connects the emergency power system loads to both the normal and emergency sources. There are two features on ATS that can add another level of reliability when testing and maintaining the facility’s emergency power system:

  • The bypass/isolation feature allows staff to bypass the transfer mechanism when performing routine maintenance on the switch. It can also improve system reliability in the event that a switch is damaged or does not operate, because it can be easily transferred manually.

  • The closed transition feature eliminates the blip when transferring from one energized source to another, whether from emergency to normal—after an outage—or from normal to emergency for testing. This limits possible disruptions in the essential functions of the facility during test periods of the emergency power system by keeping equipment from going down and having to be restarted.

Of course, the system must be maintained to guarantee any level of reliability. For example, the NFPA requires a maintenance schedule of more than 20 weekly, six monthly, five quarterly, seven semi-annual tests and more than 20 annual item checkups, where the items must be inspected, checked, changed, cleaned or tested.

More specifically, the draw-out circuit breakers that provide increased reliability require scheduled maintenance. The generator sets will be even more reliable if they are tested strenuously to 80% of load for six to eight hours once a year. ATS need to be “exercised” monthly to ensure they function during an emergency. And, as a psycho-logical aside, testing gives the facility staff confidence in the capabilities of the equipment.

In a nutshell, hospital electrical systems can only reach their full potential relative to reliability with an all-inclusive testing program, as well as a maintenance plan that is ever-diligent in its execution.

Get the big picture

When it comes down to it, hospital power system reliability is not about one or even two pieces of equipment. It is about developing a comprehensive plan from the original design to the implementation of a rigorous maintenance program. There are many ways to increase the reliability of a hospital’s electrical power system through the quality of electrical equipment and components; the timing and quality of maintenance and testing procedures; and the number of system redundancies and backups—given commensurate budgets.

Without going into details, it is true that as a general rule of thumb, the more reliable the system, the more costly. In other words, the “ideal” electrical system configuration offers a high level of reliability, but comes with a big price tag.

At the same time, many of the design and equipment suggestions outlined above are, in fact, in place among the largest hospitals in the country, partly because these institutions have the largest budgets. Nevertheless, in the future, some of these alternatives may not only be advantageous, but also more affordable to a wider health-care audience. Meanwhile, the largest hospitals will likely be onto even more reliable and expensive alternatives.

Generator System Reliability

Number of Generators In the System Level of Redundancy for Critical Loads
None N+1 N+2 N+3
Reliability figures for single vs. multiple generator sets with the effect of having one, two or three redundant generators. Source: U.S. Army Engineering Study
1 98.2%
2 96.4% 99.97%
3 94.7% 99.94% 99.999%
4 93.0% 99.90% 99.999% 99.99999%
5 91.3% 99.87% 99.998% 99.99998%
6 89.7% 99.84% 99.998% 99.99997%

An Even More Reliable Future

As Shariar Zaimi, a national expert in digital paperless hospitals, states, “The hospital of the future is the ultimate mission-critical facility due to the amount of risk and the lives that depend on it.”

Consequently, assuring a hospital’s doctors and nurses access to data at all times will eventually increase the use of uninterruptible power systems within health-care facilities.

UPS are designed to provide ride-through for the time before the facility generators can start and the loads transfer. They come in two energy forms as there are two main types: battery inverter units providing up to 30 minutes of backup power and rotary- or flywheel-propelled units providing up to 30 seconds of backup power.

In the past, the battery units were used, but with the increased use of multiple generators, the rotary units are becoming more common because they require less maintenance. In any case, both systems have bypass/isolation maintenance features.