An emergency automatic power transfer system is designed to provide backup power when the normal electrical utility source has been interrupted. Electrical codes require an emergency power source to be designed and installed as an independent system. Typically, a diesel fuel-powered generator is the backup power source.
During an electric utility outage, the power distribution system is required to start the generator and transfer critical loads. When the normal utility source is restored and after a stabilization period, the system reconnects the loads to the primary electric utility source.
Some systems have multiple levels of redundancy, including an automatic control power transfer scheme. A main-tie-main generator backup power system configuration is most common.
Hospitals, correctional facilities, water treatment plants, data centers, and airports are some good examples of facilities requiring critical power automatic transfer systems.
Electrical codes require periodic testing of these systems for reliability and to uncover any deficiencies in a controlled condition, where, if the emergency supply fails during testing, the loads can be returned to the electric utility source and corrective action taken before an actual outage occurs.
What can go wrong?
A new multi-story 400-bed hospital in a major city lost electric utility power. The hospital building is served by two electric utility feeders from different substations. A 27/47 relay in the hospital switchboard responded to the outage by transferring critical loads from one electric utility feed to another. The remaining utility feeder was heavily loaded, and the electric utility decided to reduce some of its load on this feeder to prevent a total blackout. However, this resulted in an outage of the remaining electric utility feed.
The hospital’s emergency automatic power transfer system responded by starting its emergency generators. Due to an error in the transfer system’s programmable logic controller (PLC), the system went into auto-fail mode, and the hospital was plunged into darkness. Fortunately, patient equipment with battery UPS systems allowed some critical life-sustaining equipment to continue to operate.
People were trapped in elevators; one of those trapped was a critical care patient en route from the emergency room to an operating room where they required immediate emergency surgery. Suction pumps, oxygen, medication, food delivery, HVAC, and fire suppression equipment were all compromised without power. The pneumatic tube system shut down, and a tube containing a blood sample taken from an infant was lost somewhere between the emergency room and the lab. Finding the tube was a priority, but there was no power to operate the laboratory equipment.
The hospital maintenance staff were overwhelmed. Eight automatic transfer switchboards on three levels were flashing “auto fail.” All had been tested per the manufacturers’ instructions as required within the last 30 days and seemed to be working properly. The electrician confirmed the generator was running and pressed the close button for the generator breaker, but nothing happened. An attempt was made to close the generator breaker at all eight boards, but none would close.
The fire department arrived and was confronted by the fact that the elevators were inoperable. A helicopter landed on the roof to move the critical patients to other facilities. The problem was how to get them to the roof.
Less than half a mile away, a high-rise court and correctional facility also lost power because of the same storm. Its backup generator started, and the load transferred. Five minutes later, the generator stopped, and the facility was dark. As required, the system has been tested monthly. The loss of power impacted electronic security and safety systems. Elevators were also inoperable.
The correctional facility's electrician manually closed the electric utility breaker, realizing the utility source was not available, and proceeded to restart the generator. He then attempted to manually close the generator breaker. It closed and immediately reopened. Because the electric utility breaker was closed, the PLC was tripping the generator breaker to prevent paralleling sources.
Follow-up investigations revealed that maintenance personnel (e.g., electricians) at both facilities were not properly trained. If the electricians had been properly trained, the power could have been restored to critical loads at both facilities.
Training needs
Power distribution and control system technology has evolved rapidly in recent years. However, the training provided to electrical maintenance personnel has proven to be inadequate. Many of these workers aren’t prepared to effectively and efficiently operate and troubleshoot power distribution transfer systems.
Today’s electricians must understand and be trained on a variety of topics and technologies such as thermal imaging, zone selective interlocking schemes, power quality and harmonics, trip curves, line isolation monitors, trip unit elements, and ground fault. In addition, all hospital personnel who operate and maintain facility electrical systems must be familiar with the following standards as they apply to health care facilities:
- NFPA 99, Healthcare Facilities Code;
- NFPA 70, National Electrical Code (NEC);
- NFPA 70E, Standard for Electrical Safety in the Workplace;
- and NFPA 70B, Standard for Electrical Equipment Maintenance.
Electrical codes require equipment owners and their employees to perform preventive maintenance, arc flash studies, and equipment-specific training to identify deficiencies under controlled conditions to assure system reliability. Failure to fully comprehend today’s technology and its practical applications can result in catastrophic equipment failures, leading to disaster.
