Commissioning mission critical standby power systems

Commissioning ensures that all components of the mission critical power system function according to design specifications and the owners’ expectations.


A permanently installed backup power system is defined as critical when it is used to provide electrical power when normal electrical service is interrupted. The owner of these systems needs to ensure that their critical life safety systems—key processes, vital data, or essential goods—are protected and continue to operate when normal power is interrupted. Mission critical standby power (MCSP) systems are designed to protect these critical assets.

The National Fire Protection Association (NFPA), National Electrical Code (NEC) categorizes backup power systems into categories:

  • Article 700 Emergency Power Systems: “These systems are intended to automatically supply illumination, power, or both, to designated areas and equipment in the event of failure of the normal supply or in the event of accident to elements of a system intended to supply, distribute, and control power and illumination essential for safety to human life.” These systems are required to be energized in less than 10 seconds after normal power is lost. Emergency power systems support life safety systems such as egress and exit lighting.
  • Article 701 Legally Required Standby Systems: “Circuits and equipment intended to supply, distribute, and control electricity to required facilities for illumination or power, or both, when the normal electrical supply or systems is interrupted.” These systems support the life safety system and include fire pumps, facility smoke evacuation fans, and control of health hazards.
  • Article 702 Optional Standby Systems: “Those systems intended to supply power to public or private facilities or property where life safety does not depend on the performance of the system. Optional standby systems are intended to supply on-site generated power to selected loads either automatically or manually.” Systems in this category include data centers.
  • Article 708 Critical Operations Power Systems (COPS): “Power systems for facilities or portions of facilities that require continuous operation for the reasons of public safety, emergency management, national security, or business continuity.” Systems covered by this article consist of those that are permanently installed in their entirety, including prime movers, those that are arranged for a connection to a premises wiring system for a portable alternate power supply, and those required to support long-term requirements. Equipment and systems in this category are often refrigerators and freezers required to preserve medications or food.

Commissioning is the process of providing baseline tests that verify the operational sequences of electrical equipment and electrical systems. It is a documented and orderly testing of all aspects of the equipment and systems to the owner’s specifications. Sebesta Blomberg performs MCSP commissioning as a collaborative process. Commissioning is not the start-up of the MCSP.

After the contractor has installed the equipment and ensured it is operating, commissioning can begin. It is important to have the owner and contractor on board with the commissioning process. Before the process begins, we hold a kickoff meeting with the owner and contractors. At this meeting, we emphasize that the commissioning process is essential to ensuring equipment and system reliability. We also emphasize the importance of getting the operations and maintenance staff involved in the commissioning process to train and familiarize them with the equipment and operation of the system.

MCSP systems consist of myriad designs required to protect the owner’s critical assets. This article cannot address every MCSP design permutation. Instead, it will address a general overview of MCSP commissioning. The major components of an MCSP system include the engine, generator, engine fuel supply system, automatic transfer switches (ATSs), and UPSs. Each of these components is commissioned individually before they are commissioned as an integrated system. This approach ensures that each component functions successfully before the entire MCSP system is commissioned in a final loss-of-power test.

Figure 1: Verifying the electrical grounding system integrity is part of the initial safety inspection prior to testing. Courtesy: Hartsfield-Jackson Atlanta International AirportMCSP commissioning begins by ensuring that the installation is safe and the equipment is installed as specified. We verify that all electrical safety equipment is in place, that circuit breakers and relay settings meet the coordination study values, and verify the electrical grounding system integrity (Figure 1). We prove that the engine, generator, and fuel system pre-alarms and alarm systems function at the control panels, remote annunciator panels, and at the BAS. We confirm all engine fluid levels are adequate, that there are no fluid leaks in the fuel, oil, and coolant systems, and that flexible connectors are installed between the engine, fuel, and radiator systems. We complete this verification before starting any equipment.

Fuel system testing

MCSP engine fuel systems are vital to engine operations. The engine fuel systems can be external or internal to the engine/generators. In large MCSP systems involving large or multiple generators, the fuel systems are usually external, providing fuel to the engine day tanks. On smaller MCSP operations, the generator fuel tank is often part of the engine/generator skid package. In this case, the tank is located under the engine/generator and fuel is pumped from this tank directly to the engine.

Figure 2: The integrity of the fuel supply system is critical to reliable engine/generator operation, which includes ensuring that generator fuel hoses are insulated from vibration. Courtesy: Hartsfield-Jackson Atlanta International AirportThe reliability of the external fuel systems is rigorously tested during commissioning. This includes inspecting the system piping and tanks for leaks, and individually checking all system pre-alarms and alarms, and that they indicate at the applicable control panels and the BAS. The operation of the fuel transfer pump and the day tank fill and shutoff controls are also confirmed to ensure that they are operating to specification. Confirmation of the fuel supply system integrity is fundamental to reliable engine generator operations (Figure 2).

Load testing

Generator load testing is the enjoyable part of the commissioning process (Figure 3). First, the generator/engine is started to ensure that the engine starts and runs, air intake and exhaust louvers open, and that there are no engine fluid or exhaust system leaks.

Figure 3: During the generator load test, readings are taken to verify that the engine is operating within specified operating limits. Courtesy: Hartsfield-Jackson Atlanta International AirportWe perform two engine generator load tests: one for 2 hours and one for 4 to 8 hours. The 2-hour load test is the shakedown cruise. This test is started with a cold engine, which means that it has not been run for 24 hours prior to the start of the test. The engine is started by removing the normal power source to the ATS. The generator is immediately loaded to 100% capacity using external load banks. These load banks are connected to the ATS in smaller systems, or the generator for large systems with multiple ATSs.

The engine/generator is timed from the start signal initiation to when the generator picks up the full load. For life safety systems, the interval from initiation to the system providing full load must be less than 10 seconds. Pertinent engine and generator readings are taken at short intervals during the engine test. The 2-hour test provides the opportunity to take the generator for a test drive to ensure that all functions meet standards.

The 4- to 8-hour test is the long voyage. We start the engine and load the generator in increments and observe all engine and generator functions during this test. As with the 2-hour test, pertinent engine and generator readings are taken at short intervals at first. As the testing proceeds, the reading intervals are lengthened to 15 minutes. Engine readings are taken to verify that the engine is operating within specified operating limits. Generator voltage and frequency readings are taken; generator regulation is calculated from the incremental load readings. The generator harmonic distortion is measured with a harmonic distortion meter. Phase rotation is verified during this test as well. At the end of this engine generator load test, the load is removed. Toward the end of the engine cool down cycle, the emergency stop buttons are exercised to ensure they shut down the engine. After the test, the field-landed feeder terminations are re-torqued, in case the terminations loosened during testing.

ATS testing

An ATS actuation initiates the MCSP system start. Modern ATSs are microprocessor controlled, enabling them to perform many functions. Closed-transition ATSs are used in most MCSP applications. Time delays are also common in ATSs. These time delays can be programmed to control switching, delays to switching, and engine cool down times. These programmed functions require testing to ensure they meet the owner’s specifications.

ATSs are tested in a documented logical sequence to verify their operation. Insulation resistance testing is performed to ensure the integrity of the insulation after it has been shipped from the factory and set in place. The normal, emergency, and bypass switch contacts are tested with a digital low-resistance ohmmeter to ensure they are capable of conducting high currents reliably. This testing is performed by an electrical test firm. However, we coordinate and witness these tests and commissioning activities.

The ATS transfer function from normal to emergency is tested manually while the switch is still de-energized. This test is performed to ensure that the switch operates with smooth transitions between functions. The mechanical interlocking mechanisms are tested to prove that the ATS cannot have simultaneous closures between the normal and emergency sources. The closed transition portion is tested at a later time. When an ATS is equipped with bypass switches, these switch operations are also tested manually to ensure they operate smoothly.

Figure 4: The MCSP system at the Atlanta International Airport was recently commissioned. Courtesy: Hartsfield-Jackson Atlanta International AirportWe test the ATS alarms and function indicators to verify they properly indicate at the ATS local panel and all remote annunciation panels. On a recent project at the Atlanta Airport, we tested the monitoring system at the ATS only, since the BAS was not yet installed (Figure 4). This interface will be tested later. This test ensures that the “Normal Power,” “Emergency Power Available,” the “ATS in Normal,” and “ATS in Emergency” indicators function. Properly functioning indicators let operations and maintenance personnel know that the ATS in this MCSP system is operating correctly during both normal and emergency situations.

The ATS operational transfer test becomes a systems integration test by incorporating the engine/generator into the commissioning process. At this point, the applicable time delays have been programmed into the ATS and are confirmed during this test. I prefer to initiate this test by interrupting the normal power source. However, this test can also be initiated by using the ATS “Test Switch.” The ATS operation from the loss of normal power to the generator picking up standby power is timed with a stopwatch. In the Atlanta Airport project, the Life Safety (S) ATSs switched to emergency in less than 10 seconds. The Emergency (E) ATS switches were programmed with a delay and transferred in less than 20 seconds. The Legally Required (R) ATSs transferred in about 30 seconds.

In this testing, normal power was restored to the ATS. The ATS switching from emergency generator power to normal power was again timed. The return-to-normal power is not instantaneous. The normal power must be stable for a 10- to 12-minute interval before the ATS initiates the “return-to-normal” signal. In an open-transition ATS, this switching causes a momentary loss of load power. With a closed transition ATS, we monitor the generator-to-normal phase-angle readout to ensure that the ATS transfers within phase-angle specifications.

Other ATS function tests completed during commissioning include engine cool down, engine shutoff, and transfer from emergency to normal power when the emergency source fails.

UPS testing

A UPS is often used in MCSP systems such as data centers where computer power cannot be interrupted. UPS commissioning is usually performed in cooperation with the UPS and battery systems manufacturers’ representatives. All pre-alarm and alarm conditions and the specified communication to all applicable alarm panels and the BAS are tested. All UPS switching operations are confirmed, including the static switch, normal-to-battery operation, and emergency-to-normal operations. The final UPS test is to remove all normal and standby power, then load-test the UPS to 100% load with a load bank terminated at the UPS output. This load test is recorded and timed to confirm that the UPS meets the owner’s requirements.

Final testing

The final commissioning test is an integrated system or a loss-of-power test. All MCSP components are tested during the loss-of-power test. In the most comprehensive test, we load the MCSP system to 100% using load banks. We initiate this test by having the local power company interrupt normal power to the site. We test the generator start-up, ATS, and UPS operations as a system. This is what would happen during a normal power outage. We interrupt the engine/generator to ensure that the secondary backup equipment functions, i.e., the data center UPS systems. When all nuances of the MCSP have been tested on generator power, normal power is returned to the site.

With the resumption of normal power, the loss-of-power test is still not completed. Now, we test to ensure that the MCSP systems components transfer the load properly. We ensure that the ATSs switched back, the UPSs maintained power to the systems, the engine generators go into cool down and shut off properly, and that the fuel day tanks are at the proper level. In short, we ensure that the MCSP system is prepared to pick up another real-world power outage.

If the equipment commissioning has been properly performed, the loss-of-power test is enjoyable. This test also involves management, operations, and maintenance personnel. They get to experience the MCSP system functioning as it is designed and specified. When executed correctly, the loss-of-power test is a good training experience and a confidence builder. It provides the reassurance in knowing how the MCSP functions and what it can do. When that happens, facility managers and facility engineers sleep better at night.

Belerman is a facility engineer and senior project manager with Sebesta Blomberg. He is an electrical engineer with more than 30 years of experience in facility operations, maintenance, and design, and a member of IFMA.

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