Commissioning on-site electrical systems
Commissioning is the systematic process by which a piece of equipment, system, or facility is tested to verify that it functions in accordance with the design intent and owner's operational requirements.
Commissioning is the systematic process by which a piece of equipment, system, or facility is tested to verify that it functions in accordance with the design intent and owner’s operational requirements.
In the past, the primary focus of commissioning has been on HVAC systems, but because of the need for increased electrical system reliability and complexity, owners are now starting to realize the importance and benefits of commissioning on-site electrical systems.
Some of the advantages include:
Electrical systems that meet the operational needs of the owner
Reduced downtime due to power outages caused by utility loss and/or failures within the electrical system
Coordinated electrical systems that balance protection with reliability and meet the recent code requirements and standards for critical facilities
Confidence that the electrical systems will operate correctly when required
Knowledge of and experience with the operation of the electrical equipment.
Many share a common perception that commissioning is the final stage of a project, performed when a facility is complete or nearly complete. This perception is not true. Commissioning is a process, and in order to maximize commissioning success, it must begin in the pre-design phase of a project and continue through construction until that final verification is executed.
ASHRAE Guideline 0-2005, “The Commissioning Process,” breaks down the process into the following phases:
Although this guideline was developed for the commissioning of HVAC systems, it is a very comprehensive description of the commissioning process, and the phases it outlines can be used as the basis for commissioning on-site electrical systems.
In the pre-design phase, the owner’s requirements and expectations for the facility are defined. It is important for those performing commissioning (commissioning agents, or CxA) to be involved in this phase so that they can understand the design objective and operational intent of the facility. In this phase, the commissioning scope and budget for the project are determined, and a preliminary commissioning plan is developed identifying the role of the commissioning agent.
The commissioning scope will be dictated by the type and size of the facility. Critical facilities like data centers, call centers, and hospitals have more complex electrical distribution, standby, or emergency generation and other backup systems than a standard office facility, and therefore will require a more comprehensive commissioning scope.
The following is a list of on-site electrical systems to consider when determining the commissioning scope for a project.
Normal power systems:
- Switchgear/switchboards (medium- and low-voltage)
- Main-tie and auto throw-over schemes
- Transient voltage surge suppressors
- Motor controllersBus duct and tap devices
- Fuse/circuit breakers
- Relay protection systems.
Emergency/standby power systems:
- Generator paralleling switchgear
- Automatic/static transfer switches
- Roll-up generator tap boxes
Lighting control systems
Emergency power off systems
Supervisory control and data acquisition systems
In the design phase, the owner’s requirements are translated into construction documents. The commissioning agent’s role in the design phase is to review and comment on the construction documents to verify that the goals and requirements set forth in the pre-design are being met.
In this phase, the commissioning procedures and acceptance criteria are outlined, and the contractor and manufacturer’s expectations are identified. Determining how a system will be constructed and commissioned/tested is important during this phase because it may have an impact on how the distribution system is designed.
For example, phased construction may require additional load bank connections and/or isolation breakers to allow for testing without affecting those portions of the facility already online. Systems with automated (often programmable logic) controls and interlocks should be given special attention to ensure that the design documents include sufficient operational details, such as timer presets/ranges and operational sequences for all operational modes.
The construction phase is when the systems are manufactured, inspected, tested, and installed in accordance with the construction documents. This phase can be broken down into three steps for commissioning:
Shop drawings submittal review
Finalizing the on-site commissioning plan.
A review of shop drawings submittals for all major electrical equipment provides the design team and the commissioning agent with the opportunity to confirm that the manufacturers are providing the equipment as specified and that the systems meet the design intent.
Factory testing provides the design team and commissioning agent with an opportunity to inspect and test the functional operation of the equipment before it arrives on-site. Once on-site, any equipment defects or problems can cause delays in the construction schedule. The standard manufacturer’s factory testing procedures typically do not fully test the function of the equipment, especially interfaces with building controls, mechanical, and fire/life safety systems. It is the responsibility of the commissioning agent to confirm that the factory testing procedures are adequate or develop additional testing procedures to ensure that the equipment operates as required to meet the design intent.
The commissioning agent also may be responsible for overseeing the factory testing, confirming that the results meet the acceptance criteria, and documenting any deficiencies.
In this phase, the on-site commissioning plan is finalized. All of the on-site commissioning test procedures and checklists are developed, and the commissioning schedule is coordinated with the construction schedule.
The coordination study and arc flash analysis should be reviewed, implemented, and verified during this phase. For safety, it is recommended that those performing the commissioning follow the industry standards regarding use of the proper personal protective equipment in accordance with the hazard risk category determined by the arc flash analysis.
In the operation phase, installed equipment and systems are tested to verify and ensure that they perform in accordance with the design intent and owner’s operational requirements. This phase also can be broken down into three steps for commissioning:
Individual equipment test
Discrete system test
Integrated system test.
The first step tests each piece of equipment separately to ensure that it functions correctly before testing the equipment as an electrical system. This stage generally starts with a visual and mechanical inspection of the equipment to make sure that it was installed properly and that no damage occurred during shipping or installation. During a visual inspection of a piece of equipment, the commissioning agent should:
Compare nameplate data with design drawings
Inspect the physical condition
Inspect anchorage, alignment, and grounding
Verify that the unit is clean
Verify breaker and timer settings.
After successful completion of the visual inspection, electrical and functionality tests are performed on the individual piece of equipment to verify operation.
Once the operation of each individual piece of equipment in the electrical system is confirmed, the equipment will be examined as a discrete system. For example, in the first step the power distribution unit, UPS, and switchgear are tested as individual components. In the second step they would be tested as a system to verify their compatibility under load and various operating conditions, such as on generator power, where harmonics can sometimes be an issue. Smaller facilities may not have any discrete systems.
The integrated system test is the final step in the verification process. This is where the entire facility as a whole is tested. During this integrated system test, the mechanical, control, and life safety systems should be incorporated to evaluate the true operation of the facility’s combined systems.
The most common electrical integrated system test is a simulated site-wide power outage, also known as the “black start” test. During this test, various partial systems failures can be initiated to stress the system and validate backup system performance.
It is vital that the O&M personnel be involved in all testing so that they can gain experience with the systems. It is also imperative that periodic testing and/or re-commissioning of an existing electrical system be performed to help ensure that it continues to operate per the design intent.
The following is an example of how these phases were implemented to successfully commission the electrical systems for a critical data center in North Carolina.
The owner’s pre-design requirement was for a data center facility that had a concurrently maintainable infrastructure with fault-tolerant critical systems. During this phase the owner also determined that all critical electrical systems would be factory tested and then validated through on-site testing. Because the commissioning agent was involved in the pre-design discussions, he was aware of the owner’s expectations.
The data center’s design was based on an isolated redundant-type system with a primary distribution system for each section of the data center, and a redundant distribution system to back up the primary systems. Many crucial decisions made during the design phase impacted the operation of the facility and commissioning. For example, the owner preferred to have two sources of power to this facility, but only one medium-voltage source was available in the area. The client decided to spend extra money in redundant backup systems. Having knowledge of key design decisions helped the commissioning agent to develop the validation testing procedures.
Commissioning factors also affected the design of the distribution system. The owner required that a portion of the data center be live, serving critical load before the entire facility could be completed. The redundant systems were installed first in a section of the existing building, and the existing service was used to temporarily serve the data center until the new service and UPS plant were constructed. Once the new primary systems were installed, they had to be tested and commissioned around a live data center. Developing the commissioning plan early in the project was vital in providing guidance on how to design and build the facility so that the later phases of construction could be tested and validated without affecting the portion that was already online.
During the construction phase, all parties reviewed equipment submittals, and all critical electrical equipment was factory witness tested. Due to the complexity of the electrical systems, the manufacturer developed a simulator for testing. Through the use of the simulator, various failure scenarios were tested and the control sequence was modified so that the system operated per the requirements of the owner. Commissioning procedures and checklists were written. In addition, the arc flash analysis and coordination study were reviewed, and all protection device trip settings were verified.
The operational phase was split into multiple sections because of the phased construction. In each phase of construction, the individual pieces of equipment were tested; the discrete systems required to bring that particular phase online were then tested. Once all phases of construction were completed, the entire facility was turned over for integrated systems testing, where a “black start” test was conducted with multiple failure scenarios (loss of generator, loss of primary backup system, UPS failure, etc.). Problems did occur in each phase of testing (defective breakers, interaction of systems during a failure, coordination issues with inrush, etc.). All of these problems were corrected and retested until the system operated per the design intent.
The month after the facility was fully commissioned, the owner started a worldwide migration to the new facility. Halfway through the migration, a snake crawled across two phases of a 25 kV utility service switch and caused a fault that interrupted service to the facility. During the utility power outage, one of the standby systems tripped and went offline. The electrical system reacted properly and transferred the critical load to the redundant standby power system. Because the electrical system was commissioned, it operated as designed and the owner never lost power to the critical load. The owner estimated that the cost to recover from losing power to the critical load during the migration would have been $5 million.
Two key tasks of commissioning electrical systems are:
Defining the value to the client
Becoming involved early in the design process.
The more complex and critical the electrical system becomes and the greater the exposure to risk involved with loss of power, the more crucial it is to commission the system and verify that it will operate as designed.
|Kutsmeda is engineering design principal/assistant electrical chief with Kling-Stubbins, Philadelphia. For more than 15 years, he has been responsible for the engineering, design, and commissioning of electrical power and lighting distribution systems. His project experience includes 7×24 mission critical facilities, highly specialized research and development buildings, and large-scale technology projects.|
References for inspecting and testing electrical distribution equipment are:
• ANSI C37.50—Low-Voltage AC Power Circuit Breakers Used in Enclosures—Test Procedures
• IEEE 450—Recommended Practice for Maintenance, Testing and Replacement of Vented Lead Acid Batteries for Stationary Applications
• IEEE 1188—Recommended Practice for Maintenance, Testing and Replacement of Valve Regulated Lead Acid Batteries for Stationary Applications
• NEMA AB4—Guidelines for Inspection and Preventive Maintenance of Molded Case Circuit Breakers Used in Commercial and Industrial Applications
• NETA ATS—Acceptance Testing Specifications for Electrical Power Distribution Equipment and Systems
• NFPA 70B—Recommended Practice for Electrical Equipment Maintenance
• NFPA 70C—National Electrical Code
• NFPA 70E—Standard for Electrical Safety in the Workplace
• NFPA 101—Life Safety Code
• NFPA 110—Standard for Emergency and Standby Power Systems
• NFPA 111—Standard for Stored Energy Emergency and Standby Power Systems