Considerations for electrical testing and commissioning

Apesar de mais aculturada em relação aos processos de comissionamento em suas instalações (me refiro em relação as demais modalidades de engenharia), a modalidade de engenharia elétrica ainda requer um enorme cuidado ao se planejar previamente a atividade de comissionamento.

Questões como conceitos e qualidade dos projetos e detalhamentos, modos de operação imaginados / considerados para se atender ao tipo de uso e ocupação de empreendimentos, integrações e interfaces, assim como código e leis federais / regionais devem ser observados, assegurando-se com que a customização de um processo de comissionamento atinja plenamente aos requisitos técnicos e legais.

O artigo abaixo demonstra de forma bastante didática os diferentes tipos de comissionamento e suas características, sendo bastante recomendada a sua leitura.

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Fonte (Source): Consulting – Specifying Engineer

Por (By): Brian Rener, PE, LEED AP, SmithGroup, Chicago (Brian Rener is a principal and electrical discipline leader at SmithGroup. He is a member of the Consulting-Specifying Engineer editorial advisory board)

Acesse aqui a matéria em seu site de origem / Click here to read this article directly from its source website.

The need for testing and commissioning electrical equipment and systems varies by project, client, system, and building codes.

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Figure 3: Parallelling generators on switchgear requires careful testing and simulation of possible operating scenarios to confirm control sequences. Courtesy: SmithGroup

Learning objectives

  • Understand the differences between electrical testing and commissioning.
  • Know about the code requirements for testing and commissioning.
  • Learn why testing and commissioning enhances building performance,and understand the benefits of third-party involvement.

Electrical testing has become a key component in all modern electrical equipment and installations. It has expanded beyond the key foundations for equipment safety to include performance, operations, and energy requirements for electrical facilities.

Types of testing

Manufacturer factory tests: Electrical equipment manufacturers test their equipment in the factory according to established standards, frequently handled by organizations like UL or National Electrical Manufacturers Association.

However, consulting engineers may wish to specify additional “factory witness testing.” This additional witness testing permits the consulting engineer to perform preinstallation inspection of the equipment and request simulated functional testing performed by the manufacturer. Often, witness testing is only required for large or complicated electrical equipment and for mission critical projects. Witness inspections can include confirmation of equipment dimensions and weights, proper nameplates and labels, locations and sizes of conduit openings, communication wiring points, and cable lug configurations. Functional witness testing may include simulated sequences of operations, such as start-ups and load transfers, fault conditions, load loss, and alarms and display information.

Common challenges for the busy engineer and budget-constrained owner is the time and cost for the travel to the factory—and deciding who from the team should attend. Depending on the awarded manufacturer, the factory may even be located outside of the country where the engineer or project resides. In these cases, the option of “virtual factory witness testing” is a possibility using video conferencing. This allows engineers, owners, and contractors to participate remotely in witness testing and preinstallation inspections.

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Manufacturer field tests: More commonly specified than factory witness tests are requirements for the electrical equipment manufacturer to require factory-trained technicians to perform additional testing and adjustments in the field during or after installation. Often, larger and/or complex electrical equipment is shipped in parts, and having a factory-authorized technician onsite to test equipment after the contractor has installed it can be helpful.

The most common tests are functional tests and demonstrations for the owner and staff. Additional work may include relay- and protective-device settings.

Contractor field tests: Field testing by the installing electrical contractor is a common specification requirement. Some of the more common contractor field tests include medium-voltage cable testing, load balancing, phase rotation, and infrared (IR) scanning of terminations and connections.

Medium-voltage cable testing is accomplished under IEEE 400-2012: IEEE Guide for Field Testing and Evaluation of the Insulation of Shielded Power Cable Systems Rated 5 kV and Above, which has several options for testing cables in the field. The point of this testing is to check the integrity of cables (usually medium-voltage) immediately after pulling but before energizing, or as a condition assessment after years of operation. Years ago, direct current (dc) high-voltage (also called hi-pot) was the common test for medium-voltage cables. The simplest way to explain hi-pot testing is the application of a very high voltage to cables to see if the insulation breaks down or remains intact. It is basically a pass-or-break test. Concerns over damage to cables from hi-pot testing—especially on existing cables—has led to the preferred use of partial-discharge (PD) testing. There are several PD testing methods depending on whether the cable is live. Commonly in pre-energized new installs, PD involves the use of very low-frequency voltage, which is raised to a minimal level at which partial discharges would appear in insulation weakness, and sensors measure where this takes place. PD testing also has the benefit of being used on new, old, and live cables.

Load balancing is another electrical test that is specified by consulting engineers. During design, electrical engineers will design loads across a 3-phase system, typically on panelboard schedules, to be relatively balanced among each phase. NFPA 70: National Electrical Code (NEC), Article 210.11 (B), discusses unbalanced loading on panels, and Article 220.61 discusses unbalanced loading on neutral conductors. Overheating, power-quality issues, and energy loss can occur with unbalanced loads. During construction, however, loads often change from what is in original design documents, and it is good practice to specify final load balance testing.

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IR scanning has become a very common requirement over the years. It is used in both new installation start-ups and ongoing maintenance. IR thermography images show excess heat is present in electrical systems due to unbalanced loads, loose or defective electrical connections, harmonics, overloads, and more. IR testing is an important part of pre-occupancy testing, when loads are being energized but the facility is not fully operational and can be worked on.

However, there is an important need to continue IR testing after occupancy, as prescribed in NFPA 70B. On complex primary electrical equipment, it is now common to require IR “ports” or windows in the gear to allow for IR scanning while the gear is operational and without removing covers (see Figure 4).

Soils testing: Often overlooked by electrical engineers is the option to specify soils testing for conductivity and thermal resistivity. An effective grounding system is one of the more critical factors for a trouble-free and safe electrical system.

Soils vary greatly by region. Soil conditions also vary over seasonal time frames, rain, drought, and the application of landscaping materials and chemicals. NEC Article 250 discusses the need to achieve a maximum earth ground of 25 ohms. However, the origin of this number is unknown. Currently, both IEEE and NFPA recommend an earth ground resistance of 5 ohms or less.

Power cables generate heat, and heat affects resistivity and current-carrying capacity. The NEC has numerous tables adjusting capacity depending on the method of running those conductors in conduit, including underground. When placing power cables underground, it’s important to perform heating calculations; and the thermal characteristics of the soil should be tested and known. The best time to require electrical conductivity and thermal characteristic tests is during geotechnical testing. Electrical engineers should coordinate with their civil or structural engineering team members to include these electrical tests.

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Thirdparty field testing

For some types of critical facilities, such as health care, data centers, laboratories, and government facilities, it is important to specify additional electrical testing by independent third-party contractors. The primary recommended standard for independent testing of the installation of electrical systems is ANSI/NETA ATS-2017: Standard for Acceptance Testing Specifications for Electrical Power Equipment and Systems.

The ANSI/NETA ATS standard includes procedures for testing many parts of the electrical system including:

  • Switchgear and switchboards.
  • Transformers: dry and liquid-filled.
  • Cables: low- and medium-voltage.
  • Circuit breakers, relays, and switches of various types.
  • Instrumentation and metering devices.
  • Motors including drives and controllers.
  • Emergency systems including generators, fuel systems, alarms, and automatic transfer switches (also see NFPA 110: Standard for Emergency and Standby Power Systems).

While it is possible that some, or all, of these tests could be performed by the installing contractor, there is a benefit to the consulting engineer and the owner to use a third-party testing agency who can independently assess that electrical equipment complies with the engineer’s design and specification documents and has been installed to meet all codes. It is beneficial for the engineer to specify that this third-party testing firm is an accredited member with documented and verified experience and abilities to objectively validate the electrical system.

A cost-benefit comparison is usually warranted on how much of the electrical system should be specified to be tested to ANSI/NETA ATS. The consulting engineer may wish to confine the testing to certain parts of the system, such as emergency or standby systems, or may wish to limit the testing to certain voltage levels or amperage ratings. A discussion with the building owner can also help in defining the limits of NETA testing.

Commissioning

Beyond testing individual electrical equipment components, there is a need to verify that installed electrical systems match design documents, construction submittals, and owner’s project requirements (OPR), and to document functional performance testing. Electrical commissioning may be optional or required depending on the code or certifications required by the project. The commissioning agent (CxA) or commissioning provider (CxP) is a critical part of the design and construction team and should be engaged early in the design and construction process.

Some of the codes or standards that provide requirements or recommendations for commissioning include:

U.S. Green Building Council LEED-rated facilities require fundamental commissioning. For electrical systems, this includes lighting, controls, daylight-harvesting controls, and any sustainable green power systems, like solar photovoltaic systems. Fundamental commissioning activities performed by the CxA include:

  • Participate and review in development of OPR and basis of design (BOD).
  • Design review prior to 50% construction documents.
  • Confirm incorporation of commissioning requirements into construction documents.
  • Develop or approve construction checklists.
  • Develop or approve system test procedures.
  • Witness at least a portion of the electrical system’s functional testing.
  • Review an issue log throughout the commissioning process.
  • Report findings directly to the owner throughout the process.
  • Develop or approve the summary commissioning report.

LEED-rated facilities also offer additional credits for Enhanced Commissioning, which can provide additional points. It should be noted that enhanced commissioning is done by a third party independent of the design and construction teams. The third-party professional will:

  • Review contractor submittals applicable to systems being commissioned.
  • Develop or approve system’s manual updates and delivery.
  • Verify the delivery and effectiveness of operator and occupant training.
  • Perform seasonal testing.
  • Develop or approve an ongoing commissioning plan.
  • Develop or approve a monitoring-based commissioning plan.
  • Review building operation within 10 months after substantial completion.

Both the IECC and ASHRAE 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings mandate the commissioning of lighting systems. ASHRAE 90.1 now requires lighting and controls functional testing, design documentation, submittals, operation manuals, complete narrative, and daylighting documentation. The functional testing can’t be performed by the design or construction team members.

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Mission critical facilities

Hospitals are key mission critical facilities where commissioning is required. ASHE publishes the Health Facility Commissioning Program, an extensive document that includes recommendations for the CxA to be involved in all phases of the facility design including schematic, design development, and construction documents. This is important, as CxAs should  be involved in the early development of the OPR, specification development, and reviews of design documents against owner’s requirements.

Data centers are another type of mission critical facility with some of the more rigorous requirements for commissioning electrical power systems. While some data centers will also pursue LEED certification, the commissioning process is much more extensive and includes many of the testing requirements identified here. The data center commissioning process is commonly expressed in levels.

Level 1Factory witness testing: The consulting engineer should outline the testing protocol in bid specifications. The engineer should be present, along with the possible installing contractor, CxA, or owner’s representative, to witness that the equipment performs according to the owner/operator’s standards before the equipment is approved and shipped to the site.

Level 2: Site-acceptance inspectionWhen the equipment arrives onsite, it is inspected to confirm it meets specified requirements. Although Level 1 can minimize issues found in Level 2, changes often occur after factory testing and shipping have caused damage or because shipped items have missing parts.

Level 3: Pre-functional testing (PFT)This level involves the inspection of the initial install equipment to verify that all equipment is installed properly and that installation meets specified standards and requirements. Equipment also is started for the first time to check basic functionality.

Level 4Functional performance testingAfter basic start-up, the CxA will review functional performance testing. This includes the review of any protective-device settings, automatic controls and functions, remote communications or controls, and more.

Level 5: Integrated systems testing (IST)This is often referred to as the “pull-the-plug” tests. The utility power source(s) can be shut off, and the entire system (multiple paths, generators, uninterruptible power supplies)  is observed to confirm it functions as intended under loss of power.

Post-occupancy testing 

For a facility to effectively and reliably operate initially and over its lifespan, it is important to consider post-occupancy commissioning and testing.

A standard provision of the enhanced commissioning under the LEED rating system is for the CxA to return to the facility after 10 months of operation. This allows for systems, particularly HVAC, to have operated throughout seasonal variations and to allow for owner-operator adjustments as needed. The CxA will verify that systems are still operating to the original BOD and owner’s requirements.

The most common post-occupancy testing for electrical systems is on emergency generator systems. It is important to understand the code differences between emergency classified systems (fire pumps, egress lighting), legally required standby generator loads, and optional standby.

Beyond NETA/NFPA start-up acceptance, emergency generators require weekly inspection and monthly testing. The monthly testing must be done for 30 minutes under partial load (30%) or to achieved rated minimum exhaust-gas temperatures. It can be difficult in some circumstances to provide 30% of the generator’s rated load every month. In this case, NFPA 110 allows for yearly testing at higher loads.

The question then becomes: Do you test the generator under actual loads monthly or yearly or provide a generator load bank to simulate facility loads? Often, a good solution is to provide a load-bank hookup box so that a portable load bank can be brought to the site as needed for testing (see Figure 5).

A companion standard for post-occupancy testing is called ANSI NETA MTS 2015: Standard for Maintenance Testing Specifications for Electrical Power Equipment and Systems. According to NETA, this document “was developed for use by those responsible for the continued operation of existing electrical systems and equipment to guide them in specifying and performing the necessary tests to ensure that these systems and apparatus perform satisfactorily, minimizing downtime and maximizing life expectancy.”

ANSI NETA MTS 2015 is an excellent resource for ongoing testing as part of a preventive maintenance program in a facility. It also provides electrical engineers with an excellent resource to specify electrical tests on equipment that may not have been maintained prior to renovations or expansions of existing facilities. For example, 15-year-old switchgear is supposed to have new breakers installed and additional loads placed on it; the testing guidelines are provided. The consulting engineer can request the owner hire a contractor to perform tests according to NETA MTS to verify the condition of the switchgear prior to new work.

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Energy performance

With the proliferation of the internet of things (IoT) and standardized building automation protocols, such as BACnet and Modbus, it is easier to integrate electrical power monitoring systems (EPMS) into a facility wide maintenance and test system. Common power-use meters can help track and record loading and energy use, alerting owners to potential capacity issues or even low-load inefficiencies. Energy-performance verification is an important part of post-occupancy and may even be required in certain projects—such as data centers, where it is used to track power-usage effectiveness (PUE)—and for LEED or ASHRAE compliance where fuel sources and end uses are metered independently.

Information also is critical for future renovations and expansions, as consulting engineers can determine the ability to add new loads to existing systems. More sophisticated power-quality monitoring can help owners avoid damage to equipment or to identify sources of poor power quality either inside the facility or from the utility. Common alarms from various systems can be collected and presented for instant remote decision-making and action plans.

Electrical monitoring systems are making even greater strides with leading-edge systems that are “aware” of occupant use and traffic, adjusting light levels to constant illumination levels and energy use. This constant evaluation or “testing” of space use blurs the line between the roles of electrical engineers and interior architects and planners, requiring an integrated team approach to improving the performance of both electrical systems and the spaces we work and live in.

Today we have numerous requirements and optional recommended practices for testing and commissioning electrical systems. The consulting engineer should consider the project type, client, building codes, and desired outcomes when specifying electrical testing.

Sobre Alexandre Fontes

Alexandre Fontes é formado em Engenharia Mecânica e Engenharia de Produção pela Faculdade de Engenharia Industrial FEI, além de pós-graduado em Refrigeração & Ar Condicionado pela mesma entidade. Desde 1987, atua na implantação, na gestão e na auditoria técnica de contratos e processos de manutenção. É professor da cadeira "Comissionamento, Medição & Verificação" no MBA - Construções Sustentáveis (UNICID / INBEC), professor na cadeira "Gestão da Operação & Manutenção" pela FDTE (USP) / CORENET e professor da cadeira "Operação & Manutenção Predial" no curso de Pós Graduação em Avaliação e Perícias de Engenharia pelo IBAPE / MACKENZIE. Desde 2001, atua como consultor em engenharia de operação e manutenção.
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