By Jack Smith
With the Fluke 1587 Insulation Multimeter you can test insulation integrity by inducing current on a circuit under test, measuring the resulting voltage, and calculating the circuit resistance.
You frequently hear the word "commissioning" at architectural, construction, and certain types of engineering and consulting firms. It’s a big word with big implications and big expectations and big consequences if not done correctly.
Many times, commissioning is associated with buildings, especially new construction. Within this context, commissioning requires thorough planning, accurate documentation, scheduling, testing and more testing, correcting, adjusting, verifying, and training. The goal is to ensure that a facility operates as designed, and as a fully functioning system.
To some, commissioning can apply to a project, system, or an individual piece of equipment. Energy audits, acceptance testing, harmonics analyses, power quality audits, and system inspections frequently get lumped into the category of commissioning.
Electrical system commissioning
But the focus of this column isn’t as large in scale as new-construction building commissioning. While buildings and facilities require electrical power and other utilities to support their subsystems and function properly, this column will focus on electrical systems - not so much a complete explanation of electrical system commissioning, but what we can learn from it.
The primary reason for electrical system commissioning is to verify that the electrical system was properly designed, ensure the installation matches the design, identify and correct problems, and provide baseline parameters for comparison during tests conducted in the future. In addition to operating as designed, a properly commissioned electrical system should be reliable and efficient.
In addition to being a good idea, some codes and standards require some level of electrical testing and/or commissioning. In the US, NFPA 70®: National Electrical Code requires certain tests such as equipment ground fault protection, service grounding electrode resistance, and fixture wiring short-circuit and ground tests. Some states or local electrical inspectors may require additional tests. In Canada, the installation and maintenance of electrical equipment is regulated by the Canadian Electrical Code, also known as CE or CSA22.1. The Canadian Standards Association (CSA) publishes the CSA22.1 standard.
NFPA 70B: Recommended Practice for Electrical Equipment Maintenance recognizes the need for electrical equipment and system commissioning. It also provides a definition as well as establishes a strong connection between commissioning and maintenance. According to NFPA 70B 31.1.1, “Commissioning, also referred to as acceptance testing, integrated system testing, operational tune-up, and start-up testing, is the process by which baseline test results verify the proper operation and sequence of operation of electrical equipment, in addition to developing baseline criteria by which future trend analysis can help to identify equipment deterioration.”
So what can we learn from commissioning?
If your facility has been involved with commissioning efforts in one form or another, no doubt this process established a baseline. For example, if insulation tests were performed during commissioning or electrical acceptance testing, the results determined the insulation integrity of the conductors in the electrical distribution system. By properly documenting the insulation test results, facility personnel have records that reveal the insulation parameters when the system was new, or at least when the baseline was established.
Insulation deteriorates at a rate determined by time and temperature factors. High leakage current indicates dielectric breakdown, which is a precursor to insulation failure. Periodically repeating insulation tests allows facility maintenance personnel to track insulation deterioration rate and correct the situation before readings fall to unacceptable levels.
An insulation resistance tester is used to test insulation integrity by inducing current in a circuit under test, measuring the resulting voltage, and calculating the circuit resistance. Insulation testing can be performed on switchgear, motors, generators, and cables. Each conductor is tested with respect to ground and to each adjacent conductor. Typical test voltages are 250, 500, and 1,000 - and can be either ac or dc. However, tests should be conducted beginning with the lowest voltage, and then working up to the higher voltages. The circuit under test must be disconnected from its power source.
The Fluke 1587/Fluke 1577 Insulation Multimeters combine a digital insulation tester with a full-featured, True RMS digital multimeter in a single, compact, handheld unit. The Fluke 1555/Fluke 1550C Insulation Resistance Testers allow testing at voltages up to 10 kV.
Discovering issues before they become problems
Manufacturers of circuit protection devices such as circuit breakers and ground fault relays typically ship their products with current pickup and time delays set at their minimum values. Although commissioning usually does (or should) include a protective device coordination study, sometimes the electrical designer or contractor fails to communicate these settings as determined by the study. Also, sometimes these parameters are provided, but no one bothered to program these settings into the devices.
Commissioning should include a protective device coordination study as well as verification that protective devices have been set properly. Inspections during routine maintenance should confirm these devices match these documented baseline settings. Delays or trip levels should never be adjusted to prevent nuisance tripping.
Electrical system commissioning verifies the design, installation, and operation of an electrical distribution system and the components therein. Most failures associated with new construction (or system refurbish/overhaul) include defective components from the manufacturer, improper system design, improper installation, and inadequate testing before startup. If done properly, commissioning can catch these issues before they become problems that affect uptime.
Most failures that occur after the system is operational can be attributed to inadequate operating procedures and improper or insufficient maintenance. Following operation and maintenance best practices can help minimize or prevent these types of failures.
Whether it’s a new facility with a new electrical system or an existing system, the lessons learned from commissioning can help keep it operating efficiently and safely.
Until next time, keep standing on “Solid Ground.”
National Electrical Code: www.necplus.org
Canadian Electrical Code: www.csa.ca
NFPA 70B: Recommended Practice for Electrical Equipment Maintenance: www.nfpa.org