An integral part of any electric utility infrastructure, substations that are properly designed and maintained by qualified and trained workers are safe and reliable. If a failure occurs, however, it can be catastrophic and even disastrous.
The integrity of any substation starts with its design. Initial considerations include excavating the area, installing forms for concrete pads used as a foundation for equipment and the structure, installing an effective ground grid and conduit for associated wiring, laying down a high-resistance sand/gravel base and topping it off with a five-side aggregate stone for maximum resistance and good compaction. The equipment and structures are then installed and tied to the ground grid, insulators are added, current carrying parts are installed and tied to the system, and signs are attached. Once the substation is up and running, ongoing maintenance and inspections are critical components to continued reliability and safety. The following issues are among those that an electric utility must consider in order to keep the lights on for customers and its crews safe.
QUALIFICATIONS AND TRAINING
Qualified employees must understand the construction and operation of substation equipment, including what is normally energized, what the nominal voltage is, the minimum approach distance to the nominal voltage identified, and special precautions such as the hazardous gradient potential just outside the ground grid during a fault. In addition, employees should be trained to rescue fellow workers, and understand the proper use of personal protective equipment, barricade material and fall protection. Employers of electric utility qualified workers are required to observe each worker at least once annually to ensure that employees demonstrate abilities, although this is not an adequate representation of technical aptitude and should be done more
The first and most critical task for a qualified worker is the job briefing, often called a tailboard discussion. All field workers for electric utilities are required to perform this briefing and discuss the hazards associated with the job, work procedures and special precautions. During the discussion, energy source controls should be considered for properly de-energizing the work area and personal protective equipment needs should be reviewed. Substation workers also have to discuss the location of the energized equipment adjacent to the work area and the limits of the de-energized area. An initial discussion should start outside the substation to determine if there are any hazardous conditions before approaching the ground grid area outside the fence or entrance gate. In addition, an effective discussion should include emergency procedures if evacuation becomes necessary due to a fault.
Qualified substation workers will often work with testing equipment
for which they should receive adequate training to fully understand
the operation of the equipment and any associated hazards. Some
hazardous testing includes Hi-Pot™, Meggar™, TTR, and Capacitance
(Doble™) testing. When these tests are performed, the test area
should be barricaded with safety tape at least waist high with signage
attached. Other less hazardous tests that are a major component of a
good maintenance program include gas in oil tests, oil dielectric
tests, dew point tests for SF6 gas equipment, and micro-ohm breaker
contact, relay and breaker control tests.
Switching and tagging policies and training are required to ensure
that isolating circuits and equipment can be done sequentially and
without incident. Every system has its idiosyncrasies and each must be
fully understood by qualified workers and system operators. In order
for substation workers to be authorized to switch on an electric
utility system, they should have all of the necessary training of a
qualified worker and have specific training to operate, switch, tag,
test and ground equipment, including completion of written and field
tests to document competency.
INSPECTIONS AND MAINTENANCE
In order to maintain a safe and reliable system, substation
inspections should be conducted regularly and documented consistently.
Regular equipment maintenance is usually based on the number of
operations or time in service and should be scheduled according to
manufacturer recommendations. Batteries should receive monthly, annual
and periodic maintenance. Safety requirements for batteries should be
adhered to by all qualified workers and include the use of PPE such as
nitril gloves and apron, face shield and safety glasses, and boot
covers. Signs and eyewash stations should be installed in the
immediate area of the battery bank.
To ensure a hazard-free environment and continuous service from
electric substations, utilities design facilities properly and use
qualified and trained personnel to perform regular inspections and
Lee Marchessault, President of Workplace Safety Solutions, Inc. (WSSI)
has 27 years of experience in the electric utility industry. He also
currently serves as President and Board Chair for Vermont Utilities
for Electrical Education, Inc., a non-profit organization comprised of
the 21 electric utilities in the state, and as editor of the National
Safety Council Utilities Division Newsletter. Marchessault is also an
active member in many safety and electrical-related organizations,
including the Electric Division of the National Fire Protection
Association, Utilities Division of the National Safety Council, IEEE,
NEPPA, ECNE, and ASSE. WSSI provides education and training designed to increase safety awareness. Visit www.workplacesafetysolutionsinc.com