37 Outcome 3: Powerline Hazards and Risk Mitigation
Outcome/Competency: You will be able to identify powerline hazards and risk mitigation.
Time for this outcome: 1h45
Rationale:
Why is it important for you to learn this skill?
The ability to identify and describe powerline hazards ensures that you can properly evaluate your work environment and respond accordingly. Mitigation strategies are particularly important in the powerline trade because you must be able to recognize and respond to hazards quickly.
Objectives:
To be competent in this area, the individual must be able to:
- Identify and describe powerline hazards and procedures to mitigate hazards.
Learning Goals
- Identify and describe hazards and ways to mitigate.
- Identify main principles of bonding, grounding, equi-potential bonds, and types of induced voltages.
Introduction:
This section will cover common example of hazards, mitigation strategies such as tailboard meetings, how to address electrical hazards, bonding, and grounding principles. There will be quizzes throughout to confirm understanding.
Instructions:
- Cover the following content in each topic as a group (either reading out loud or independently), then give an opportunity to answer any questions.
- Have students do the review questions independently, then take up answers.
Topic: Hazards (10m)
The Powerline industry and the work associated with the construction, maintenance, and operation of it contains may inherent dangers. Some dangers include working from heights, electrical, mechanical, and vehicular. As with any trade, these dangers as well as others can be mitigated by good planning, good discussion, and training.
When working from heights, appropriate safety equipment must be utilized to ensure the protection of the worker. When working off the pole, all climbing gear including climbing belt, fall arrest strap, fall restraint strap, and climbers (climbing hooks) must be inspected before each use. It is particularly important to use the secondary pole strap when climbing structures with obstacles in the climbing path.
Electrical hazards in the powerline trade can be mitigated using the Standard Protection Code which is SaskPower’s LOTO (Lockout/Tagout) procedure, along with bonding and grounding. Good planning, good discussion, and training are essential to the success and safety of any job when it relates to electricity.
Topic: Mitigation Procedures (10m)
One of the best ways of mitigating powerline hazards is to have a good job plan. Job plans are communicated formally by using a tailboard or Hazard, Aspect, and Risk Assessment (HARA) meeting. This provides a platform in which the scope of the work and roles of each worker on site are communicated.
A Tail Board is a meeting conducted at the job site by the workers to assess the adequacy of the job plan and to ensure that all hazards are identified and mitigated. Tail boards are used to identify and address conditions that are or can be a safety hazard. Once a hazard is identified, controls must be put in place to either minimize or eliminate the hazard. Some examples of controls that can be put in place or engineered are: design changes, lockout tagout procedures, personal protective equipment or rubber protection. Tail boards are required before starting any type of work. If conditions change throughout the job the tail board must be revisited and any changes must be documented.
Topic: Electrical Hazards (5m)
When working in the powerline trade, one of the main dangers that a powerline technician will encounter is electricity. Because electricity is invisible, proper steps must be followed to ensure what state the electrical equipment is in prior to being worked on. Not only are electrical hazards present in electrical equipment and conductors where we would find touch potential, they are also present where electricity enters the earth creating step potential.
How were 300 reindeer killed by a single lightning strike? (20m)
In late August, 300 reindeer were killed by a single lightning strike in Norway, an incident that showed the deadly potential of high-voltage electricity, including the dangers posed by fallen power lines.
Incident in Norway underlines the danger of high voltages on the ground
At BC Hydro, we have a great respect for the power of electricity, and we stick to specific safety guidelines to stay safe around electricity, on and off the job. But once in a while, the science of electricity becomes big news, such as with a recent report that 300 reindeer were killed by a single lightning strike in Norway.
We particularly like wired.com’s version of the story because it investigates the science of how it happened, and it uses terms, such as “step potential”, that you don’t usually hear about outside of a utility like BC Hydro.
The article explains that when current is flowing through the ground following an accident (or lightning strike), the step potential is the difference in voltage between the points contacting the ground; in this case, the reindeer’s legs.
Because the voltage at each “step” is different, it causes the current to continue flowing from one leg to the other. For these reindeer, this path caused the current to travel straight through their hearts, killing the poor creatures instantly.
Chart explaining step potential
When electrical current flows through the ground from a fallen power line or a lightning strike, the ‘step potential’ is the difference in voltage between the points contacting the ground. Electricity passing through a human, or another animal can be fatal.
While we don’t have that much in common with reindeer (aside from those of us who share a love of leafy greens), this story is a reminder of how we can all stay safe around power lines. Earlier this year, we told you about our newest public safety campaign – Down. Danger. Dial. If it’s down, it’s a danger, stay back 10 metres and dial 911.
“This situation is exactly why we remind people to shuffle with their feet together as they move away from the downed line – taking normal steps will cause a step potential, and result in electricity flowing through you, possibly causing harm,” says Jonny Knowles, BC Hydro’s public safety lead. “Also, you can’t be too sure how far the current has travelled from its point of origin, so it’s best to continue shuffling and move at least 10 metres away from the fallen line.”
“When a voltage source, like a bolt of lightning or a fallen power line, hits the ground it creates a lot of electrical pressure at that point,” says Marc Spencer, a senior safety advisor with BC Hydro. “That pressure spreads out, much as the ripples spread out when you throw a rock into a pond. The electrical pressure, or voltage, is different at each point as it dissipates over a distance.”
With a fallen power line, it’s important to know that even if you’re standing a distance away, you could still be in danger if you’re within the range of what would have been the pond “ripples”. Each walking step within this distance creates a step potential and a path for the electricity to continue travelling – through you.
Just as with these unfortunate reindeer, the power could still be flowing through the ground, and walking normally could create a perfect path for the current to flow from the ground up through one of your legs and down the other, potentially causing serious injury.
Always remember to shuffle with your feet together until you’re at least 10 metres, or a bus-length, away from the source of the accident. This will ensure the current keeps flowing past your body through the ground, so that you can escape, unharmed. As you do this, it might be helpful to warn anybody in the surrounding area to also stay back, especially young children.
From BC Hydro Smart website, staff writer, https://www.bchydro.com/news/conservation/2016/reindeer-killed-by-lightning.html, published sept 28, 2016, accessed August 20, 2021
Watch the Following Video
Figure 6 https://www.youtube.com/watch?v=ida0ejH7y6c
Review Questions (15m)
1. What are two main electrical hazards.
2. (T / F ) You cannot be injured by step potential, but touch potential is lethal.
3. ( T / F ) If inadvertent contact is made between a piece of equipment that you are operating and a powerline, you must jump, then shuffle away from the equipment.
4. ( T / F ) If a piece of equipment you are operating comes in contact with a powerline, as long as you don’t touch the equipment and the ground at the same time, you will be safe.
Answer Key
1. Step potential and touch potential
2. F
3. T
4. F
Topic: Bonding and Grounding (30m)
There are two main principals that, if properly maintained, will enable most line work to be carried out without undue risk to personal safety from electric shock hazard.
The first principle is to maintain “zero potential” between the work contact point and the supporting point of the workman (usually identified as the workman’s feet).
The second principle is to reduce the resistance between the work contact point and ground to an absolute minimum value.
Bonding
Bonding is the connecting, with low resistance conductor, of all apparatus and exposed metallic surfaces (whether grounded or not), to provide an equipotential zone around the workman, and to provide a path for currents to bypass the work area.
Safety Grounding
Grounding is the application of approved grounding conductors to isolated electrical primary apparatus, to render and maintain such apparatus at or near ground potential.
Figure 7 Attr. SaskPower training manual.
Once again, all practices concerning the first of these principles are covered by the general term of “bonding” and should not be confused with the second principle of grounding.
As we will later discuss, bonding by itself may, indeed, protect the individual or lineman at the work point; however, a safety hazard may still exist in the general surrounding area due to inadequate grounding.
NOTE: Remember, grounding is not bonding, and vice-versa; however, a combination of the two practices will minimize the risks for all workers involved.
Reasons for Safety Grounding
Lightning
Although the isolated work area or power line may be bathed in sunlight, a storm on some other portion of the system could result in lightning striking the isolated system, thereby rendering the work location extremely unsafe in the instance that it is not properly “Bonded and Grounded.”
Figure 8 Attr. SaskPower Training Manual
Accidental Energizing
There are three ways in which lines may become “accidentally” energized:
- Switching error
- Conductor contact
- Backfeed.
Switching error
Workers will, undoubtedly, make certain that the system is isolated before beginning their work; however, through carelessness or misunderstand switches may be closed. As a result, the isolated system may be energized.
Figure 9 Attr. SaskPower Training Manual
Conductor Contact
Accidents on adjacent systems, at crossover points, or on rebuilds involving overstringing (stringing over live conductors) could result in energized lines coming in contact with the isolated system.
Backfeed
Our electricity-oriented world has forced our customers to rely very exclusively on a power supply to ensure normal, day to day operations. For example, many farmers depend on a power supply to the point that they have employed backup systems or standby generators to ensure that electrical interruptions are kept to a minimum.
SaskPower has accepted this fact, and in turn has given farmer the option of replacing their standard meter boxes with standby/meter boxes that ensure a proper isolation point between the customer’s generators and our system.
Keep in mind that, if a customer connects an external power source to his system, in the event of an outage, this voltage source could possibly “backfeed” through SaskPower’s transformation, and enter our isolated system at the “Stepped-up” voltage (14.4 kV)
Figure 10 Attr. SaskPower Training Manual
These, and other possible situations, call for adequate “Bonding and grounding” procedures to ensure that a safe work area is maintained. Any other method of grounding is considered sub-standard and is not acceptable.
Induced Voltages
The problem of “induction” is a rising concern of line personnel, both operating and maintenance. This is due to the effect of high levels of induced voltage and current on isolated and de-energized electrical circuits running in parallel with, and/or at close spacing to, other energized high-voltage power lines.
In order to give a better understanding, it is necessary to explain in brief terms the two phenomena that cause induction:
- Electrostatic induction
- Electromagnetic induction
Electrostatic induction
When an isolated line is crossed by an energized line, the isolated line will assume a potential. This effect is caused due to the fact that any insulated object in the proximity of live equipment has two capacities associated with it:
- Object to line
- Object to ground
Figure SEQ Figure \* ARABIC 11 Attr. SaskPower Training Manual
It does not matter where the object is in the field, it will always assume a voltage which is proportional to its location in the “electrostatic field” as long as it is isolated from the ground or “floating.” The value of this induced voltage depends upon two factors:
- Voltage of the energized line
- Distance between the insulated object and the line.
- When a floating object in an electrostatic field is shorted to the ground, the magnitude of current flow is directly related to the size of the object being grounded.
Figure 12 Attr. SaskPower Training Manual
Remember, that a capacitor is simply two plates or conductors separated by insulation; therefore, increasing the size of the object or increasing the conductor’s length, in effect, increases the size of the plates. Increasing the size of the plates in a capacitor increases the size of the capacitor, thereby allowing more current to flow.
As described, when an isolated line is grounded two events occur:
- The electrostatic potential drops
- Steady current flows. The current that flows is not usually regarded as being great; however it can still be lethal on long parallel lines or even extremely large objects.
A common example of “electrostatic voltage” is the buildup of charge on a worker’s body when he/she is on or near an energized line. This “charge” is often felt as a “bite”
Figure SEQ Figure \* ARABIC 13 Attr. SaskPower Training Manual
Review Questions: Bonding and Grounding (15m)
- (T/F) Grounding is the connecting, with low resistance conductor, of all apparatus and exposed metallic surfaces (whether grounded or not), to provide an equipotential zone around the workman, and to provide a path for currents to bypass the work area.
- (T/F) Bonding is the application of approved grounding conductors to isolated electrical primary apparatus, to render and maintain such apparatus at or near ground potential.
- (T/F) If a customer connects an external power source to his system, in the event of an outage, this voltage source could possibly “backfeed” through SaskPower’s transformation, and enter our isolated system at the “Stepped-up” voltage (14.4 kV)
Answer Key
1. F , 2. F , 3. T