Category : Power Lines
Aerial Power Lines Patrol / Inspection
By Ofonime Essien
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Photo: Hayward Helicopters
History and Purpose
Helicopters have been in use to support the utility industry since 1947 when the first civilian certified aircraft became available in the United States (US). As the aircraft became more capable and reliable, their use expanded and continues to expand to provide cost effective support. Operators conducting aerial work in support of the utility industry encounter different hazards because of the various types of operational envelopes or flight profiles, terrain, infrastructure, and weather environments. At the same time, aerial work involved with the utility industry exposes aircraft and operators to the same hazards of any aircraft that operates at low altitudes and slow speeds.
Related: Power Lines Are Deadly
Aerial Work Power Line Patrols
Routine power line patrols provide cost effective means of visually inspecting electric utility’s structures, conductors, and identifying encroachment of man-made or naturally occurring elements that pose hazards to the reliability of the system. In conducting routine power line patrols it must be clearly understood the aircraft is “flying through” the wire environment, which greatly increases the potential for the aircraft to collide with the infrastructure or terrain. Aerial work like this requires a minimum crew of an observer and a pilot to effectively and safely perform the work. The aircraft may be operated at speeds of 20 to 70 knots of forward speed along the power line right-of-way depending on the type of structures and voltage of the power line.
Generally, the industry practice is to operate the aircraft slightly above and one to two rotor discs of distance to the side of the power line so that an observer can visually inspect the power line, structures, and right-of-way. By maintaining the appropriate distance and speed, the observer is able to visually inspect the structures, insulators, and conductors. Properly positioned the visual perception is one in which the structures and conductors are passing by the observers line of sight at a slow walk allowing the observer time to inspect.
However, at 20 knots, the aircraft has a rate of closure of 35.2 feet per second or at 70 knots a rate closure of 123.2 feet per second to an obstacle in its flight path. In order to mitigate the potential risk of a collision the crew must identify a potential collision hazard and make corrective actions well in advance, if not, there is very limited action that a pilot can take to avoid a collision. At these rates of closure, it requires the crews to exercise extreme concentration, maintain situational awareness, be knowledgeable of their area of operations, maintain effective communications, and establish clear roles and responsibilities.
Aerial work, whether it is power line or pipeline patrol, construction or repair work, requires effective communications, due diligence to maintain situational awareness and an understanding that the pilot, observer and/or mission crew are team. They are reliant on each other to effectively communicate observed hazards or safety concerns as they are noted. Each person onboard has a role, responsibility and authority to make the other team member(s) aware of any hazard or safety concern and to effectively communicate that concern to the other team member.
Each person on-board should be delegated “stop-work authority” by the operator or owner. It is essential to safety management of risks that if even if one team member has a concern, then work should be stopped, it should be! Evaluate the situation and determine if passive or active safety measures can be instituted to mitigate the hazard or safety concern before initiating work again.
Identified Hazards (Hazards Associated With Power Line Patrol)
The following hazards were identified that require mitigation to manage the risk to acceptable levels.
- Collision with static wires, guy wires or conductors;
- Cantenary or suspension cables
- Collision with structures or towers;
- Controlled flight into terrain
- Engine failure at low altitude
- Settling with Power
- Loss of Tail Rotor Effectiveness
- Tail rotor failure at low altitude
- Bird Strikes
- Loss of situational awareness due to sun, low light, or haze
- Fatigue related stress resulting in “complacency” or “over confidence”
Inspection and Patrols
Aerial patrols are performed on power lines to identify major problems requiring maintenance.
Examples of these problems are broken or damaged insulators, structure damage, right-of-way access problems, encroachment problems, weather damage, and emergency outages. Each mile of power line is flown on a periodic basis to identify such problems.
The illustration below is an example of minimum clearances:
Transmission lines are susceptible to many problems as a result of weather, age, vandalism, etc.
Some problems are more serious than others are. Problems should be classified into two categories–primary and secondary.
- Primary problems are those that may result in an imminent outage or pose a serious threat to the safety and/or welfare of the public. If the damage, in the observer’s view, poses a serious threat, the observer should immediately notify the Utility.
- Secondary problems are those that may not result in an imminent outage and/or not pose a serious threat to the safety or welfare of the public. These problems can be put on an inspection report to rectify at a later date. The observer must use discretion in classifying problems as primary or secondary. Listed below are problems usually considered as primary or secondary:
(a) Broken or split cross arms. (May also be secondary)
(b) Downed or loose conductor
(c) Downed or loose static line
(d) Severely damaged conductor
(e) Severely damaged insulators
(f) Foreign material in line (bird nests, wires, shrubs, etc.)
(g) Lines that cross over and under other lines coming into contact with each other because of ice loading, wind damage, etc.
(h) Severe structure damage
(i) Equipment operation (farm equipment, cranes) under the line not within safe clearances
(Note: In cases like these, the helicopter may land so the observer can notify the operator or owner of the hazard.)
(a) Loose X-braces
(b) Structure damage (leaners caused by farm equipment or animals, burnt wood poles, woodpecker damage)
(c) Right-of-way access problems
(d) Right-of-way and/or structure erosion
(e) Loose or damaged guy wires (May also be primary)
(f) Loose or damaged structure ground wires
(g) Loose or damaged dampers
(h) Loose or missing hardware
(i) Missing or faded structure numbers
Electric Utility Systems and Patrol Procedures
1. General. Develop a working knowledge and a basic understanding of the transmission system facilities is necessary so that the worker understands the reason for work methods employed and to avoid the hazards that are present at the work site.
In addition, it provides a pilot and crewmember the ability to forecast where to expect wires rather than total reliance on visual contact with the wire itself. It is important to recognize that electric utility systems are not static, they are dynamic and constantly changing so pilots and crewmen need to maintain vigilance even on systems they may have become familiar.
2. Knowledge of Transmission Facilities
a. Circuit Voltage: Crews need to know how to identify the circuit being worked and its voltage, by use of various aids such as geographical circuit prints, insulation design, proper marking by circuit signs and/or structure markings.
b. Minimum Approach Distances: To avoid potential electrical shock, crews should observe minimum approach distances.
c. Structures: The worker needs to have a basic knowledge of various transmission structures including:
- Lattice types;
- Steel poles types;
- Wood pole; and
- Composite and concrete poles.
d. Types of Insulators: Pilots and crews need to have knowledge of various types of insulators, including:
- Ceramic suspension;
- Ceramic post;
- Glass; and
- Non-ceramic (NCI).
e. In the US, according to the “National Electric Safety Code” higher-voltage lines SHOULD cross over the top of lower-voltage lines. It is an imperative for the pilot and crewmembers to know what voltage is being patrolled in order to know what to expect above and below the line.
3. When patrolling an unfamiliar system or for the first time:
a. Begin with the highest voltage in the system. This provides the ability to observe wire crossings from the top down.
b. To enhance the quality and safety of the patrol, the pilot or observer must be familiar with the system being patrolled. There should never be a circumstance that a pilot and observer be dispatched to perform a patrol when neither is familiar with the system. Prior to commencing work the pilot and observer must be briefed using maps, system photos, and other information necessary to perform the patrol safely.
c. The pilot must concentrate on flying the aircraft that includes obstacle avoidance such as identification of wire crossings, antennae, and sensitive areas while providing the observer the best view possible to safely inspect the line. Observer emphasis should focus on developing aerial observation skills and techniques rather than achieving quality, thorough inspection. The pilot and observer should strive to work as a team.
d. The likelihood of seeing a wire in time to take evasive action is much greater at slower airspeeds. Keep it slow.
e. The lower the voltage of the lines being patrolled, the more skills will be required. The greater complexity of the lower-voltage systems increases the patrol workload.
f. Request that the utility provide current circuit maps and information on new lines and construction projects.
g. Work with the utility in the development of a program for marking power lines, wire crossings, and identifying hazards to flight on the mapping resources provide. Remember that electric utilities are not the only organizations that may install wire hazards.