Hazards and Safety in High Voltage Power Lines

What are High Voltage Transmission Lines?

High voltage transmission lines are overhead power lines used for efficient bulk power transmission.  Since the power needs to be transmitted over long distances, the voltage level of transmitted power is increased to reduce the current to minimize I²R i.e., power losses during transmission. The lower the current, the lower the resistive losses in the conductors. That's why these lines are termed as high voltage transmission lines. 

Transmission lines or overhead Power Lines transmit electricity from the generating stations to other places such as large industries or to distribution networks from where the electricity is further supplied to different consumers. Step-up transformers are used at the generation end to increase the voltage level of transmission. 

According to ANSI, transmission lines can be categorized based on different voltage levels as:

• HV (High-voltage) Lines: Transmission lines having a voltage level between 100kV to 230kV lie under the category of HV lines.
• EHV (Extra-high voltage) Lines: EHV lines are those transmission lines whose voltage level is between 230kV to 1000kV.
• UHV (Ultra-high voltage) Lines: Those transmission lines whose voltage level is above 1000kV are categorized as UHV lines.

Structure of Transmission Tower

A Transmission tower consists of the following constructional parts:

• Peak: Part of the tower above top cross arm is known as the peak. Earth shield wire is connected to the tip of this peak.
• Cross Arms: They hold the main conductor lines. The dimensions of cross arms depend upon the voltage level on which the transmission line is to be operated.
• Cage: This portion holds the cross arms of the tower. It lies between the peak and body of the tower.
• Tower Body: The portion of the tower between the bottom cross arms and the ground is known as the tower body. The purpose of the tower body is to provide adequate clearance between the ground and conductors.

Important Terms

• Right of Way: It is defined as the land across the transmission lines which is set aside to provide a safe margin for the nearby areas. This corridor is used by relevant authorities to repair, construct, or maintain transmission lines and towers.
• Safe Distance: Safe distance is the distance from the transmission tower to the end of the corridor defined by the right of way. It can also be named as a border zone.

• Span: The horizontal distance between two transmission towers is called a span.
• Sag: It is defined as the difference between the level of point of support and the lowest point of the conductor.
• Ground Clearance: The distance from the lowest point of the conductor to the ground is known as ground clearance.

Dangers of High Voltage Power Lines

There are a number of hazards related to high voltage power lines. Electricity can be very dangerous for surrounding. The dangers are as follows:

• Overhead high voltage transmission lines are not insulated and if a person comes in contact or even closer to them through a ladder, crane, truck or any other means, he may get a life-threatening electrical shock
• Sometimes due to any fault or other factors electricity from these lines can flow to ground through the equipment or a person. It can cause serious injuries or death to that person.
• Electricity can flash over a gap, so any equipment or a person at some distance from the power lines can still be in danger.
• During storms or strong winds, overhead electric lines may fall to the ground and thus create danger in the surrounding.
• Working at heights on overhead power lines is not safe as an operator may fall to the ground if he is not properly equipped with relevant PPE (personal protective equipment).
• Underground power lines can also be hazardous during digging works. An operator not armed with appropriate PPE may mistakenly come in contact with the conductor causing a deadly electric shock.

Health Hazards Due to Overhead High Voltage Power Line

The concern for health hazards related to overhead power lines was first raised in 1979. In this study, it was discussed that electromagnetic radiations emitting from powerlines can cause childhood leukemia. Some researches stated that power lines can cause cancer and other critical health problems and the closer we get to HV overhead lines, the more dangerous the electromagnetic radiations become.

According to the research of the World Health Organization, we can suffer from insomnia, anxiety, headache, skin burns, fatigue, and muscle pain because of radiations from HV power lines. If such conditions really do occur, then electromagnetic radiations can be prevented from entering the human body by providing adequate shielding using metal. Things like buildings, trees, etc. can also serve as shielding for this purpose. In this way, we can reduce the health hazards caused by these dangerous radiations.

However, contrary to this belief, there are several arguments by experts stating that power lines create no such health hazards at all. In 1995 APS (American Physical Society) rejected linking childhood leukemia with power lines as there was no evidence that whether power lines caused it or rather it was just a coincidence. National Institute of Environmental Health Sciences (NIEHS) reported in 1999 that there is no such evidence to prove any health hazards of power lines nor their safety.

Electrical Shock and Arcing

Electric shock occurs when current passes through the human body when coming in contact with an energized conductor. Damage caused by electric shock depends on the severity of the shock or can say it depends on the level of voltage of the shock. It can cause skin burns and, in some cases, can lead to internal injuries or even death.

Step Potential and Touch Potential

Step potential is created when a fault occurs in power lines and current from the conductor starts to flow towards the earth. The voltage level of the area surrounding the grounding point is not uniform due to non-uniformity in resistivity of soil, so a potential difference is created there.

A person entering the vicinity of grounding has the difference of voltage between the two steps and thus due to potential difference current enters the body through the foot which is at higher potential and leaves through the other. This is known as step potential.

Power Lines Safety Rules and Precautions

There are some precautions which must be followed to avoid electrical hazards and risks:

• Towers carrying live conductors must not be climbed as it can cause electric shock if the tower is energized.
• Animals should never be tied to a transmission tower or pole as it can risk their life.
• Any object made up of metal or conducting material should not be thrown on overhead lines.
• During rain, towers or poles must not be touched by any person because the tower body becomes energized due to the conductivity of water.
• During storms or strong winds, we should keep a safe distance from powerlines as live conductors may accidentally fall over a person.
• If a person sees any spark on overhead live conductors, his first responsibility should be to inform the relevant authorities to avoid any accident.
• Any construction work should not be carried out under or near HV power lines.

Besides the precautions, there are also some safety rules for the linemen who work on HV transmission lines. These areas following:

• Linemen must be familiar with all the safety rules and regulations.
• A lineman who is going to do any operation must be trained well. Without any experience or training, he should not try to take any risk as it can put his life in danger.
• A lineman must be equipped with all necessary PPEs before starting operation.
• Before the start of work, it should be made sure that the tower on which the lineman is going to work is completely de-energized.
• If a lineman is not familiar with any tool, then he should never try to use it as it can be risky.
• A lineman must be in continuous communication with other team members when doing an operation.
• A lineman must not be in a hurry as it can cause an accident to him or other team members.

Conclusion

Electricity is a great blessing for us as it has advanced and automated our life to an infinite extent. But along with these benefits, electricity is also very dangerous at the same time. It creates a number of hazards and health issues thus endangering our life. If we properly follow the safety rules, standards, and precautions, then we can reduce and even eliminate the risks and hazards caused by electricity. Conclusively, it's up to us that either we make our life comfortable or full of risks.