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QUOTE
Setting a Steel Pole in a Live Circuit
by Wayne Vansoelen
Setting a pole in a live circuit is an everyday practice in most electrical utilities and the communications industry. Many utilities have taken the position that all poles are conductive and, therefore, the same procedure for setting a pole in a live circuit should apply, whether the pole is wood, steel or concrete. However, the historical procedure for setting poles in live circuits should be reviewed, considering the changes that have been introduced into the workplace. The trend to higher distribution voltages changes the impact of an accidental electrical contact. A higher voltage contact with a treated wood pole is not as forgiving as it was at four, eight or 12 kV. Also, the increased popularity of steel poles prompts the need to reduce any risks in existing procedures.
Why Steel Poles?
From an engineering point of view, steel poles have advantages, such as, consistent strength, no environmental hazards from pole treatment, fully recyclable, and no insect or woodpecker damage. Because there are eighty-year-old galvanized steel transmission towers out there, in good condition, it is predicted that a galvanized steel pole could also have a similar long life.
Steel poles also offer the following operational advantages:
There is a lower risk of pole falling accidents. Pole testing, pole treating and pole replacement programs will be much smaller than they are for wood poles.
There is no need to run a ground wire down a pole. In some utilities, especially on the Canadian prairies, the earth is used as the neutral. The pole down-ground wire on a transformer pole is the primary neutral and a full line-voltage could appear across any break. A steel pole would eliminate that hazard and there would be no more theft of copper down-grounds.
When a live conductor contacts a wood pole, a voltage gradient can occur along the pole. For a person working on a pole, the voltage at the contact point would be higher than the voltage at a spot farther from the contact point. Anyone on the pole would have a potential difference between the hands and the feet. On a steel pole, there would be virtually no potential difference between the hands and feet because both are in contact with the same object at the same potential.
When a conductor is lying on a cross-arm or an insulator is leaking, the circuit should trip out quickly.
No pole fires.
A comparatively smaller butt allows for a smaller pole hole and for an easier pull out of the ground for salvaging.
Steel poles weigh less than wood poles.
Equipotential grounding would work better because it is easier to make an electrical connection to a steel pole than a wood pole. When the conductor, grounds, neutral and steel pole are all bonded together electrically, a worker on the structure is quite safe from an accidental electrical reenergization or induction.
Operational Concerns
For distribution system work, there are concerns about doing hot-line work around a steel pole and concerns about installing steel poles in a live circuit. The concern is that any contact will immediately generate a fault current high enough to trip-out the circuit as well as generate hazardous step potentials around the pole, truck and attachments.
Grounded steel is a very good second-point-of-contact when working near a live circuit. While a wood pole has always been considered a second-point-of-contact for hot work, steel has the perception of being a more obvious hazard to a powerline worker. However, regardless of the type of pole being worked on, the same minimum approach limits along with the use of plentiful cover-up, reduces the risk of an electrical accident when doing hot line work.
by Wayne Vansoelen
Setting a pole in a live circuit is an everyday practice in most electrical utilities and the communications industry. Many utilities have taken the position that all poles are conductive and, therefore, the same procedure for setting a pole in a live circuit should apply, whether the pole is wood, steel or concrete. However, the historical procedure for setting poles in live circuits should be reviewed, considering the changes that have been introduced into the workplace. The trend to higher distribution voltages changes the impact of an accidental electrical contact. A higher voltage contact with a treated wood pole is not as forgiving as it was at four, eight or 12 kV. Also, the increased popularity of steel poles prompts the need to reduce any risks in existing procedures.
Why Steel Poles?
From an engineering point of view, steel poles have advantages, such as, consistent strength, no environmental hazards from pole treatment, fully recyclable, and no insect or woodpecker damage. Because there are eighty-year-old galvanized steel transmission towers out there, in good condition, it is predicted that a galvanized steel pole could also have a similar long life.
Steel poles also offer the following operational advantages:
There is a lower risk of pole falling accidents. Pole testing, pole treating and pole replacement programs will be much smaller than they are for wood poles.
There is no need to run a ground wire down a pole. In some utilities, especially on the Canadian prairies, the earth is used as the neutral. The pole down-ground wire on a transformer pole is the primary neutral and a full line-voltage could appear across any break. A steel pole would eliminate that hazard and there would be no more theft of copper down-grounds.
When a live conductor contacts a wood pole, a voltage gradient can occur along the pole. For a person working on a pole, the voltage at the contact point would be higher than the voltage at a spot farther from the contact point. Anyone on the pole would have a potential difference between the hands and the feet. On a steel pole, there would be virtually no potential difference between the hands and feet because both are in contact with the same object at the same potential.
When a conductor is lying on a cross-arm or an insulator is leaking, the circuit should trip out quickly.
No pole fires.
A comparatively smaller butt allows for a smaller pole hole and for an easier pull out of the ground for salvaging.
Steel poles weigh less than wood poles.
Equipotential grounding would work better because it is easier to make an electrical connection to a steel pole than a wood pole. When the conductor, grounds, neutral and steel pole are all bonded together electrically, a worker on the structure is quite safe from an accidental electrical reenergization or induction.
Operational Concerns
For distribution system work, there are concerns about doing hot-line work around a steel pole and concerns about installing steel poles in a live circuit. The concern is that any contact will immediately generate a fault current high enough to trip-out the circuit as well as generate hazardous step potentials around the pole, truck and attachments.
Grounded steel is a very good second-point-of-contact when working near a live circuit. While a wood pole has always been considered a second-point-of-contact for hot work, steel has the perception of being a more obvious hazard to a powerline worker. However, regardless of the type of pole being worked on, the same minimum approach limits along with the use of plentiful cover-up, reduces the risk of an electrical accident when doing hot line work.
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