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Transmission and Facility Siting Electric and Magnetic Fields (EMF) 60 Hertz (Hz) Electric and magnetic fields (known as “EMFs”) are produced by all devices which use, carry or produce electricity, including household appliances, office equipment, power lines and wiring in buildings. These are actually two separate fields, the electric field is caused by the voltage on a conductor, while the magnetic field is caused by the current flowing in a conductor. For power lines this means that the electric field is relatively constant (since the voltage of a power line does not fluctuate), while the magnetic field varies throughout time depending on the current flowing in the power line (this is a function of how much electricity our customers are using at any given time). The strength of both fields decreases as distance from the source increases. In addition, the electric field is easily shielded by solid objects such as buildings, trees, etc., while the magnetic field is generally not shielded by these objects. Due to these factors, and the fact that high voltage power lines are placed on poles high in the air, the field strengths at ground level, particularly the magnetic field strengths, near high voltage power lines are often similar to those encountered in close proximity to common household, school and office electrical appliances. There have been scientific studies on the potential health effects of EMFs for more than 25 years. For a more thorough understanding of this research we recommend reviewing web sites of organizations such as the National Institute of Environmental Health Sciences (NIEHS at http://www.niehs.nih.gov/emfrapid/home.htm) and the World Health Organization (WHO at http://www.who.int/peh-emf/about/en/). Two relevant conclusions found on the WHO web site (June 2006) state “[T]he focus of international research is the investigation of possible links between cancer and electromagnetic fields at power line and radiofrequencies” and “Despite extensive research to date there is no evidence to conclude that exposure to low level electromagnetic fields is harmful to health.” APS recognizes that research into potential health effects from exposure to EMFs is on-going and we try to respond appropriately. We follow this research closely and over the years we have helped to fund, and have participated in, some of this research. We also include EMF considerations into the design and siting of new power lines or structures. In addition we can provide educational materials and field strength information on existing and proposed power lines as necessary. All of our construction standards and practices meet or exceed the nationally accepted standards of the National Electrical Safety Code. Below are some important technical facts regarding transmission lines. Corona Corona is defined as the breakdown of air into charged electrical particles. The amount of corona for a transmission line is a function of several things including:
Effects of corona can include:
Audible Noise Audible noise from the power lines is created by:
Transmission line noise can be described as humming or crackling Suggested Noise levels:
Noise levels on a typical extra high voltage transmission line are expected to be less than the suggested levels. Communications When in very close proximity, transmission lines have been known to cause interference with radio and TV transmissions. Electric Field Electrostatic induction can occur with insulated objects near a transmission line. This can result in nuisance shocks to individuals touching a grounded object under or near the line. Institute of Electrical and Electronics Engineers (IEEE) has set standards for electric field values (maximum) inside and outside of transmission line right-of-ways. APS meets the IEEE standards for electric fields to insure public safety.
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