Power outages can occur at any time and can greatly impact daily life. They are usually a result of:
 
Downed power lines
The most common cause of power loss. Downed power lines can happen for a number of reasons. Most often they are a result of severe weather including lightning, high winds, ice buildup, and more. With severe weather possible nearly anywhere, it is the most common cause of a power outage.
 
Additional causes of downed power lines include: 

• Interference from wildlife
• Fallen trees and debris
• Damage from vehicles or construction equipment

The time it can take to repair depends on the extent of the damage.

Blown transformers
When a transformer failure occurs it can impact all connected homes and businesses. Typically this is caused by a lightning strike or an overload that results in a blown fuse. Frayed wires and damaged equipment are also a common cause for a blown transformer.
 
Substation Failure
Power outages due to substation failure are less common, and are usually a result of a significant equipment failure or operator error. However, the impact is often felt far and wide, often affecting several thousand customers.
 
Physical attacks on substations have become a larger concern in recent years. Cyber attacks are also a risk, however few instances have been reported. Substation failure can take weeks or longer to restore service.