Power transmission

1
Power transmission

• Energy is lost in transmission lines
• Materials that allow electrons to flow through
  them (current) are called conductors.
• Every conductor has some resistance to the flow
  of current.
• Energy is lost as the current flows through the
  transmission lines
• Relationship between voltage, current and the
  resistance to current flow is given by V IR

2
Power transmission

• The losses in the line are proportional to the
  resistance and the current squared or RI2 and the
  power in the line is proportional to VI (voltage
  times current)
• The solution to these losses is to transmit the
  power at much higher voltages than the users
  need, and step the voltage down along the way.
  That way the current in the line is low, so the
  power losses are low.
• So the voltage is increased before the
  electricity leaves the power station and then
  decreased as needed.
• This is accomplished with a device called a
  transformer

3
Transformers

• No not these guys..

4
Transformers

• A device that transfers energy from one
  electrical circuit to another using the concept
  of induction
• A changing current in the first circuit (the
  primary) creates a changing magnetic field. This
  changing magnetic field induces a changing
  voltage in the second circuit (the secondary).
  This effect is called mutual induction.

5
Transformers

• The number of coils in the windings determine if
  the voltage is increased (stepped up) or
  decreased (stepped down)
• If the number of coils in the secondary is larger
  than the primary, voltage is stepped up, if it is
  less it is stepped down.

6
Power transmission

• At the power station, the generator produces
  13-25kV.
• A step up transformer boosts this to 115 to 765
  kV.
• Substations reduce the voltages for local
  distribution.
• Transformers on power poles reduce it further to
  the 240 V generally fed into our homes.

7
Power Transmission
8
Health Risks from Power Lines

• Power lines are live, if you touch them (and are
  in contact with the ground) you provide the
  current a path to ground. AC currents can induce
  heart fibrillations and cause death.
• NO strong link to overhead power lines and
  increased cancer due to the lines themselves.

9
Power Grid

• A network of power transmission systems
• Usually more than one path between points on a
  network

10
Power Grid

• The US and Canadian power companies are
  integrated into a single power grid
• Allows backups in case of emergencies, utilities
  can trade electrical energy and it is economical
• Circuit breakers (devices which cut off the flow
  of electricity through the circuit) protect
  against sudden surges in power
• They can isolate the problem and help the grid
  reroute the power flow
• If the problem is not isolated, the problem can
  spread throughout major portions of the grid,
  causing power interruptions we call blackouts.