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

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

Transformers No not these guys…..

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.

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.

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.

Power Transmission

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.

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

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.