Transcript 12.3 - HRSBSTAFF Home Page

Topic 12: Electromagnetic induction

12.3: Transmission of electrical power
Energy losses

Energy is lost when it is transmitted
At the power transmission lines
 transformers

Large amounts of electrical energy Are
transmitted each second, from the
power stations to the consumers, often
over large distances.
 Since power = current x voltage, we
could use:
 either a) a low voltage and a high
current,
 or b) a high voltage and a low current.

Why does the National Grid always use
method (b)?
 Remember that a current always produces
heat in a resistor.
 If the cables have resistance R, and carry
a current I, the energy converted to heat
each second is I2 R
 P = I2 R


This means that in method (a) the high current
produces a lot of heat in the cables and little of
the energy from the power station gets to the
consumer.

Method (b) is used because the low current
minimises the power loss.
Transformers at each end of the system step the
voltage up and then down.

Losses in transformers
Copper losses: the wires have some
resistance
 Hystereis loss: Magnetising and
demagnetising uses power
 Eddy currents: small currents form in the
core

Transmission of Power
At the power station side:
 Voltage is stepped up with a transformer to
275000 V
 This reduces electrical loss in the
transmission lines

At the end of the line
 Voltage is stepped-down with a
transformer to
 33000 V: heavy industry
 11000 V: Light industry
 230 V : Homes

Health risks
How many transformers are there in your
home?
 How many electric fields are you exposed
to everyday?
 What about wireless internet?
 Can these pose a threat to our health?

Electric fields from power lines and mobile
phone masts are all around us
 Electric fields are known to interact with
tissues by inducing electric fields and
currents in them.
 Some studies have found a higher rate of
cancer in people living close to power lines

How can these fields do this?
Results from animal studies conducted so
far suggest that electric fields do not
initiate or promote cancer.
 Electric fields and magnetic fields were
classified as possibly carcinogenic to
humans based on epidemiological studies
of childhood leukaemia


"Possibly carcinogenic to humans" is a
classification used to denote an agent for
which there is limited evidence of
carcinogenicity in humans and less than
sufficient evidence for carcinogenicity in
experimental animals.
What about high-voltage power
lines?
Do not touch them!!
 Again no risk of cancer has been found
