Transformers

When electricity is transmitted over long distances, high voltages are used to reduce the amount of energy lost to heat.

A transformer is an electrical device that takes electricity of one voltage and changes it into another voltage. You'll see transformers at the top of utility poles and even changing the voltage in a toy train set.

What is a transformer?

When electricity moves from a power plant to your home, it is put into a very high voltage to be able to travel long distances. The high voltage lines can be as high 155,000 to 765,000 volts to travel many hundreds of miles.

In order for your home, or a store, to use the electricity, it has to be at a lower voltage than on the long-distance lines. So, the electricity is stepped down to a lower level using a transformer.

Energy created must be stepped up to a high voltage, and stepped down to be used.

The alternating current in the primary coil causes a changing electric field which causes a magnetic field that is carried by the core to the second coil, causing a current in the second coil.

A transformer takes in electricity at a higher voltage and lets it run through lots of coils wound around an iron core. Because the current is alternating, the magnetic field in the core is changing.

Also around the core is an output wire with fewer coils. The magnetic field changing back and forth makes a current in the wire. Having fewer coils means less voltage. So the voltage is "stepped-down."

The change in voltage is directly dependant on the ratio of turns in the two coils.

Vp = Np

Vs Ns

Number of turns in the coil

Voltage

In your neighborhood, a transformer on top of a utility pole, or one connected to underground wires, transforms the 7,200 volts into 220-240 volts. This is then sent into your home over three wires. The three wires go through the electric meter, which measures how much electricity you use.

Some of the electrical appliances in your home use the 220-240 volts. These are things like a water heater, stove and oven, or air conditioner. They have very special connections and plugs. Other devices, like your TV or computer only use one-half of the electricity -- 110-120 volts.

Oven plugComputer plug

Energy in a transformer

The rate of energy in a transformer is equal to

Power = VI

If the transformer is 100% efficient (no energy is lost), then

VpIp = VsIs

Power in = Power out

If the transformer is not 100% efficient, you can determine the efficiency using

VsIs VpIp

x 100

The less energy lost, the more efficient.

Induction Coils

Electric devices that use time-varying DC voltages to provide a spark for the ignition of fuel.

Sometimes also know as “spark coils”, it is a type of transformer used to produce high-voltage pulses from a low-voltage DC supply.

Examples:•Lawn mower•Car engine