Transformers (RADS 354)

Transformers are used to

make the high voltage necessary for x-ray production by supplying power

Transformers are sometimes called

x-ray generator

How much power do transformers supply?

110-120 volts from the department, but not high enough to operate x-ray tube

when voltage goes up, amperage goes...

down

The transformer works on the principle of...

electromagnetic mutual induction

Primary Coil or Input Side of Transformer

the coil supplied with current, connected to AC which has 110-120 volts

-will produce a magnetic field

Secondary Coil or Output Side of Transformer

The coil not connected to a source of electricity/current

-lies on the magnetic field from the primary coil and cuts across it to build electrical energy)

How do transformers work?

tranfers electrical energy from one coil of wire to another but there is no connection between the two coils of wire (mutual induction)

Transformer Law

The secondary voltage is to the primary voltage as the number of turns in the secondary coil is to the number of turns in the primary coil (direct)

Transformer equation

Vs/Vp = Ns/Np relates voltage and turns

step-down transformer

lowers the voltage with more turns on primary than secondary

step-up transformer

increases voltage and decreases current with more turns on secondary than primary

Turns ratio of a transformer is

ns (number of turns secondary) / np (number of turns primary)

Law of Conservative Energy

there can be no more power coming out than going in the transformer this means for step up transformer as voltage increases current would decrease and vice versa for step down transformer

Current Value Formula

Is/Ip = Vp/Vs relates current/intensity and voltage

Types of Transformers

-air core

-open core

-closed core or doughnut

-shell type or figure eight

Air Core Transformer

two insulated coils of wire side by side

-least efficient because low magnetic field

What is the simplest type of transformer?

air core transformer

Open Core Transformer

two insulated coils of wire with an iron core

-increases the magnetic field

Closed Core or Doughnut Transformer

will have 4 iron cores that are laminated to increase efficiency due to eddy currents and it will close off the air at the top and bottom

-increasing magnetic field

Shell Type or Figure Eight Transformer

consists of both primary and secondary coils around a center iron core

-will have 4 more iron cores, 2 across the top and 2 on each side of the center iron cores

efficiency of transformers is determined by...

the ratio of power output to power input

Formula for transformer efficiency

% efficiency = power output/power input x 100

in practice efficiency of a transformer equals:

90% - 95%, ideally we want 100%

The 5%-10% loss of efficiency in a transformer is in the form of energy amd appears in what ways:

copper loss, eddy current loss, and hysteresis loss

copper loss

loss of electrical power due to resistance

How do we overcome copper loss of a transformer?

increasing the diameter of the wire causing less resistance

Eddy Current Loss

small circular electrical currents in the iron core itself resulting from alternating magnetic flux

Hysteresis Loss

magnetic domains changing with alternating current

Both eddy and hysteresis loss can be reduced by...

laminated iron cores