Ch 14 transformers

What is a transformer

A device that changes the level of voltage in a electrical circuit

What's the major advantage of using higher voltages for transmiasion

As voltage rises the current falls for the same amount of power

Transformer losses are divided into what two categories

Copper losses and core losses

How do you know which fuse to use when fusing the secondary windings

Divide VA by secondary volts

An electrical current flowing through the core is

Eddy-current

If a core is made of numerous thin pieces of metal they are ___________ from each other

Electrically insulated

If a conductor is looped or is wound into a coil, magnetic lines of force cut across the loops as the magnetic fields expand and collapse causing _______

Emf (electromotive force)

What is the emf generated across the secondary windings

Emf of mutual induction

Magnetic fields ______ when current rises and ______ when current falls

Expands and collapses

True or False Transformers must be sized appropriately, they must not exceed the rating or be lower than the approved rating

False; they can be higher but never lower

What's one way to reduce eddy current failure in a transformer

Get transformers that have multiple thin layers in its core as opposed to just a solid block of iron

Copper losses in transformers are caused by

High current through wires

A transformer transfers energy from one circuit to another by __________

Induction

Iron cores have thin metal sheets of steel, what are they called

Laminations

If current flows through a conductor this causes _______ to be formed

Magnetic fields

How do you minimize hysteresis loss

Making the cores of silicon steel

What's the principal operation of a transformer

Mutual inductance

What are the three principal parts of a transformer

Primary winding, secondary winding, and it's iron core

List three uses for transformers

Radios, TV's, electronic circuits

The output power of a transformer is calculated how?

Secondary voltage times the ampere rating

What is a transformer that has more turns in the secondary than the primary

Step up transformer

What's the main purpose of the iron core in a transformer

Strengthen the magnetic flux and increase efficiency, reduce hysteresis, and eliminate eddy current losses

What's the most important use for a transformer

The distribution of electrical power

What will happen if you put in a transformer that is too small for the application

The transformer will burn up due to overload conditions

Explain copper losses in transformers

They occur due to the resistance of the wire

What does KVA stand for

Thousands of voltamperes

Why is the core in a transformer laminated

To reduce eddy current losses

True or False When the current is zero in a transformer there will be no magnetic field around it

True

True or False A transformer is a device that has no moving parts

True

These individual sheets are coated with _______

Varnish

The lower the current is the lower the ________ will be and the lower the ________ will be in the transmission line

Voltage drop; power loss

What causes core losses in a transformer

When the direction of the magnetic field is reversed rapidly (friction between molecules of metal)