Unit 4

Assume that an iso transformer has 240 turns on the primary and 60 turns on the secondary. The ratio is 4:1 (240/60=4). Now, assume that 120 V is connected to the primary winding. The voltage of the secondary winding is

30

The turns ratio of a transformer is proportional to what?

All the values

What are things that affect a transformers impedance?

Amount and type of core material, wire size of the windings, number of turns, and degree of magnetic coupling between the windings

The polarity of a transformer windings can be determined by connecting one lead of the primary to one lead of the secondary and testing for an increase or decrease in voltage. This is often referred to as

Buck or boost connection

A common type of iso transformer found throughout industry is the control transformer, which is used to increase the line voltage to the value needed to operate control circuits.

False

There will always be some amount of current flow in the primary of any voltage transformer even if there is no load connected to the secondary. This is called relaxation current of the transformer.

False

A very common type of iso transformers is the distribution transformer, which is used to supply power to

Homes and businesses

Transformers can be divided into several classifications, which include

Iso, auto, and current

Magnetic materials contain tiny magnetic structures in their molecular material known as

Magnetic domains

What type of transformer is basically an iso transformer with a high voltage rating on the primary and is intended for use in metering circuits?

Potential

Power in a transformer must equal to

Power out

What determines the amount of core material needed for a particular transformer?

Power rating

What will the name plates of a transformer list?

Primary and secondary voltage and kVA rating

What winding is connected to the driven load of a transformer?

Secondary

The amount of inrush current in the primary of a transformer is limited by the amount of applied voltage, resistance of the wire in the primary and flux change of the magnetic field in the core.

True

The reason that the isolation transformer can greatly reduce any voltage spikes before they reach the secondary is because of the rise time of current through an inductor.

True

When the primary of a transformer is connected to power but there is no load connected to the secondary, current is limited by the inductive reactance of the primary.

True

A transformer nameplate doesn't list the current rating of the windings. The current rating for a winding can be determined by diving the kVA rating by the what?

Winding voltage

According to ANSI rules, the high voltage leads of a transformer are to be marked as H1-H2 and so forth. The low voltage leads are marked as?

X1-X2