Unit 22

Wasteful circulating _____ in the iron core cause(s) the core to heat up without any useful purpose.

Eddy Currents

_____ can be reduced by dividing the core into many flat sections or laminations.

Eddy Currents

True or False: Autotransformers use separate windings for the primary and secondary.

False

The transformer winding that is connected to the source is called the "_____" winding and the transformer winding that is connected to the load is called the "_____."

Primary, Secondary

Transformers are rated in _____.

kVA

If the primary phase voltage is 480V and the secondary phase voltage is 240V, the turns ratio is _____.

2:1

Three-phase, _____ wye-connected systems can overheat because of circulating odd triplen harmonic currents.

4 wire

As current flows through the transformer, the iron core is temporarily magnetized. The energy required to realign the core molecules to the changing electromagnetic field is called "_____ loss."

Hysteresis

The relationship of the number of turns of wire on the _____ as compared to the number of turns on the _____ is called "turns ratio."

Priamary, Secondary

A _____ is used to raise or lower voltage and it has the ability to transfer electrical energy from one system to another with no physical connection between the two systems.

Transformer

True or False: Because of conductor resistance, flux leakage, eddy currents, and hysteresis losses, not all of the input power is transferred to the secondary winding for useful purposes.

True

True or False: Current flow in a secondary transformer winding creates an electromagnetic field that opposes the primary electromagnetic field resulting in less primary CEMF. The primary current automatically increases in direct proportion to the secondary current.

True

True or False: For most practical purposes, transformer efficiency can be ignored.

True

True or False: The energy transfer ability of a transformer is accomplished because the primary electromagnetic lines of force induce a voltage in the secondary winding.

True

True or False: The heating from harmonic currents is proportional to the square of the harmonic current.

True

True or False: The leakage of electromagnetic flux lines between the primary and secondary windings of a transformer represents wasted energy.

True

True or False: The primary electromagnetic field induces a voltage in the secondary. As the secondary current flows, it produces an electromagnetic field that reduces the strength of the primary flux lines. This results in an increase in primary current.

True

True or False: Voltage induced in the secondary winding of a transformer is dependent on the number of secondary turns as compared to the number of primary turns.

True