Third Year Electrical Study Set

How many conductors from the source to a service are required in a single-phase 120/240 V system?

A single phase 120/240 V system requires three conductors. These are L1, L2, and N.

Single-phase

A single-phase connection is supplied by a single winding. It can be an ungrounded and grounded (identified) conductor, two ungrounded conductors, or the winding can be centre-tapped with two ungrounded and one grounded (neutral) conductor.

Three-phase wye connection

A three-phase wye connection is three windings all connected to a common connection point known as a start point. The connection has three line conductors and a neutral, and it will display two voltages.

Three-phase delta connection

A three-phase delta connection is three windings all connected end to end to form a triangle. It has three conductors from the transformer to the panelboard and only one available voltage.

The number of ______ determines the number of phases/

Windings

What type of three-phase system does 240 V, 3 phi identify?

A delta-connected service

What is the minimum number of coils in an ac generator required for producing a three-phase supply?

Three

An alternator is constructed so that all three windings have a common connection to one point. This is known as a _____ connection.

Wye

What happens when a coil cuts the magnetic lines of force?

A voltage is induced in the coil when the coil cuts the magnetic lines of force

As the turns of a coil rotate in an alternator, when is the induced voltage maximum?

The induced voltage is maximum when the turns of the coil are at 90 degrees to the magnetic lines of force

As the turns of a coil rotate in an alternator, when is the induced voltage zero?

The induced voltage is zero when the turns of the coil are moving parallel with the magnetic lines of force