3rd Period Electrical SAIT > Three-Phase Systems 030301a > Flashcards

Three-Phase Systems 030301a Flashcards

Explain the difference between single-phase power and three-phase power. Explain the generation of the phase voltages of a three-phase system. Explain the phase sequence of three-phase sine waves. State three main advantages of three-phase power over single-phase power. (12 cards)

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1
Q

What determines the number of phases in a system?

Three-Phase Systems ILM

A

The number of windings.

Three-Phase Systems ILM
Page 3

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2
Q

How many conductors are required for a single-phase 120/240 V system?

Three-Phase Systems ILM

A

Three. 2 ungrounded and 1 neutral.

Three-Phase Systems ILM
Page 2

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3
Q

How many conductors are required for a three-phase wye connection system?

Three-Phase Systems ILM

A

Four. 3 line conductors and 1 neutral.

Three-Phase Systems ILM
Page 4

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4
Q

An alternator that has all three windings connected at a common point is called?

Three-Phase Systems ILM

A

Wye Connection.

Three-Phase Systems ILM
Page 8

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5
Q

What is a positive phase sequence?

Three-Phase Systems ILM

A

A phase rotation where coil A reaches a maximum voltage first.
ABC

Three-Phase Systems ILM
Page 11

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6
Q

What is a negative phase rotation?

Three-Phase Systems ILM

A

Coil C reaches maximum phase voltage first.
CBA

Three-Phase Systems ILM
Page 12

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7
Q

How can a phase sequence be changed?

Three-Phase Systems ILM

A

Reversing the direction of rotation of a three-phase alternator.
Interchanging of any two of the three line conductors.

Three-Phase Systems ILM
Page 12 & 13

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8
Q

What are three ways to observe a phase sequence?

Three-Phase Systems ILM

A

An oscilloscope.
Phase sequence indicator.
Phase rotation meter.

Three-Phase Systems ILM
Page 13

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9
Q

What are the three main advantages of a three-phase system?

Three-Phase Systems ILM

A

Constant power.
Smaller equipment for the same output. (25% less copper used)
Efficient energy transmission.

Three-Phase Systems ILM
Page 15

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10
Q

How can three-phase equipment be used on a single-phase supply?

Three-Phase Systems ILM

A

Phase converter.
Variable frequency drive (VFD).

Three-Phase Systems ILM
Page 15

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11
Q

How many mechanical degrees apart are the coils in a basic three-phase alternator?

Three-Phase Systems ILM

A

120 degrees.

Three-Phase Systems ILM
Page 7

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12
Q

How many electrical degrees apart are the voltages produced by a three-phase ac generator?

Three-Phase Systems ILM

A

120 degrees.

Three-Phase Systems ILM
Page 8

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3rd Period Electrical SAIT
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