Three-Phase Systems Flashcards
Why is a residential service 1Φ instead of 2Φ?
This is because only one AC voltage is provided across a single Φ transformer, it is just split by a center tapped, grounded neutral conductor.
How many ungrounded conductors are brought out from a 3 phase alternator?
3.
Which three phase connection uncommonly uses a neutral conductor.
3 Φ (high-leg) delta.
In a single Φ service, are the line voltages out of phase?
No, they are in phase; this is why it is single Φ.
What is another name for wye connection?
Star (point).
What are the two adjustable factors which affect voltage generation?
Rotational frequency (speed).
Magnetic flux density.
Who’s law states that Voltage generated is proportional to number of flux lines cut per second?
Faraday’s law of induction.
When is generated voltage at it’s maximum?
When the coils cut flux at 90º.
Why is phase voltage in a three phase system generated 120 electrical degrees apart?
Because the phase coils in the generator are placed 120 mechanical degrees apart.
What is the preferred method of generation for most large generators?
Rotating the magnetic flux within the conductor coils.
What is positive phase sequence?
ABC.
BCA.
CAB.
What is negative phase sequence?
CBA.
BAC.
ACB.
How could one switch the way a piece of equipment receives phase voltages in sequence?
Interchange any two leads.
Change the rotation of generation at it’s source.
How many phase sequence be observed?
An oscilloscope.
A phase sequence indicator.
Which panelboard would you connect a 125V receptacle to in a typical commercial installation?
120/208 V 3Φ.
