Theory Flashcards
In a Wye System, EL =
Ep x Root 3
In Wye, line current =
phase current
In Wye, Vab =
Van + Vnb
In Wye, Vbc =
Vbn + vnc
In Wye, Vca =
Vcn + Vna
In Wye, In =
Ia + Ib + Ic
In Wye, S =
Eline x Iline x Root 3
In Wye, P =
Eline x Iline x Root 3 x pf
In Wye, Q =
Eline x Iline x Root 3 x Sin Angle
In Wye, the phase voltage ____ the line voltage by ____ degrees
lags, 30 degrees
In an unbalanced three-phase wye system, positive rotation is in the ___ direction
counterclockwise
Define power factor
the displacement between phase voltage and phase current
What is the purpose of the neutral conductor in a three phase wye system?
To maintain proper phase voltage and to carry the unbalanced load
What determines the rotation of electrical generation
The prime mover
How many conductors are in a three phase system?
Three or four
When does voltage inducted reach its maximum?
At 90 degrees
How many mechanical degrees apart are coins placed?
120
How many electrical degrees apart are the voltages produced by a three-phase generator?
120
True or false: the CAB phase sequence is the same as the ABC phase sequence
True
The BAC sequence is the same as the ABC phase sequence. True or False?
False
What can be used to observe phase sequence?
Oscilloscope
Name two ways that we can change the phase sequence?
Swap two leads or change the direction of the prime mover
What are three advantages of a three phase system over a single phase system?
Constant voltage, smaller equipment (conductors), more efficient
Would you expect less vibration in a three phase or single phase system?
Three phase
How much more copper is used in a single phase system than a three phase system and why?
25% because the conductors must be bigger to get the same supply
What requirements must be met for a three phase system to be balanced?
same impedance, same power factor
In what order do the phase voltages follow one another for positive phase sequence in a three phase system?
ABCABCABC
In a balanced system, each line current is separated by how many electrical degrees?
120