SYNC MOTORS - Vee + Bell Flashcards
What is PF when the lowest current is across the stator field?
PF = 1 (unity)
What happens to excitation as load is added?
It increases
The torque angle on a phaser diagram on a sync motor is between which values?
180 reference line and Egen
PF is the cosine angle between which values?
I arm and V phase
A Vee curve is a plot of:
Armature current vs Field current
Unity Power Factor (PF) operation means the lowest line current for a particular load condition.
True.
Normal excitation results in lagging power factor.
True
High excitation results in leading power factor.
True
The Input apparent power (S) to the motor is.
3 x Vphase x Iarm
A slightly loaded sync motor is operating at a leading PF. What would adding load cause?
Less leading.
What are sync motors operating at a leading PF also called?
Synchronous condensers or Rotary Capacitors
Three levels of excitation
Normal excitation
Under excited
Over excited
What condition does under excited sync motor provide?
Lagging PF. Larger torque angle. Iarm decreases
What condition does over excited on a sync motor provide
Leading power factor. Decreased torque angle. Iarm increase
Normal excitation is when the state of the sync motor is;
At a unity PF
What does a bell curve represent?
PF vs field current
How do you calculate Erestant.
Vectorly with Egen and Vphase
What are the four possible load conditions for a SYNC motor
No load/no losses
Light load and Leading PF
Rated load and unity PF
Overload and lagging PF
What is the torque angle of a sync motor running in a no losses/no load operation?
Zero.
Egen is at 180 out-of-phase with Vphase
What is the combination which equates ‘synchronous reactance’
Inductive reactance of the armature AND armature reaction.
What has the greats affect on torque angle?
Mechanical load
Changing DC excitation drastically changes the torque angle of a sync motor; (T/F)
False
It is normal for a sync motor to run at a lagging PF ; (T/F)
False;
Usually operated at unity or leading
A synchronous motor running with a constant mechanical load and minimal line current is known at what excitation?
Normal excitation
Synchronous motors can be used for PF correction: (T/F)
True
