Formulas Flashcards
What is the formula for finding El in a Wye system?
El = Ep x root 3
What is the formula for finding Il in a Delta system?
Il = Ip x root 3
What is the formula for finding VAt on both Delta and Wye systems?
VAt = El x Il x root 3
What is the formula to find total power delivered on both a Wye and Delta system?
Pt = El x Il x root 3 x PF
Or
Pt = El x Il x root 3 x cos theta
What is the formula to find power out of a motor?
Pout = Pin - losses
What is the formula to find copper losses?
I^2 x R
What is the formula to find Regulation?
Enl - Efl / Efl x 100
How do you find E gen of a short shunt generator?
V drop across armature resistor + V drop across shunt winding
How do you find efficiency of a generator?
Add both of the wattages produced in the generator (armature and resistor). Divide terminal power by the armature and resistor power.
Pa + Par / Pload
Or Pout / Pin
What is the formula for Output Voltage of a generator?
Egen - IR drop in armature and brushes
What is the formula to find frequency?
F = P x N / 120
Frequency = number of poles x RPM / 120
What is the formula for the 1 wattmeter method?
Pt= W1 x 3
What is the formula for the 3 wattmeter method?
Pt = W1 + W2 + W3
What is the formula for the 2 wattmeter method?
Pt = W1 + W2
Formula for finding synchronous speed in AC motors
S = 120 x f / P
P is number of poles per phase
Formula for rotor slip
Slip % = sync speed - rotor speed / sync speed
Slip amount = sync speed - rotor speed
Formula for finding rotor frequency
f = P x Sr / 120
P is number of stator poles
S is slip speed
How do you find impedance of a transformer?
E short circuit / E rated
How do you find efficiency of a transformer?
Power out / power out - power losses
How do you find fault current of a transformer?
I full load of the secondary / %Z
Horsepower of an AC motor
HP = (torque x speed) / constant
