(A, B) Formulas Flashcards
An induction motor consists of
A stator and motor assembly
The motor speed lags the….
Magnetic field speed
Synchronous speed formula
ΠSYNC= (120 • f{Hz}) / NPOLES
Slip speed formula
Ns = Nsyn - Nr
Ns = S x Nsyn
Nr = speed of rotor (r/min)
Slip formula
S = Ns ÷ Nsyn
NS - slip speed
Define rotor resistance
Rr (constant)
rotor voltage formula
Er = S x Ebr
Ebr = blocked rotor
Rotor frequency formula
Fr = S x Fbr
Fbr = 60
rotor reactance formula
Xr = S x Xbr
rotor impedance formula
Zr = squared root of Rr squared + Xr squared
Rotor current formula
Ir = Er ÷ Zr
Speed of rotor (rotational frequency)
Nr = Nsyn - ns
Reactive rotor current formula
Ir(R) = Ir x Pfr
Producers torque
Is the only quantity that increases then decrease as rotor accelerates.
define EZFIX
Induced voltage
Impedance
Frequency
Induced current
Inductive reactance
PF
Resistance
Power factor formula
Rr ÷ Zr
Torque formula (Nm)
T = F x r
T - tourque
F - force in newtons (N)
r - radius in meters
Mechanical power formula
Also known as full load torque
P = T(fl) x n ÷ 9.55
P - power in watts
n - rotational speed / frequency in revolting per minute. (r / m)
When mechanical power is required to be in horse power the formula is
Hp = T x n ÷ 7121
7121 is 9.65 x 746
Motor Efficiency formula
P out ÷ p in
P out = hp x 746
P in = P out plus P losses (heat) or (V x FLA) full load current rating.
1 hp = ___ kilowatt
0.746
Motor % speed regulation formula
%nreg = n (nl) - n (fl) devided by (fl) x 100
n - speed
nl - no load r/min
fl - full load r/min
N full load = Nsyn - ns
Permissible output power formula
Service factor x nameplate horse power
Breakdown torque means
Rr = Xr
Breakdown torque occurs at what pf?
0.707
