Motor Shaft RPM
A 4 pole induction motor operates with a 0.05 slip, and a line voltage frequency of 30 Hz. What is the motor shaft's rotational speed (rpm)?
Expand Hint
The synchronous speed for ac motors is:
$$$n_s=120*f/p$$$
where
$$f$$
is the line voltage frequency in Hz, and
$$p$$
is the number of poles.
Hint 2
The slip for an induction motor is:
$$$slip=\frac{(n_s-n)}{n_s}$$$
where
$$n$$
is the rotational speed.
The synchronous speed for ac motors is:
$$$n_s=120*f/p$$$
where
$$f$$
is the line voltage frequency in Hz, and
$$p$$
is the number of poles.
For a 4 pole motor operating on 30 Hz voltage:
$$$n_s=120*30/4=900\:rpm$$$
The slip for an induction motor is:
$$$slip=\frac{(n_s-n)}{n_s}$$$
where
$$n$$
is the rotational speed.
$$$0.05=\frac{(900rpm-n)}{900rpm}$$$
Solving for
$$n$$
:
$$$n=900rpm-0.05(900rpm)=900rpm-45rpm=855\:rpm$$$
855 rpm
Time Analysis
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