Part 2 – Alternator Relationships

Generator Poles

The relationship between alternator speed, frequency, and the number of pole pairs can be summarized by the following formula:

$f = \frac{pN}{60}$

Where,

Example 1:

A generator connected to a hydraulic turbine turns at a speed of 300r/min and generates 60 Hz power. How many pairs of poles does it have?

Solution 1:

$\begin{align*} p &= \frac{f \cdot 60}{N} \\ &= \frac{60 \cdot 60}{300} \\ &= 12 \text{ pairs of poles} \end{align*}$

Example 2:

A generator connected to a hydraulic turbine has 4 pole pairs and generates 60 Hz power. How fast is it turning?

Solution 2:

$\begin{align*} N &= \frac{f \cdot 60}{p} \\ &= \frac{60 \cdot 60}{4} \\ &= 900 \text{ rpm} \end{align*}$