# Change in frequency in a grid that has lost generation?

I have an example about droop and it asks to calculate final frequency in a grid after one generator power generation is lost. The answer is given as 59.889 Hz; however, I am calculating as 59.99 Hz. What am I missing?

The question is

Assume a grid has lost one generator (42MW) and the remaining
generation is 1132 MW. All generators have governors set to 5% droop.
What is the final frequency?


This is the given formula

$$\Delta(f) = \frac{R.\Delta P_{gen,MW}}{\sum S_{online, MVA}}.$$

$$\Delta(f) = \frac{0.05 \times 42}{1132}=0.0019.$$ Final frequency is 60-0.0019=59.9981

• From the formula you've applied, I'm confused how did you arrive at a S=1132 MVA, since the power factor of the grid is not mentioned nor is anything about capacitor banks used at generation end being mentioned. In that way, I could see it's possible for your S (complex power VA) to be higher than 1132 MW if the load is not purely resistive (UPF). – Aditya Madhusudhan Dec 2 '17 at 16:04
• power factor is not mentioned in the question, for that reason I assumed it is 1. – Reiso Dec 2 '17 at 16:43