National Grid frequency trace

The attached dataset provides the GB grid frequency every second
for two hours (02.00-04.00) on 1 September 2015 (at some location that I
do not remember).  I used it to test some linear stochastic
process models for the frequency as a function of time.  On the
2-hour timescale the trace fit reasonably well to an Ornstein-Uhlenbeck
(OU) process with a decay time of around 30 minutes.  On a
shorter timescale, in particular the first 3 minutes 20 seconds, the trace
looked smooth so I fitted it to a first-order filtered OU process, which
gave me time constants of 11 minutes and 1.9 seconds.  This was
important evidence that a useful model for power imbalance as a function
of time is a filtered white noise.  Furthermore, the power
spectrum of the 2-hour trace showed a regime with slope around -4 for
periods shorter than 25 seconds, consistent with being a first-order
filtered OU process, until the Nyquist cutoff at 2 seconds.