I think that is time to write a short treatise on the small hydroelectric
turbines Governor principles for those that are not well versed on them.

The hydro electric turbines are becoming a very common sight along the farm
and rural lands where the electricity may be absent or extremely expensive
to tend power lines to feed power to a farm in the boondocks.

Too many farms have small stream, some continuous flow even during the hard
freezing  winter when the farm owner needs most to supply energy to keep the
home warm without burning the whole forest for heating wood.

The hydro electric governor , the electronic one, may take information from
the turbine or the generator to keep the output of the generator stable.

We are assuming that the generator is going to produce AC voltage, 120 or
240 , single or 3 phase -- and will initially aim to detail the governors
for a single phase generator.

GOVERNOR PARTS simple unit.

1) Sensor
2) controller
3) ballast loads

1) SENSOR

There are different forms to detect the RPM or the Voltage or  the Frequency
of the generator.

1A) Frequency detector : this method is the most common, it uses a small
transformer, usually the same transformer that supplies the low power to
feed the governor itself.

Zero cross detector feeds a pulse every time the sine wave crosses zero
volts and that is 2 times per hertz, this short pulse is phase compared to a
reference oscillator that has the same time period that the frequency of the
local GRID, 60 or 50 HZ  -- the comparison produces an error with direction
that directs the controller to load or unload the generator to make it to
decrease or increase its RPM to keep it constantly within the parameters set
for such hydro electric system.


1B ) RPM detector, a sensor applied to the shaft of the turbine to detect
the RPM and its changes to do the same procedural control of the generator.
.

There are several methods to compare the RPM,

Small generator ( in a sense a PMG motor ) that is couple to the shaft of
the generator producing an output voltage proportional to the RPM, in a
sense it has a KV= V/RPM that is compared to a reference voltage and the
direction of the comparison defines loading or unloading the generator
within certain range.

Photo cell aimed to the shaft with reflecting surfaces and the number
depends on the design.--

Magnetic pickup this type has different arrangements, one common is external
to the generator coupled to the shaft that has one or more small magnets to
generate pulses into the magnetic pick up.

Internal magnetic pickup set to sense the pole of the generator rotor -- now
a days rarely used .!!

1C) Voltage level detector :  Some generators do not have the requirement to
have the operating frequency fixed , they have the requirement to have the
generated voltage output fixed with the frequency often varying a bit above
the local national grid frequency.

With the generators producing Vac there is a transformer to bring the
voltage down for the controller power supply and this same rectified voltage
is also used to detect the generator output voltage for the sensor to report
the changes to generate the correction.

The sensor output is reported to the controller  -- will continue.

This detector is also used to level detect the DC generated voltage if such
is the case..