JM> Follow up on Risky Hydro thread...
 
 JM> Generator:  20hp, 1750rpm, 3ph, 575V, TEFC Toshiba Premium
 JM> efficiency motor used as an induction generator at 480V system
 JM> voltage 
 JM>  
 JM> Wire run:  about 2000' of #8AWG Tray Cable strung on insulators
 JM> attached to trees.  (Up to 60V drop in transmission = 1.5 kw loss
 JM> at max. power)
    ***********    CORRECTION: IT WAS #10AWG TRAY CABLE.
 JM>  
 JM> Capacitors:  7 Kvar at generator end of transmission line to
 JM> correct power factor and minimize amps and losses in the wire
 JM> run.
 JM>  
 JM> Grid Intertie:  Power Co. required  Over & Under Voltage, and
 JM> Over & Under Frequency relays.  We used inexpensive devices from
 JM> TimeMark Corp. and got off cheep at about $350 total for the two.
 
 
AC> Good one! Seems you knew what you were doing and had some good
AC> theoretical advice.
 
AC> Do those Relays prescribed by your Power Co, operate with the
AC> contacts in a battery supply? Control and protection relays don't
AC> always function correctly, if the control circuits are AC.
 
AC> I am remembering the technical reports, after the [in]famous NE USA  
AC> blackouts 15? 20? years ago? Control room operators at some sites
AC> were examining their switch console settings by flashlight, and 
AC> airliners were circling blacked out airports whose radio comms
AC> [failed] were driven from 60Hz supply. We had quite
AC> a few giggles here, because AUS utilities followed the UK practice
AC> of battery dependence for secure circuits.
 
Alec,
No, there is no battery backup on the O/U Voltage or O/U Frequency
relays, but they "fail safe". That is, they are in series with the motor
contactor holding coil and the solenoid shut down latch.  They are
normally open, and close on freq.& voltage in normal limits, enabling
startup,  and drop out in a fault condition causing a full system
shutdown.  The control circuitry is my design.  
 
 JM> We have a manual reset arrangement to turn off the water in the
 JM> event of an electrical fault or grid outage.  This is advisable
 JM> so as not to waste water or overspeed the motor and bearings. 
 JM> This shutdown arrangement is a real Rube Goldburg.  A solenoid
 JM> keeps a latch closed until a fault condition.  On a fault , a
 JM> cable is released allowing a weight to drop which pulls on
 JM> another line closing the ball valves feeding the turbine.  To
 JM> prevent rapid closing of the valves and possible water-hammer
 JM> trouble, the weight is restrained by another cable connected to a
 JM> hydraulic door closer used as a dashpot.
 
 
 
AC> Hope you have an independent speed governor or overspeed device. An
AC> overfrequency relay is *NOT* an adequate detector for overspeed. If
AC> add a governor [eg flyballs] suggest you *DON'T* use a belt drive
AC> for it unless you  figure carefully, the results of belt failure.
AC> Which is often to open wide the water gate [sorry! Politics
AC> again....]
 
Well, no, we don't.  Had the Power Co. not required it, I wouldn't have
used any protective relaying at all, other than the overloads relays
(heaters) and fuses in the motor contactors, and the valve shut-off
device.
 
No speed regulation is required with the line synced induction generator
arrangement.  The O/U Voltage and O/U Frequency relays are there just to
satisfy the Power Co.'s concern there could be a possibility, however
slight and remote,  that with the associated capacitors nearby, the
induction generator could become self-exciting and back-feed the Power
Co.'s line during a power outage or a fault on their system.  The O/U
frequency relay does not adjust water flow.  It can only act to totally
shut down the system electricly and to trip the mechanical water shut-
off.  
 
It was my position, (tho I didn't really argue because it was not a lot
of money to keep them happy) that no back feed into their lines could
occur in an outage because the load, just on our side of the meter, was
too large for our little Gen to support, and that supporting the system
voltage for even a scant instant was not a realistic possibility.  As
soon as the system voltage is lost, the holding coils in the motor
contactors will drop out, taking the Gen off-line. It then would need to
be manually reset.  The capacitors are on a separate contactor, so that
they are isolated from the motor if either holding coil drops out.
 
The relays they asked for do, however, protect my Gen system, if, say,
the long transmission line to its remote location were to be severed by
a falling tree or some such.  The Gen would then have no connected load,
and voltage  could build to damaging levels in the Gen/Cap circuit.  So
probably I would have needed to rig an Overvoltage device of my own had
I not bought the relays.  
 
I'm not too much worried about mechanical damage from overspeed.  Normal
speed is 1800 rpm so runnaway speed would be about 3600 rpm.  The runner
and bearings should take that OK.  Less certain from my knowledge is the
rotor of the motor.  I don't think, tho, that 3600 rpm would damage the
rotor of a motor designed for 1800 rpm,  It may even be the identical
design.  Of greater concern to me is the wasted water, in an off-line
but still spinning under power situation, as we have no excess in our
pondage.
 
 JM> We spent about $7,000 on pipe, wire, motor and other items, but
 JM> much of the electrical stuff, starters and meters, was scrounged
 JM> or salvaged from storage.
 
 
AC> Cheap! More fun than buying a cute old auto.
 
 
Yes, it is cheap, Alec.  Much R&D and labor is not included in that
figure, but the system is still a lot for a little expense in material. 
The use of an induction generator is a big factor there.  The control
system, cost of generator, protective relaying,... all the electrical
stuff, is kept cheap using the induction generator.  I'm taken with the
idea, and have used it in several applications.  I've been promoting it
here on the echo as I think it deserves to be more widely known and may
be an excellent solution for many home-power applications.
 
I am considering adding a power-flow direction relay.  That was one
of the reasons for my inquiry on the echo.  This relay would be used
to shut things down if the induction generator started consuming
power, as might be the case if the water flow were interrupted by a
plugged intake or something, or if a bearing goes bad.  I was given a
slick, diode based circuit by a fellow on the electronics echo (an
adaption of a double balanced mixer circuit).  If folks are
interested, I will post it here.
--- FLAME v1.1
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