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re: power-return notification
13 aug 2000
h.g.  wrote:

>you only need one cycle of phase locking to do the transfer,
>though several were used to insure clean operation.

how would that be done with the scheme you described? 

>current measurements and conditions met assures that you are not coupling
>grid and backup  that may be disastrous if backup goes out of phase.

sounds good. a circuit breaker might do that more easily.

>please do no complicate your life with such arrangement. and life
>is short, make it pleasant, this scheme make "explode" ( ;-{) .

sounds dire. perhaps the generator should live in a small concrete block
room in the basement, a thermal accumulator with the holes in the blocks
exposed, ie horizontal, and lots of 4" pvc pipes full of water in the
ceiling, and a good vapor barrier with no insulation. the exhaust could
exit the room via a flexible steel hose and a long copper coil as a heat
exchanger. the intake could depressurize the room, which might also have
a smoke detector and co monitor. a fan would blow air across the motor
and generator for better cooling.

let's see: a $900 92 pound 1500 w honda burns 0.23 gal/h of gasoline,
producing about 26k btu/h of heat as well as the electrical output, so
we need about 26k/(10x1.5) = 1733 ft^2 of thermal mass surface (eg 173
4" x 10' water pipes) for a 10 f temperature rise with 1.5 btu/h-f-ft^2
of still air surface film thermal conductance, or 400 ft^2, with more
fan power and 8 mph of air velocity. a 40 f temp rise over a 6 hour run
requires 26kx6/40 = 3800 btu/f of thermal capacitance, eg 70 water pipes.
the blocks each add about 3 ft^2 and 5 btu/f. seems doable. now how do
we control the house temperature?

>generator parallel operation is very troublesome and very expensive,
>the only way to do it is to have the generator rotor field phase
>angle to be variable.

induction generators are easy and cheap, but hondas don't come that way. 

>some years ago that arrangement was experimented and tested...
>it worked great until one day the scrs, used to switch the magnetic field,
>short-circuited and presented an instantaneous lock to the gasoline motor,
>parts of metal flew everywhere, happily nobody was hurt.

sounds like a circuit breaker or a big fast fuse might prevent this.

>to parallel two power sources you need to determine who is supplying power,
>the amount , the direction etc. this setup can be done by using three
>current transformers, one at the grid input, one at the generator output
>and one at the load. the setup is somewhat complicated and would require
>much of my time to explain it.

pity. sounds like overkill. perhaps we can hear more about that system
if you should find time.

>i think that home gasoline fed power co-generation tied to the grid is
>highly un-economical.

not if we can use the heat, with an inexpensive grid interface and a
long-life generator. it tends to eliminate the smaller of the house
heating and electric bills. my exploration of hondas indicates that
a 1500 w version will last about 6,000 hours before needing a $100
ring job, and another 6,000 before scrapping. meanwhilst, we've made
18,000 kwh of electrical energy and about 60,000 kwh of useful heat
while burning 2760 gallons of gasoline, about $4.1k at $1.50/gallon,
(or less, with off-road gas), plus $900 for the generator and $100
for rings and $100 for 72 quarts of oil (which might also be burned.)
that's $5200 for 18,000 kwh of electrical energy and the equivalent
of about 2400 gallons of oil heat.

>hydro co-generation tied to the grid is great...

where's the heat? we need to distinguish parallel operation from
cogeneration, ie combined heat and power. most utilities that burn
fuel waste about 2/3 of the fuel's heating value. people with local
heat needs don't have to do that. 

>...quite few states in usa limit the pay back to a maximum of zero money
>due to the grid power company, any surplus fed to the grid is not
>reimburse as profit for the hydro co-generator.

the trend is in the other direction. one trace microsine dealer suggests
that users "might want to inform the utility" :-)

nick




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