I can control the hydro power output via a motorized butterfly valve and controller. I can (manually) balance the power generated so that my meter stops and all the power generated is used in the local load. Of course as soon as the load drops I end up sending power back into the grid and paying for it as if I were drawing it from the grid.

How can I use a Square D PM-620 to control (limit to say 100ma) the reverse power flowing to the grid from a generator? But when the generated power falls off (due to local loading) the grid should carry the local load. Or in other words, since the PM-620 can accumulate kWh in signed mode, if I can get an output that reflects this sign, (by reading a register on the PM-620's Modbus?) I could feed this output to the generator power control valve and continually adjust the power generated to cover the local loading but no more.

Maybe Square D makes a reverse power controller to solve this problem? Any application notes out there telling me how to use a PowerMonitor-620 to stop reverse power flow?

If the grid and generator were all DC, a simple diode would solve this problem.

For more info about this Micro Hydro see: http://energyindependence-rob.blogspot.com/

 

Try to check power factor of your system. If the PF goes capacitive, definitely you will have reverse power. Try controlling your voltage regulator using power factor as reference.

 

Rob,

The utility is charging you for the cost of reactive Volt-Amperes (VAr) the induction-motor requires when used as an induction-generator!

Look into providing the motor's reactive VAr requirement with three capacitors installed across the motor's terminals!

Regards,

Phil Corso ([email protected])

 

Rob, further to my earlier post! As you suggested, I reviewed your website. You are to be lauded for your project.

The earlier kWh meter was based on the disk being rotated by an magnetically-induced torque resulting from power flow directed toward your home.

The newer digital kWh meters are all electronic. It appears, to me, that you must negotiate with the utility to have them install a bi-directional kWh meter!

BTW, what is the head (in meters) and water flow-rate (liters per sec) to produce 12 kW?

Regards,
Phil Corso ([email protected])

 

Hi Phil,
We have 65 meter head and 30 L/sec design flow.
I'm about to install another turbine to take advantage of higher winter flows, which can be 1000X summer flows. I just posted that info to the Blog.

So, no 'off the shelf' device to control reverse power flow or power flow direction? Seems to me there have to be situations out there were 2 AC generators are run in parallel, and when one goes down the other must be prevented from feeding back power to the down machine and still support its loads.

Cheers
Rob

 

Rob,

You are being charged by the utility because the calculation for power is equal to:

P = |V|x|A|xPF where,
|V|= Magnitude of Phase-to-Phase current.
|A|= Magnitude of Line current.
PF = Cosine of theta, the angle between V & A.

Let's say that PF for an induction-motor is 0.8, thus the angle of the Ampere vector equals -36 deg. Then, on a polar-coordinate graph it lies in the fourth quadrant. The PF angle is found by:

theta = Cos[(arctan(-kVAr/kW)]

This yields a negative value for theta and current is said to be lagging!

However, when an induction-motor is used as an induction generator, the angle of the Ampere vector, say -130 deg. On the polar-coordinate graph it lies in the third quadrant. The PF angle is found is found by:

theta = Cos[arctan(-kVAr/-kW)]

This yields a positive value for theta and current is said to be leading!

But, the digital-kWh meter just calculates a magnitude without being able to discern between leading or lagging.

Regards, Phil Corso (cepsicon at aol. com)

 

Rob,
Here is an off-the-shelf solution:

http://www.hoytmeter.com/products/Reverse_Power_Relay.html

The M200 Reverse Power Relay is used to monitor the direction of power from AC generators. If the current in the system being monitored is reverse to a value greater then the customer-adjustable presen limit, the relay will energize. The adjsutable trip point is 2 to 20% of input current.

An adjustable time delay of 0 to 20 seconds is provided. Correct setting of the trip point and time delay will ensure protection against motoring in the event of a generator failure and prevent tripping due to transients encountered during synchronization.

I hope this helps,
William Hinton