# Monitoring a hydro-electric power station

Hallo OpenEnergyMpnitor Team!

I would like to buy your product. However, I need it to monitor a small hydro-electric power station with a power of about 15-25 kwh.

Can you use emonPI or emonTx?

thank you

Certainly, provided you use the correct voltage and current transformers.

Is 15-25 kWh you average hourly/daily energy generation? That doesnât really help me. What I need to know to be able to advise you is the voltage at the point where you want to monitor (or points if there is a choice), the number of phases you need to monitor, and the rated phase current or the rated capacity of the generator.
You will be able to use only an emonPi if it is a single phase system that you have, or if it is a 3-wire delta system (the generator has no neutral connection), but you must add an emonTx if you have a star connected 4-wire system.

It is a small hydro-electric power station with a generator with 3 phases / 400V and a power of max. 20 kW.

The previous 25kwh was wrong and can be forgotten.

Are the above statements sufficient?

Is it possible with an emonTx and a basestation?
Could one also switch an emonPI in between so that one also has a display?

greetings from Austria

Thank you - here are my calculations:

Max power: 20 kW
System voltage: 400 V line-line, or 230 V line-neutral (or to earth if no neutral).
Line current at max. power: 29 A

If the load on all 3 phases is exactly the same (the system is âbalancedâ), then you need monitor only one phase, and you can have an emonPi only.

However, that is unlikely to be the case, therefore I think you need an emonTx with its 4 current inputs. You will use 3 of the current inputs, and you must choose one phase where you measure the voltage. But a small warning: the voltages of the other two phases cannot be measured with only one emonTx, therefore we must assume that the voltages of all 3 phases will be the same. When they are not, there will be a small error introduced proportional to the difference.

If you think that the error might not be acceptable, then you must have 3 Ă emonTx so that you can measure the voltage of each phase.

If you have an emonTx, I recommend that you have an emonBase and not an emonPi. The emonBase will receive by radio the data from the emonTx, and send it to emonCMS running on the emonBase itself, or to emoncms.org, or to both. The display will be a web page on any computer, smartphone or tablet.

You could have an emonPi instead of (not as well as) the emonBase, but the display on the emonPi is not intended as the principal display of your data. There should be no need for both an emonBase and an emonPi, an emonBase is an emonPi but without the display and the voltage and current inputs.

If you have an emonBase or an emonPi, you need a 5 V d.c USB power supply.
If you have one emonTx, you need one a.c. adapter to measure the voltage.
If you have 3 Ă emonTx, you need 3 Ă a.c. adapters to measure the voltages.
You need 3 Ă 100 A current transformer.
You will probably need a programmer, you will certainly need a programmer if you use only one emonTx because you will need to upload the 3-phase sketch.
You can change 3 resistors in the emonTx to increase the sensitivity of the 3 current inputs, so that they are more suited to measuring 30 A. If you wish to do this, I can tell you exactly what you must do.

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Alternatively, if you just want a feed of power generated you could use an emonPi with an optical pulse sensor to read the Kwhâs elapsed data from the utility meter:

But we do not know if there is a generation meter equipped with an LED pulse output!

Hello Robert!

Unfortunately, the load on the 3 phases is not the same.

I have an emonTx incl. 4x 100A clip-on.

Can you tell me what I must adjust so I then in the CMS see which line I create or how much I leave.

@glyn.hudson:
Thanks for the note but a reading with the optical pulse sensor is not possible.

thank you

You do not need to change the burden resistors, but you will have better accuracy at low currents if you do.

If you take your emonTx out of the case and look at it, you will see the 4 sockets for the CTs, and immediately behind each socket is a SMT resistor with a hole at each end into which you can insert a wire-ended resistor. You will unsolder the SMT resistor and fit a wire-ended resistor instead. We calculate the value of that resistor by knowing the current flowing in it and the voltage we need across it. The current is 29 A (the max current you want to measure) divided by the CTâs current ratio (100 A : 50 mA) = 14.5 mA, and the voltage, after allowing for component tolerances etc, is 1.1 V. Therefore the resistor should be 75 Î©. This will leave you almost no âheadroomâ to allow for overload, so I suggest you should use a 68 Î© resistor. The power rating is not important, 1/10 W is enough but any bigger than 0.33 W will probably not fit between the holes.
(68 Î© will give you a maximum current of 32.3 A, giving you at least 10% overload capacity.)

You will need to download from Github the 3-phase sketch âemonTxV3_4_3Phase_Voltageâ and configure it for your emonTx. The instructions for this are in the sketch. Because of the different burden resistor, the current calibration constants Ical1, Ical2, Ical3 should be 29.41. You can adjust this value to suit the particular combination of input channel and current transformer, or you can write these values into the sketch and in your emonBase, change the numbers in the âscales = âŠâ line in emonhub.conf to give the correct calibration. The numbers are in order, so if L1 is reading 1% too big, the line will read "scales = 0.99,1,1,1,0.01,0.1,0.1,0.1,0.1,0.1,0.1 "