SMA STP 50-40 - Generating the I-V Characteristic Curve; Setting the Rated Residual Current of the Residual-Current Device

8 Operation
SMA Solar Technology AG
Operating manual STP50-4x-BE-en-23 83
8.22 Generating the I-V Characteristic Curve
Only the STP 50-41 is equipped with this function.
During the measurement, the inverter can briefly interrupt the feed-in or feed in with reduced power.
The duration of a measurement is approx. 20 seconds per MPP tracker. To avoid misuse of the
function and thus yield loss, the measurement can be carried out a maximum of 10 times per day. If
more than 10 measurements per day are to be carried out, the inverter must be restarted.
The measuring curve has over 200 measuring points. The display is from 0V up to the maximum
MPP voltage of the inverter. The current is limited by the maximum possible input current of the
inverter.
The data is stored on the user interface until the next measurement.
Further information as well as help for the interpretation of the I-V-characteristic curve can be found
in the technical information "I-V diagnostic function: Determination of the generator characteristic
curve by the inverter for fault detection in the PV array".
Using the function when using external module optimizers is not
recommended.
Using the function when using external module optimizers does not produce interpretable
results and is therefore not recommended.
Requirements:
☐ In order to avoid misinterpretation of the determined characteristic curve at low powers, a
measurement should be carried out at at least 50% of the inverter's nominal power.
☐ In the case of comparative measurements (e.g. at annual intervals), similar ambient conditions
(solar irradiation, shading, temperature) should prevail.
Procedure:
1. Log on to the user interface of the inverter.
2. Click on Diagnosis in the menu.
3. Select the required MPP tracker.
4. Click on [Start new measurement].
5. Go to [PDF export] or [CSV export] to export the data shown.
8.23 Setting the Rated Residual Current of the Residual-
Current Device
When using residual-current devices with a rated residual current of <500mA, set the rated
residual current to the respective value in the inverter. In this way the inverter reduces the
operational leakage currents and prevents a false triggering of the residual-current device (further
information see technical information "Leading Leakage Currents" at www.SMA-Solar.com).
The basic procedure for changing operating parameters is explained in another section (see
Section8.14, page77).