Functional Grounding; Installation Requirements; Inverter Settings; Multiple Cs Inverters On Asingle Transformer - Mastervolt CS15TL RP User And Installation Manual

11 FUNCTIONAL GROUNDING

11.1 FUNCTIONAL GROUNDING
During normal operation, the CS inverter will balance the DC
voltage on its terminals around the PE potential. This means
the negative DC terminal will operate on a negative poten-
tial with respect to PE and vice versa for the positive DC
terminal. Certain PV module types cannot withstand this bal-
anced operation and may suffer accelerated degradation in
case the array is left floating. In such a case, one of the DC
terminals of the PV array must be grounded. This is called
Functional Grounding. For more information, refer to www.
mastervoltsolar.com.
The SunMaster CS inverter cannot operate
when functionally grounded, unless an isolation
transformer is used.
Protective grounding is not the same as
functional grounding. The mechanical structure
of the PV array should always be grounded.
This also applies for the AC side of the CS
inverter (see section 5.4)
11.2

INSTALLATION REQUIREMENTS

The CS inverter can support operation with functional
grounding if the following conditions are satisfied:
• A suitable isolating power transformer such as
CS-IT20 is installed.
• The secondary neutral terminal of the isolation
transformer is NOT grounded.
• Both DC inputs are paralleled.
• The inverter PE terminals are always grounded.
Either the Positive or Negative DC terminal can be
grounded. Refer to figure 11-2 for a SIMPLIFIED
installation diagram.
11.3

INVERTER SETTINGS

When the installation is complete, the inverter can be
commissioned according to the procedure described in
section 5.6. After the initial start-up and first configuration
steps, the inverter will report an insulation failure on the
DC terminals. The inverter will not switch on.
1. On the CS inverter display, go to Configuration Page.
2. Enter the Installer Code.
3. Go to the Grid interface menu and select Options
4. The Options menu will show the isolation detection
settings. Refer to section 8.9.2.3 for details.
EN / SunMaster CS15TL RP / CS20TL RP / CS30TL RP
Figure 11-1: Isolation detection
5. Set the Function parameter to "Pos GND" or "Neg GND"
depending on which DC terminal has been grounded.
Push the OK button to confirm.
6. Adjust the Rlimit value to the lowest setting. Push the OK
button to confirm.
7. The settings are now saved in the inverter memory. You
can return to the Home Screen with the BACK button.
The inverter will now start up.
During every start-up from now on, the inverter will check
the integrity of the functional grounding.
If grounding has failed and the isolation resistance of the PV
array is higher than the Rlimit threshold value, the inverter
will issue an error message and remain in stand-by mode.
DC
+
DC
-
+
-
PE
CS 30 TL
Figure 11-2: PE at DC input isolation transformer
11.4 MULTIPLE CS INVERTERS ON A
SINGLE TRANSFORMER
If more than one inverter is connected to one transformer,
the ground connections may cause the insulation detection
to trip.
It is not recommended to install multiple CS inverters on a
single transformer. Ground loops may occur and trigger the
RCD protection in the inverter. Installations with multiple CS
inverters requiring functional grounding can best apply a
separate transformer for each inverter. Alternatively, a
transformer with multiple isolated windings may be used.
AC
CS-IT20
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