Eaton Power Xpert Solar 1500 User Manua page 67

During normal operation while exporting power (current) to
the grid, should a PV ground fault occur, either CB3 will trip
(open) or the fuse clear (based upon actual fault). In either
case, the inverter will stop, opening contactors K8/K9/K10,
CB1, and disconnects DS1-3. This will isolate the inverter
stacks from the fault and annunciate the required Ground
Fault Error Message, DC Ground on the HMI and Modbus.
Once fuse F3 and/or CB3 is tripped, the GFDI circuit
continues to maintain system safety through the 4000 Ohm
RG1-4 resistors. With either/both CB3-open or F3-cleared,
the resulting single-point-ground's open-circuit will allow a
small electric current (Voc/4000 = X mA | 1000/4000 =
250 mA) to trickle through resistors RG1-4 to the PV-negative
conductors grounded bus at the inverter's re-combiner.
Understanding Kirchhoff's Voltage Law (KVL), each RG1
resistor will drop (X mA x 1000 = XV | 250 mA x 1000 =
250 V) volts, in essence the entire Voc potential (disregarding
PV-system conductor resistance). This will minimize the
shock-potential between equipment ground and
grounded-PV conductors. Note: When diagnosing a PV
ground fault, if voltage measured across RG1-4 is lower than
the expected string-voltage (Voc), expect a ground-fault along
the string(s) at the relative voltage corresponding to the
number of modules (Voc). Furthermore, individual Module Isc
is equal to the "string Isc" due to the series-connection of
the modules per string. Only at the source-combiner, post
string fuses, is the module or string Isc additive (increased).
Critical to an effective GFDI is the PV grounding electrode
system, and its bonding to the inverter GET (i.e., GET bus-1).
The PV system must always be built with a PV Grounding
Electrode System, bonded to the inverter's GET. The
minimum bonding conductor size is 3/0 as per UL1741 for
the 1500/1670 kW inverters.
DANGER of Electric Shock Hazard
When a Ground-Fault is present.
WARNING!
When a Ground-Fault is present.
NOTICE!
IF A GROUND FAULT IS INDICATED,
NORMALLY GROUNDED CONDUCTORS
MAY BE UNGROUNDED AND ENERGIZED.
Power Xpert Solar 1500/1670 kW Inverter MN141001EN—October 2014 www.eaton.com
Ground Fault Troubleshooting Checks
Figure 29 shows the GFDI connections. The circuit is
comprised of 3 components:
1. Ground Fault Device (sensor) GFD1 set to 5 A.
2. Fuse—opens the ground path during a ground fault.
Fuse has a trip-indicator, evoking the holder's
●
microswitch change-state.
Operates even when AC power is removed from the
●
inverter
3. Circuit-breaker—shunt tripped by the CS1 or fuse-holder
microswitch during a fault.
Operates when the inverter is ON (control power
●
must be present).
The fault-interrupter design is a redundancy system, as either
CB3 or F3 (both are in series connection) can react to open/
operate/function during a ground fault event.
Step 1: Verify the GFDI tripped CB3 or cleared 5 A F3
If tripped or cleared; determine if the fault is a positive or
negative ground fault.
Measure the DC voltage across resistors RG1-4, looking for a
"negative" value if the DMM ground-lead is placed on GET.
GET Bus-1 to Grounded-PV-Conductor bus
●
If voltage is present, there is a faulted PV positive conductor
in the PV-array system. Typical damage is found in
non-protected module string-conductors in-route to the
source-combiners, or source-combiner output circuits faulted
inside conduit in-route to the PV-Disconnects or inverter.
Once the fault is repaired, install a new 5 A F3 fuse if
●
damaged
(check fuse for an open circuit: ∞ Ohms)
●
Re-set (close) CB3
●
Re-cycle inverter power
●
Turn-on the inverter
●
If voltage is NOT present across resistors RG1-4, suspect
a negative PV ground fault. Typical damage is found in
non-protected module string-conductors in-route to the
source-combiners, or source-combiner output circuits faulted
inside conduit in-route to the PV-Disconnects or inverter ...
circumventing the fundamental single-point-ground of a
grounded PV system.
Once the fault is repaired, install a new 5 A F3 fuse if
●
damaged
(check fuse for an open circuit: ∞ Ohms)
●
Re-set (close) CB3
●
Re-cycle inverter power
●
Turn-on the inverter
●
Troubleshooting
57