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2.2 PE Connection and Leakage Current
PV System Residual Current Factors
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In every PV installation, several elements contribute to the current leakage to protective earth (PE). these
elements can be divided into two main types.
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Capacitive discharge current - Discharge current is generated mainly by the parasitic capacitance of the PV
modules to PE. The module type, the environmental conditions (rain, humidity) and even the distance of the
modules from the roof can effect the discharge current. Other factors that may contribute to the parasitic
capacitance are the inverter’s internal capacitance to PE and external protection elements such as lighting
protection.
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During operation, the DC bus is connected to the alternating current grid via the inverter. Thus, a portion of
the alternating voltage amplitude arrives at the DC bus. The fluctuating voltage constantly changes the
charge state of the parasitic PV capacitor (i.e capacitance to PE). This is associated with a displacement
current, which is proportional to the capacitance and the applied voltage amplitude.
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Residual current - if there is a fault, such as defective insulation, where an energized cable comes into
contact with a grounded person, an additional current flow, known as a residual current.
Residual Current Device (RCD)
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All Energizer Force S Series inverters incorporate a certified internal RCD (Residual Current Device) to
protect against possible electrocution in case of a malfunction of the PV array, cables or inverter (DC). The
RCD in the Energizer Force S Series inverter can detect leakage on the DC side. There are 2 trip thresholds
for the RCD as required by the DIN VDE 0126-1-1 standard. A low threshold is used to protect against rapid
changes in leakage typical of direct contact by people. A higher threshold is used for slowly rising leakage
currents, to limit the current in grounding conductors for the safety. The default value for higher speed
personal protection is 30mA, and 300mA per unit for lower speed fire safety.
Installation and Selection of an External RCD device
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An external RCD is required in some countries. The installer must check which type of RCD is required by
the specific local electric codes. Installation of an RCD must always be conducted in accordance with local
codes and standards. Energizer Force S Series recommends the use of a type-A RCD. Unless a lower value
is required by the specific local electric codes, Energizer Force S Series suggests an RCD value between
100mA and 300mA.
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In installations where the local electric code requires an RCD with a lower leakage setting, the discharge
current might result in nuisance tripping of the external RCD. The following steps are recommended to avoid
nuisance tripping of the external RCD:
1. Selecting the appropriate RCD is important for correct operation of the installation. An RCD with a rating of
30mA may actually trip at a leakage as 15mA (according to IEC 61008). High quality RCDs will typically trip at a
value closer to their rating.
2. Configure the trip current of the inverter’ internal RCD to a lower value than the trip current of the external RCD.
The internal RCD will trip if the current is higher than the allowed current, but because the internal inverter RCD
automatically resets when the residual currents are low it saves the manual reset.
2.3 Surge Protection Devices (SPDs) for PV Installation
WARNING!
Over-voltage protection with surge arresters should be provided when the PV power system is installed. The
grid connected inverter is not fitted with SPDs in both PV input side and mains side.
Lightning will cause damage either from a direct strike or from surges due to a nearby strike.
Summary of Contents for Force 10.5S
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