Sunny Boy 700
Technical Description
SB700-11:EE
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13
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SMA Regelsysteme GmbH
Disconnection from Grid (MSD)
This section covers the safe disconnection and shutdown of the inverters in case the
public electricity grid goes down. If the electricity supplier disconnects part of his
electricity grid e. g. to make repairs one has to make sure that nobody working on the
grid is harmed. In August 1994 a new safety concept was included into the VDEW
regulation initiated by the “Berufsgenossenschaft für Feinmechanik und Elektrotech-
nik“ (German Employee Association of Precision Mechanics and Electronics Engi-
neering).
The Sunny Boy string inverter is designed only for utility interactive operation. To en-
sure safe shut-down in case of grid disconnection etc. and to avoid an “islanding
condition” the inverter is equipped with an independent disconnection device that has
been certified by the “Berufsgenossenschaft für Feinmechanik und Elektrotechnik“.
The regulation is called “Automatic disconnecting facility for photovoltaic
installations with a nominal output
≤
4.6 kVA and a single phase parallel feed
by means of an inverter into the public low-voltage mains“.
For maximum safety this independent disconnection device consists of two separate
MSD (Mains monitoring with allocated Switching Devices) that are connected in se-
ries. Each of these MSD constantly monitors the grid quality by checking the fre-
quency, voltage and impedance. The redundant circuit and an automatic self test on
each system startup ensure a reliable function of the disconnection.
Older islanding detection systems only evaluated the voltage of the 3 phase electric-
ity grid. The new detection system additionally evaluates the grid impedance of the
feeding phase as well as the voltage and the frequency of the connected phase.