Sunny Boy 2000
Technical Description
SB2000-11:EE
- 13 -
SMA Regelsysteme GmbH
Automatic Grid Disconnection Device (MSD)
This chapter covers the safe disconnection of the inverters in case of a grid discon-
nection from the electricity company. That means that in the case that the electricity
company disconnects part of its grid e.g. in order to conduct maintenance work on
the grid sufficient safety for maintenance personnel must be guaranteed. In order to
guarantee this safety the employee association for precision mechanics and electric
engineering developed a safety concept that became part of the VDEW guidelines in
August 1994.
The Sunny Boy String Inverter is absolutely restricted to supplementary grid feeding
operation - i.e. the grid feeding must stop in case the local electricity supply is cut off.
The Sunny Boy is equipped with a certified automatic disconnection device for the
safe disconnection when the external grid is down in order to avoid islanding. This
disconnection device is officially certified by the employee associations.
The device is a ”Selbsttätige Freischaltung für Eigenerzeugungsanlagen einer
Nennleistung
≤
4,6 kVA mit einphasiger Paralleleinspeisung über Wechselrichter in
das Netz der öffentlichen Versorgung“ (i.e.: "Automatic Disconnection Facility for
Photovoltaic Plants with a Rated Output
≤
4.6 kVA and a Single Phase Parallel Feed
by Means of an Inverter into the Public Low-Voltage Mains").
For maximum safety it is important that the automatic disconnection device consists of
two independent units for mains monitoring, each equipped with a disconnecting de-
vice and connected in series. Each of these devices permanently supervises the pa-
rameters of the connected grid by checking the voltage, frequency, and impedance.
The redundant design and an automatic self-test before each connection to the mains
guarantee its reliable function.
While former disconnection devices for islanding detection only checked the voltage of
the connected three-phase mains, the new concept uses above all the mains imped-
ance alterations in the one-wire mains (feeding phase) as a measured value for dis-
connection. In addition voltage and frequency in the one-wire mains are also checked.
