Safe Torque Off (Sto) - Bitzer VARIPACK FD+6 Instructions De Service

Fig. 16: Table for the analysis of the harmonics FEU+24 .. FKU+260
Assumptions: Rsce = 120 at 400 V
FEU+24 - FKU+260 meet all requirements of the stand-
ard EN61000-3-12:2011 (see figure 14, page 23).

5.6 Safe Torque Off (STO)

As standard, the VARIPACK frequency inverters are
equipped with a certified and safety-tested shut-off
function, Safe Torque Off (STO).
• This function can be used as cut-out device for pre-
vention of unexpected start-up as described in
EN60204-1, 5.4. This so-called STO function makes
sure that no drive energy is transferred to the motor
as long as the function is active. Thus the com-
pressor motor is safely free of torque but not de-en-
ergized. This function was tested at the factory.
• The STO function is active if the STO circuit is open
or less than 21.6 V are applied. It then cancels each
compressor start command and also start com-
mands that could be triggered internally by a firm-
ware error. The hardware of the STO control circuit
consists of two redundant channels which are de-
signed in a way that, in case a channel fails intern-
ally, the other channel is still able to prevent any un-
intentional FI operation. The hardware meets the so-
called high requirements regarding functional safety.
Due to the related classification as high demand
24
mode, their functionality needs to be checked once a
year.
• Due to the STO function, the main contactor before
or after the VARIPACK may be omitted. Instead of
being switched as before via the main contactor, the
STO, switched via the high pressure switch or other
safety-relevant protective functions, can shut off the
compressor directly.
DANGER
Risk of electric shock!
The STO function is not a galvanic isolation of
the voltage supply and may therefore not be
used for maintenance or repair work!
It is only an electronic protective function during
normal operation of the VARIPACK frequency
inverter.
Prior to performing maintenance or repair work,
the VARIPACK frequency inverter must be com-
pletely disconnected from the mains supply us-
ing a suitable electrical disconnecting device
and proper insulation of all voltage connections
must be checked!
Switch off the main switch and secure it against
being switched on again.
Wait for at least 5 minutes until all capacitors
have been discharged!
CB-100-2