16 ATEX-certified motor thermal protection function with PTC thermistor relays (+L513+Q971)
Description
This protection function monitors the temperature of a motor with PTC resistor sensors
(PTC thermistors) in a potentially explosive atmosphere. It is possible to
• monitor either the motor’s bearings or windings (+L513+Q971) or
• monitor both the motor’s bearings and windings (+2L513+Q971 or +3L513+Q971).
The function is activated when the PTC sensor resistance exceeds the overtemperature
limit. The function activates the Safe torque off (STO) function of the drive. This disables
the control voltage of the power semiconductors of the drive output stage. This prevents
the inverter from generating the torque required to rotate the motor. The motor coasts to a
stop.
ACS880-07/17/37 drives with the option +Q978:
Also the main contactor/breaker is
opened.
ACS880-07 drives, frames nxDXT + nxR8i with a main contactor/breaker (option +F250/
+F255) and ACS880-17/37 drives, frames nxR8i + nxR8i: When the STO function is
activated in the inverter unit, the main contactor/breaker is opened after user-defined delay
(defined with parameter 94.11, the default value is 600 s). See hardware and firmware
manuals for more information.
Other safety functions in the drive can also use the STO function. In addition, the FSO
module can be included in the activation sequence of the ATEX-certified motor thermal
protection function. See the circuit diagrams delivered with the drive for the actual safety
circuitry.
The FSO safety functions module (FSO-12 or FSO-21) is an optional device used with the
ACS880 drives to implement safety functions. When installed, it reserves the standard
STO connection of the drive. In this case, the FSO module activates the STO function of
the drive (that is, opens the drive STO circuit) either immediately or after a deceleration
ramp.
You can implement the motor thermal protection function with or without an FSO safety
functions module:
• Without an FSO module, the opening contacts of the PTC relay(s) open the STO
circuit of the drive (see section Without an FSO module on page17).
• With an FSO module, the opening contacts of the PTC relay(s) activate the STO or
Safe stop 1 (SS1) function of the FSO module and the FSO module opens the STO
circuit of the drive (see section With an FSO module on page 18). For more
information on the safety functions of the FSO module, see FSO-12 safety functions
module user’s manual (3AXD50000015612 [English]) or FSO-21 safety functions
module user’s manual (3AXD50000015614 [English]).
Always consider which stop category (0 = immediate STO or 1 = delayed STO after SS1)
is more appropriate for the motor in overtemperature situations.
The protection function circuit is motor specific, also in multidrives where several motors
are connected. The function stops only the motor where overtemperature is detected.
It is possible to get information on the status of the protection function by means of a
normally-open contact. The information can be obtained separately from the bearing and
stator thermistors. The contact can be wired to a digital input on the drive control unit or to
an external control system. For instructions, see section Wiring on page 23.
The temperature measurement circuit of ABB Ex motors has basic insulation. For
information on the insulation of the thermistor relays, see its data starting on page 56.
00 ACS880 ATEX cabinet.book Page 16 Tuesday, May 28, 2019 10:25 AM
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