Thermistor/ptc protection – Rockwell Automation 7763 Medium Voltage OneGear SMC Flex Motor Controller (10-15 kV) User Manual
Page 33
Rockwell Automation Publication 7760-UM001D-EN-P - October 2014
33
Product Overview
Chapter 1
Ground Fault Alarm
The MV SMC Flex will indicate a Ground Fault Alarm if:
•
No warning currently exists
•
Ground fault alarm is enabled
•
GF Inhibit Time has expired
•
GF Current is equal to or greater than the Gnd Flt A Lvl
Parameter 77,
Gnd Flt A Lvl, allows the installer to define the ground fault
current at which an alarm will be indicated. It is adjustable from 1.0…5.0 A.
Parameter 78,
Gnd Flt A Dly, allows the installer to define the time period a
ground fault alarm condition must be present before a trip occurs. It is adjustable
from 0.1…25 seconds.
Thermistor/PTC Protection
The MV SMC Flex provides terminals 23 and 24 for the connection of positive
temperature coefficient (PTC) thermistor sensors. PTC sensors are commonly
embedded in motor stator windings to monitor the motor winding temperature.
When the motor winding temperature reaches the PTC sensor’s temperature
rating, the PTC sensor’s resistance transitions from a low to high value. Since
PTC sensors react to actual temperature, enhanced motor protection can be
provided to address such conditions as obstructed cooling and high ambient
temperatures.
The following table defines the MV SMC Flex PTC thermistor input and
response ratings:
Table 5 - PTC Input Ratings
IMPORTANT
The ground fault inhibit timer starts after the maximum phase of load current
transitions from 0 A to 30% of the device’s minimum FLA Setting or the
GF Current is greater than or equal to 0.5 A. The MV SMC Flex does not begin
monitoring for a ground fault condition until the Gnd Flt Inh Time expires.
Response Resistance
3400 Ω ± 150 Ω
Reset Resistance
1600 Ω ± 100 Ω
Short-circuit Trip Resistance
25 Ω ± 10 Ω
Maximum Voltage at PTC Terminals (RPTC - 4 k )
< 7.5V
Maximum Voltage at PTC Terminals (RPTC = open)
30V
Maximum Number of Sensors
6
Maximum Cold Resistance of PTC Sensor Chain
1500 Ω
Response Time
800 ms