Siemens SAMMS-MV User Manual
24
3 Operating the SAMMS-MV Device
ture of the rotor and provides a signal to trip the motor off-line
when it reaches a trip temperature value. The motor model
takes into account the change of the rotor resistance during
motor startup. Rotor resistance is a function of motor slip;
therefore, it is highest at locked rotor and decreases as the
motor speeds, and the slip decreases.
You can select motor cold stall time from 5 to 100 seconds in
increments of 1 second. The selected time will adjust the rotor
loop elements so that the maximum temperature limit in the
rotor is reached under locked rotor conditions for the time
selected. If cold stall time is not known, the rotor model will
assume a cold stall time based on the type of motor used. The
user is allowed to select an open drip proof (ODP) motor or a
totally enclosed fan-cooled motor (TEFC) motor. The default
value for the ODP motor is 10 seconds. The default value for the
TEFC motor is 20 seconds.
3.21 Repetitive Starts
The motor model allows repetitive starts without nuisance
tripping while protecting the motor against overload and stall
conditions. Repetitive starts can occur as long as the following
conditions are met:
1. The energy exerted by the motor during start does not
exceed the energy defined by the overload class selected.
2. The motor winding temperature does not exceed the maxi-
mum temperature allowed.
3. The rotor temperature does not exceed the maximum
temperature allowed.
4. The SAMMS-MV is not in start inhibit (See Section 3.22).
For example, a motor starting from cold condition could have
4 or more typical starts of 5 seconds without nuisance tripping
and without damaging the motor insulation. Figure 3.12 shows
a multi-start scenario for an ODP motor.
3.22 Start Inhibit
When the motor temperature reaches the maximum values
allowed, the SAMMS-MV device trips. If you attempt a restart,
the overload LED flashes and the motor will not start until the
motor winding and rotor temperatures cool down to the full load
temperature. HHC function F25 displays the motor winding
temperature as a percentage of the full-load temperature. HHC
function F10 displays the time to enable restart in seconds.
3.23 Cooling Time Constants
The motor time constant is a function of the motor type. The
values listed in Table 3.4 are used in the motor model.
Motor
Condition
Delta
Temperature
Motor Type
TEFC
ODP
Stopped
80º C to
29º C
9900 s
6000 s
Running Idle 80º C to
39.4º C
7200 s
4500 s
Table 3.4 Motor time constants
TEFC motors include the following types of motors:
•
Totally Enclosed Fan Cooled
•
Totally Enclosed Fan Cooled Explosion Proof
•
Totally Enclosed Air-to-Air Cooled (TEAAC)
ODP motors include the following types of motors:
•
Drip Proof Weather Protected I (WP-1)
•
Weather Protected II (WP-2)
•
Open Drip Proof
•
Totally Enclosed Water-to-Air Cooled (TEWAC)
3.24 Normalized Temperature Rise for Class
B and Class F Insulation
Steady state and maximum winding temperature are functions
of the motors insulation class. In this motor model, normalized
temperature rise for both Class B and Class F insulation are
used. The motor winding temperature is displayed as a per-
centage of the steady-state full-load temperature rise as shown
in Table 3.5.
Boundary
Parameters
Class B
Insulation
Class F
Insulation
% Full Load
Temperature
Rise
Steady State
Temperature
rise at
full-load
current
80º C
105º C
100
Maximum
allowed
winding
temperature
140º C
185º C
175
Table 3.5 Steady state and maximum winding temperature rise
3.25 Ground Fault Detection
In SAMMS-MV devices, HHC function F12 selects ground fault
protection or warning.
•
protection = ON
•
warning = OFF
The device detects a ground fault if the fault current exceeds the
pickup level for 360 msec. If you have selected protection (ON),
the motor trips and the Ground Fault LED illuminates until reset.
If you selected warning (OFF), the Ground Fault LED flashes as
long as the fault current exceeds the pickup level. Table 3.6 lists
the pickup levels for each overload size. Ground fault protection
is locked out for 1.4 seconds following a start.