Siemens MCC-3298 - Manual (Page 19)

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3 Operating the SAMMS-LV Device
3.7 Incomplete Sequence
Sometimes the motor contactors do not respond in a timely
manner to start, stop, transition, speed or direction change
commands from the controller. If the SAMMS-LV device does
not detect motor current one second after issuing a start
command or if the SAMMS-LV device detects motor current
one second after issuing a stop command, an Incomplete
Sequence trip occurs. The motor contactors are opened and
the Incomplete Sequence LED illuminates solidly. In standard
reduced-voltage autotransformer (RVA) starters, an incomplete
sequence also occurs if the remote RUN seal-in contact wired
to pin 9 does not close within one second of the transition from
starting to full-speed operation. This function can be disabled
when configured at the factory. You can also disable it with the
Hand Held Communicator to the SAMMS-LV device. This is
helpful when the controller is tested before connecting to the
motor. After connecting the HHC, use the function UP and
DOWN buttons to select F1. While pressing the ENTER button
for a period of one second push START. Repeating the same
process enables the incomplete sequence protection function.
3.8 Intelligent Reduced-Voltage Starting
(SAMMS-LVX Only)
Intelligent reduced-voltage starting is provided in all standard
reduced-voltage Siemens starters. The advantage of this fea-
ture is that the transition from reduced to full voltage is deter-
mined by the magnitude of the actual motor current and not by
a timer. This optimizes the transition.
When a motor with intelligent reduced-voltage starting is started,
a 30 second timer is energized. If the timer times out, the
transition to full voltage commences as a fail-safe measure. If,
before the 30 second timer times out, the motor current drops
to below the full-load current setting, the transition commences.
The state of the RUN contactor, whose auxiliary contact is
connected to Remote input 4 (pin 9), is checked one second
after the transition. If the contactor is not closed, an incomplete
sequence trip occurs.
3.9 Ridethrough Upon Loss of Power
(SAMMS-LVX Only)
If a motor is running and control power is lost, the motor restarts
automatically with two-wire control as soon as power is re-
stored. With three-wire control, you must restart the motor
manually. The optional ridethrough feature available with
SAMMS-LVX allows three-wire controls to ride through power
outages of up to one second. This feature is especially useful
where the power system is subject to momentary interruptions.
If, while the motor is running, power is lost to a three-wire control
having the ridethrough option, the contactors are opened to
prevent chattering and then reclosed automatically if power
returns within one second.
The ridethrough option should be used with caution, because
of the possibility of motor damage in the event that the contactor
recloses while the motor residual voltage is significantly out of
phase with the system supply voltage.
3.10 Overload Protection
The motor overload protection function is based on calculating
the motor’s winding and housing temperatures. These tem-
peratures are compared to the allowable temperature limits for
the motor’s winding and housing. On the basis of this compari-
son, the SAMMS-LV device either stops the motor or allows it
to run.
For example, consider the motor winding temperature rise
illustrated in Figure 3.5. The motor starts for 5 seconds and runs
for a period of 2200 seconds. Then, the motor is subjected to
a running overload condition that raises the winding tempera-
ture to the maximum allowable winding temperature rise result-
ing in an overload trip. At this temperature, the motor cannot
start until the motor winding temperature cools down to the full-
load temperature. The motor can then start and run at full-load
current.
In the motor model, the greatest of the root mean square (rms)
current values for the motor phases is converted into a heat-like
quantity. This is done by a mathematical function that depends
on the ratio of the rms current to the full-load current set for the
motor. The function is based not only on ideal overload
characteristics, but also on empirical motor data. The heat-like
quantity is analogous to an input source of current to the
electric-circuit analog. The exact values of some of the various
elements in the circuit depend on nameplate data entered for
the particular motor being protected. Unlike the method of
protection in conventional overload relays, the motor model is
general enough to protect many classes of motors, yet sophis-
ticated enough to offer customized protection to particular
motors. To customize protection to the motor enter the follow-
ing nameplate data:
• full-load current setting (F4)
• service factor (F6)
• motor ambient temperature (F0)
3.11 Motor Ambient Temperature
Motors are used in a wide range of temperatures. However,
motors designed according to NEMA standards are rated at
40°C ambient temperature.
The SAMMS-LV allows you to decrease or increase the motor’s
thermal capacity according to the motor’s ambient tempera-
ture. You can select ambient temperature from 0° to 70°C in
increments of 5°C, with HHC function F0.
Important: Do not use this feature with motors rated for
ambient temperature other than the standard 40°C.
3.12 Protection Curves and Overload
Classes
The specific motor protection curve selected depends upon the
overload class setting. The overload class is defined as the
maximum tripping time in seconds for a current level of 600%
of the full-load current or I
FLC
. (The typical starting current of
motors is 600% of I
FLC
.) For example, an overload class setting