Siemens MCC-3298 Manual Do Utilizador

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 motors winding and housing temperatures. These tem-

peratures are compared to the allowable temperature limits for

the motors 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 motors

thermal capacity according to the motors 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