Siemens SAMMS-MV Manual De Usuario

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3 Operating the SAMMS-MV 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-MV device does

not detect motor current one second after issuing a start

command or if the SAMMS-MV 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

permanently when configured at the factory. You can also

disable it with the Hand Held Communicator to the SAMMS-MV

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-MVX 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-MVX 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-MVX 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.

3.10 Overload Protection

Medium-voltage motors are rotor limited under locked rotor

conditions, and stator limited under running overload condi-

tions. Additionally, the type of motor construction affects the

thermal behavior of the rotor. For example, open drip-proof

motors have significantly shorter cold stall times than totally

enclosed fan-cooled motors. The motor protection algorithm in

the SAMMS-MV device is designed specifically to provide rotor

protection based on the type of motor construction, and to

differentiate between a stalled rotor and a rotor accelerating to

running speed.

The motor overload protection function is based on calculating

the motor’s winding, housing, and rotor temperatures. These

temperatures are compared to the allowable temperature limits

for the motor’s winding, housing, and rotor. On the basis of this

comparison, the SAMMS-MV device either stops the motor or

allows it to run.

For example, consider the motor winding and rotor temperature

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

stator winding during a 10 second stall for an ODP motor. In this

case, the rotor temperature rises at a rate faster than the

winding temperature, and reaches the maximum allowable

value resulting in a trip. In order to prevent damage to the motor,

SAMMS-MV will not allow the motor to start until the winding

and the rotor temperatures cool down to the full load tempera-

ture or less.

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 the various elements

in the circuit depend, in some cases, 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

sophisticated enough to offer customized protection to particu-

lar motors. To customize protection to the motor enter the

following nameplate data:

•

full-load current setting (F4)

•

service factor (F6)

•

type of motor construction (Open Drip Proof (ODP) or Totally

Enclosed Fan Cooled (EFC) (F6)

•

cold stall time, if available (F7)

•

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-MV allows you to decrease or increase the

motor’s thermal capacity according to the motor’s ambient