Siemens TIASTAR Manuel d'instruction - Page 39
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Hazardous voltage.
Will cause death or serious per-
sonal injury.
Disconnect power before working on
this equipment
Problem
Overload relays trip
during starting or soon
after motor is up to speed.
Overload relay trips during
motor operation.
Overload relay fails to trip
on overload current.
Siemens Energy & Automation, Inc.
.
Probable Cause
Motor overloaded.
Motor being started too frequently
at close intervals.
Excessive motor acceleration time.
Low Line voltage.
Motor being overloaded.
Overload relay not adjusted to motor
capabilities or sized properly.
Relay tripping mechanism jammed.
Incorrect relay or relay set incorrectly.
Current transformers with improper
ratio or with short-circuited secondary
terminals.
Corrective Action
Limit starting load and running load to motor
capabilities.
Jogging and starting operations must be limited
to capabilities of the motor and control. Check
starting limitations in motor instruction manual
before repeated starts.
The starting of high inertia loads may not permit
the use of standard overload relay application.
Where accelerating time approaches 12 seconds
or more, special overload relay bypass devices
and circuits would usually be required. Contact
Siemens regarding such problems and supply
complete data on locked-rotor starting current
and total accelerating time under maximum load
conditions.
Line voltage should be maintained between
- + 10% of motor nameplate voltage.
Reduce load or correct conditions causing
overload.
Adjust relay setting in accordance with
instructions for the overload relay.
Adjustment should correspond to thermal rating
of the motor, including temperature rise, duty,
and service factor. Replace overload if not sized
properly.
Replace relay.
Check relay selection and adjustment per
overload relay instructions.
Current transformers must have step-down ratio
to correspond to full load motor current and
relay selection. Protective jumpers may be pro-
vided at current transformer secondary termi-
nals or on terminal block connections to guard
against open transformer secondary circuit, and
jumpers must be removed before placing equip-
ment in operation.
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