Schweitzer Engineering Laboratories SEL-749M, Instruction Manual

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4.5
Date Code 20080918 Instruction Manual SEL-749M Relay
Protection and Logic Functions
Basic Motor Protection
If the thermal model is turned off (
E49MOTOR := N
), the thermal model is
disabled, the output of the thermal model is blocked, and the relay reports the
% Thermal Capacity as 999 as noted in
Section 5: Metering and Monitoring .
When you enable overload protection, the relay requires information about the
protected motor capabilities. Obtain the required information (except the
acceleration factor) from the motor specifications.
Rating Thermal Method
The SEL-749M thermal element always operates in one of two modes:
STARTING (50S = 1) and RUNNING (50S = 0). In starting mode, the thermal
element trips in locked rotor time at locked rotor current whether the motor is
at ambient or at normal operating temperature. In running mode, the thermal
element provides overload protection by limiting the motor heat energy
estimate to a value represented by the overload settings.
The 50S overcurrent element uses the sum of positive- and negative-sequence
magnitudes, 2.5 • FLA as a pickup threshold, and 2.4 • FLA as a dropout
threshold.
Note that the locked rotor time setting is for a hot-rotor condition. If only one
locked rotor time is specified for a particular motor, unless the specification
states otherwise, assume the time is the cold locked rotor time. Multiply the
cold locked rotor time by 0.833 to determine a hot locked rotor time that is
acceptable for most motors.
EXAMPLE 4.3 Thermal Element Setting
A 4000 V, 600 HP motor is protected by the SEL-749M Thermal
Overload Element. The motor data sheet includes the following
information.
Rated Horsepower = 600 HP
Rated Voltage = 4000 V
Rated Full Load Current = 80 A
Rated Locked Rotor Amps = 480 A
Safe Stall Time at 100% Volts:
Cold = 18 seconds
Hot = 15 seconds Service Factor = 1.2
Table 4.4 Overload (Thermal Model) Settings
Setting Prompt Setting Range Setting Name := Factory Default
OVERLOAD ENABLE Y, N E49MOTOR := Y
THERMAL METHOD Rating, Curve SETMETH := RATING
OL RESET LEVEL 10–99 %TCU 49RSTP := 75
SERVICE FACTOR 1.01–1.50 SF := 1.15
THERM OL CURVE1 1–45 CURVE1 := 5
THERM OL CURVE2 1–45 CURVE2 := 7
MOTOR LRA 2.5–12.0 xFLA LRA1 := 6.0
LOCKD ROTOR TIME 1.0–600.0 sec LRTHOT1 := 10.0
ACCEL FACTOR 0.10–1.50 TD1 :=1.00
RUN STATE TIME K Auto, 1–2000 min RTC1 := AUTO
MOTOR LRA–2nd 2.5–12.0 xFLA2 LRA2 := 6.0
MOTOR LRT–2nd 1.0–600.0 sec LRTHOT2 := 10.0
ACCEL FACT–2nd 0.10–1.50 TD2 :=1.00
RUN ST TC–2nd Auto, 1–2000 min RTC2 := AUTO
NOTE:
The relay automatically
raises the initial heat estimate at
Starting (motor current > 2.5 per unit
of FLA) to an operating level and
ramps up the trip value to the
starting element threshold. The
ramping feature ensures that an
overload condition during the start-
to-run transition period of the model
will result in trip time equal to or
faster than hot overload-trip time.
You may observe a sudden rise in %
Thermal Capacity value when you
start the motor. This is normal
operation for the SEL-749M.
NOTE:
The SEL-749M normally uses
settings CTR1, FLA1, LRA1, LRTHOT1,
TD1, and RTC1. When setting E2SPEED
is Y and SPEED2 control input is
asserted, the relay will instead use
CTR2, FLA2, LRA2, LRTHOT2, TD2,
and RTC2 (see
Table 4.32 ).
Courtesy of NationalSwitchgear.com