4.17
Date Code 20080918 Instruction Manual SEL-749M Relay
Protection and Logic Functions
Basic Motor Protection
NOTE: With Star-Delta (Wye-Delta)
starting, the total starting time (Star
and Delta) is monitored. If immediate
tripping is required in the event of
stalling, monitoring must be provided
by a speed switch function.
If motor starting has not finished by the START_T time, the relay produces a
trip. The start monitoring is independent of the overload protection provided
by the thermal model. Figure 4.8 shows the typical current during motor start
and the START_T time setting.
Figure 4.8 Monitoring Starting Time
Star-Delta (Wye-
Delta) Starting
The SEL-749M issues the command to switch from Star to Delta (Wye to
Delta) as soon as the starting current has dropped to the rated value and the
motor has reached its normal speed in Star (Wye). If starting has not been
completed within the normal time for this application (STAR_MAX setting, if
used), the relay makes the change to delta, regardless of the speed attained.
You can switch on or off, as desired, the maximum permissible time for star
(wye) operation. If it is off, the change to delta is made solely based on the
motor current. If the motor has to be switched off when the total start time
(Star and Delta) exceeds a set time, start monitoring must also be used.
Start Inhibit Function
When the protected motor is rated for a specific maximum number of starts
per hour or minimum time between starts, set the MAXSTART and TBSDLY
settings accordingly. If the relay detects MAXSTART starts within 60 minutes
and the motor stops or is tripped, the relay asserts the TRIP output contact to
prevent an additional start until 60 minutes after the oldest start. If the motor
stops or is tripped within TBSDLY minutes of the last start, the relay asserts
the TRIP output contact to prevent a new start until TBSDLY minutes after the
most recent start.
≤
1.1 FLA
1
2
3
t
t
v
≥
1.2 FLA
I
Relay
Word
Bits
STARTING = 1
RUNNING = 1
1 = Motor starting current
≥
1.2 FLA
2 = Rated conditions
t
v
= START_T time
3 = Tripping if starting lasts too long
Table 4.15 Star-Delta Settings
Setting Prompt Setting Range Setting Name := Factory Default
STAR-DELTA ENAB L Y, N ESTAR_D := N
MAX STAR TIME Off, 1–600 sec STAR_MAX := OFF
NOTE: In addition to enabling the
Star-Delta, you must assign Star and
Delta to Auxiliary output relays (one
each); see Ta bl e 4. 37 , and Figure 2.14
for typical connection diagrams.
Table 4.16 Start Inhibit Settings
Setting Prompt Setting Range Setting Name := Factory Default
STARTS/HR. Off, 1–15 MAXSTART := OFF
MIN. OFF TIME Off, 1–150 min TBSDLY := OFF
RESTART BLK TIME Off, 1–60 min ABSDLY := OFF
NOTE: See Figure 4.20 and
Figure 4.23 for the logic diagrams.
Courtesy of NationalSwitchgear.com
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