Schweitzer Engineering Laboratories SEL-701, Instruction Manual

Page: 89 / 468

Date Code 20010719
701 Motor Protection Relay
Settings Calculation
Basic Motor Protection
4.25
Use the negative-sequence overcurrent element in addition to or instead of the 46
Current Unbalance Element to detect phase-to-phase faults, single phasing, and heavy
motor unbalance. Sensitive unbalance protection is provided by setting the Negative-
Seq. O/C Pickup (50QP) equal to 0.1 • ITAP with a 4-second time delay.
Jogging Block Elements
Table 4.15 Jogging Block Element Settings
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. The relay retains accurate
start time data (within ±5 seconds) through control power cycles.
The relay will maintain the trip signal until enough time passes that the motor can
be safely restarted. During the lockout period, the relay will display a countdown time
in minutes to the next allowed start if a start is attempted through the relay. The
Emergency Restart function overrides both of these limits allowing the motor to be
placed back in service in an emergency.
Load-Jam Elements
Table 4.16 Load-Jam Function Settings
When the motor is running, the relay offers load-jam detection. When the motor
load jams, stalling the motor, the phase current will increase to near the locked rotor
value. When Load Jam Tripping is enabled, if the phase current exceeds the Load Jam
Trip Pickup setting for longer than the time delay setting, the relay will trip. Set the
Load Jam Trip Pickup greater than the expected normal load current but less than rated
locked rotor current. This setting is entered in per unit of the Full Load Amps (FLA)
setting.
Table 4.15 Jogging Block Element Settings
Setting Prompt
Setting Range Setting Name =
Factory Default
Maximum Number of Starts per Hour OFF, 1–15 MAXSTART = 3
Minimum Time Between Starts OFF, 1–150 min TBSDLY = 20
Table 4.16 Load-Jam Function Settings
Setting Prompt Setting Range Setting Name = Factory Default
Load Jam Trip Pickup OFF, 0.5–6.0 pu FLA LJTPU = 2.0
Load Jam Trip Delay 0.00–400.00 s LJTDLY = 1.00