Schweitzer Engineering Laboratories SEL-701-1, Instruction Manual

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SEL-701-1 Monitor
Date Code 20011009
Settings Calculation
Basic Motor Protection
3.20
automatically builds the thermal limit curve between the nearest
two specified points. For instance, the monitor thermal limit char-
acteristic between 2.5 and 4.0 times Full Load Amps forms a con-
tinuous curve between 225 seconds and 72 seconds.
Thermal Capacity Alarm Setting
For all thermal element settings methods, the monitor provides a thermal alarm.
When the motor thermal capacity used exceeds the Thermal Capacity Alarm Pickup
(TCAPU), the monitor issues an alarm. The early alarm may allow you to correct the
load problem before a thermal trip occurs.
Thermal Capacity to Start Settings
The motor tripping and starting functions include supervision to help prevent a
thermal trip on a normal start. The monitor prevents motor starting until the thermal
element has enough available thermal capacity to allow a motor start without tripping.
The available thermal capacity required to start is (100% – 10% – TCSTART), where
the Thermal Capacity Used To Start (TCSTART) setting or the monitor can learn a
value.
When you use the Use Learned Starting Thermal Capacity function
(TCLRNEN = Y), the monitor records the thermal capacity used during the past five
starts and uses it in the thermal model in place of the Thermal Capacity Used to Start
setting. The monitor adds 10% to the largest of the last five starting thermal capacities
and requires that the motor thermal model cool enough to permit that start.
EXAMPLE 3.7 Learned Starting Thermal Capacity Calculation
Over the past five starts, a motor has used 24%, 27%, 22%, 25%,
and 26% of thermal capacity. The largest thermal capacity to start
is 27%. The monitor requires that the present thermal capacity
drop below 63% (100%–37%) before a new start is allowed.
Table 3.11 Thermal Capacity Alarm Setting
Setting Prompt Setting Range
Setting Name =
Factory Default
Thermal Capacity Alarm Pickup 50%–100% TCAPU = 90
Table 3.12 Thermal Capacity to Start Settings
Setting Prompt Setting Range
Setting Name =
Factory Default
Thermal Capacity Used To Start 20%–100% TCSTART = 85
Use Learned Starting Thermal Capacity Y, N TCLRNEN = Y