CHAPTER 6: SETPOINTS
S3 PROTECTION
345 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
6–81
THERMAL MDL FUNC
Range: Disabled, Trip, Latched Alarm, Alarm
Default: Disabled
The output relays #1 “TRIP W1 BKR” and #2 “TRIP W2 BKR” will operate only if the
Trip
function is selected, and the accumulated thermal capacity for any of the phases is over
100%. The “ALARM” LED will turn on if the thermal capacity for any phase is over the
Transformer Thermal Alarm setting, regardless of whether
Alarm
,
Latched Alarm
or
Trip
is selected as the function. The “ALARM” LED will turn off when the thermal capacity
value of all phases is below 97% of the Transformer Thermal Alarm setting. If
Latched
Alarm
is selected as the function, the “ALARM” LED will flash when the thermal capacity
on any phase is over the Transformer Thermal Alarm setting, and will stay on even after
the thermal capacity for all phases drops below 97% of the Transformer Thermal Alarm
setting. The LED can be reset upon initiation of the "Reset" command. Any of the output
relays 3 to 6 can be selected to operate when the Thermal function is selected as
Latched Alarm
,
Alarm
or
Trip
.
THERMAL MDL PKP
Range: 0.05 to 20.00 x CT(W1) in steps of 0.01 x CT(W1)
Default: 1.00 x CT(W1)
This setting sets the level of phase current above which the thermal model starts timing
out the time-to-trip per the logarithmic formula above.
THERMAL MDL ALARM
Range: 1.0 to 110.0% in steps of 0.1%
Default: 80.0%
This setting sets the alarm level for the accumulated thermal capacity above which the
element generates an alarm.
HEAT TIME CONSTANT
(
τ
H
)
Range: 3.0 to 600.0 min in steps of 0.1 min
Default: 6.0 min
The Winding 1 heating time constant is used to compute the thermal capacity when the
thermal capacity at each time step is greater than the one computed in the previous
time step. The transformer winding heating constant is usually provided by the
manufacturer.
COOL TIME CONSTANT
(
τ
C
)
Range: 1.00 to 6.00 x
τ
H
in steps of 0.01 x
τ
H
Default: 1.00 x
τ
H
The cooling time constant is used to compute the thermal capacity when the thermal
capacity at any time step is smaller than the one computed in the previous time step.
The range for this setting is given as multiples of the Heating Time Constant setting.
NOTE
NOTE:
The thermal capacity is displayed on the relay even if the Thermal Model Function is set
to “Disabled”.
