GE Multilin 345 Instruction Manual page 169

CHAPTER 6: SETPOINTS
345 TRANSFORMER PROTECTION SYSTEM – INSTRUCTION MANUAL
The time to operate calculated by the formula, starts from thermal level with no load
before overload occurs, meaning the equipment temperature is considered as the ambient
temperature and its thermal level is considered equal to zero.
The time to trip will start timing out once the level of the computed thermal capacity (%)
becomes higher than 100% thermal capacity (
Thermal capacity falls below 97% of the pickup level.
Calculating the PICKUP setting
In some applications, it is required to apply overload factor (K-factor) to achieve the
thermal rating of the protected equipment. In such cases the pickup level need to be
calculated based on the K-factor and the base current (rated equipment current). The time
to trip is then estimated when the ratio of actual current above the programmed pickup
current is higher than 1. The pickup is calculated as follows:
Where:
K = overload factor (usually provided by the equipment manufacturer)
I = base current (rated current of the equipment)
base
The following path is available using the keypad. For instructions on how to use the
keypad, please refer to Chapter 3 - Working with the Keypad.
PATH:
SETPOINTS > S3 PROTECTION > SETPOINT GROUP 1(2) > THERMAL OVLD
THERMAL OVLD 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
THERMAL OVLD 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 THERMAL OVLD 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 THERMAL OVLD ALARM setting, and will stay on even after the thermal
capacity for all phases drops below 97% of the THERMAL OVLD ALARM setting. The LED
can be reset upon initiation of the "Reset" command.
THERMAL OVLD PKP
Range: 0.05 to 20 x CT in steps of 0.01 x CT
Default: 1.00 x CT
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 OVLD ALARM
Range: 70.0 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.
θ
=1 ). The trip flag will dropout when the
S3 PROTECTION
Eq. 14
Eq. 15
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