GE L90 Instruction Manual page 413

5 SETTINGS
In the above equations,
• Δt is the power cycle duration.
• n is the power cycle index.
• t is the trip time calculated at index n as per the IEC255-8 cold curve or hot curve equations.
op(In)
• t is the reset time calculated at index n as per the reset time equation.
rst(In)
• I is the measured overload RMS current at index n.
n
• E is the accumulated energy at index n.
n
• E is the accumulated energy at index n – 1.
n – 1
The thermal overload protection element removes the
emergency, the thermal memory and
All calculations are performed per phase. If the accumulated energy reaches value 1 in any phase, the thermal overload
protection element operates and only resets when energy is less than 0.05 in all three phases.
Table 5–29: TYPICAL TIME CONSTANTS
PROTECTED EQUIPMENT
Capacitor bank
Overhead line
Air-core reactor
Busbar
Underground cable
The logic for the thermal overload protection element is shown below.
Figure 5–145: THERMAL OVERLOAD PROTECTION SCHEME LOGIC
GE Multilin
E = E –
n n 1 –
THERMAL PROT 1 OP
output operand can be reset using
THERMAL PROT 1 OP
TIME CONSTANT MINIMUM RESET TIME
10 minutes 30 minutes
10 minutes 20 minutes
40 minutes 30 minutes
60 minutes 20 minutes
20 to 60 minutes 60 minutes
L90 Line Current Differential System
t
-------------- -
t
rst In
output operand when E < 0.05. In case of
5.7 CONTROL ELEMENTS
(EQ 5.32)
setting.
THERM PROT 1 RESET
5-267
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