GE T60 Instruction Manual page 456

5.7 CONTROL ELEMENTS
When current is less than the dropout level, I
In the above equations,
• ∆t 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 5–35: TYPICAL TIME CONSTANTS
5
PROTECTED EQUIPMENT
Capacitor bank
Overhead line
Air-core reactor
Busbar
Underground cable
The logic for the thermal overload protection element is shown below.
5-310
E E
=
n
> 0.97 × k × I
n
E E
=
n
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
Figure 5–157: THERMAL OVERLOAD PROTECTION SCHEME LOGIC
T60 Transformer Protection System
t Δ
-------------- -
+
n 1
– t
op In ( )
, the element starts decreasing the thermal energy:
B
t Δ
-------------- -
–
n 1
– t
( )
rst In
output operand when E < 0.05. In case of
THERMAL PROT 1 OP
output operand can be reset using
5 SETTINGS
(EQ 5.53)
(EQ 5.54)
setting.
THERM PROT 1 RESET
GE Multilin