GE Multilin G650 Manual page 188

5 SETTINGS
5.4.3.3 GENERATOR THERMAL MODEL ELEMENT (49S)
This unit provides protection against overheating due to overloading conditions. The operating time curve is set from the
time curve family available, as a function of the time constant ô1 (settable between 3 and 600 minutes). The cooling time
constant ô2 can be set between 1 and 6 times the heating time constant ô1.
The thermal unit measures the three phase currents of the motor. The algorithm to calculate the thermal image
value is based on the positive and negative sequence values, I
Where K1 is a constant that overvalues the effect of the negative sequence I2 component, and is selectable between 1 and
8.
The negative sequence is included in the above formula in order to protect the generator from the effects caused by the
system light unbalanced currents, such as the ones produced by load unbalance. High negative sequence values, such as
those produced by uncleared external faults (phase-to-phase or phase-to-ground), long lasting loss of a phase, etc. will be
detected by function 46 in a faster way, as it works with a different algorithm. The phenomena that cause a supplementary
overheating in the machine are described in section 2.5.
The resulting time for reaching an overheating condition due to Ieq including both overload and unbalance is defined by the
following equation:
Where,
τ is the heating/cooling time constant.
Ieq is the ratio current/pickup
Table 5–41: THERMAL MODEL ELEMENT SETTINGS
SETPOINT > PROTECTION ELEMENTS > PHASE CURRENT > THERMAL MODEL >
GENERATOR THERMAL MODEL 1> GENERATOR THERMAL MODEL 2 > GENERATOR THERMAL MODEL 3
SETTING DESCRIPTION
Function permission
Heating time constant
Cooling time constant
Pickup level
Alarm level
Negative sequence influence
Snapshot event generation
The cooling constant is given in times the heating constant.
The snapshot event setting enables or disables the snapshot event generation for the thermal model elements.
GEK-113285A
I
=
I
eq
NAME DEFAULT
VALUE
Function DISABLED
Heat Time Constant 6.0
Cool Time Constant 2.00
Pickup Level 1.00
Alarm Level 80.0
K1 constant 1.0
Snapshot Events ENABLED
G650 Generator Protection & Control System
and I as follows:
1 2
2 2
+
K * I
1 1 2
2
I
pickup
STEP
N/A
0.1 min
0.01 times Heat Time
0.01 A
0.1 %
0.1
N/A
5.4 PROTECTION ELEMENTS
RANGE
[DISABLED – ENABLED]
[3.0 : 600.0]
[1.00 : 6.00]
[0.05 : 160.00]
[1.0 : 110.0]
[1.0 : 8.0]
[DISABLED – ENABLED]
5
5-45