8.15.8
Technical data
Table 255:
GSPTTR technical data
Function
Range or value
Accuracy
Current start level for overload
protection
(105.0–900.0)% of IBase
±1.0% of I
r
at I ≤ I
r
±1.0% of I at I > I
r
Reset ratio
>95%
Start time at 0 to 2 x I
set
Min. = 50 ms
Max. = 170 ms
Thermal time characteristic
According to
IEEE Std C50.13–2005
±1.5% or ±200 ms
whichever is greater
Minimum operate time for thermal
characteristic
(1.0–120.0) s
±1.5% or ±200 ms
whichever is greater
Maximum operate time for
thermal characteristic
(100.0–2000.0) s
±1.5% or ±200 ms
whichever is greater
8.16
Generator rotor overload protection, GRPTTR
8.16.1
Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Generator rotor overload protection
GRPTTR
49R
8.16.2
Functionality
The generator overload function, GRPTTR is used to protect the rotor winding against
excessive temperature as a result of overcurrents. The functions operating
characteristic is designed in accordance with the American standard IEEE-C50.13.
If internal generator components exceed its design temperature limit, damage can be
the result. Damage to generator insulation can range from minor loss of life to
complete failure, depending on the severity and duration of the temperature excursion.
Excess temperature can also cause mechanical damage due to thermal expansion.
Rotor components such as bars and end rings are vulnerable to this damage. Since
temperature increases with current, it is logical to apply overcurrent elements with
inverse time characteristics.
For its operation the function either measures the true RMS current of the excitation
transformer or calculates the DC current in the rotor winding. The rotor winding DC
current can be calculated from the AC currents measured on either high voltage side
(HV) or low voltage side (LV) side of the excitation transformer. For the HV side
measurement ratings of the excitation transformer shall be given. The use of the DC
1MRK502052-UEN B
Section 8
Current protection
463
Technical manual
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