GUID-5D825381-66DE-404D-B3E9-471B13A394A5 V1 EN-US (Equation 166)
The average DC current value I
DC
is used further within the rotor overload function for the
operating characteristic calculations and for the service value.
• When CT_Location = HV_winding is selected, it means that the used CT is located on the
primary, high-voltage side (HV) of the excitation transformer, see Figure317. In that case the
measured HV side three-phase currents (I
A
, I
B
, I
C
) are first transferred to the LV side currents
(i
a
, i
b
, i
c
) by using the rating data of the excitation transformer. The excitation transformer
ratings are specified by the following three setting parameters:
VrLV
: LV winding rated ph-ph voltage in Volts.
VrHV
: HV winding rated ph-ph voltage in kV.
PhAngleShift
: HV side to LV side phase angle shift in degrees (it has value of +30º for Dy1 excitation transformer
and -30º for Dy11 excitation transformer)
Once the measured currents are transferred from the HV side to the LV side of the excitation
transformer the same calculations are performed as in case when CT is located on the LV side.
The measured current used by the function is available as a service value.
Overload characteristics
Rotor winding temperature increases with the current. Thus, it is logical to apply over current
elements with inverse time-current characteristics for overload protection. The function operating
characteristic is designed in accordance with the American standard IEEE-C50.13. This standard
specifies the following operating points:
Table 331: Operate time in accordance with IEEE-C50.13 standard
Current (% of IBase) Trip time (s)
113 120
125 60
146 30
209 10
In order to obtain such operating characteristic the rotor overload function utilizes the following
formula in order to calculate the operate time:
GUID-7CF0FE5A-F5CE-44EC-A2D7-F1E05849171C V1 EN-US (Equation 167)
Where:
Section 8 1MRK 502 066-UUS B
Current protection
592
Technical manual
To Next Page
Loading...
