ABB REG670 - Page 474

Step-up
transformer
G
Field breaker
Excitation
transformer
I
L1
I
L2
I
L3
U
A
U
a
Pri-side (HV)
Sec-side (LV)
IEC12000019-1-en.vsd
Two alternative
measurement points
for the rotor overload
function
L1
i
L2
i
L3
i
IEC12000019 V1 EN
Figure 220: Measurement of rotor currents
The selection of current measurement is done by using the parameter
MeasurCurrent:
• When MeasurCurrent = RMS; The maximum true RMS current value from the
three-phase input currents is used as the measured quantity for the rotor overload
protection.
• MeasurCurrent = DC (default); The calculated rotor winding DC current in
primary amperes is used as the measured quantity for the rotor overload
protection. The DC current is calculated from the connected three-phase input
currents, see Figure
220. This DC current calculation is valid for any type of three
phase rectifier bridge (i.e. either diode or thyristor based).
In order to properly calculate the rotor winding DC current the physical location of the
used CT is defined by the parameter CT_Location
• When CT_Location = LV_winding (default) is selected, it means that the used CT
is located on the secondary, low-voltage side (LV) of the excitation transformer
which directly feeds into the rectifier bridge, see Figure
220. In that case the rotor
winding instantaneous DC current i
DC
is calculated as per the following equation
i
i i i
DC
L L L
=
+ +
1 2 3
2
GUID-17CD8C1A-C1C2-4A9C-9339-2C99C3A3F120 V2 EN
(Equation 101)
Section 8 1MRK502052-UEN B
Current protection
468
Technical manual