ABB Relion Technical Manual page 119

1MRK 502 048-UUS A
Technical manual
1. Instantaneous values of currents (samples) from the HV, and LV sides for two-
winding power transformers, and from the HV, the first LV, and the second LV side
for three-winding power transformers.
2. Currents from all power transformer sides expressed as fundamental frequency
phasors with their real and imaginary parts. These currents are calculated within the
protection function by the fundamental frequency Fourier filters.
3. Negative sequence currents from all power transformer sides expressed as phasors.
These currents are calculated within the protection function by the symmetrical
components module.
The power transformer differential protection:
1. Calculates three fundamental frequency differential currents and one common bias
current. The zero-sequence component can optionally be eliminated from each of the
three fundamental frequency differential currents and at the same time from the
common bias current.
2. Calculates three instantaneous differential currents. They are used for harmonic, and
waveform analysis. Instantaneous differential currents are useful for post-fault
analysis using disturbance recording
3. Calculates negative-sequence differential current. Contributions to it from all power
transformer sides are used by the internal/external fault discriminator to detect and
classify a fault as internal or external.
Section 6
Differential protection
113