ABB Relion 670 series, Техническое руководство

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where:
ID_A is the fundamental frequency differential current in phase A (in W1 side primary
amperes)
ID_B is the fundamental frequency differential current in phase B (in W1 side primary
amperes)
ID_C is the fundamental frequency differential current in phase C (in W1 side primary
amperes)
I_A_W1 is the fundamental frequency phase current in phase A on the W1 side
I_B_W1 is the fundamental frequency phase current in phase B on the W1 side
I_C_W1 is the fundamental frequency phase current in phaseC on the W1 side
I_A_W2 is the fundamental frequency phase current in phase A on the W2 side
I_B_W2 is the fundamental frequency phase current in phase B on the W2 side
I_C_W2 is the fundamental frequency phase current in phaseC on the W2 side
Vn_W1 is transformer rated phase-to-phase voltage on the W1 side (setting parameter)
Vn_W2 is transformer rated phase-to-phase voltage on the W2 side (setting parameter)
As marked in equation 1 and equation 2 , the first term on the right hand side of the equation,
represents the total contribution from the individual phase currents from the W1 side to the
fundamental frequency differential currents, compensated for eventual power transformer phase
shift. The second term on the right hand side of the equation, represents the total contribution
from the individual phase currents from the W2 side to the fundamental frequency differential
currents, compensated for eventual power transformer phase shift and transferred to the power
transformer W1 side. The third term on the right hand side of the equation, represents the total
contribution from the individual phase currents from the W3 side to the fundamental frequency
differential currents, compensated for eventual power transformer phase shift and transferred to
the power transformer W1 side. These current contributions are important, because they are used
for calculation of common bias current.
The fundamental frequency differential currents are the "usual" differential currents, the
magnitudes which are applied in a phase-wise manner to the operate - restrain characteristic of
the differential protection. The magnitudes of the differential currents can be read as service
values from the function and they are available as outputs IDMAG_A, IDMAG_B, IDMAG_C from the
differential protection function block. Thus they can be connected to the disturbance recorder and
automatically recorded during any external or internal fault condition.
On-line compensation for load tap changer movement
M13039-424 v5
A load tap changer is a mechanical device, which is used to step-wise change number of turns
within one power transformer winding. Consequently the power transformer overall turns ratio is
changed. Typically the load tap changer is located within the HV winding (that is, winding 1, W1) of
the power transformer. By operating load tap changer, it is possible to step-wise regulate voltage
on the LV side of the power transformer. However at the same time the differential protection for
power transformer becomes unbalanced. Differential function in the IED has built-in feature to
continuously monitor the load tap changer position and dynamically compensate on-line for
changes in power transformer turns ratio.
Differential currents are calculated as shown in equation and equation . By setting parameters, the
winding location of the OLTC is defined. Also, the voltage change of each step. Thus, if for example
the load tap changer is located within winding 1 the no-load voltage Un_W1 will be treated as a
function of the actual load tap changer position in equation and equation . Thus for every load tap
changer position a corresponding value for Vn_W1 will be calculated and used in the above
Section 6 1MRK 502 066-UUS B
Differential protection
124
Technical manual