External Polarizing For Earth-Fault Function; Base Quantities Within The Protection; Internal Earth-Fault Protection Structure - ABB REC650 Technical Manual

Section 6
Current protection
6.4.7.3
6.4.7.4
6.4.7.5
102
order to calculate equivalent polarizing voltage UIPol in accordance with the
following formula:
= × = + ×
UIPol Z IPol (RNPol
0s
EQUATION1877 V2 EN
which will be then used, together with the phasor of the operating directional current,
in order to determine the direction to the earth fault (Forward/Reverse).
In order to enable current polarizing the magnitude of polarizing current shall be
bigger than a minimum level defined by setting parameter IPolMin.
Dual polarizing
When dual polarizing is selected the function will use the vectorial sum of the voltage
based and current based polarizing in accordance with the following formula:
+
UTotPol=UUPol UIPol=UPol
IECEQUATION2408 V1 EN
Upol and Ipol can be either zero sequence component or negative sequence
component depending upon the user selection.
Then the phasor of the total polarizing voltage UTotPol will be used, together with the
phasor of the operating current, to determine the direction of the earth fault (Forward/
Reverse).

External polarizing for earth-fault function

The individual steps within the protection can be set as non-directional. When this
setting is selected it is then possible via function binary input BLKSTx(where x
indicates the relevant step within the protection) to provide external directional
control (that is, torque control) by for example using one of the following functions if
available in the IED:
1. Distance protection directional function.
2. Negative sequence based overcurrent function.

Base quantities within the protection

The base quantities are entered as global settings for all functions in the IED. Base
current (IBase) shall be entered as rated phase current of the protected object in
primary amperes. Base voltage (UBase) shall be entered as rated phase-to-phase
voltage of the protected object in primary kV.

Internal earth-fault protection structure

The protection is internally divided into the following parts:
×
j XNPol) IPol
(
+ × = +
Z IPol UPol RNPol
0s
1MRK 511 287-UEN A
(Equation 13)
)
+ ×
jXNPol Ipol
(Equation 14)
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