order to calculate equivalent polarizing voltage UIPol in accordance with the
following formula:
0s
UIPol Z
IPol (RNPol j XNPol) IPol
=
×
=
+ ×
×
EQUATION1877 V2 EN
(Equation 47)
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:
(
)
0
s
UTotPol=UUPol UIPol=UPol Z
IPol UPol
RNPol
jXNPol Ipol
+
+
×
=
+
+
×
IECEQUATION2408 V1 EN
(Equation 48)
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).
8.4.7.3
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.
8.4.7.4
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.
8.4.7.5
Internal earth-fault protection structure
The protection is internally divided into the following parts:
Section 8
1MRK 504 135-UEN A
Current protection
164
Technical manual
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