External Polarizing For Earth-Fault Function; Base Quantities Within The Protection; Internal Earth-Fault Protection Structure - ABB REG650 Technical Manual

Section 7
Current protection
7.2.7.3
7.2.7.4
7.2.7.5
160
which will be then used, together with the phasor of the operating 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
EQUATION1878 V3 EN
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:
1. Four residual overcurrent steps.
2. Directional supervision element for residual overcurrent steps with integrated
directional comparison step for communication based earth-fault protection
schemes (permissive or blocking).
3. Second harmonic blocking element with additional feature for sealed-in
blocking during switching of parallel transformers.
Each part is described separately in the following sections.
(
+ × = - +
3 U Z IPol 3 U RNPol
0 0 s 0
1MRK 502 034-UEN -
)
+ ×
jXNPol IPol
(Equation 43)
Technical Manual