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Section 10
Multipurpose protection
The parameters for the general current and voltage protection function (CVGAPC) are set via
the local HMI or Protection and Control Manager (PCM600).
Common base IED values for the primary current (
power (
GlobalBaseSel : Selects the global base value group used by the function to define IBase , UBase
SBase . Note that this function will only use IBase value.
and
10.1.3.1
Directional negative sequence overcurrent protection
Directional negative sequence overcurrent protection is typically used as sensitive earth-fault
protection of power lines where incorrect zero sequence polarization may result from mutual
induction between two or more parallel lines. Additionally, it can be used in applications on
underground cables where zero-sequence impedance depends on the fault current return
paths, but the cable negative-sequence impedance is practically constant. It shall be noted
that directional negative sequence OC element offers protection against all unbalance faults
(phase-to-phase faults as well). Care shall be taken that the minimum pickup of such
protection function shall be set above natural system unbalance level.
An example will be given, how sensitive-earth-fault protection for power lines can be achieved
by using negative-sequence directional overcurrent protection elements within a CVGAPC
function.
This functionality can be achieved by using one CVGAPC function. The following shall be done
to ensure proper operation of the function:
1.
Connect three-phase power line currents and three-phase power line voltages to one
CVGAPC instance (for example, GF04)
2.
Set
NOT 3I2 current; this is essential for proper OC pickup level setting)
3.
Set
intentionally inverted in order to simplify directionality
4.
Set base current
5.
Set base voltage
6.
Set
voltage for this angle during the fault)
7.
Set
8.
Set
will be enabled)
9.
Enable one overcurrent stage (for example, OC1)
10. By parameter
in accordance with your network protection philosophy
11. Set
12. Set
coordination with other earth-fault protections installed in the vicinity of this power line
13. Set
14. Set
15. Set
•
230
SBase ) are set in global base values for settings function GBASVAL.
The overcurrent steps has a
the minimum operate current. Set
achieve ANSI reset characteristic according to standard. If
StartCurr_OCx for any step the ANSI reset works as if current is zero when
current drops below
CurrentInput to NegSeq (please note that CVGAPC function measures I2 current and
VoltageInput to -NegSeq (please note that the negative sequence voltage phasor is
IBase value equal to the rated primary current of power line CTs
UBase value equal to the rated power line phase-to-phase voltage in kV
RCADir to value +65 degrees ( NegSeq current typically lags the inverted NegSeq
ROADir to value 90 degree
LowVolt_VM to value 2% ( NegSeq voltage level above which the directional element
CurveType_OC1 select appropriate TOC/IDMT or definite time delayed curve
StartCurr_OC1 to value between 3-10% (typical values)
tDef_OC1 or parameter "k" when TOC/IDMT curves are used to insure proper time
DirMode_OC1 to Forward
DirPrinc_OC1 to IcosPhi&U
ActLowVolt1_VM to Block
In order to insure proper restraining of this element for CT saturations during three-
phase faults it is possible to use current restraint feature and enable this element to
NegSeq current is bigger than a certain percentage (10% is
operate only when
IBase ), primary voltage ( UBase ) and primary
IMinx ( x =1 or 2 depending on step) setting to set
IMinx below StartCurr_OCx for every step to
IMinx .
1MRK 505 370-UEN D
M13088-237 v4
IMinx is set above
M13088-3 v5
Busbar protection REB670
Application manual
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