Setting Guidelines; Directional Negative Sequence Overcurrent Protection - ABB Relion REC670 Applications Manual

Section 10
Multipurpose protection
will, with a delay for example 10 s, detect the situation when the generator is not connected to
the grid (standstill) and activate the overcurrent function. The overvoltage function will detect
the situation when the generator is taken into operation and will disable the overcurrent
function. The overcurrent function will have a pick-up value about 50% of the rated current of
the generator. The trip delay will be about 50 ms.
10.1.3

Setting guidelines

The parameters for the general current and voltage protection function (CVGAPC) are set via
the local HMI or Protection and Control Manager (PCM600).
GlobalBaseSel : Selects the global base value group used by the function to define ( IBase ),
UBase ) and ( SBase ).
(
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)
204
When inverse time overcurrent characteristic is selected, the operate time of
the stage will be the sum of the inverse time delay and the set definite time
delay. Thus, if only the inverse time delay is required, it is important to set the
definite time delay for that stage to zero.
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
IMinx ( x =1 or 2 depending on step) setting to set
IMinx below StartCurr_OCx for every step to
IMinx .
1MRK 511 358-UEN A
IP15009-1 v2
GUID-F7AA2194-4D1C-4475-8853-C7D064912614 v4
M13088-237 v4
IMinx is set above
M13088-3 v5
Application manual