ABB Relion 670 Series Applications Manual page 236

Section 10
Unbalance protection
In addition to the cascading failures, this protection principle covers all the unbalanced types
of SCB internal faults.
The negative sequence based function also covers internal phase-to-phase faults.
To prevent unwanted operation for close external faults, this protection may be additionally
blocked by separate logic with the UV2PTUV and the OC4PTOC functions for the following
conditions:
• If any SCB phase-to-earth or phase-to-phase voltage is too low (U < 20%).
• If any SCB phase current is too high (I > 200%).
However, the definite time delays in the function shall help to avoid such application problems
and such external blocking is typically not required.
10.1.3 Setting guidelines
Guidelines for some important settings are as follows:
Operation : This is used to turn the function On/Off .
UBase : Rated Ph-Ph Voltage of the capacitor bank.
IBase : This should be set as rated primary current for the capacitor bank.
=
IBase
IECEQUATION19012 V1 EN-US
CurrentInput : If the SCB is earthed, select 3 × ZeroSeq , else negSeq .
VoltageInput : If the SCB is earthed, select 3 × ZeroSeq , else negSeq .
I > : Setting of over-current Stage 1, Typical Value : 125%.
tDef1 : Definite time setting for stage 1, Typical value: 0.2 sec.
VDepFact1 : A factor for multiplying the setting I> in stage 1. This setting must be set as
(1-117)/I> . For I> =125%, VDepFact1 should be set as 0.064.
I >> : Setting of over-current Stage 2, Typical Value : 130%.
tDef2 : Definite time setting for stage 2, Typical value: 0.05 sec. This makes this stage as a high
speed stage.
VDepFact2 : A factor for multiplying the setting I>> in stage 2. This setting need to be set as
(1-117)/I>> . For I>> =130%, VDepFact2 is set as 0.100.
HarmRest1 : On if 3×Zero Seq mode is used for the CurrentInput and the VoltageInput setting.
HarmRest2 : On if 3×Zero Seq mode is used for the CurrentInput and the VoltageInput setting.
I_2nd/I_Fund : This setting depends on the system condition. Typical value is 0.4 or 40%.
10.1.4 Setting example
For 200 MVAr, 400 KV star connected SCB
For the given SCB configuration, X
230
UBase
´
3 X
SCB
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for each phase is calculated as:
SCB
1MRK 511 401-UEN Rev. K
GUID-573C032B-67C6-4C34-ADA4-AE7C5FE70358 v1
(Equation 103)
GUID-DF0147E6-D5BE-4AA2-9CB8-D49775F72419 v1
Bay control REC670
Application manual