Overview
Any internal fault in the capacitor bank leads to unbalance in the Shunt capacitor banks (SCB) and severe damage to the entire bank, which can result in an explosion or fire. Generally internal faults in the shunt capacitor bank are due to the open or short-circuit of the capacitor units or elements. The “Current unbalance protection of SCB” function uses measured phase current (I3P) and measured unbalance current (I3UNB). Based on the measured unbalance current deviation from the stored reference current value, the function identifies the severity of the internal fault in the SCB.
For more detailed information on “Current unbalance protection of SCB” function, refer to ABB, Relion 670 Series manuals.
To see other supported functions, click here.
Function Identification
| Function description | IEC 61850 identification |
IEC 60617 identification |
ANSI/IEEE C37.2 device number |
| Current unbalance protection of SCB | SCUCPTOC | dI > C | 60N |
Signals & Setting Parameters
SCUCPTOC Function block
SCUCPTOC Input signals
| SCUCPTOC Input signals | |||
| Name | Type | Default | Description |
| I3P | GROUP SIGNAL | – | Group signal for phase current input |
| I3UNB | GROUP SIGNAL | – | Group signal for unbalance current input |
| BLOCK | BOOLEAN | 0 | Block of function |
| BLKTR | BOOLEAN | 0 | Block of trip |
| BLKALM | BOOLEAN | 0 | Block of alarm |
| BLKWRN | BOOLEAN | 0 | Block of warning |
| INHIBIT | BOOLEAN | 0 | Inhibit the function |
| TRIGCOMP | BOOLEAN | 0 | Trigger input to store the measured quantities into the IED memory. The stored values will be used for future compensation of the function measurement. |
| RESETCOMP | BOOLEAN | 0 | Force the stored natural unbalance current and stored reference current to zero. |
SCUCPTOC (60N) Output signals
| SCUCPTOC (60N) Output signals | |||
| Name | Type | Description | |
| TRIP | BOOLEAN | Common trip signal | |
| TR_A | BOOLEAN | Trip signal from either phase A or from the neutral unbalance depending how many unbalance currents are used (3 or 1). | |
| TR_B | BOOLEAN | Trip signal from phase B. Forced to zero when only one unbalance current is used. | |
| TR_C | BOOLEAN | Trip signal from phase C. Forced to zero when only one unbalance current is used. | |
| BFI | BOOLEAN | Common pickup signal | |
| PU_A | BOOLEAN | Start signal from either phase A or from the neutral unbalance depending how many unbalance currents are used (3 or 1). | |
| PU_B | BOOLEAN | Start signal from phase B. Forced to zero when only one unbalance current is used. | |
| PU_C | BOOLEAN | Start signal from phase C. Forced to zero when only one unbalance current is used. | |
| ALARM | BOOLEAN | General alarm signal | |
| ALMA | BOOLEAN | Alarm signal for either phase A or for the neutral unbalance depending how many unbalance currents are used (3 or 1) | |
| ALMB | BOOLEAN | Alarm signal from phase B. Forced to zero when only one unbalance current is used. | |
| ALMC | BOOLEAN | Alarm signal from phase C. Forced to zero when only one unbalance current is used. | |
| WARNING | BOOLEAN | General warning signal | |
| WRNA | BOOLEAN | Warning signal for either phase A or for the neutral unbalance depending how many unbalance currents are used (3 or 1). | |
| WRNB | BOOLEAN | Warning signal from phase B. Forced to zero when only one unbalance current is used. | |
| WRNC | BOOLEAN | Warning signal from phase C. Forced to zero when only one unbalance current is used. | |
| BLKDA | BOOLEAN | Phase A or neutral unbalance operation blocked, depending how many unbalance currents are used (3 or 1), when corresponding reference current going lower than set IMin value | |
| BLKDB | BOOLEAN | Phase B operation blocked when corresponding reference current goes lower than set IMin value. Forced to zero when only one unbalance current is used. | |
| BLKDC | BOOLEAN | Phase C operation blocked when corresponding reference current goes lower than set IMin value. Forced to zero when only one unbalance current is used. | |
| COMPEXED | BOOLEAN | Indicates that a trigger was made for natural unbalance current calculation | |
| IUNBCLCA | REAL | Magnitude of calculated unbalance current for either phase A or neutral unbalance depending how many unbalance currents are used (3 or 1). | |
| IUNBCLCB | REAL | Magnitude of calculated unbalance current of phase B. Forced to zero when only one unbalance current is used. | |
| IUNBCLCC | REAL | Magnitude of calculated unbalance current of phase C. Forced to zero when only one unbalance current is used. | |
SCUCPTOC Non group settings (basic)
| SCUCPTOC Non group settings (basic) | |||||
| Name | Values (Range) | Unit | Step | Default | Description |
| SCBConf | 1 unbalance curr 3 unbalance curr |
– | – | 1 unbalance curr | Number of unbalance currents available |
| GlobalBaseSel1 | 1 – 12 | – | 1 | 1 | Global base value selector for phase current |
| GlobalBaseSel2 | 1 – 12 | – | 1 | 1 | Global base value selector for unbalance current |
SCUCPTOC Group settings (basic)
| SCUCPTOC Group settings (basic) | |||||
| Name | Values (Range) | Unit | Step | Default | Description |
| Operation | Off On |
– | – | Off | Operation Off / On |
| IMin | 5.0 – 100.0 | %IB1 | 0.1 | 10.0 | Minimum reference phase current for operation in % of IBase1 with reference to phase current CT |
| IUnbalWrn> | 1.0 – 1000.0 | %IB2 | 0.1 | 10.0 | Current unbalance warning level for unbalance current in % of IBase2 with reference to unbalance current CT |
| tDefWrn | 0.00 – 60.00 | s | 0.01 | 5.00 | Definite time delay for warning |
| IUnbalAlm> | 1.0 – 1000.0 | %IB2 | 0.1 | 20.0 | Current unbalance alarm level for unbalance current in % of IBase2 with reference to unbalance current CT |
| tDefAlm | 0.00 – 60.00 | s | 0.01 | 5.00 | Definite time delay for alarm |
| IUnbal> | 1.0 – 1000.0 | %IB2 | 0.1 | 30.0 | Current unbalance trip level for unbalance current in % of IBase2 with reference to unbalance current CT |
| CurveType | Definite time Programmable |
– | – | Definite time | Selection of time delay curve type for trip |
| tDefTrip | 0.00 – 60.00 | s | 0.01 | 5.00 | Definite time delay for trip. Note that when Programmable IDMT curve is used, this definite time delay will be added to the calculated IDMT time. |
| k | 0.05 – 999.00 | – | 0.01 | 1.00 | Time multiplier for programmable curve for trip |
| tMin | 0.00 – 60.00 | s | 0.01 | 0.00 | Minimum operate time for programmable curve for trip |
| tReset | 0.00 – 60.00 | s | 0.01 | 0.02 | Reset time delay for warning, alarm and trip |
| tPCrv | 0.005 – 3.000 | – | 0.001 | 2.00 | Parameter P for programmble curve for trip |
| tACrv | 0.005 – 200.000 | – | 0.001 | 28.200 | Parameter A for programmble curve for trip |
| tBCrv | 0.0000 – 20.0000 | – | 0.0001 | 0.1217 | Parameter B for programmble curve for trip |
| tCCrv | 0.1 – 10.0 | – | 0.1 | 1.0 | Parameter C for programmble curve for trip |
SCUCPTOC Non group settings (advanced)
| SCUCPTOC Non group settings (advanced) | |||||
| Name | Values (Range) | Unit | Step | Default | Description |
| BlockTrip | Trip disabled Trip enabled |
– | – | Trip enabled | Trip blocked / enabled |
SCUCPTOC Monitored data
| SCUCPTOC Monitored data | ||||
| Name | Type | Values (Range) | Unit | Description |
| LASTCOMP | GROUP SIGNAL | – | – | Indicates date and time when last trigger was made for natural unbalance current calculation |
| IUNBCLCL1 | REAL | – | A | Magnitude of calculated unbalance current for either phase L1 or neutral unbalance depending how many unbalance currents are used (3 or 1). |
| IUNBCLCL2 | REAL | – | A | Magnitude of calculated unbalance current of phase L2. Forced to zero when only one unbalance current is used. |
| IUNBCLCL3 | REAL | – | A | Magnitude of calculated unbalance current of phase L3. Forced to zero when only one unbalance current is used. |
| IL1 | REAL | – | A | Reference quantity which is either phase L1 current or positive sequence current depending how many unbalance currents are used (3 or 1). |
| IL2 | REAL | – | A | Current in phase L2. Forced to zero when only one unbalance current is used. |
| IL3 | REAL | – | A | Current in phase L3. Forced to zero when only one unbalance current is used. |
| IUNBL1 | REAL | – | A | Unbalance current in either phase L1 or neutral depending how many unbalance currents are used (3 or 1). |
| IUNBL2 | REAL | – | A | Unbalance current in phase L2. Forced to zero when only one unbalance current is used. |
| IUNBL3 | REAL | – | A | Unbalance current in phase L3. Forced to zero when only one unbalance current is used. |
| IMEML1 | REAL | – | A | Stored value for either phase L1 current or positive sequence current depending how many unbalance currents are used (3 or 1). |
| IMEML2 | REAL | – | A | Stored phase current of phase L2. Forced to zero when only one unbalance current is used. |
| IMEML3 | REAL | – | A | Stored phase current of phase L3. Forced to zero when only one unbalance current is used. |
| IMEMUNBL1 | REAL | – | A | Stored unbalance current for either phase L1 or neutral depending how many unbalance currents are used (3 or 1). |
| IMEMUNBL2 | REAL | – | A | Stored unbalance current of phase L2. Forced to zero when only one unbalance current is used. |
| IMEMUNBL3 | REAL | – | A | Stored unbalance current of phase L3. Forced to zero when only one unbalance current is used. |
| IREFUNBL1 | REAL | – | A | Magnitude of stored unbalance current scaled to the reference quantity for either phase L1 or neutral depending how many unbalance currents are used (3 or 1). |
| IREFUNBL2 | REAL | – | A | Magnitude of stored unbalance current scaled to present phase current of phase L2. Forced to zero when only one unbalance current is used. |
| IREFUNBL3 | REAL | – | A | Magnitude of stored unbalance current scaled to present phase current of phase L3. Forced to zero when only one unbalance current is used. |
Logics & highlights
Typical earthed/unearthed double WYE connected SCB
Typical earthed/unearthed single WYE connected SCB with strings in each phase
Typical earthed/unearthed H-bridge connected SCB
Different terminologies of currents used in the function
Unbalance current calculation
Trigger logic
Minimum reference current check logic
Programmable curve
Simplified Warning, Alarm, and Trip logic
Typical programmable curve
INHIBIT and BLOCK behavior in the function
Reporting over IEC 61850
