Protection Coordination Studies
Short-circuit calculation, relay coordination and setting tables for industrial networks and substations.
Protection coordination means setting relays so the one closest to the fault operates first and the rest of the network stays healthy. Wrong settings, or settings copied from another project, are the most common cause of nuisance trips and widespread outages. ENP bases the study on real network data, and the output can be loaded directly into the relays.
Study stages
| Stage | Description |
|---|---|
| Data collection | Single-line, transformer, cable and motor data, CT/VT, upstream short-circuit level |
| Modelling | Build the network model (ETAP, DIgSILENT PowerFactory, SKM) |
| Short circuit | Calculation per IEC 60909 or ANSI; maximum and minimum faults |
| Load flow | Loading and voltage drop check |
| Coordination (TCC) | Time-current curves and setting selection |
| Arc flash | Incident energy per IEEE 1584 and labelling |
| Delivery | Setting table and study report |
Coordination principles
Coordination time interval (CTI) ≈ 0.2 to 0.4 s between upstream and downstream relays
- Pickup above load and motor starting current, and below minimum fault current
- Riding through transformer inrush without nuisance trips
- Curves: Normal Inverse, Very Inverse, Extremely Inverse and Definite Time per IEC 60255
- Earth fault protection according to neutral earthing (solid, resistance, isolated)
- Supplementary functions: 50BF, 27/59 and zone selective interlocking (ZSI)
CT selection and checking
- Accuracy class (5P20, 10P10, PX) and rated burden
- Saturation check at maximum fault current
- Knee-point voltage calculation for differential and distance relays
Deliverables
- Full study report with assumptions and results
- Coordination curves
- Setting table for every relay (ready to load)
- Single-line diagram with short-circuit data
- Arc flash hazard map and warning labels
- Review of existing network settings after expansion or an outage
Scope of work
- Short-circuit (IEC 60909) and load flow study
- TCC coordination curves and setting selection
- CT checking and selection for differential and distance relays
- Arc flash study (IEEE 1584) and warning labels
- Setting tables ready to load into relays
- Review of existing network settings