When was the last time a complete sectionalizing study was developed for your distribution system? Does your utility only “update” its coordination plan from year to year, or work plan to work plan? Do you want to reduce outage hours and clock blinks? What benefits would your system realize from reduced fault currents and equipment operations?
The above are a few questions utility personnel should ponder as they plan for the future. Each year utilities typically experience load growth, eventually demanding larger conductors and additional substations, which in turn increases fault currents. The increasing load and fault currents tend to decrease the coordination between in-line sectionalizing devices, often leading to undesirable operation of those devices.
Most utilities rely on the mainstays of coordination equipment – the hydraulic recloser (OCR) and the fused-cutout. Although such devices are very useful and have been used for decades, in recent years other devices, procedures and philosophies have emerged. Each utility operates differently, and each utility’s “coordination expert” has his or her own way of sectionalizing. However, there is a significant benefit to reviewing as many of the available coordination “tools” as possible. When developing an effective and reliable coordination plan, consider following:
Equipment
- Electronic 1-phase reclosers
- Electronic sectionalizers
- Current limiting fuses
- Different speed fuses
- Digital recloser controls
- Digital fault current recorders
- Fault indicators
- Transformer fusing (type / speed)
- Smart-Grid and SCADA equipment
Procedures & Philosophies
- 30 or 40 ohm for minimum fault
- Fast / delay curves vs all delay
- 2 or 3 reclose operations
- reclose vs time delayed reclose
- Fusing of all side-taps on 3-phase lines
- Development of reliability zones
- High current trip and/or high current L.O.
- Fuse sacrificing vs fuse blowing (or a mix)
- CSP vs conventional transformers
- Replace gapped arresters
- Maintain marginal vs recommended cycles
- 1-Ph tripping vs 3-Ph tripping of 3-Ph
- Phase balancing of multi-phase lines
- Suitable ratio of peak current to OC pickup
- Preferred TCCs for full range currents
- Preferred TCCs of ground trip
- Tree clearances (reliability zones)
- Sectionalizing training for personnel
- Cold-load & in-rush currents consideration
For assistance with your distribution sectionalizing and coordination planning, contact us.