Voltage is not selected by one fixed power threshold. The same capacity serving nearby concentrated loads or distant distributed loads produces different cable, switchgear, loss, protection and expansion outcomes.
What boundary this article establishes
Teams planning a new mine power station, extending an LV station or approaching cable and bus limits.
Compare capacity, distance, existing distribution, protection, operational capability and expansion in one decision.
Produce traceable LV paralleling, MV generation or step-up transmission options and triggers for the next design stage.
Calculate current, voltage drop, losses and switchgear limits for each option under continuous and fault conditions, then include the existing bus, protection and operating capability. Total capacity is an input, not the sole answer.
01
Map load location and transmission distance
LV can be direct when generation is close to a concentrated load. As crushers, pump stations, shafts and camps spread out, high LV current increases cable quantity, drop and installation complexity.
- Map generating, distribution and load points
- Record route, installation and environment
- Calculate normal, standby and expansion flows
02
Compare current, cables and switchgear
Higher voltage reduces current for the same power but adds MV switchgear, protection, earthing and operating requirements. Compare the complete installed system.
- Calculate feeder and bus continuous and starting current
- Compare cable quantity, size, tray and terminations
- Check breaker interrupting duty and equipment availability
03
Check what the existing system can accept
Expansion is constrained by bus voltage, transformer capacity, fault level, earthing and selectivity. Retaining LV generation with step-up transmission can sometimes be more practical than replacing every unit.
- Verify single-line diagrams and nameplates
- Calculate fault current with new generation
- Confirm interconnection, transformer and protection compatibility
04
Include operation and maintenance capability
MV requires clearances, interlocks, test equipment, switching procedures and qualified personnel. LV paralleling also needs synchronization, load sharing and selective protection.
- Define switching, isolation and service boundaries
- Confirm local skills and support
- List protection and recurring tests
05
Use expansion stages to define architecture
An LV solution today may reach its limit in the next phase. State how many units can be added, which component reaches its limit first and when step-up or a new station is required.
- Model current, approved and long-term stages
- Record margin in cables, bus, switchgear and fuel
- Define interfaces and voltage-transition triggers
Inputs for low- and medium-voltage comparison
| Capacity | Unit and total rating, online units, reserve and load factor |
|---|---|
| Distance | Generator-to-bus and load routes, installation and environment |
| Electrical | Voltage, current, drop, losses, fault and starting duty |
| Existing system | Bus, transformers, switchgear, earthing and protection |
| Operations | Competence, switching, tests, spares and service |
| Expansion | Stages, interfaces, margins and upgrade triggers |
Three common errors
Selecting voltage from total power only
Distance, distribution and the existing bus may set the boundary first.
Comparing generator price only
Cables, switchgear, transformers, civil work, losses and service change lifecycle cost.
Ignoring fault and protection coordination
Added generation can exceed switchgear duty and remove selectivity.
Information required before selection
- Load locations, capacities and distances are mapped
- LV and MV single-line options exist
- Current, drop, losses and fault calculations are traceable
- Existing bus, transformer and protection data are complete
- Local MV operating and maintenance capability is confirmed
- Expansion stages and transition triggers are documented