Voltage determines current, cables, breakers, switchgear, protection, transformers, construction and operator competence. MV is not automatically better at high power, and LV is not always simpler. Begin with the loads and existing distribution.
LV normally fits moderate power, nearby LV loads and an aligned existing system. MV deserves comparison when power and distance are high or the site already operates 6.3/10.5 kV buses. Finalize with a one-line, short-circuit and protection study, grounding and lifecycle cost.
1. Voltage changes more than the alternator winding
At the same power, higher voltage reduces current and changes cable size, parallel runs, voltage drop, breakers and busbars. It also increases insulation, switchgear, protection, grounding, operating and testing requirements.
This is a system decision: generator, switchgear, transformer, loads and construction interfaces belong in one design.
2. Confirm eight electrical inputs
- Total, per-set and future power.
- Load voltage distribution.
- Distance and route to main distribution.
- Motor starting and allowed drop.
- Existing buses, transformers and switchgear.
- Single, parallel, island or utility-parallel operation.
- Grounding, fault level and selectivity.
- Codes, supply and qualified MV maintenance.
3. When low voltage is the rational choice
400/415/440/480 V generally fits nearby LV loads where current can be handled by practical cables and switchgear. Supply and maintenance are broadly available and the system has fewer voltage levels.
Large LV power creates high current, parallel cables, large busbars and high interrupting duties. Verify terminals, routes, drop, heat and protection—not only the set price.
4. When 6.3 or 10.5 kV deserves evaluation
MV can reduce current and extensive LV cabling where power or distance is high, an MV bus exists, or large motors use MV. This is common in mines and industrial infrastructure.
It adds MV alternators or transformers, switchgear, relays, grounding, insulation tests and qualified operators. Compare the full system.
5. Direct MV generation versus LV plus step-up transformer
Direct MV removes the step-up stage but uses more specialized generation and maintenance. LV with a transformer may use common set platforms while adding losses, footprint, protection and another failure point.
Compare efficiency, fault current, paralleling, motor starting, spares, transport, repair and expansion.
6. Protection, grounding and safety are approval gates
Complete fault calculations, coordination, ground-fault detection, insulation coordination, surge protection, CTs and relays. Define interlocks, isolation, testing and grounding procedures for MV.
Qualified engineers and local codes govern this work; an article cannot replace project settings and safety rules.
7. Decide on total system cost and execution
Compare sets, switchgear, transformers, cables, civil work, testing, spares, losses, maintenance and training over the project life.
The final specification should record rationale, one-line, voltage, frequency, grounding, fault and protection basis, equipment ratings, tests, interfaces and responsibilities.