Why frequency matters as much as voltage
A three-phase induction motor's synchronous speed is n = 120 f / p, where f is frequency and p the number of poles. A machine designed for 60 Hz therefore runs about 17 % slower on a 50 Hz supply at the same pole count, while its cooling fan also turns more slowly. At the same time, torque capability scales roughly with the square of the applied voltage ratio. A 480 V / 60 Hz motor connected to 380 V / 50 Hz is simultaneously under-voltage, slower and less effectively cooled.
In a VVVF-driven elevator the drive controls the motor, but the drive's input stage, DC bus and motor parameters are all sized around the specified supply. "A converter will fix it later" is the assumption that causes commissioning failures on export projects.
Grid comparison
| Supply | Where it is common | Design implications for the lift |
|---|---|---|
| 380 V / 50 Hz, 3-phase | China and many 50 Hz markets | Baseline for many domestically built machines; 220 V phase-to-neutral control circuits |
| 415 V / 50 Hz, 3-phase | Qatar, UAE, Bahrain and other Gulf grids | ~230 V phase-to-neutral; check drive input range, motor rating, transformer taps and SPD/contactor ratings |
| 480 V / 60 Hz, 3-phase | North America and some industrial / compound supplies | Different frequency and voltage class; motor, drive, transformer and protection all re-specified |
| 220–240 V / 50 Hz, 1-phase | Private villas without three-phase | Suitable for compact home lifts; limits motor power and starting current |
Always design to the measured supply and its tolerance, not the nominal figure on a brochure. Ask the local electrical contractor for voltage tolerance, frequency, earthing arrangement and available short-circuit level.
The 480 V → 380 V conversion case
A common export scenario is a machine or a project specification written around 480 V / 60 Hz that must be installed on a 380 V / 50 Hz network. Converting it is not a single transformer purchase. The following items must be reviewed together:
| Item | What must be checked / changed |
|---|---|
| Traction machine / motor | Rated voltage and frequency class; torque and thermal margin at 50 Hz; cooling arrangement |
| VVVF drive | Input voltage range, DC bus level, motor nameplate parameters, braking resistor sizing |
| Control transformer / SMPS | Primary taps for 380 V vs 480 V; control voltage (e.g. 24 V DC, 110/220 V AC) for circuits, lighting and alarms |
| Contactors, relays, SPDs | Coil voltage and rated operational voltage of every device in the cabinet |
| Cables & protection | Conductor cross-section, MCB/MCCB curves, fuse ratings, RCD type, earthing conductor |
| Door operator & auxiliaries | Door machine supply, fan, light, intercom and battery backup inputs |
| Documentation | Electrical schematic, terminal diagram and test record must show the final configuration |
If a step-down transformer is used to retain 480 V equipment on a 380 V network, add its losses, inrush current, physical space, heat dissipation and noise to the design. In most new-build export orders it is cleaner to specify the machine and drive for the destination grid from the start.
Motor power selection: why 15 kW and 18.5 kW are not interchangeable
For a 16-stop machine-room-less passenger lift, two quotations may specify 15 kW and 18.5 kW machines. The larger number is not automatically "better": rated motor power follows the rated load, speed, car weight, counterweight balance, duty cycle and drive efficiency. A higher-power machine increases the supply cable size, protective device rating, starting current and — if oversized — can reduce part-load efficiency.
| Factor | Effect on required power |
|---|---|
| Rated load (e.g. 800 / 1000 / 1250 kg) | Higher load → larger unbalanced mass → more torque |
| Rated speed (1.0 / 1.5 / 1.75 m/s) | Power is roughly proportional to force × speed |
| Counterweight balance ratio | Typically balances the empty car plus a fraction of rated load |
| Gearless machine efficiency & duty cycle | Determines continuous vs peak power and thermal margin |
| Supply voltage / frequency | Affects current, cable size, protection and drive sizing |
| Number of stops | Affects duty cycle and starts per hour, not the peak torque on its own |
How to compare two quotations: put them side by side on rated load, speed, machine model, supply voltage/frequency, cable and breaker size, brake voltage, and the declared duty cycle. Then ask each supplier for the calculation sheet behind the motor selection. A quotation that changes motor power without changing load or speed deserves a written explanation. See also MRL passenger lifts.
Pre-shipment power-supply checklist
- Record nominal voltage, tolerance, frequency, phase count and earthing system from the site's electrical contractor.
- Confirm the available fault level and the upstream protective device, so the cabinet's breaking capacity is adequate.
- Agree the motor, drive, transformer taps, contactor coils and auxiliary voltages on a power-supply confirmation sheet.
- Freeze that sheet together with the GA drawing before production starts.
- Verify the electrical schematic, terminal diagram and factory test record all show the agreed configuration.
- Ship a printed copy inside the control cabinet crate as well as in the digital document pack.