What is an MV Soft Starter
- MV soft starters are solid-state devices for medium-voltage (MV) motors (typically in the kV range) that provide controlled ramp-up and ramp-down of voltage, reducing inrush current and mechanical stress.
- They use thyristors (or similar power electronics) to modulate voltage during start.
- Often used with large, three-phase squirrel-cage induction motors in industrial settings (pumps, compressors, large conveyors, etc.).
MV Soft Starter Specification Matrix
1. Electrical Ratings
| Parameter | Typical / Example Range | Remarks |
|---|---|---|
| Rated Line Voltage (L-L) | 2.3 kV / 3.3 kV / 4.16 kV / 6.6 kV / 7.2 kV / 11 kV / up to ~13.8 kV | Must match MV system and motor voltage |
| Frequency | 50 Hz / 60 Hz (typ. 45–65 Hz) | Industrial power systems |
| Control / Auxiliary Voltage | 110 V AC, 220–240 V AC, or DC (optional) | For control and protection circuits |
| Rated Motor / Starter Current | Up to approx. 800–900 A (model dependent) | Shall be ≥ motor FLC |
| Overload Capability | 500% FLC – 60 s / 600% FLC – 30 s | Heavy-duty starting capability |
2. Starting & Control Functions
| Parameter | Typical / Example | Remarks |
|---|---|---|
| Starting Method | Voltage ramp / Current ramp / Torque ramp | Selectable per application |
| Acceleration Time | Adjustable (e.g. 1–60 s) | Soft starting profile |
| Deceleration / Soft Stop | Adjustable / Optional | Reduces mechanical stress |
| Current Limiting | Approx. 100–400% FLC | Limits inrush current |
| Kick Start | Optional | For high breakaway torque loads |
3. Protection & Monitoring
| Parameter | Typical / Example | Remarks |
|---|---|---|
| Overcurrent Protection | Yes (adjustable) | Protects motor and starter |
| Thermal Overload | Yes (I²t / motor model) | Motor thermal protection |
| Phase Loss / Phase Imbalance | Yes | Phase failure detection |
| Under / Over Voltage | Yes | Supply voltage protection |
| Ground Fault Protection | Optional | System dependent |
| Fault History & Diagnostics | Yes | Event and fault logging |
4. Communication & Interface
| Parameter | Typical / Example | Remarks |
|---|---|---|
| Local Interface | Keypad / HMI / LED indicators | Local monitoring & settings |
| Communication Protocols | Modbus RTU / TCP, PROFIBUS, Ethernet | PLC / DCS / SCADA integration |
| Digital Inputs | Start, Stop, Reset, Interlock | External control |
| Relay Outputs | Run, End of Start, Fault | Status and alarms |
5. Mechanical & Environmental
| Parameter | Typical / Example | Remarks |
|---|---|---|
| Operating Temperature | −10 °C to +60 °C | Derating may apply |
| Storage Temperature | −20 °C to +70 °C | Transport & storage |
| Cooling Method | Air cooling | Natural or forced ventilation |
| Enclosure / IP Rating | IP00 / IP20–IP42 | Indoor / enclosed installation |
| Installation | Indoor (typical) | Outdoor with suitable enclosure |
6. Insulation & Dielectric Characteristics
| Parameter | Typical / Example | Remarks |
|---|---|---|
| Insulation Level | As per IEC MV class | Based on system voltage |
| Power Frequency Withstand | As per IEC | Dielectric test |
| Impulse Withstand (BIL) | According to MV voltage level | Lightning / surge withstand |
7. Standards & Compliance
| Parameter | Typical / Example | Remarks |
|---|---|---|
| Applicable Standards | IEC / IEEE / NEMA (if specified) | Project requirement |
| EMC / Harmonics | IEC / IEEE 519 (system level) | Minimal harmonic generation |
| Factory Tests | Routine Tests | Manufacturer FAT |
8. Key Selection Notes
| Item | Description |
|---|---|
| Motor Voltage & FLC | Must match soft starter rating |
| Starting Duty | Normal / Heavy / Very Heavy |
| Load Type | Pump, fan, conveyor, crusher, compressor |
| Environment | Indoor / Outdoor / Ambient / IP class |
| System Integration | PLC / DCS / SCADA |
| Standards | IEC / IEEE / Project specification |