Challenge
A new energy center at a Beijing automotive plant (Beijing-Benz) supplies chilled water, compressed air and other utility services to the production lines. Its pump and compressor motors are 10 kV class loads: starting them direct-on-line (DOL) draws six to eight times full-load current, which can pull down the plant bus voltage, stress transformers and switchgear, and subject pumps and compressors to mechanical shock and water hammer.
The project required controlled, low-stress starting for every pump and compressor motor, with consistent parameters across multiple units.
Solution
Ten Xichi medium voltage soft starters from the CMV-10 series were supplied for the energy center:
- 5 × CMV-355-10
- 1 × CMV-643-10
- 4 × CMV-1313-10
The units cover both the pump and compressor motors. Site parameters were set to 30% initial voltage, a current limit of 3.5× Ie, and a start ramp time of 8 s, giving smooth acceleration for each motor. The CMV-10 series soft starters ramp the applied voltage up gradually instead of switching full voltage on instantly, limiting starting current, reducing voltage dips on the plant bus, and protecting pumps and compressors from mechanical stress during every start. See the CMV series product page for ratings and options.
Results
- All ten CMV-10 series soft starters were supplied and parameterised on site: initial voltage 30%, current limit 3.5× Ie, start ramp time 8 s
- Starting is now controlled across every pump and compressor motor in the energy center, avoiding the 6–8× inrush and voltage dips of direct-on-line starting
- Three current ratings (355 A, 643 A, 1313 A) cover the full range of utility motors on site from a single product series
- Each motor starts with a smooth voltage ramp, reducing mechanical shock, water hammer and thermal stress on windings and bearings
FAQ
Why use a soft starter instead of direct-on-line starting for large pumps and compressors?
Direct-on-line starting switches full voltage onto the motor instantly, drawing six to eight times full-load current. This inrush pulls down bus voltage, stresses transformers and switchgear, and shocks the pump or compressor mechanically — including water hammer in pipework. A soft starter ramps the voltage up gradually, limiting starting current to a set level and giving a smooth, low-stress start.
What does a 3.5× Ie current limit mean on a soft starter?
Ie is the motor’s rated current. A current limit of 3.5× Ie means the soft starter regulates the thyristor firing angle so the starting current never exceeds 3.5 times full-load current — typically 2.5 to 4 times in good practice — instead of the 6 to 8 times seen with DOL starting. In this project the limit was set at 3.5× for every unit.
What do the CMV-355-10, CMV-643-10 and CMV-1313-10 model numbers mean?
CMV is Xichi’s medium voltage soft starter series; the number after CMV is the rated current in amperes (355 A, 643 A, 1313 A), and the -10 suffix indicates the 10 kV voltage class. The energy center used all three ratings to cover pumps and compressors of different motor sizes from one product series.
Where are MV soft starters typically used in an automotive plant?
Automotive plants concentrate their large fixed-speed motors in the energy center: chilled water circulation pumps, cooling water pumps, air compressors, boiler feed pumps and fire pumps. These 10 kV class motors run at constant speed, so soft starters control the start instead of a VFD, which would add cost without speed benefit.
What is the difference between a soft starter and a VFD?
A soft starter controls voltage during starting and stopping only, and is built for fixed-speed loads such as pumps, compressors and fans. A variable frequency drive controls both speed and torque continuously. For motors that run at constant speed, a soft starter is the economical, reliable choice. See our medium voltage VFD range if your process needs continuous speed control.
Can one soft starter series cover both pumps and compressors?
Yes. The same CMV-10 series handled every utility motor in this project: five CMV-355-10, one CMV-643-10 and four CMV-1313-10 units covering the plant’s pumps and compressors with identical starting parameters (30% initial voltage, 3.5× Ie, 8 s ramp).