Challenge
A natural gas compressor is a high-power, high-inertia load. Started across the line, its 10 kV motor can draw several times the full-load current (industry references cite 6-8 times for large compressor motors), causing voltage dips on the station bus and torsional stress on the compressor shaft and driven train. On a gas compression site — frequently a hazardous, unmanned environment — the starting equipment must be reliable, keep the grid impact low, and support remote monitoring.
Solution
We supplied a CMV-630-10 medium voltage soft starter for the natural gas compressor. The CMV series ramps the motor voltage through SCR thyristor firing with CFT optical-fiber trigger isolation, cutting inrush current and reducing mechanical and grid impact. A built-in vacuum bypass contactor with redundant direct-start function keeps the compressor running even in the event of a valve-group fault.
The driven motor is a 4-pole, 10 kV machine rated at 39 A, within the CMV-630-10 rating (45 A at 10 kV). Site parameters were set as: initial voltage 40%, current limit 300% Ie (3.0 times rated current), start time 15 s. Communication via Modbus RTU/TCP over RS485 allows the starter to be monitored from a remote control room or SCADA system.
Results
- Xichi CMV-630-10 10 kV medium voltage soft starter supplied for a natural gas compressor (10 kV, 39 A, 4-pole motor)
- Site parameters set: 40% initial voltage, 300% Ie current limit, 15 s start time
- SCR-based voltage ramping limits inrush current and reduces mechanical and grid impact on compressor starts; the built-in vacuum bypass takes over at full speed
FAQ
Why does a natural gas compressor need a medium voltage soft starter?
Gas compressor motors are large, high-inertia loads. Direct-on-line starting can draw 6-8 times the full-load current, causing voltage dips on the station bus and torsional stress on the compressor shaft. A medium voltage soft starter ramps the motor voltage through SCR control, limiting inrush current and protecting both the grid and the compressor drive train.
What do the site parameters — 40% initial voltage, 300% Ie current limit, 15 s start — mean?
Initial voltage is the voltage applied at the moment of starting (40% of rated). Ie is the motor rated current, so a 300% Ie current limit caps the starting current at 3 times rated (here about 117 A peak for the 39 A motor). The 15 s ramp accelerates the motor to full voltage over 15 seconds, giving a controlled, low-stress start.
What is the starting current limit for a 10 kV gas compressor motor?
With a 300% Ie current limit setting, the starting current is capped at 3 times the motor rated current. For the 39 A motor in this project, that means a maximum starting current of about 117 A, versus the much higher peak of across-the-line starting.
Is the CMV series suitable for hazardous gas environments?
The CMV series is an IP40 indoor cabinet design with an explosion-proof version available for hazardous areas. For natural gas installations, confirm the site’s zone classification and we will match the correct cabinet configuration.
Soft starter or VFD for a natural gas compressor?
If the compressor runs at fixed speed and only needs smooth starting, a soft starter is the lower-cost, lower-complexity solution. A VFD adds continuous speed control, which matters for load-following applications, but it is significantly more expensive at medium voltage. For variable-speed gas compression, see our medium voltage VFD.
How is the starter monitored at a remote compressor station?
The CMV series supports Modbus RTU and Modbus TCP over RS485, with up to 31 units networked on one bus. Operators can read running status and motor parameters and perform remote start/stop control from a SCADA or DCS system — designed for unmanned gas stations.
