10 Precautions to Follow Before Retrofitting a Screw Air Compressor with a VFD

Retrofitting screw air compressors with a Variable Frequency Drive (VFD) has become a mainstream solution to reduce energy consumption, especially in facilities where compressors account for a significant portion of total electricity usage.

Since screw compressors are high-power, long-running systems, upgrading to a frequency-controlled solution offers great potential for energy savings and optimized performance. However, before proceeding with a VFD retrofit, several technical aspects must be carefully considered to ensure safe, efficient, and reliable operation.

In this article, we outline 10 key precautions you should take before converting your screw air compressor to variable frequency control.

Preserve the integrity of both the main power circuit and the control circuit. Avoid extensive rewiring. This allows the compressor to switch back to its original operating mode in case of VFD failure or maintenance, without the need to reprogram the PLC.

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を確認する。 start signal for the VFD is controlled by the delta contactor (KM1) in a star-delta starter. This prevents the VFD from activating while still in the star connection phase.

Set the time-delay relay (JS) to a value greater than or equal to the VFD start time. This ensures that the compressor starts without load and avoids abrupt torque spikes.

Utilize the VFD’s delayed stop at lower frequency to ensure smooth shutdown and to reduce mechanical stress on the system.

A frequency setpoint below 35 Hz may cause oil separation failure, leading to oil leakage due to insufficient centrifugal force in the oil-air separator. Adjust the lower frequency limit based on your compressor’s specific wear level and design characteristics.

Select a VFD that is one size larger than the compressor motor’s rated power to avoid frequent tripping during startup and to handle startup current peaks.

Install an AC output reactor to filter out high-frequency harmonics from the VFD output. This reduces electromagnetic interference (EMI) そして noise, and extends the life of the motor insulation.

Install pressure sensors close to the compressorそして before any filters or valves. Do not place any shut-off valves between the compressor and the sensor. Retain the original mechanical pressure cut-off switch as a backup to ensure safety and prevent overpressure accidents.

After the VFD retrofit, lower the system’s supply pressure if possible, and switch from a high-pressure, variable-flow setup to a constant-pressure, variable-flow strategy. This enhances energy efficiency while maintaining a stable supply.

Design the control system with both VFD and direct line (power frequency) operation options. If the VFD fails or triggers a protective stop, the system should be able to automatically switch to bypass mode to maintain production uptime.

A well-executed VFD retrofit on a スクリューエアコンプレッサー can result in significant energy savings, quieter operation, and extended equipment life. However, skipping these critical precautions may cause startup problems, sensor inaccuracies, or even safety hazards.

For a successful upgrade, always work with professional technicians and refer to manufacturer specifications. Baldor provides advanced solutions including intelligent VFD control, permanent magnet compressors, and system-level energy audits.