200Hz-400Hz Sine Wave Filters Liquid Cooled-S4L Series


Product Overview

Developed specifically for high frequency PMAC applications, CTM High Frequency Liquid Cooled Sine Wave Filters transform the output of high frequency Variable Speed Drives (VFDs or VSDs) from a Pulse-Width Modulated (PWM) square wave with voltage spikes and high frequency harmonics to a near perfect sinusoidal waveform. CTM’s patented liquid cooled technology traps and removes 97% of the filter’s heat in the highest power density solution available to the market. The largest companies in the world rely on CTM technology, with more than 200,000 installed units in some of the harshest environments on the planet.

Liquid Cooled Advantages

  • Highest power density
  • Lowest audible noise
  • Sealed design for harsh conditions
  • Thermally isolated from ambient

High Freq. Sine Wave Filter

  • Specially developed for permanent magnet AC (PMAC) motors
  • Fundamental frequencies up to 400 Hz
  • Extra filtering provided to minimize motor heating caused by higher harmonic content
Typical Applications

High Speed Motor Drives PMAC Motor Drives

Harmonic Voltage Distortion

<5% @ 5 kHz

Voltage Range

Up to 500 V

Fundamental Frequency

S2L: Up to 200 Hz S3L: Up to 320 Hz S4L: Up to 400 Hz - For line freq. applications, see SWL Series Sine Wave Filters

Maximum Altitude

No Limit

Switching Frequency

5 - 20 kHz Above 20 kHz, contact CTM for application verification

Current Range

130 - 1560 A

Overload Capability

200% rated current for 1 minute

Maximum Coolant Temperature

50 °C (122 °F) (higher with de-rating)

Motor Cable Length

Up to 15,000 feet

Approved Coolants

Drinking water Water-glycol mixture For R134A, contact CTM

Plumbing Material Options

Aluminum (standard) Copper

Heat Removal

97% to Liquid Coolant 3% to Ambient Air

Maximum Ambient Temperature

65 °C (149 °F)


  • Motor Protection: Harmful square waves, voltage spikes, and harmonic distortion are all filtered from the inverter output, reducing motor heating, wear, and winding stress, thereby extending motor longevity.
  • PMAC Motor Optimized: Designed specifically with PMAC motor applications in mind, CTM high frequency sine wave filters incorporate features to address concerns unique to these applications. For example, high frequency inverters often output higher harmonics than at line frequency. To address this issue, these filters are attenuated to remove a larger percentage of drive harmonics (see next page for additional details).
  • High Frequency: Thermally designed to withstand frequencies that would burn other inductors, CTM H.F. filters utilize advanced, proprietary materials to minimize heating and high current saturation.
  • Multiple Designs for Enhanced Performance: Two different filter designs are offered at each current level, so that filter performance, capacitor current percentage, and cost are optimized for your application’s needs.


  • Highest Power Density: Superior heat removal technology enables smaller magnetics, yielding the highest power density reactors available. Low surface temperatures eliminate clearance requirements, further increasing “effective” power density.
  • Thermal Isolation: With up to 97% of heat removed through the coolant, liquid cooled reactors have negligible effects on cabinet air temperature. No climate control required.
  • Sealed Design for Harsh Environments: CTM inductors are environmentally sealed in potting, creating an extremely rugged and reliable design ideal for use in the harshest environments.
  • Extremely Low Audible Noise: Due to superior materials and geometric shapes, magnetostriction-induced noise is significantly lower in CTM filters. When combined with a sealed package, the result is a nearly silent solution.

Thermal Isolation

CTM liquid cooled reactors will have negligible temperature effects when installed in an existing cabinet. Liquid cooled inductors are thermally isolated from their enclosures, meaning a majority (97%) of the heat is removed directly through the liquid coolant.

In this example, both an air cooled and a liquid cooled reactor are sized for a 600 HP motor application; both reactors are identically 99.5% efficient (0.5% power loss). The air cooled reactor rejects 3,000 watts to the cabinet air, while the equivalent liquid cooled reactor only rejects 90 watts to the air. The remaining 2,910 watts are removed directly by the liquid coolant.

As can be seen in the graph, in a typical NEMA 3R cabinet, installation of an air cooled reactor will increase cabinet air temperature by 20.9°C . The equivalent liquid cooled reactor raises cabinet air temperature by only 1.4°C. The low temperature rise provided by liquid cooled reactors yields increased reliability for all electronics within the cabinet. Low surface temperatures also allow the liquid cooled reactor to smaller clearances, increasing effective power density further.

200Hz-400Hz Sine Wave Filters Liquid Cooled-S4L Series