Anyhz FST series input output filters are passive EMC filters designed to solve electromagnetic compatibility (EMC) challenges in variable frequency drive (VFD) installations. Available from 5A to 1600A for 220V, 380V, and 440V systems, these harmonic filters effectively suppress conducted interference along power lines and reduce EMI (electromagnetic interference) generated by inverters.

The FST input filters protect the VFD from grid-side disturbances and prevent inverter-generated harmonics from polluting the power network, ensuring compliance with IEC 61800-3 and IEEE 519 standards. The FSTL output filters protect motors from destructive dv/dt voltage stress, eliminate audible whistling in long cable runs, and extend motor insulation life—critical for applications in textile, CNC machine tools, pumps, and industrial automation.

• Three-Stage Filtering Design: Superior attenuation across wide frequency range without active cooling
• Special Magnetic Materials: High impedance characteristics ensure effective harmonic suppression
• Dual Protection: Input filters protect VFD, output filters protect motors and cables
• Long Cable Solutions: FSTL output filters eliminate motor whistling and overheating in runs >50m
• Wide Current Range: 5A-1600A covers applications from small servo drives to large industrial VFDs
• High Voltage Options: 660V/690V/1140V filters available for medium voltage applications
• Flexible Connections: Terminal blocks (≤300A) or copper busbars (≥300A) for easy installation

The three-stage LC filtering design provides superior attenuation of both common-mode and differential-mode interference across a wide frequency spectrum (150kHz to 30MHz). Unlike single-stage filters that only address specific frequencies, our multi-stage design ensures compliance with stringent EMC standards without requiring active cooling or complex electronics. The passive design means no fans, no maintenance, and MTBF >100,000 hours.

• Stage 1: Common-mode choke for high-frequency noise
• Stage 2: Differential-mode capacitors for line-to-line harmonics
• Stage 3: Output balancing for optimal performance
• Attenuation: >40dB at 1MHz, >60dB at 10MHz

We use nanocrystalline and ferrite core materials specifically selected for high impedance across the critical frequency ranges where VFDs generate harmonics. These advanced magnetic materials provide 10x higher permeability than standard iron cores, enabling compact size without sacrificing performance. The cores are designed to avoid saturation even under high harmonic current conditions.

• Nanocrystalline cores for common-mode chokes
• High-frequency ferrite for differential-mode filtering
• Non-saturating design under harmonic loads
• Low core losses minimize heating

FST input filters install between the power grid and VFD, preventing high-frequency switching noise from feeding back into the supply network. This protects sensitive equipment sharing the same transformer and ensures compliance with utility harmonic limits (IEEE 519, EN 61000-3-6). The filter also suppresses grid-side voltage transients, protecting the VFD's rectifier stage from damage.

• THDi reduction: 8-12% typical (without filter) to <5% (with filter)
• Protects VFD from grid surges and fast transients
• Prevents nuisance tripping of upstream breakers
• Reduces transformer and cable heating

FSTL output filters install between VFD and motor, solving the dv/dt problem that destroys motor insulation in modern IGBT-based drives. The filter limits voltage rise time to <500V/μs, preventing partial discharge and bearing currents. For long cable runs (>50m), the filter eliminates motor whistling, prevents standing wave reflections, and allows standard motor cables instead of expensive shielded or armored types.

• dv/dt limitation: <500V/μs (vs 5000-10000V/μs from VFD)
• Maximum cable length: 150m (unshielded), 300m (shielded)
• Eliminates motor terminal overvoltage (up to 2×DC bus without filter)
• Reduces motor bearing currents and EMI

For large industrial applications, we offer 660V, 690V, and 1140V rated filters compatible with medium voltage VFDs and special motor applications. The 300A-1600A range uses copper busbar connections meeting international standards (IEC 60439-1), ensuring safe, low-resistance connections for high currents. Custom voltage and current ratings available for OEM applications.

• Standard: 220V/380V/440V, 50/60Hz
• Medium voltage: 660V/690V/1140V options
• High current: Copper busbars (≥300A)
• Custom designs for special applications

Terminal block connections (≤300A) provide secure, tool-accessible wiring with IP20 finger protection. For high-current applications, copper busbar terminals (≥300A) allow direct cable lug connection or busbar linking, complying with IEC standards for switchgear connections. All filters are designed for panel or chassis mounting with flanged enclosures.

• Terminal blocks: M4-M6 studs, torque 2-5 Nm
• Copper busbars: Drilled for M8-M12 bolts
• Panel mount: Flanged enclosure with mounting holes
• Chassis mount: Base plate with clearance holes

• Rated Voltage: AC 220V/380V/440V (50/60Hz)
• High Voltage Options: 660V/690V/1140V (custom)
• Operating Frequency: 50/60Hz ±5%
• Test Voltage: P-E: 2700VDC, P-P: 2250VDC
• Insulation Resistance: >100MΩ (1000VDC)
• Operating Temperature: -25°C to +85°C
• Attenuation: >40dB at 1MHz, >60dB at 10MHz
• dv/dt Limitation (FSTL): <500V/μs output
• THDi Reduction: 8-12% to <5% (typical)

Bottom line: Anyhz three-stage passive filters offer the optimal balance of performance, reliability, and cost. Unlike basic single-stage filters, they provide effective harmonic suppression across the full frequency range. Unlike active filters, they require no maintenance, no fans, and have infinite MTBF. The integrated dv/dt limiting in output filters provides motor protection that competitors charge extra for.

Compared to , ABB, and Schaffner EMC filters, Anyhz offers identical three-stage filtering performance with wider current range (up to 1600A) and more flexible voltage options. Our special magnetic materials and optimized design provide equivalent or better attenuation at competitive pricing. For cost-effective EMC compliance without compromising reliability, Anyhz is the proven choice.

★★★★★ 4.7/5 based on 312 EMC filter installations

• Shanghai Water Treatment (2024): 24 units FST-300A and FSTL-300A for 132kW pump VFDs with 150m cables
• Indonesia Textile Plant (2023): 60 units FST-30A for loom VFDs to meet utility harmonic limits
• Germany Machine Tool OEM (2023): 80 units FSTL-45A for CNC spindle motor protection
• Brazil Paper Mill (2023): 18 units FST-600A for 315kW refiner drives
• Thailand Food Processing (2022): 36 units FST-16A for packaging line VFDs
• South Africa Mining (2022): 12 units FSTL-500A for 500m conveyor cables

It depends on your application requirements. Use input filters (FST) when you need to: comply with utility harmonic limits (IEEE 519), prevent interference with other equipment, or protect the VFD from grid disturbances. Use output filters (FSTL) when you have: long motor cables (>50m), motor whistling/noise issues, bearing current problems, or need to protect old motors from dv/dt stress. Many installations benefit from both—input filters for compliance and output filters for motor protection. We can assess your specific needs and recommend the optimal configuration.

Use our VFD matching tables —simply find your VFD model and the corresponding filter current rating is listed. The current rating is based on VFD input current (typically 1.1-1.3× motor FLA). For non-Anyhz VFDs, select the filter current rating closest to your VFD's input current. When in doubt, choose the next higher current rating for safety margin. For output filters, cable length is also a factor—use higher current ratings for very long cables (>150m). Contact our technical team for complex applications.

Line reactors provide inductive impedance that reduces current harmonics and limits inrush, but offer minimal high-frequency attenuation. EMC filters use a combination of inductors and capacitors in multi-stage configuration to provide broadband attenuation from 150kHz to 30MHz. For best results, use both: line reactor on VFD input (for harmonic current reduction) and EMC filter (for high-frequency noise suppression). Our output filters also provide unique dv/dt limiting that reactors cannot achieve.

Minimal impact —our filters are designed with low insertion loss (<3% voltage drop at full load). The output filter adds slight impedance (typically 1-2% voltage drop), which is negligible for most applications. For sensitive applications, you can compensate by increasing VFD output frequency slightly. The benefits of harmonic reduction and motor protection far outweigh the minimal voltage drop. For critical torque applications, we can provide low-impedance custom designs.

Generally no —each motor should have its own output filter, or use a single filter sized for the total current with individual motor reactors. Sharing one filter between motors can cause circulating currents and uneven filtering. For multi-motor systems, we recommend: individual FSTL filters for each motor (best performance), or one large FSTL with individual motor chokes (cost-effective). Contact us for system design assistance with complex multi-motor applications.

Yes —custom engineering available. We manufacture filters for servo drives (lower current, higher frequency attenuation) and for large VFDs up to 2000A and 690V/1140V. These use multiple filter stages and custom magnetic components. For very large systems (>1MW), we offer rack-mounted filter banks with individual stage monitoring. Contact our engineering team with your drive specifications, cable lengths, and compliance requirements for custom solutions.