690V Direct Busbar AHF for Substations and Heavy Industry

Mining, steel and cement plants often run 690V distribution with high harmonic loads from VFDs, crushers and hoists. Conventional harmonic filters are installed downstream of a step-down transformer, adding losses, floor space and commissioning time. A direct busbar active harmonic filter connects to the 690V bus itself and removes that extra stage.

What direct busbar connection changes

Connecting the AHF directly to the main busbar shortens the compensation path. The filter sees the same voltage as the loads, so compensation is more accurate and the response to load steps is faster. It also removes the need for a dedicated step-down transformer and its associated protection, cabling and cooling losses.

• Voltage: 380V, 400V, 415V, 480V and 690V three-phase options
• Connection: direct busbar or cable entry, three-phase three-wire or four-wire
• Enclosure: IP54 floor-standing cabinet with medium-voltage style busbar compartment
• Capacity: modular cabinets in parallel for 200A to 600A and above
• Controls: DSP-based detection with a response below 10 milliseconds

Where it pays back fastest

Projects with long cable runs between the transformer and the load centre benefit most. Eliminating a step-down transformer typically removes 1.5% to 3% of conversion losses and reduces the switchgear footprint in an already crowded substation room.

In mining, harmonic distortion from hoist and conveyor drives causes transformer overheating and nuisance protection trips. A filter on the 690V bus stabilises voltage during starting and reduces THDi on the upstream network, which extends transformer life and avoids derating.

Engineering checks before ordering

• Verify busbar short-circuit withstand and the filter's internal protection coordination
• Confirm the neutral arrangement if single-phase loads share the 690V distribution
• Check ambient temperature and altitude; derate above 2000 m
• Plan CT installation points so they capture both filter and load current correctly
• Agree the compensation target in writing: THDi below 5% and the required power factor

Commissioning sequence

Start with the filter in monitor-only mode and record a full production cycle. Set harmonic order selection to the dominant orders, then raise the compensation ratio gradually while watching bus voltage and temperature. Enable dry-contact alarms for over-temperature, over-current and fan failure before handing over.

For hybrid projects that combine harmonic filtering with power factor correction in one cabinet, see our hybrid compensation cabinet guide.