What Switchgear Builders Should Ask Before Choosing an AHF Module Supplier

Buying a filter cabinet means the supplier owns the thermal design, coordination, CT wiring and commissioning risk. Buying a module means you inherit all of it — a qualification exercise, not a price comparison.

Active harmonic filter module mounted inside a low-voltage switchgear cabinet, with copper busbars, current transformer and control wiring

The module decision transfers engineering risk to you

Your engineers now own the airflow path, clearance distances at 690 V, auxiliary supply, the interface to the end customer's BMS, and the service call when something trips. The specification, risk register and acceptance test all move to your side of the table. So the question is not "what is your price per amp" but "what do you guarantee once the module is inside my cabinet, on my busbar, at my site". Ask who performs the thermal calculation, who signs off the coordination study, and whether the warranty survives integration into a third-party enclosure. A supplier who answers only the price is selling a box; one who answers the rest has done this before, for other builders, at volume — the only reference that matters, because it proves the supplier can work to your drawing set and your schedule. Ask for two references where the module sits inside another builder's cabinet.

Three technical questions decide whether it fits your cabinet

What is the rating basis — current at which temperature?

A module sold as 100 A may be 100 A at 35 °C, 80 A at 45 °C and 60 A at 55 °C. Switchgear compartments run hotter than the room, especially beside reactors or drives. Demand the derating table and the evidence behind it: a full-load burn-in at elevated ambient proves the rating was measured, not calculated. YT Electric runs 100% full-load thermal and grid-tie verification at 45 °C before dispatch.

Which topology, and what are the losses at part load?

Two-level or three-level NPC, IGBT or silicon carbide, changes efficiency, footprint and heat. Ask for the loss curve, then multiply it by operating hours and tariff: on a 200 A module over 6,000 hours, two percentage points is a visible line on the bill.

How does it behave on a real, imperfect grid?

Confirm the response time and the behaviour during a voltage sag — a unit that trips and waits for clean supply is useless during the events that stop production. Confirm how it avoids resonance with an existing capacitor bank, and that a reversed CT gives a clear fault message.

Three commercial questions decide whether it survives ten years

Do you get the drawings before the purchase order?

Obtain outline dimensions, mounting points, busbar interface, airflow clearance and cable entries up front, plus the auxiliary supply range, upstream protection and the supported coordination study. On the control side, fix the protocol list — Modbus RTU/TCP, Profibus, Profinet, EtherNet/IP — the register map and dry-contact assignments. A gateway you did not budget for becomes your problem.

Who answers at 2 a.m. on a Sunday?

Remote diagnostics with event-log access is the minimum; on-site commissioning by the supplier's own engineers is the standard above low voltage. Ask where those engineers are based — a warranty that requires shipping the module back to Asia is not one a European end customer will accept.

What proves the supplier can deliver at your volume?

Three numbers: annual module capacity, units shipped in the last twelve months, countries installed. One document: the qualification file — ISO 9001, certification for the target market, and an FAT record you may audit. Add OEM/ODM history: seventeen years building to another company's drawing set outweighs a page of project logos.

The five-item shortlist

Keep this as the technical annex to your RFQ. Each line must return a number, a curve or a drawing.

A supplier who fills it in one pass is one you can quote with confidence. One who needs three rounds to produce a derating curve is telling you about your next three years of service calls.

YT Electric, part of CSG Smart Science (300222.SZ), has built AHF and SVG modules for over seventeen years, with 10,000+ units of annual capacity across 50+ countries. For OEM/ODM enquiries, contact the engineering team (https://www.ytelect.com/contact-us_d2).