High altitude and pollution affect transformer insulation in different ways. Reduced air density at altitude lowers the dielectric strength of air and can require larger clearances. Pollution increases the chance of conductive surface paths and can require greater creepage distance, better material selection, coating, or a controlled enclosure. Treating both as generic “extra insulation” can leave the wrong weakness unaddressed.
Insulation coordination connects expected electrical stress with the withstand capability of the complete transformer. It includes working voltage, transient overvoltage, impulse stress, creepage, clearance, solid insulation, material group, pollution degree, altitude, grounding, and the applicable equipment standard.
Clearance and creepage solve different problems
Clearance is the shortest air distance between conductive parts and is strongly influenced by transient voltage, field geometry, altitude, and insulation level. Creepage is the shortest path along an insulating surface and is influenced by working voltage, pollution, material tracking resistance, and contamination.
More tape can increase solid insulation but does not automatically increase external pin clearance. A longer bobbin flange may improve creepage, but a crossing lead can shorten the effective path. The assembled geometry, including solder, sleeving, terminals, clips, shields, and mounting hardware, must be reviewed.
Why altitude changes air insulation
At higher altitude, lower pressure makes air-gap breakdown more likely for the same geometry and voltage. Many standards apply correction above a reference elevation. The exact method depends on the standard and insulation requirement, so maximum installation altitude belongs in the customer specification. An oversized guess adds cost and size; ignoring altitude removes intended margin.
Pollution degree describes the micro-environment
The relevant condition is the environment immediately around the insulation, not simply whether equipment is called indoor or outdoor. Dust, condensation, salt, humidity, and process residue can create leakage paths. A sealed enclosure may establish a cleaner micro-environment, but that assumption must be documented and validated.
Material tracking resistance can influence creepage. Coating or encapsulation may help when it forms a controlled insulation system, but coverage, adhesion, voids, repair rules, thermal behavior, and compatibility must be defined. Casual coating is not a substitute for coordinated design.
Information the transformer manufacturer needs
- Maximum continuous working voltage across each barrier
- Overvoltage category and expected surge or impulse
- Basic, supplementary, double, or reinforced insulation
- Maximum installation altitude and pollution degree
- Enclosure and micro-environment assumptions
- Applicable product standard and edition
- Temperature, humidity, condensation, and contamination exposure
- Grounding arrangement and accessible circuits
These inputs allow the manufacturer to select bobbin geometry, margin system, wire insulation, tape, sleeving, lead routing, terminal spacing, potting or varnish, and dielectric tests coherently.
Verify the real assembly
Transformer dimensional inspection is necessary, but PCB integration can introduce new conductive parts and shorter paths. Review the component with heatsinks, shields, connectors, fasteners, and enclosure surfaces installed. Where required, verify impulse, dielectric withstand, insulation resistance, and environmental conditioning on representative samples.
BaoHui Tech encourages customers sourcing a power transformer or high frequency transformer to state altitude and pollution assumptions at quotation. Early information is easier to incorporate than a late request after the core, bobbin, and pin layout are frozen.
Frequently asked questions
Does a higher hipot voltage compensate for insufficient clearance?
No. A short withstand test does not change the air path or guarantee long-term behavior under altitude, surge, contamination, and aging.
Is potting always the best solution for pollution?
No. Potting can create a controlled solid insulation system, but adds thermal, process, stress, void, repair, and compatibility considerations.
When should altitude be discussed?
Before magnetic size and terminal arrangement are fixed. Altitude can affect clearance, bobbin choice, lead routing, dimensions, and cost.