ABB / Hitachi Energy HiDry dry-type power transformer (above 40.5 kV, to 72.5 kV)
HiDry vacuum cast-resin power transformers to 72.5 kV and 63 MVA, the oil-free option at subtransmission voltage
ABB / Hitachi Energy HiDry dry-type power transformer (above 40.5 kV, to 72.5 kV) is one of 32 data center transformers tracked in the SecondWatt catalogue, each with specifications, lead times and indicative secondary-market pricing.
ABB and Hitachi Energy HiDry dossier: vacuum cast-resin power transformers to 72.5 kV and 63 MVA, oil-free subtransmission specs, inspection, market notes.
Why it matters
At subtransmission voltage the alternatives to HiDry all carry oil: fire separation, containment, and FM Global data sheet 5-4 requirements follow. An oil-free 72.5 kV unit lets dense urban and indoor sites take higher-voltage service directly, cutting a transformation stage. Buyers should treat the line as new-build only and benchmark against ester-filled liquid units on total installed cost.
Who buys it
Urban utilities placing substations inside buildings, high-rise and tunnel projects, offshore platforms, and data center campuses that want 66-69 kV service without oil systems. The buyer profile is new-build specification rather than secondary-market bargain hunting, since used supply is effectively zero and each unit is engineered to order.
Role in the data center
Oil-free 66-69 kV intake transformer for urban campuses and indoor substations where oil-filled units would force fire-separation and containment redesign.
Key specifications
| Power range | up to 63 MVA |
|---|---|
| HV maximum | 72.5 kV |
| LV maximum | 36 kV |
| Partial discharge | <10 pC |
| Insulation classes | F and H |
| Enclosures | IP00-IP55 |
| Cooling classes | AN / ANAF / AFWF |
| Line origin | ABB HiDry72 (IEEE paper 7000447) |
Technical summary
Power range: up to 63 MVA HV: above 40.5 kV, up to 72.5 kV; LV up to 36 kV Frequency: 50 / 60 Hz Technology: vacuum cast resin Cooling: AN, ANAF, AFWF Insulation classes F and H; PD below 10 pC Enclosures: IP00 to IP55 Connections: Y or D; indoor or enclosed outdoor Applications: urban, indoor, offshore, fire-critical substations Direct dry-type competitor at 72.5 kV: none identified Launched as ABB HiDry72 (IEEE-published design)
Pricing and availability
Trend: up Lead time, new: Engineered to order; dry-type class 20-32 weeks at small MVA, longer at power class. Lead time, used or refurbished: 2-12 weeks. Warranty, used: 3-year typical from major US rebuilders.
Lifecycle and maintenance
Cast-resin and VPI dry-type transformers typically serve 25-30+ years with minimal maintenance: periodic cleaning, PD testing on critical units, fan service on AF designs, and torque checks. There is no oil system to sample, so temperature and PD are the condition indicators. Rebuild options are limited compared with liquid units; failed coils are usually replaced rather than repaired, which makes pre-purchase PD and visual inspection decisive for used units.
Common failure points
- Partial discharge — PD in resin voids degrading insulation toward failure
- Resin cracking — Cracks from thermal cycling or mechanical shock
- Contamination — Dust and conductive debris enabling surface tracking
- Cooling fans — Failed AF fans derating capacity
- Connections — Loose terminations overheating under load
- Overheating under harmonics — Excess temperature on non-linear loads beyond K-rating
Inspection checklist
Partial discharge — PD test per IEC 60270 practice; readings above 10 pC warrant investigation on cast-resin coils Resin condition — inspect all coils per IEC 60076-11 practice for cracks and crazing from thermal cycling; any through-crack fails Insulation resistance — megger HV/LV/ground; polarization index of 2.0 or higher passes Turns ratio — TTR on all tap positions; deviation beyond 0.5% from nameplate fails Winding resistance — three-phase balance within 2% between phases Contamination — inspect for dust and conductive debris between coils; contamination is a leading dry-type failure driver Cooling fans (AF units) — run-test all fans and verify temperature controller setpoints Temperature sensors — verify RTD or thermocouple channels read within 5 C of a reference at ambient Connections — torque-check HV and LV terminations; thermal-scan at first energization and re-check within 12 months Clearances — verify electrical clearances and enclosure IP rating match the installation environment Class verification — confirm fire/environmental/climatic classes (F1, E2/E3, C2/C3) against nameplate Harmonic suitability — verify K-factor rating (K-4/K-13) against the intended non-linear load profile Core and frame — inspect for shipping damage and loose core bolts; verify single core ground Energization test — verify secondary voltage within 5% on all phases and no abnormal sound level Records — factory test certificate, PD test data, and service history; missing PD data reprices the unit