10kV 100kVA Three-Phase Copper-Winding Oil-Immersed Transformer for Smart EV Charging Station

Model:S20-M-100/10 (S13-M-100/10 and S22-M-100/10 optional)

Rated Capacity:100 kVA

Phase:Three-phase

Rated High Voltage (HV):10 kV (11 kV, 12 kV, 13.8 kV, 20 kV optional)

HV Tapping Range:±2×2.5% off-circuit (±5% optional, OLTC on request)

Rated Low Voltage (LV):0.4 kV (0.415 kV / 0.48 kV optional)

Vector Group:Dyn11 (Yyn0 optional)

Cooling Method:ONAN (oil natural, air natural)

Send Inquiry Live Chat

Product Details
FAQs
Packing & Delivery

Quick Answer

A 100 kVA 10 kV three-phase oil-immersed transformer for an EV charging station is a hermetically sealed, copper-wound distribution transformer that steps 10 kV medium voltage down to 400 V to feed DC fast chargers, AC chargers, canopy lighting and site services. Charging sites choose sealed oil-immersed units over dry type for outdoor hubs because the corrugated sealed tank removes the conservator and every periodic oil maintenance task, absorbs the thermal cycling of pulsed charging loads, and costs roughly 10–15% less per kVA than cast resin. For DC fast charging, specify a K-9 or K-13 rated design and Dyn11 vector group.

Product Overview

This is a three-phase, 50/60 Hz oil-immersed distribution transformer rated 100 kVA with a primary voltage of 10 kV and a secondary voltage of 0.4 kV (415 V or 480 V on request). Both HV and LV windings are copper. The active part is sealed inside a corrugated-fin steel tank with no conservator, so the insulating oil never contacts air, never needs sampling, filtration or topping-up, and the unit is genuinely maintenance-free for its design life of 25 years.

It is built for smart EV charging sites: highway charging plazas, fleet and bus depots, workplace and destination charging at malls and hotels, and PV-plus-storage charging hubs. The standard supply includes oil-temperature monitoring and an RS485/Modbus RTU interface, with an optional 4G or LoRa DTU so winding and oil temperature, load current and voltage can be read directly by the charging management platform (OCPP backend) or the site SCADA. Manufactured under ISO 9001 and designed and tested to IEC 60076-1/-2/-3/-5/-10, GB 1094 and GB 20052-2024.

Why EV Charging Stations Choose Sealed Oil-Immersed Over Dry Type

Our recommendation: for an outdoor charging hub, fleet depot or motorway service area, specify a hermetically sealed oil-immersed transformer. Reserve cast resin dry type for indoor electrical rooms, underground parking and any location where the local fire code rules out combustible oil.

The reason is duty cycle. Chargers do not draw steady current — a DC fast charger pulls hard for 10 to 30 minutes then drops away. Oil has far greater thermal mass than air, with a thermal time constant of roughly 15–25 minutes on a 100 kVA unit, so the tank absorbs each charging peak without driving the winding hot spot up. A sealed tank also removes the OPEX item most charging operators forget to budget: no annual oil sampling, no filtration, no conservator breathers to replace.

Consideration	Sealed Oil-Immersed (this product)	Cast Resin Dry Type	Charging-Site Impact
Installation	Outdoor compound, fenced or walled	Indoor room, underground garage	Fire code usually decides it, not engineering preference
Fire and oil	Combustible oil — needs bund or spill plan per local code	Self-extinguishing, no oil	Indoor or underground → dry type
Pulsed load	Excellent — oil thermal mass absorbs 10–30 min peaks	Lower overload tolerance, faster hot-spot rise	DCFC peaks favour oil
Maintenance	None — sealed, no oil sampling ever	None	Sealed oil removes a recurring OPEX line
Cost per kVA	Lowest	Typically 10–15% higher	Oil wins capex-sensitive sites
Harmonics	K-9 / K-13 winding design available	K-rated designs standard	Both can be specified — state it explicitly
Noise	≤ 55 dB(A), low-noise build ≤ 50 dB(A)	Slightly quieter	Near retail, hotels and offices specify a dB limit

Energy Efficiency Grades and 20-Year Running Cost

A 100 kVA transformer at a charging site stays energised 24 hours a day, so no-load loss runs 8,760 hours a year even when no car is charging. That is why the grade you specify matters more than the purchase price.

GB 20052-2024 Grade	Model	No-load loss P0	Load loss Pk (75 °C)	Annual loss (kWh)	20-year electricity cost
Class 3	S13-M-100/10	150 W	1,580 W	≈ 3,010 kWh	≈ USD 7,220
Class 2	S20-M-100/10	135 W	1,265 W	≈ 2,540 kWh	≈ USD 6,100
Class 1	S22-M-100/10	120 W	1,140 W	≈ 2,275 kWh	≈ USD 5,460

Key Features

Hermetically sealed corrugated tank — no conservator, the oil never contacts air. No oil sampling, filtration or topping-up for the whole 25-year design life; this removes the OPEX item most charging operators forget to budget.
Built for pulsed charging duty — ONAN cooling with high oil thermal mass (time constant roughly 15–25 minutes) absorbs 10–30 minute DC fast-charging peaks without winding hot-spot excursions.
Harmonic-capable winding design — K-4 for AC Level 2 clusters, K-9 or K-13 for DC fast chargers whose total harmonic current distortion commonly exceeds 15% and would otherwise overheat a standard transformer.
Dyn11 vector group as standard — traps zero-sequence and 3rd-order harmonics inside the delta winding so they do not travel upstream into the utility feeder or other site loads.
Copper windings on both HV and LV — lower load loss, lower temperature rise and better short-circuit withstand than aluminium, verified by type test to IEC 60076-5.
Class 1 or Class 2 efficiency available — S22 (120 W / 1,140 W) or S20 (135 W / 1,265 W) per GB 20052-2024; Chinese Tier 1 limits at 100 kVA are already about 8% tighter than EU Regulation 548/2014.
Outdoor-ready construction — fluororubber gasket sealing proven from -25 °C to +55 °C, optional C4 / C5-M coating for roadside de-icing salt and coastal sites, IP54 cable boxes, anti-theft locks and vandal-resistant hardware.
Smart-ready for the charging backend — oil and winding temperature, load current and voltage via RS485/Modbus RTU, with optional 4G or LoRa DTU feeding the OCPP charging management platform or site SCADA.
Low noise — ≤ 55 dB(A) at 1 m as standard, with a low-noise core and clamping design available at ≤ 50 dB(A) for sites adjacent to retail, hotels and offices.

Typical Applications

Highway fast-charging plazas and motorway service areas
Fleet depots, bus and logistics charging yards
Workplace and destination charging at retail malls, hotels and offices
Public parking structures and surface car parks
PV + battery + charging integrated sites
Residential community charging clusters fed from a 10 kV distribution room
Compact substation (YBW-12) for turnkey charging station delivery

Standards and Certifications

Designed and tested in accordance with IEC 60076-1 (general), IEC 60076-2 (temperature rise), IEC 60076-3 (insulation levels and dielectric tests), IEC 60076-5 (short-circuit withstand) and IEC 60076-10 (sound level), plus GB 1094 series and GB/T 6451. Energy performance meets GB 20052-2024 Class 2 as standard and Class 1 with the S22 design. Manufactured under ISO 9001, ISO 14001 and ISO 45001. CE conformity available; third-party type test reports (CNAS-accredited laboratory, KEMA or equivalent) available on request. Harmonic duty designed with reference to IEEE C57.110 and IEEE 519.

Q1: What size transformer does an EV charging station need?

A: Size it from the coincident load, not the sum of charger nameplates. Multiply the total charger kW by a diversity factor of 0.7–0.9 depending on site type (highway plazas are staggered and sit near 0.7; fleet depots with shift charging approach 0.9), divide by the power factor, then add 10–20% for future stalls. A 100 kVA unit typically serves around 4–8 DC fast chargers of 60–120 kW under load management, or a larger bank of AC destination chargers.

Q2: Can an oil-immersed transformer be used at an EV charging station?

A: Yes, and it is the standard choice for outdoor charging hubs, fleet depots and highway plazas. Oil-immersed units cost less per kVA and handle pulsed charging loads better than dry type. Local rules usually require a bund, spill containment or a suitable setback; where the transformer sits indoors or in an underground car park, most fire codes require cast resin dry type instead.

Q3: Do EV chargers require a K-rated transformer?

A: For DC fast charging, yes in practice. Charger rectifiers inject harmonic current, with THDi commonly above 15% on dense fast-charging sites, and harmonic current heats windings beyond what the nameplate kVA suggests. Specify K-4 for AC Level 2 clusters and K-9 or K-13 where DC fast chargers dominate. K-rating protects the transformer; it does not clean up the upstream supply, so active filtering may still be needed to meet IEEE 519 limits at the point of common coupling.

Q4: Why is Dyn11 the standard vector group for EV charging transformers?

A: The delta-connected HV winding gives zero-sequence and 3rd-order harmonics a circulating path inside the transformer instead of passing them upstream into the utility feeder. The star LV side also provides a neutral for single-phase site loads such as lighting, canopy and payment systems. Dyn11 is the default on almost every EV charging specification for these two reasons.

Q5: Is a hermetically sealed oil transformer really maintenance-free?

A: For the oil, yes. A sealed corrugated-fin tank has no conservator, so the oil never breathes air and does not absorb moisture or oxidise. There is no periodic oil sampling, testing, filtration or topping-up for the 25-year design life. What still needs an occasional look are the external items: bushings, cable terminations, gasket faces and the pressure relief valve — a visual inspection once or twice a year is enough.

Q6: What is the difference between S13, S20 and S22 oil-immersed transformers?

A: They are the Chinese performance-level codes mapped to the three energy efficiency grades of GB 20052-2024. At 100 kVA, S13 (Class 3) allows 150 W no-load and 1,580 W load loss; S20 (Class 2) is 135 W and 1,265 W; S22 (Class 1) is 120 W and 1,140 W. On a 24/7 charging site the Class 1 unit saves roughly 14,700 kWh over 20 years compared with Class 3 — usually several times the price difference between the two.

Q7: Is 400 V or 415 V available on the low-voltage side, and can it run at 60 Hz?

A: Both. The standard secondary is 400 V for 50 Hz markets; 415 V is supplied for 50 Hz markets using 415 V utilisation voltage, and 480 V for 60 Hz markets such as the Americas, parts of Asia and the Gulf. Voltage ratio, tapping range, vector group and frequency are all configurable at order.

Q8: Can the transformer be monitored by the charging management platform?

A: Yes. Standard supply includes an oil temperature indicator with alarm and trip contacts plus an RS485/Modbus RTU interface. An optional 4G or LoRa DTU publishes oil and winding temperature, load current, voltage and alarm status to the OCPP charging management platform, the site SCADA or a cloud dashboard, so the operator can see thermal headroom and plan stall additions from real load data.

Q9: What is the typical delivery time and packing?

A: Production is typically 3–6 weeks depending on specification, voltage class and order quantity — well below the 30+ week lead times quoted by many domestic suppliers during recent transformer shortages. Units ship oil-filled and sealed on a steel-reinforced wooden pallet, wrapped in moisture-barrier film with desiccant, bushings and cable boxes guarded by plywood, with lifting lugs and shock/tilt indicators. Full export plywood crating is available on request.

Shipped oil-filled and factory-sealed on a steel-reinforced wooden pallet, wrapped in moisture-barrier film with desiccant, HV and LV bushings plus cable boxes protected by plywood guards, fitted with lifting lugs and shock/tilt indicators. Suitable for sea, road and rail transport; full export plywood crate available on request. Where destination regulations require, the unit can be shipped drained with oil in sealed drums. Final gross weight, crate dimensions and packing list confirmed before shipment.