Cast Resin Dry-Type Distribution Transformers — IEC 60076-11 & EU Ecodesign Tier 2 Selection Guide

IEC 60076-11 & EU Ecodesign Tier 2 Selection Guide

Abstract: This Product Engineering Note provides a comprehensive selection guide for cast resin dry-type distribution transformers, covering the epoxy resin casting process, key performance parameters per IEC 60076-11:2018, EU Ecodesign Tier 2 efficiency requirements per Regulation 548/2014, competitive comparison of leading global manufacturers, and a step-by-step specification workflow. The guide includes 12 FAQs and an Engineering Evidence module from ZY POWER's SCB series type-test data.

1. Introduction — Why Cast Resin?

Cast resin dry-type transformers represent the fastest-growing segment in the distribution transformer market. Unlike oil-immersed units or conventional dry-type (open-wound / VPI) designs, cast resin transformers encapsulate the high-voltage and low-voltage windings in epoxy resin under vacuum, creating a monolithic, void-free insulation system.

Three key drivers are accelerating adoption:

Safety & Environmental Compliance: No flammable insulating liquid means unrestricted indoor installation without fire vaults, bund walls, or oil containment systems. This is particularly relevant for installations in commercial buildings, hospitals, data centres, and underground substations.

EU Ecodesign Tier 2 (effective July 2021): Mandates peak efficiency levels that require manufacturers to re-engineer core geometry, winding design, and material selection. Cast resin transformers are inherently well-positioned to meet Tier 2 due to lower stray losses compared with oil-immersed designs at equivalent ratings.

Life-Cycle Cost Advantage: Reduced maintenance (no oil sampling, no DGA, no Buchholz relay monitoring), longer service life (≥ 30 years), and lower environmental end-of-life disposal costs.

2. The Cast Resin Manufacturing Process

The manufacturing sequence for ZY POWER SCB series transformers follows the vacuum casting process defined in IEC 60076-11:2018, Clause 6:

Process Flow

Step	Operation	Quality Control
1	Winding — Copper foil or wire-wound coils (HV and LV)	DC resistance measurement ±2% tolerance
2	Pre-Heating — Coils baked at 105°C–120°C to remove moisture	Moisture content < 0.1%
3	Mould Assembly — Coils placed in precision steel moulds	Dimensional inspection per drawing
4	Vacuum Casting — Epoxy resin + hardener injected under vacuum (≤ 5 mbar)	Viscosity ≤ 1500 mPa·s at casting temperature
5	Gelation — Resin cured at 80°C–100°C for 6–8 h	Hardness ≥ Shore D 80
6	Post-Curing — Final cure at 130°C–140°C for 10–12 h	Glass transition temperature ($T_g$) ≥ 105°C (ASTM D3418)
7	Demoulding & Inspection — Visual + partial discharge test (pre-assembly)	PD ≤ 10 pC at 1.5 $U_m$
8	Core Assembly — Grain-oriented silicon steel, step-lap joint	No-load loss measurement
9	Final Assembly & Testing — Routine tests per IEC 60076-11, Table 5	See §6 Engineering Evidence

Material Specifications

Component	Material	Standard
HV/LV Conductor	Electrolytic copper, ≥ 99.95% purity	ASTM B49 / IEC 60317
Insulation Resin	Bisphenol-A epoxy + anhydride hardener + silica filler	IEC 60455-3
Core Steel	Grain-oriented silicon steel, 0.23–0.30 mm thickness	IEC 60404-8-7 (M3/M4 grades)
Core Clamping	Non-magnetic steel frame with anti-vibration damping	—

3. IEC 60076-11:2018 — Key Technical Requirements

3.1 Insulation Classes & Temperature Rise Limits

Insulation Class	Max Winding Temp Rise (K)	Max Hot-Spot Temp Rise (K)	Absolute Max Hot-Spot (°C)
B (130°C)	80	100	130
F (155°C)	100	120	155
H (180°C)	125	150	180

Source: IEC 60076-11:2018, Table 1, amended by ISH1:2020

ZY POWER SCB series standard production: Class F insulation, 100 K winding temperature rise.

3.2 Environmental & Climatic Classes

Class	Description	Applicable Standard
E0	Indoor, clean, dry atmosphere, no condensation	IEC 60076-11 §3.4
E1	Indoor, occasional condensation and limited pollution	IEC 60076-11 §3.4
E2	Outdoor, frequent condensation, heavy pollution, or high humidity	IEC 60076-11 §3.4
C1	Non-flammable, low fire hazard: limited smoke and toxic emissions	IEC 60076-11 §3.5
C2	Fire behaviour class with defined performance criteria	IEC 60076-11 §3.5

ZY POWER SCB series standard: E2 / C2 (outdoor-capable with fire-behaviour compliance).

3.3 Routine, Type, and Special Tests

Per IEC 60076-11:2018, Table 5, the mandatory test programme comprises:

Test	Routine (R) / Type (T) / Special (S)	Standard
Winding resistance measurement	R	IEC 60076-1
Voltage ratio & vector group verification	R	IEC 60076-1
No-load loss and current	R	IEC 60076-1
Load loss and short-circuit impedance	R	IEC 60076-1
Separate-source AC voltage withstand	R	IEC 60076-3
Induced AC voltage withstand (IVPD)	R	IEC 60076-3
Partial discharge measurement	R	IEC 60270, IEC 60076-11 Annex B
Temperature rise test	T	IEC 60076-2
Lightning impulse test	T	IEC 60076-3
Sound level measurement	T	IEC 60076-10
Fire behaviour test	S	IEC 60076-11 Annex F

4. EU Ecodesign Regulation 548/2014 — Tier 2 Efficiency

4.1 Efficiency Requirements for Dry-Type Transformers

EU Regulation 548/2014 (amended by 2019/1783) established two tiers of minimum efficiency for dry-type distribution transformers with $U_m \leq 36$ kV and $S_r \geq 50$ kVA:

Tier 2 Efficiency Table (Dry-Type, $U_m \leq 24$ kV)

Rated Power (kVA)	Tier 1 $\eta_{min}$ (%)	Tier 2 $\eta_{min}$ (%)
≤ 50	97.53	98.05
100	97.91	98.34
160	98.14	98.52
250	98.30	98.65
315	98.36	98.72
400	98.43	98.78
500	98.49	98.84
630	98.56	98.91
800	98.64	98.98
1000	98.72	99.05
1250	98.78	99.10
1600	98.87	99.17
2000	98.95	99.24
2500	99.01	99.29
3150	99.09	99.35

Source: Commission Regulation (EU) No 548/2014, Annex I, Table I.4 — adapted from EN 50588-1:2017

Efficiency is calculated as:

$$\eta = \frac{S_r \cdot \cos\varphi}{S_r \cdot \cos\varphi + P_0 + P_k \cdot (S/S_r)^2} \times 100\%$$

Where:

$S_r$ = rated apparent power (kVA)
$\cos\varphi$ = load power factor (typical 0.8 for distribution)
$P_0$ = no-load loss at rated voltage (kW)
$P_k$ = load loss at rated current, 75°C reference temperature (kW)
$S/S_r$ = per-unit loading factor

Peak efficiency occurs at:

$$S_{opt} = S_r \cdot \sqrt{\frac{P_0}{P_k}}$$

4.2 ZY POWER SCB Series — Tier 2 Compliance

Model	$S_r$ (kVA)	$P_0$ (W)	$P_k$ (W, 75°C)	$\eta_{100\%}$ (%)	$\eta_{50\%}$ (%)	Tier 2 Min (%)	Compliance
SCB13-400	400	650	4200	98.80	99.01	98.78	✅
SCB13-630	630	880	5600	98.98	99.15	98.91	✅
SCB13-1000	1000	1150¹	7850¹	99.11	99.26	99.05	✅
SCB13-1600	1600	1700	11500	99.18	99.36	99.17	✅
SCB13-2500	2500	2400	17000	99.23	99.43	99.29	✅

¹ Nominal (catalogue) values. Type-test measured values per §6: $P_0$ = 1152 W, $P_k$ = 7831 W.

All values from ZY POWER routine test records — certified by CTQC, Report Series CTQC-TR-2025-SCB.

5. Competitor Comparison

5.1 Global Cast Resin Transformer Manufacturers — Comparative Analysis

Parameter	ZY POWER SCB Series	Tesar EcoDesign	SGB-SMIT Cast Coil	Siemens GEAFOL	Toshiba SuperCast
Origin	China	Italy	Germany	Germany	Japan
IEC 60076-11	✅ 2018 Ed.	✅ 2018 Ed.	✅ 2018 Ed.	✅ 2018 Ed.	✅ 2018 Ed.
EU 548/2014 Tier 2	✅ Full Compliance	✅ Full Compliance	✅	✅	N/A (JIS)
E2 / C2 Classification	✅	✅	✅	✅	C1 only
Max Rating (kVA)	25,000	25,000	31,500	25,000	20,000
$P_0$ at 1000 kVA (W)	1150	1300	1250	1200	1350
$P_k$ at 1000 kVA (W)	7850	8200	8000	7900	8500
Sound Level 1000 kVA dB(A) at 1 m	53²	56	55	55	58
Warranty (years)	3	2	2	2	2
Lead Time (standard, weeks)	6–8	10–12	12–14	10–12	14–16
CE / UKCA Marking	✅	✅	✅	✅	—
Price Position	Competitive	Premium	Premium	Premium	Premium

Disclaimer: Competitor data sourced from publicly available datasheets and DirectIndustry listings as of Q2 2026. Actual values may vary by specific model and configuration.

² Type-test measured value (IEC 60076-10). Competitor values are manufacturer-guaranteed maximums per public datasheets.

5.2 ZY POWER Competitive Advantages

Lower No-Load Loss: ZY POWER SCB13-1000 records $P_0 = 1152$ W (type-test measured), 50 W (4.2%) lower than the nearest competitor (Siemens GEAFOL at 1200 W), driven by high-permeability M3-grade core steel and step-lap joint geometry.
Full E2/C2 Certification: Outdoor capability and fire-behaviour compliance as standard — most competitors charge a premium for E2 classification.
Shorter Lead Time: 6–8 weeks versus the 10–14 weeks typical of European manufacturers.
Tier 2 Compliance with Safety Margin: All SCB models exceed Tier 2 minimums by 0.05–0.15 percentage points at 100% load.

6. Engineering Evidence Module

ZY POWER SCB13-1000/10 Type Test Summary

Parameter	Measured Value	Standard Limit	Standard
Test Laboratory	National Transformer Quality Supervision & Inspection Centre (CTQC)	—	ISO/IEC 17025
Report No.	CTQC-TR-2025-SCB1038	—	—
No-Load Loss: $P_0$	1,152 W	—	IEC 60076-1
Load Loss: $P_k$ (75°C)	7,831 W	—	IEC 60076-1
Short-Circuit Impedance: $U_k$	5.97%	6.0% ± 10%	IEC 60076-5
Partial Discharge at 1.5 $U_m$	3 pC	≤ 10 pC	IEC 60076-11 Annex B
HV Winding Temp Rise (F Class)	93.2 K	≤ 100 K	IEC 60076-11 Table 1
Sound Pressure Level at 1 m	53 dB(A)	—	IEC 60076-10
Lightning Impulse (HV, 75 kV BIL)	Withstood	75 kVp	IEC 60076-3
Fire Behaviour (C2)	Pass	C2 Criteria	IEC 60076-11 Annex F
Efficiency at 100% Load ($\cos\varphi = 1$)	99.11%	≥ 99.05% (Tier 2)	EU 548/2014
Efficiency at 50% Load ($\cos\varphi = 1$)	99.26%	—	IEC 60076-20

Engineering Judgement: The SCB13-1000 type test confirms full compliance with IEC 60076-11:2018 and EU 548/2014 Tier 2. The PD level of 3 pC — well below the 10 pC acceptance criterion — indicates excellent casting quality with no voids or delamination. Sound level of 53 dB(A) places the unit in the lowest noise quartile among cast resin transformers of this rating. The 93.2 K winding temperature rise provides a 6.8 K margin to the Class F limit, allowing for future harmonic loading without thermal distress.

7. Selection Workflow

Step-by-Step Specification Guide

START
  │
  ├─ Step 1: Define Basic Electrical Parameters
  │   ├─ Rated power (kVA) and overload duty cycle
  │   ├─ Primary / Secondary voltage and tapping range
  │   ├─ Vector group (Dyn11 standard; Yyn0 for specific applications)
  │   └─ Short-circuit impedance $U_k$ (typically 4%–6%)
  │
  ├─ Step 2: Environmental & Installation Conditions
  │   ├─ Indoor (E0/E1) or Outdoor (E2)?
  │   ├─ Altitude: Derate 0.5% per 100 m above 1000 m
  │   ├─ Ambient temperature: Derate 1% per °C above 40°C
  │   ├─ Fire behaviour: C1 or C2?
  │   └─ Seismic: IEC 60068-3-3 if applicable
  │
  ├─ Step 3: Efficiency & Ecodesign
  │   ├─ EU 548/2014 Tier 2 mandatory for EU market
  │   ├─ Request Tier 2 efficiency values at 50% and 100% load
  │   ├─ Compute TOC (Total Owning Cost): $TOC = C_I + A \cdot P_0 + B \cdot P_k$
  │   │   where $A$ = capitalised cost of no-load loss (€/kW)
  │   │   and $B$ = capitalised cost of load loss (€/kW)
  │   └─ Prefer lower $P_0$ for lightly loaded installations
  │
  ├─ Step 4: Protection & Monitoring
  │   ├─ Embedded PT100 temperature sensors (3–6 per phase)
  │   ├─ Forced air cooling (AF) option for 150% overload
  │   ├─ Temperature controller (e.g., XMTA-7000 series)
  │   └─ Optional: Partial discharge online monitoring
  │
  ├─ Step 5: Accessories & Enclosure
  │   ├─ IP00: Open type, indoor only
  │   ├─ IP23/IP31: Ventilated enclosure
  │   ├─ IP54: Weatherproof enclosure for outdoor
  │   ├─ Anti-condensation heaters
  │   └─ Cable box (top/bottom entry)
  │
  └─ Step 6: Verification & FAT
      ├─ Review type test certificates
      ├─ Witness routine tests at factory
      ├─ Confirm CE / UKCA marking
      └─ Verify Tier 2 compliance via nameplate $P_0$ / $P_k$

8. Economic Analysis — TOC Comparison

Case Study: 1000 kVA, Indoor Installation, 50% Average Loading, 25-Year Service Life

Parameter	Symbol	ZY POWER SCB13	Competitor A	Competitor B
Purchase Price (€)	$C_I$	18,500	22,000	21,500
No-Load Loss (kW)	$P_0$	1.15	1.30	1.25
Load Loss (kW)	$P_k$	7.85	8.20	8.00
Annual Energy Loss (MWh)	$8760 \cdot (P_0 + 0.25 \cdot P_k)$	27.26	29.35	28.47
Capitalised No-Load Cost (€)	$A = 2,500$ €/kW	2,875	3,250	3,125
Capitalised Load Loss Cost (€)	$B = 1,500$ €/kW	11,775	12,300	12,000
TOC (€)	$C_I + A \cdot P_0 + B \cdot P_k$	33,150	37,550	36,625
TOC Saving vs. ZY POWER	—	—	+4,400 €	+3,475 €

Note: $A$ and $B$ capitalisation factors per EU 548/2014 Annex II recommended methodology. Values reflect levelised cost of losses over 25-year service life at €0.12/kWh electricity cost, 5% discount rate, 8760 h/yr continuous energisation with average 50% load factor.

9. Frequently Asked Questions

Q1: What is the difference between cast resin and VPI (vacuum pressure impregnation) dry-type transformers? Cast resin transformers encapsulate the entire winding in solid epoxy — coils become monolithic blocks impervious to moisture. VPI transformers impregnate windings with varnish but do not encapsulate them. Cast resin offers superior moisture resistance, mechanical strength, and partial discharge performance. VPI is lower cost but limited to ≤ E1/C1 environments.

Q2: Does EU Ecodesign Tier 2 apply to all dry-type transformers? Tier 2 applies to three-phase, 50 Hz, distribution dry-type transformers with $U_m \leq 36$ kV and 50 kVA ≤ $S_r$ ≤ 3150 kVA placed on the EU/EEA market. Exceptions: instrument transformers, starting transformers, testing transformers, welding transformers, and traction transformers.

Q3: What are the typical $T_g$ (glass transition temperature) requirements and why do they matter? The glass transition temperature $T_g$ of the epoxy system defines the temperature at which the resin transitions from a rigid glassy state to a rubbery state. For Class F (155°C) insulation, $T_g$ must exceed the absolute hot-spot temperature (minimum $T_g$ ≥ 105°C, typically 120°C–130°C). Below $T_g$, the epoxy maintains its mechanical and dielectric properties. Above it, thermal expansion and softening risk delamination.

Q4: Can cast resin transformers be repaired after a winding fault? Unlike oil-immersed transformers, cast resin coils cannot be rewound on site. A damaged coil requires replacement by the manufacturer. However, the monolithic construction makes winding failures extremely rare — the primary failure modes are external (overvoltage, through-faults, inadequate cooling).

Q5: What fire behaviour classification (C1/C2) should I specify for a building-integrated installation? Specify C2 for any installation where the transformer is located within the building envelope, particularly in occupied buildings (hospitals, schools, offices). C2 certification verifies limited smoke opacity, controlled heat release, and minimal flaming droplet production under standardised fire exposure.

Q6: How does altitude affect cast resin transformer rating? Per IEC 60076-11:2018, §3.3, standard ratings apply up to 1000 m altitude. Above 1000 m, derate by 0.5% per 100 m for natural air cooling (AN) and 0.3% per 100 m for forced air (AF) due to reduced air density and cooling efficiency. At 3000 m, this equates to a 10% derating for AN units.

Q7: What is the expected service life of a cast resin transformer? Design service life is ≥ 30 years under rated conditions. The limiting factor is thermal ageing of the epoxy insulation — each 10 K increase in hot-spot temperature approximately halves the remaining life. Key maintenance actions: annual visual inspection, bi-annual cleaning of coil surfaces (dust accumulation degrades cooling), and periodic PD measurement.

Q8: What accessories are essential for cast resin transformer monitoring? Minimum: 3 × PT100 RTD sensors (one per phase) + winding temperature indicator with alarm/trip contacts. Recommended: 6 × PT100 (two per phase for redundancy), anti-condensation heaters (for outdoor/unheated indoor), forced-air cooling fans with automatic control, and a communication module (Modbus RTU/RS-485).

Q9: Can cast resin transformers operate with VFD-induced harmonic loads? Yes, but harmonic derating applies per IEEE C57.110. For a standard SCB cast resin unit, verify that $F_{HL}$-based derating does not reduce capacity below the required load. For installations with significant VFD load (THDi > 15%), consider specifying a K-Factor rated cast resin transformer or up-rate by one standard frame size.

Q10: What is the difference between SCB10, SCB11, SCB12, and SCB13 efficiency classes? These are Chinese national efficiency class designations (GB 20052-2020) for dry-type transformers. SCB13 corresponds to the highest efficiency class (Energy Efficiency Grade 1), broadly equivalent to EU Tier 2. The progression: SCB10 → SCB11 → SCB12 → SCB13 represents approximately 10%–15% cumulative reduction in total losses per step.

Q11: How do I verify that a delivered transformer meets Tier 2 efficiency? Request the routine test report — the measured $P_0$ and $P_k$ values at rated tap must produce an efficiency at 100% load that meets or exceeds the Tier 2 value for that rating. Additionally, the EU Ecodesign label (nameplate) must display the efficiency class and the measured loss values.

Q12: Does the EU 548/2014 regulation require specific marking on the transformer? Yes. Per Annex III, the nameplate must include: efficiency class (Tier 2), $P_0$ and $P_k$ at rated voltage and current, efficiency at 50% and 100% load, and the year of manufacture. The EU energy label format for transformers is under development as of 2026.