100kVA Transformer Spiral Coil With Longitudinal Oil Passage

A 100kVA Transformer Spiral Coil With Longitudinal Oil Passage with spiral-wound LV coil and 5mm longitudinal oil ducts reduces that hot spot by 9-12°C. Verified by embedded fiber optic sensors during factory heat run. Manufactured by Shanghai Industrial Transformer Co., Ltd.

The Measured Problem: Temperature Gradient in Layer-Wound 100kVA Transformers

Factory test data from 12 standard S11 100kVA units (layer-wound, no internal ducts) produced by Shanghai Industrial Transformer Co., Ltd. between January and December 2024:

• Top oil temperature at 100% load: 76-80°C
• Outer winding layer temperature: 82-88°C
• Inner winding layer temperature: 98-108°C
• Temperature difference (inner to outer): 16-22°C
• Hot spot location: Inner layer, upper 1/3 of winding height

Using IEEE C57.91 insulation life curves: at 108°C continuous, expected life is 10-12 years. At 96°C, expected life doubles to 20-24 years. This 12°C difference is the engineering target for the spiral coil design.

Spiral Coil + Longitudinal Oil Passage: How It Lowers Hot Spot Temperature

This 100kVA Transformer Spiral Coil With Longitudinal Oil Passage replaces the conventional layer-wound LV coil with a spiral-wound design. Two engineering changes work together based on actual production at Shanghai Industrial Transformer Co., Ltd. (established 2007, 40,000m² factory).

Change 1: Spiral Winding Geometry

Layer winding stacks 20-40 turns in each horizontal layer. Heat from inner turns must pass through multiple layers of copper and paper before reaching oil. Spiral winding winds one turn per layer in a helical pattern. Each turn is directly exposed to oil on three sides (top, bottom, and side). Oil contact surface area increases by approximately 35% compared to layer winding based on internal engineering calculations.

Change 2: Longitudinal Oil Ducts

Between each layer of the spiral coil, 5mm thick pressboard ducts (IEC 60641-3-1 compliant) are inserted. These ducts run vertically the full height of the coil. Oil enters at the bottom, heated oil rises, cooler oil replaces it. Natural convection creates continuous flow through the ducts. In conventional layer-wound design, oil inside the winding is stagnant.

Resulting Thermal Path

Heat travels copper → paper → oil in duct. Distance: 1-2mm. In conventional design: copper → paper → copper → paper → copper → paper → oil. Distance: 8-12mm. Shorter path plus moving oil equals lower measured temperature.

Factory Heat Run Comparison: Spiral Coil vs Layer Wound

Thermal Imaging Evidence – What the Camera Shows

During the August 2024 factory heat run, thermal images (Fluke Ti480, emissivity set to 0.95 for painted steel) of the tank surface showed:

• Layer-wound unit: Hot spot appears on upper front of tank, aligned with inner winding location. Temperature difference between hot spot and average tank surface: 12-15°C.
• Spiral coil unit (test unit #SP240804): Tank surface temperature is more uniform. Hot spot only 6-8°C above average. No concentrated hot zone visible.

Technical Specifications – 100kVA Spiral Coil Unit

All values below are from factory production records and type test reports for model S11-M-100/10 with spiral LV winding option.

Application Guidelines – Where Spiral Coil Provides Measurable Benefit

Highest benefit – recommended for spiral coil

• Ambient temperature >35°C for >3 months per year – Customer locations: Philippines, Indonesia, Nigeria, Thailand. Reduced thermal margin makes internal cooling critical.
• Indoor installation with limited airflow – Basement electrical rooms, underground substations, high-rise building utility rooms. No external airflow to assist cooling.
• Load cycles more than 2 times per day – Shopping malls, manufacturing with day/night shifts, EV charging stations. Spiral coil responds faster to load changes due to reduced thermal inertia.

Moderate benefit

• Continuous 24/7 load at 60-80% of rating – Temperature is lower than 100% load case, but extended life still provides economic value.
• Remote sites with no local repair capability – Extended life reduces replacement trips and shipping costs.

Low benefit – use standard S11 layer-wound

• Ambient temperature consistently below 25°C year-round
• Average load below 40% of rating
• Transformer is outdoors with excellent airflow (all sides exposed to wind)
• Project budget is the primary constraint (use standard unit)

Production Batch Data – Last 12 Spiral Coil Units (March 2024 - February 2025)

Manufacturing Note – Spiral Winding Requires Specialized Equipment

Spiral winding cannot be performed on standard layer-winding machines. Shanghai Industrial Transformer Co., Ltd. operates two dedicated spiral winding machines (manufacturer: Jiangxi Huadian, model: SK-1600, installed 2019 and 2022). Each 100kVA Transformer Spiral Coil With Longitudinal Oil Passage requires 45-60 minutes of winding time (compared to 20 minutes for layer winding on conventional equipment). This accounts for the higher manufacturing cost and longer lead time of spiral coil units.

Spiral winding is available only for LV coils (low voltage, high current). HV coils remain layer-wound because voltage stress insulation requirements are more critical than thermal optimization for HV windings.

FAQ

Engineering Summary – When to Specify Spiral Coil 100kVA Transformer

Based on factory test data (August 2024), production batch records (12 units, March 2024 - February 2025), and field feedback from 23 shipped units:

Specify the spiral coil design when: ambient temperature exceeds 35°C regularly, installation is indoor with limited airflow, load cycles more than twice daily, or expected service life requirement exceeds 15 years.

Specify standard S11 layer-wound when: ambient is consistently below 30°C, transformer is outdoors with good ventilation, budget is the primary constraint, or the installation is temporary (less than 10 years).

100kVA Transformer Spiral Coil With Longitudinal Oil Passage reduces measured hot spot temperature from 106°C to 95°C (-11°C), extends estimated insulation life from 11 to 22 years, and adds 8-10% to manufacturing cost. For hot climate applications, the payback period is approximately 2 years through reduced replacement cost.