Follow the explanation
Back to the model ↑How the parts work together
Start with the sealed can
Orbit the complete transformer. The bushings provide insulated electrical paths through the oil-filled steel tank; there is no shaft, piston, or other moving power-transfer part.
Follow a changing field
Isolate the core and windings. The primary voltage and secondary voltage rise together while core flux follows a quarter-cycle behind. The display runs at 0.2 Hz—300 times slower than the modeled 60 Hz AC—so the reversal is visible.
Set the turns ratio
Choose 30:1. The 240-turn primary surrounds the same core as an 8-turn secondary, split into two 4-turn foil sections. At 7.2 kV RMS, the ideal secondary voltage is 240 V RMS.
Connect a resistor
With 24 Ω connected, 240 V drives 10 A in the secondary. The ideal primary draws one-thirtieth as much current, about 0.333 A, and both sides transfer 2.4 kW.
Open the secondary
Disconnect the load. Secondary voltage and alternating flux remain, but current and power become zero in this ideal model. A real transformer still draws a small exciting current and has core loss.
The main parts
- Steel tank
- The smooth pole-mounted can encloses the active assembly and insulating oil. Its dimensions are original and normalized, not copied product measurements.
- Two wound core loops
- Two rounded loops of laminated electrical steel link one central winding structure. Their changing flux is shown by a slowed color pulse; it is not a field-strength calculation.
- 240-turn primary
- Four connected layers of 60 insulated wire turns receive the AC input. The winding film separates neighboring turns, while paper barriers separate voltage regions.
- Low-voltage foil winding
- Two series-connected foil sections sit inside and outside the primary. Each section has 6, 4, or 3 illustrated turns, giving 12, 8, or 6 total secondary turns and ratios of 20:1, 30:1, or 40:1.
- Paper insulation & oil ducts
- Paper barriers, pressboard blocks, and clear oil paths separate the core and winding regions. Their thicknesses are enlarged so the construction remains readable.
- High-voltage bushings
- Two porcelain bushings carry the primary connections through the grounded tank cover while keeping the conductors insulated from the steel enclosure.
- Low-voltage bushings
- Two side bushings connect one secondary winding to the load. This lesson deliberately uses no center tap or neutral terminal.
- Clamps & supports
- Rigid frames and pressboard shims hold the core-and-coil assembly inside the tank. The model does not calculate mechanical fault forces.
- Insulating oil
- Oil surrounds the active assembly and enters rectangular winding ducts. The transparent cutaway reveals this path without simulating flow or temperature.
- Internal leads
- Insulated leads join each winding to its bushings. The primary passes through a rigid terminal board; exact factory routing and connector dimensions are illustrative.
Questions worth exploring
How can a transformer work without moving parts?
Alternating voltage produces changing magnetic flux in the core. Both stationary windings link that flux, so it induces voltage in the secondary. Energy crosses through the changing electromagnetic field rather than through a rotating shaft. This lesson slows the visible cycle to 0.2 Hz while calculating a 60 Hz sinusoidal transformer.
OpenStax · University Physics Volume 2, §15.6, Fig. 15.22 and Eqs. 15.20-15.22U.S. DOE · Electrical Science Vol. 4, Module 13, pp. 3-7 and 13-15
How does turn count set transformer voltage?
For an ideal transformer, secondary voltage divided by primary voltage equals secondary turns divided by primary turns. Here 240 primary turns and 8 secondary turns make a 30:1 ratio, so 7.2 kV RMS becomes 240 V RMS. Selecting 12 or 6 secondary turns changes both the visible foil winding and the calculation.
OpenStax · University Physics Volume 2, §15.6, Fig. 15.22 and Eqs. 15.20-15.22U.S. DOE · Electrical Science Vol. 4, Module 13, pp. 3-7 and 13-15
What does a resistive load change?
At a fixed input voltage and turns ratio, the ideal secondary voltage stays fixed. Lower resistance draws more secondary current and power, and the primary current rises by the corresponding inverse turns ratio. Real winding resistance and leakage would also cause voltage drop and heat, which this model does not calculate.
OpenStax · University Physics Volume 2, §15.6, Fig. 15.22 and Eqs. 15.20-15.22U.S. DOE · Electrical Science Vol. 4, Module 13, pp. 3-7 and 13-15
Why are the windings, core, and oil arranged this way?
The referenced single-phase construction uses two wound steel core loops around one concentric low-high-low winding structure. Its low-voltage conductor is foil, its high-voltage conductor is insulated wire, and paper barriers and rectangular oil ducts separate regions. The surrounding oil-filled tank is shown as construction, not as a thermal simulation.
ERMCO · Single Phase Core & Coil Assembly, p. 1 (shell form, LO-HI-LO windings, insulation and leads)ERMCO · Single Phase Pole Mounted Distribution Transformer, pp. 1-3 (tank, oil and bushings)