Electrical Power Transformers ,Stablizers and Power supply

Explore the practical aspects of electrical power transformers for engineers, technicians, and students, covering design considerations, installation testing, and commissioning.

analyze transformers vs cable runs in a medium and low voltage distribution network, calculating current and voltage drop for a 2 mva transformer 1 km away, and highlight rmu solutions.

Explore transformer classifications by usage: power transformers (step-up) for generation and transmission; distribution transformers (step-down) for local networks; plus power supply, impedance transformer, isolation transformer, and arc welding applications.

Classifies transformers by cooling type, from natural air or self cooling for units under 30 kVA to air-forced and oil-immersed cooling with fins, radiators, and pumps.

Classify transformers by turns ratio using primary and secondary turns Np and Ns to relate Vp and Vs, noting step-down, step-up, and equal-turn cases, including non-power types.

Classify transformers by frequency into low frequency power transformers and medium to high frequency types used in electronic and communication circuits, which can be single or three phase.

Explore the classification of transformers by number of phases, distinguishing single-phase units used in small power supply and stabilizer circuits from three-phase transformers used in step-up, step-down, and distribution applications.

Classify transformers by power into small (500 kVA–7,500 kVA), medium (7,500 kVA–100 MVA), and large (100 MVA+), and note no-load losses are significant for distribution transformers.

Retrieve the transformer's impedance z from the datasheet or nameplate, convert it to a percentage, and use it to calculate short-circuit current and primary voltage drop under full load.

Fabricate the transformer tank from non magnetic iron to prevent electromagnetic fields and implement cooling from natural air to fins and oil-based systems, considering thickness, loads, and ventilation per recommendations.

Explore transformer oil as insulation with high dielectric strength and as a coolant with strong thermal conductivity to reduce transformer volume and diagnose faults via oil tests.

Explore standby tanks, pressure relief devices, and discharge glass tubes in oil transformers. Learn how oil expansion and gas indicators prevent explosions and guide fault diagnosis.

The Buchholz relay, installed on oil transformers, serves as a protection relay with upper and lower floats. Gas bubbles trigger an alarm; oil expansion trips breakers to disconnect the transformer.

Accommodating expansion and contraction, the breathing unit in transformers with a stand-by tank uses a pressure relief device to prevent explosions and silica gel to remove moisture.

Explain how a tape changer unit stabilizes the secondary voltage of transformers by adjusting primary windings through taps, including onload and offload types.

Demonstrates the positive nitrogen system that replaces the air gap in transformer tanks with nitrogen, using a pressure relief valve and breather to handle oil expansion and prevent moisture contamination.

Explain bushing devices in transformers, including medium and low voltage bushings, the flange isolator to prevent moisture, impurities and dust, corona and installation and maintenance considerations.

Learn about transformer measurement devices, including pressure relief valve, oil thermometer, Buchholz relay, oil level indicators, winding and oil temperature sensors, cooling fans, and air breather with silica gel.

Parallel transformers improve reliability by load sharing, but require turns ratio within 3%, same polarity, and equal impedance; for three-phase, match phase sequence and displacement to avoid short circuits.

Learn transformer losses: iron core losses (hysteresis and eddy current), copper losses, dielectric losses, and stray losses. Laminated iron cores with thin insulated sheets reduce eddy currents and stray heating.

Explore transformer efficiency by examining output over input, accounting for losses and partial loading; learn a practical method to daily-average efficiency via hourly measurements.

Explore transformer voltage regulation as the load-dependent change in secondary voltage between no-load and full-load conditions, and learn to compute it from no-load and loaded voltages using the regulation formula.

This lecture explains transformer heat and insulation ratings, including 220 C insulation and ambient plus 65 C limits, and compares 95 C sustained vs 80 C constant on insulation life.

Harmonics are integral multiples of the system frequency. Odd harmonics increase eddy currents and stray losses; even harmonics saturate the transformer core, causing noise and winding damage.

Understand the k-factor, a weighting of harmonic load currents that indicates how much nonlinear load a transformer can withstand, with examples like 4 for 50% and 13 for 100%.

Investigate transformer inrush current, driven by stored core flux during energization, and apply second-harmonic filtering to distinguish faults from rush current for protective circuit breaker control.

Identify the three main sources of transformer noise—magnetostriction in the iron core, copper coil vibrations, and cooling system noise—and note damping methods and data-sheet noise ratings for residential distance guidance.

Perform the insulation resistance (megger) test to verify primary–secondary isolation before transformer delivery, using three levels with short circuits and grounding, applying 500–1000 V, and obtaining results above 500 MΩ.

Master the polarity test for paralleling transformers, using voltmeters on the primary and secondary to verify polarity by comparing V3 with V2 and V1.

Understand transformer oil testing before site delivery: sample from top or bottom by density, evaluate insulation, impurities, and moisture, and perform yearly insulation tests with three-year intervals for other tests.

The TTR test verifies primary to secondary turns ratio matches nameplate (V1/V2 and I1/I2) and checks insulation between windings for internal shorts; ANSI allows 0.5% error, aiming 99.5% identity.

Connect voltmeters on primary and secondary with an ammeter and wattmeter, apply voltage to the primary while shorting the secondary, reach full-load current, and calculate impedance, copper losses, and efficiency.

Conduct the no-load test by applying rated secondary voltage and measuring primary and secondary voltages, primary current, and secondary wattage to determine the turns ratio and iron losses.

Explore how a voltage stabilizer uses buck and boost transformer circuits to regulate output voltage, protecting loads from over and under voltage.

Explore how power supply circuits convert AC to DC using step-down transformers, rectification, smoothing, regulation with zener diodes, and protective fuses for 5, 12, or 24 V outputs.