The tappings on the transformers is provided on

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Examoogle · Accepted Answer

h.v side at middle

Explanation: Tappings on transformers are provided on the high-voltage (HV) winding, specifically at the middle section. This configuration is chosen to maintain magnetic symmetry and minimize leakage reactance, ensuring uniform flux distribution across the core limbs.

Working Principle: Placing tappings in the middle of the HV winding helps balance the Ampere-turn distribution between the HV and low-voltage (LV) windings. If tappings were placed at the end, the physical shift of the magnetic center during tap changing would cause significant leakage flux imbalances and higher mechanical forces on the windings during short-circuit conditions.

Key Formulas: $V_{ratio} = \frac{N_{HV}}{N_{LV}}$ — Basic transformer transformation ratio; $L_e \propto \frac{\mu_0 N^2 A}{l}$ — Relationship between turns and leakage inductance

Key Points: HV windings are usually placed outside (closer to the tank), making tappings easier to access.; HV windings carry lower current than LV windings, reducing the size of the tap-changing gear contact points.; Tapping at the middle ensures minimal axial magnetic forces under fault conditions.; Symmetrical tapping prevents localized heating and magnetic unbalance.

Advantages: Improved mechanical stability under short circuits; Balanced magnetic field distribution; Easier maintenance and construction for HV access

Disadvantages: Complex winding manufacturing compared to end-tapped designs; Requires careful insulation management at the tap-changer connection

Applications: Power transformers for voltage regulation; Distribution transformers with Off-Circuit Tap Changers (OCTC); On-Load Tap Changers (OLTC) in transmission substations

Additional Info: HV windings are placed on the outside of the LV winding to reduce insulation requirements, making it physically convenient to bring out tapping leads.. Option A is incorrect because tapping at one end disturbs the magnetic symmetry. Option B and D involve the LV winding, which carries higher current, making tap-changing gear bulky and prone to higher $I^2R$ losses.

Answer: C is correct — Tappings are provided at the middle of the HV winding to maintain magnetic and electrical balance within the transformer core.

Exam Tip: Always remember: HV windings have more turns and lower current, making them ideal for tapping to ensure precise voltage control without excessive current-carrying capacity requirements on the tap changer contacts.

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