In a tap changing transformer, the tappings are provided on _________.

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Examoogle · Accepted Answer

High voltage winding

Explanation: In a transformer, tap changers are provided on the High Voltage (HV) winding to regulate the output voltage. Providing tappings on the HV side is advantageous because the HV winding carries lower current, making the design of the tap-changing mechanism simpler, and it is usually wound on the outside of the core, facilitating easier access.

Working Principle: The tap changer adjusts the effective number of turns ($N$) in the transformer winding to control the induced EMF ($E = 4.44 f N \phi_{max}$). By varying the number of turns on the HV winding, the transformation ratio ($K = V_1/V_2 = N_1/N_2$) is modified, allowing the secondary voltage to be kept within the desired range despite load fluctuations or variations in the supply voltage.

Key Formulas: $V \propto N$ — Induced voltage is directly proportional to the number of turns; $I_{HV} = \frac{S}{V_{HV}}$ — Since power $S$ is constant, HV current is lower for a given power rating

Key Points: HV winding is placed on the outside of the core (outer layer), making it easier to bring out tap connections.; HV side current is lower, resulting in reduced arcing at the tap changer contacts.; Smaller size of the current-carrying parts allows for a more compact tap changer mechanism.; Voltage regulation is achieved by varying the turns ratio.

Advantages: Lower current handling reduces contact sparking.; Ease of physical access for maintenance.; Compact tap changer design.

Disadvantages: Insulation requirement is high due to the high voltage levels.; Increased risk of insulation failure at the tapping points.

Applications: Power distribution substations.; Generator step-up transformers.; Industrial grid regulation.

Additional Info: Taps are generally located at the neutral end of the winding to minimize the insulation level required for the tap changer mechanism.. Option B (Primary) is technically correct if the primary is the HV side, but HV is the standardized answer because not all primary windings are HV (e.g., step-up transformers).

Answer: A is correct — Tappings are provided on the High Voltage winding because it carries lower current and is physically located on the exterior of the transformer core.

Exam Tip: Remember that 'High Voltage' is the primary criterion for tap placement because lower current minimizes mechanical wear and arcing on the tap changer contacts.

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