What is size of test cell in BDV?

Question

Examoogle · Accepted Answer

Option B: 50mm × 90mm × 100mm

Explanation & Concepts:
The Breakdown Voltage (BDV) test cell is a standardized container used to measure the dielectric strength of insulating oil. According to IS 6792 (or relevant IEC standards like IEC 60156), the internal dimensions of the glass or plastic vessel are specified to maintain a consistent electrode gap and oil volume during testing.

Working Principle: The cell holds the transformer oil sample between two electrodes (typically spherical or mushroom-shaped). A high voltage is applied and gradually increased at a constant rate until an electrical breakdown occurs, indicated by an arc between the electrodes. The standardized volume and dimensions ensure uniform field distribution and consistent impurity-related breakdown results.

Key Formulas: $E = \frac{V}{d}$ — Electric field intensity at breakdown, where $V$ is breakdown voltage and $d$ is electrode gap; $V_{avg} = \frac{1}{n} \sum_{i=1}^{n} V_i$ — Average breakdown voltage calculated from $n$ consecutive tests

Key Points: The BDV test is a primary indicator of moisture and impurity levels in transformer oil.; Electrodes are usually separated by a standard gap of $2.5	ext{ mm}$ for testing.; Oil should be left to settle for at least 3 minutes before starting the test to eliminate air bubbles.; The rate of voltage increase is typically $2	ext{ kV/s}$.

Advantages: Provides a quick assessment of dielectric health.; Standardized methodology allows for comparative analysis.

Disadvantages: Does not identify the specific nature of contaminants.; Requires high voltage safety precautions during operation.

Applications: Power transformer maintenance schedules.; Quality control in oil refineries and substations.

Additional Info: The dimensions 50mm × 90mm × 100mm define the inner cavity of the standard glass vessel.. Standard compliance: IS 6792:1992 is the primary Indian Standard governing this methodology.

Answer: B is correct — The standard dimensions of a BDV test cell are 50mm × 90mm × 100mm as per relevant insulation testing specifications.

Exam Tip: Always remember that while the cell dimensions are fixed, the electrode gap setting (typically 2.5mm) is the most critical parameter for consistent results in BDV tests.

Examoogle · Answer

Option A: 90mm × 50mm × 100mm

Examoogle · Answer

Option C: 50mm × 100mm × 90mm

Examoogle · Answer

Option D: 100mm × 90mm × 50mm

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