Multi-tap vs. Multi-core Current Transformers: A Clarification with Testing Strategies While both multi-tap and multi-core current transformers (CTs) seem similar, they serve distinct purposes, with key differences in design and testing. Let's demystify them: Multi-tap CTs: Function: Offer multiple transformation ratios in one unit, typically achieved through internal taps on the secondary winding. This allows users to adjust the output current to match different measuring devices or protection relay requirements. Applications: Ideal for situations where current levels may vary or where different measurement ranges are needed within the same system. Common uses include metering, protection, and monitoring. Testing: Both factory and field testing typically focus on verifying the accuracy of each tap setting (ratio and phase angle) across the specified burden range. This involves injecting precise test currents at each tap and measuring the corresponding outputs. Additionally, insulation tests, dielectric withstand tests, and winding continuity checks are crucial. Multi-core CTs: Function: Consists of multiple individual cores housed within a single unit, each measuring a separate phase current. An additional "zero core" may be present to sum the phase currents for neutral and ground fault detection. Applications: Primarily used in three-phase systems for protection schemes and fault detection. They provide accurate individual phase current measurements and combined neutral/ground fault information. Testing: Factory and field testing involve both individual core tests and combined performance evaluations. Individual core tests: Similar to multi-tap CTs, each core's ratio and phase angle accuracy are verified under different burden conditions. Combined performance tests: Evaluate the composite error (combined ratio and phase angle error) when all cores are operating simultaneously. This assesses the unit's ability to accurately represent the sum of all phase currents. Key Differences: Purpose: Multi-tap CTs offer flexibility in choosing a single ratio, while multi-core CTs provide individual phase current measurements and ground fault detection. Design: Multi-tap CTs have tap connections for different ratios, while multi-core CTs have multiple, independent cores. Applications: Multi-tap CTs are more versatile across applications, while multi-core CTs are specific to three-phase systems. Testing Similarities: Both involve verifying ratio and phase angle accuracy under various burdens. Insulation, dielectric withstand, and continuity checks are essential for both types. Testing Differences: Multi-tap testing : focuses on each individual tap setting. Multi-core testing : requires additional composite performance evaluation for combined accuracy. Remember, choosing the right type of CT depends on your specific application requirements. By understanding the differences and applying proper testing procedures, you can ensure reliable and accurate current measurement in your power systems.