The relay uses a standard equation to set TAPn, based on settings entered for the particular winding (n denotes the winding number. ): The ratio TAPmax / TAPmin ≤ 7. 5Protection Settings Calculations for Power Transformers i. SEL-787 Transformer Differential Protection The relay (SEL-787) use the transformer MVA rating as a common reference point, TAP scaling converts all sec-ondary currents entering the relay from the two windings to per unit values, thus. Calculate voltage transformer ratio for metering and protection circuits. 11kV/√3), the ratio remains the. In this technical article, we will delve into the comprehensive methodology of calculating the differential relay settings for the GE P642 relay. By following these calculations meticulously, engineers. Effective relay protection depends on accurate calculations, optimal settings, careful coordination, appropriate selection of relays, and thorough validation. Many CTs offer multiple tap ratios for flexibility: To select CT ratios for accurately measuring load current: To select CT ratios for protection relays considering short circuit requirements: 🏭 Factory Experience: Based on our manufacturing and application experience: 70% of CT primary rating.