Transcription of Transformer Differential Protection Setting Calculations
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Transformer Differential Protection Setting Calculations
Differential Protection Setting CalculationsTransformer Differential Protection Setting CalculationsTransformer Differential Protection Setting CalculationsDifferential Protection Setting Calculations Examine CT performance Calculate winding tap values Determine 87T pickup points- Determine variable percentage slope breakpoints- Determine harmonic restraint values Determine 87H pick up Determine 87GD pick upObjectivesDifferential Protection Setting Calculations Class C CTs have established secondary voltage/burden curves that are used to predict linear performance Operating a CT at values above the kneepoint on the curve invite unfaithful replication of the primary waveform and saturation Unfaithful replication (including saturation) between measurement CTs in a Differential Protection causes misoperationCT PerformanceDifferential Protection Setting Calculations Class C CTs are designed to faithfully replicate primary currents to within +/- 10% Class designations designate maximum secondary CT circuit voltage at standard burden that can be applied to maintain accuracy-Zrated = Voltage Class / 20 * Rated Secondary Current-Zrated = C800 / 20 * 5A = 8 , 800V at 8 burden-Zrated = C200 / 20 * 5A = 2 , 200V at 2 burdenClass C CTsDiff
Differential Protection Setting Calculations Where R CT is CT burden (internal) R W total resistance of the ct secondary wiring. R R is relay burden V S = I (R CT + R W + R R) Where I is the fault current and V S is the ct secondary voltage. In order to make sure that the ct is in the linear range (to avoid ac saturation of the ct’s), V
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