Differential Protection Simulator

Differential protection is the most sensitive and selective scheme available for transformers and buses, but the operate-vs-restraint characteristic at its heart is often poorly understood until you can see it move. This simulator gives you a live percentage-differential characteristic: set load, CT ratio, differential pickup, percentage slope, and harmonic restraint threshold, then inject currents to drive the operating point above or below the trip boundary. The Transformer tab applies 87T-specific logic including CT mismatch correction, magnetizing inrush harmonic restraint (2nd harmonic), and tap compensation. The Zone tab displays the protected zone boundary and shows which fault locations fall inside versus outside differential protection coverage. The Scenario tab provides guided fault conditions including through-faults, internal faults, CT mismatch, and inrush. Current waveforms, an operate-vs-restraint chart, and a current balance breakdown panel are updated in real time. An essential tool for engineers designing protection schemes and technicians verifying differential relay commissioning test results.

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A live look at the app you'll launch — every control on the left drives the visualizations on the right in real time.

• 01Explain the operate-vs-restraint characteristic and why a percentage slope is used instead of a fixed pickup
• 02Distinguish an external through-fault from an internal fault using differential current and the operating-point chart
• 03Describe why magnetizing inrush produces large differential current but should not trip the 87T relay
• 04Set harmonic restraint percentage and explain the trade-off between security and dependability
• 05Identify the protected zone boundary for transformer and bus differential schemes
• 06Interpret CT mismatch as false differential current and explain how tap compensation corrects it