CT / PT and Relay Measurement Simulator

Instrument transformers are the sensory system of every protection scheme, and misunderstanding their behavior — burden, saturation, polarity, open-secondary danger — is a leading source of protection failures in the field. This simulator builds the link between primary-side quantities and relay-terminal values by letting you set CT ratio, class, and burden, PT ratio and primary voltage, then inject load current, fault current, and ground fault current and watch scaled secondary quantities, relay pickup status, and operating point update in real time. The Relay tab supports five ANSI function types: 50 (Instantaneous OC), 50G (Ground OC), 51G (Time Ground OC), and 87 (Differential). The Scenarios tab provides eight guided fault conditions — from normal load to CT saturation, reversed differential polarity, high burden, and the open CT secondary danger condition. The Scaling tab shows the math step-by-step. A Self-Test tab quizzes knowledge. Targeted at protection engineers and NETA technicians preparing for commissioning or maintenance testing.

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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 how CT ratio and burden affect secondary current accuracy and relay input
• 02Describe the danger of an open CT secondary and identify the protective action required
• 03Identify CT saturation conditions and explain how saturation affects protection performance
• 04Configure 50, 50G, 51G, and 87 relay functions and verify pickup against injected currents
• 05Trace the differential operating vs. restraint characteristic for through-fault and internal-fault conditions
• 06Select appropriate CT class (C100, C400, C800) for a given protection application