Explore scaled measurements

Adjust the primary system value and instrument transformer ratio to see what the protection relay receives. As the value increases, the same view also shows when the simple proportional relationship begins to lose accuracy.

Secondary current = Primary current ÷ 600
Ideal relay input
0.50 A
Actual relay input
0.50 A

The accuracy limit shown here is a simplified teaching model. Actual CT and VT performance depends on the device specification, class, burden and operating conditions.

Primary system 300 A What is actually happening in the power system
→
CT 600:1 Ratio factor 600
→
Protection relay receives 0.50 A Accurate proportional measurement
Accuracy operating range Accurate
Accurate Accuracy reducing Outside range
The secondary signal is proportional to the primary value, so the relay is seeing an accurate representation of the power system.