⚡ Inverse Time Overcurrent Relay — Multi-Curve
IEC 60255 / IEEE C37.112 IDMT Curves · Transformer Fault Current Derivation
t = (
k
(
I
fault
/
I
set
)
α
− 1
+
β
) ×
TMS
I
set
= CT Primary × Pickup Multiplier | I
fault
=
MVA × 1000
kV × √3 × Z%/100
| IEC: β=0 | IEEE: β>0
Transformer
Relays
Overlays
Export
MVA
Primary kV
Secondary kV
Z %
Primary I
fault
(100%):
—
Secondary I
fault
(100%):
—
Warning: Primary kV ≤ Secondary kV — verify transformer parameters
Fault Level Multiplier
100%
Applied Primary I
fault
:
—
Applied Secondary I
fault
:
—
Cable Damage (BS 7671)
Material
Size (mm²)
Side
Primary
Secondary
TX Inrush (12× FLC)
Auto-computed from transformer parameters
TX Through-Fault Withstand
Category
Infrequent (2s)
Frequent (1s)
I
max
derived from TX impedance
MCB Curve (IEC 60898)
Type
Type B (3-5×)
Type C (5-10×)
Type D (10-20×)
Rating (A)
Side
Primary
Secondary
Report Settings
Remarks / Notes
↺ Reset
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Trip Time vs Fault Current (Log-Log)
Primary I
fault
:
—
Secondary I
fault
:
—
Fault %