📘 Busbar Protection – Differential & High Impedance Scheme
Busbar is a common connection point of multiple feeders, generators and transformers. Busbar faults are very severe and must be cleared instantly.
🔹 1️⃣ Why Busbar Protection is Important?
- Very low impedance location
- High fault current magnitude
- Multiple sources contribute to fault
- Fault can affect entire substation
Busbar fault = Extremely Dangerous Condition
🔹 2️⃣ Basic Principle – Differential Protection
Based on Kirchhoff’s Current Law:
Sum of incoming currents = Sum of outgoing currents
Under normal or external fault:
I₁ + I₂ + I₃ = I₄ + I₅
During internal bus fault:
Σ I ≠ 0 → Differential current flows → Relay trips
🔹 3️⃣ Types of Busbar Protection
(A) Low Impedance Differential Scheme
- Uses percentage differential relay
- Stable for external faults
- Used in modern numerical relays
(B) High Impedance Differential Scheme
- All CT secondaries connected in parallel
- High impedance relay used
- Stabilizing resistor included
🔹 4️⃣ High Impedance Scheme – Working
- Under normal condition → No differential voltage
- External fault → CT secondary currents circulate
- Internal fault → Voltage develops across relay
- Relay trips instantly
V = I_diff × (R_stability + R_relay)
🔹 5️⃣ Advantages
- Very fast protection (Instantaneous)
- Highly selective
- Reliable for internal faults
🔹 6️⃣ Disadvantages
- Requires identical CTs
- Costly wiring
- CT saturation can affect performance
🔹 7️⃣ Where Used?
- 132 kV substations
- 220 kV substations
- 400 kV substations
- Power generating stations
🎯 GATE & Interview Points
- Busbar faults have very high fault level
- Differential principle used
- High impedance scheme uses stabilizing resistor
- Very fast protection required
Busbar Protection = Instantaneous Isolation of Severe Fault
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