Q: People call TDR "Cable Radar." How does it find a fault without digging?
A: TDR sends a low-voltage pulse (<100V) and listens for the reflection. Any impedance change causes a bounce-back wave.
How to read the TDR screen:
|
Waveform Shape |
Meaning |
Fault Type |
|
Upward (Positive) |
Impedance → Infinity |
Open Circuit / Cut Cable |
|
Downward (Negative) |
Impedance → Zero |
Short Circuit / Phase-Ground |
|
Flat Wave |
Impedance is Constant |
Healthy Cable |
Logic: Distance = (Velocity × Time) / 2. TDR finds "dead shorts" and "broken wires" easily.
What is "Thumping" (High Voltage Surge)?
Q: TDR shows a healthy cable, but the breaker keeps tripping. Why "Thump" it?
A: TDR cannot "see" high-resistance insulation cracks. We need to create an artificial arc at the fault site.
The Thumping Process:
1. Charge: Equipment charges a massive high-voltage capacitor (The Thumper).
2. Discharge: Releases energy in one massive pulse (e.g., 15 kV) into the cable.
3. The Arc: Pulse hits the defect and creates an Artificial Arc (Flashover).
4. Signal: The arc acts as a temporary short, reflecting the TDR wave.