Q: The senior engineer told me to grab "a few reactors." I see fiberglass cylinders with handles. What are they?
A: Those are HV reactors - large inductors. They connect in series with the cable to form a resonant circuit. This is the only practical way to test long cables.
How it works - the swing analogy:
• Test transformer = you push the swing every cycle. Your arms get tired fast.
• Resonant system = you give the swing one push at the right moment. The swing keeps going. You only replace the energy lost to friction.
When to use SR:
|
You are testing... |
Capacitance |
SR? |
Why? |
|
Cable > 1 km |
> 0.2 μF |
✅ Required |
Only SR supplies the current economy |
|
Cable > 10 km |
> 2 μF |
✅ Only option |
Test TX would need 500+ kVA |
|
GIS long bus |
10–100 nF |
✅ Good |
Adjustable frequency handles anything |
|
Generator stator |
1–5 μF |
✅ Best |
SR provides a clean sine wave |
|
CT / PT/bushing |
< 1 nF |
❌ Overkill |
Test TX is simpler and cheaper |
Approximate cost (new, 2025):
• 60 kV / 2 A portable SR: $25,000–40,000
• 160 kV / 4 A (110 kV cable): $60,000–120,000
• 300 kV / 6 A (220 kV cable): $150,000–300,000
Why "stacked" - series vs parallel:
• Series = higher voltage (80 kV + 80 kV = 160 kV)
• Parallel = higher current (2 A + 2 A = 4 A)
• Both = series-parallel combination
Pro tip: Always read the nameplate. "80 kV / 2 A / 50 H" = 80 kV to ground, 2 A continuous, 50 Henry inductance.