Q: What is the difference between frequency-tuned and inductance-tuned resonance systems?
A: VFSR adjusts inverter frequency (20–300 Hz). VSR adjusts reactor core gap at 50/60 Hz. Each has distinct advantages.
|
Parameter |
VFSR (Variable Frequency) |
VSR (Variable Inductance) |
|
Tuning element |
Inverter frequency (electronic) |
Movable reactor core (mechanical) |
|
Tuning range |
Very wide: 20–300 Hz |
Narrower: inductance ratio 2:1 to 5:1 |
|
Tuning speed |
< 1 s (electronic sweep) |
10–60 s (motor-driven core) |
|
Frequency output |
Variable (not 50/60 Hz) |
Fixed at 50/60 Hz |
|
Waveform purity |
Good, needs output filter |
Excellent - pure power frequency |
|
Weight per reactor |
Lighter (fixed core) |
Heavier (movable mechanism) |
|
Cost (system) |
Higher (VFD inverter) |
Lower at low power ratings |
|
PD measurement |
Good with filter |
Excellent (no inverter noise) |
|
Long cable testing |
Excellent (low f reduces current) |
Good (limited by L range) |
|
Standard compliance |
IEC 60060-3 permits 20–300 Hz |
Direct 50/60 Hz |
Hybrid systems: coarse tuning via reactor taps + fine tuning via narrow-band VFD (45–65 Hz).
Rule of thumb:
• Mainly cables < 5 km → VFSR (30–300 Hz).
• GIS / short cables at 50 Hz → VSR (fixed frequency).
• Maximum flexibility (cables + GIS + TX) → VFSR down to 20 Hz.