Disconnecting Switch (20 kV): Essential Components for Medium-Voltage Safety
A 20 kV disconnecting switch—also called an isolator—is a key safety device in medium-voltage power systems. Its main job is to make a physical break in the circuit during maintenance. This break is a visible air gap over 150mm wide, helping workers check the circuit has no power.
The switch also stops the circuit from getting power by accident. It uses mechanical or electrical links to circuit breakers, and these links follow the “five prevention” rules. One rule, for example, stops it from switching loads.
Remember: this switch can’t stop electric arcs. So never use it to switch loads. When you use it, follow this order: the circuit breaker opens first, then you use the isolator—only after the current hits zero.
For structural design, the contact system has main contacts with silver-plated surfaces. The silver layer is at least 20 μm thick, and surface hardness is at least 120 HV. This coating keeps resistance low and stops oxidation. Finger contacts use spring pressure for stable point contact.
Insulation: air is the usual type, but some switches use SF₆ gas for polluted areas. The switch’s dielectric strength must handle 42 kV for 1 minute, following GB/T 1985.
Mechanical assembly includes a stainless steel housing and glass-filled nylon operating mechanisms. Outdoor switches have an IP65 rating, resisting corrosion and dust.
Key technical rules: system max rated voltage over 20 kV (per GB/T 1985, IEC 60947-3); handles 31.5 kA for 4 seconds (tested via dynamic stability); insulation resistance ≥1000 MΩ (tested with 500 V DC); mechanical life 10,000 cycles (M2 grade, needs regular lubrication); contact resistance ≤50 μΩ (checked with a micro-ohmmeter).
Safety and maintenance rules: before switching, check the breaker’s status and confirm no voltage with testers. Test once a year—include thermal imaging (temp rise ≤65 K at 1.05× rated current) and insulation resistance checks. Wrong use causes bad arcs, like a 2019 15 kV incident that broke equipment. Newer designs have triple interlocks (mechanical, electrical, software).
Conclusion:
The abimat 20 kV switch is a must for safe medium-voltage grid work. Follow IEC/GB standards, do careful maintenance, and use smart sensors (for real-time temp/vibration checks) to boost reliability. Following operation rules is key to stop big failures.
