Type 3 SPD

Qualified Type 3 SPDs must pass a series of rigorous tests to ensure performance and safety. These include short-circuit current characteristic tests, operating duty tests, limiting voltage tests, and TOV tests caused by low-voltage system faults.

1. Short-Circuit Current Characteristic Test
   Purpose: Verify that the internal connections of the Type 3 surge protector can withstand short-circuit currents during a fault. If external disconnectors or overcurrent protectors are required by the manufacturer, they should be tested together with the SPD. The test ensures that no burning, melting, or charring occurs when short-circuit currents pass through, preventing risks of fire, explosion, or arcing.
2. Operating Duty Test
   Purpose: Unlike static limiting voltage tests, this evaluation simulates real conditions where the Type 3 SPD operates under continuous voltage while being exposed to surge currents. It measures not only surge resistance but also the SPD’s ability to interrupt power-frequency residual currents. If external disconnectors cannot promptly extinguish residual currents, dangerous continuous ignition may occur inside the SPD.
3. Limiting Voltage Test
   Purpose: Assess the voltage protection level U_p of the Type 3 surge protector. This parameter is crucial: if too high, downstream equipment may remain unprotected; if too low, it may cause unnecessary triggering. Proper balance ensures safe surge discharge while maintaining system stability.
4. TOV Test (Temporary Overvoltage)
   Purpose: In low-voltage distribution systems, switching operations or faults (e.g., sudden load shedding or single-phase faults) can generate temporary overvoltages (TOVs) due to resonance or harmonics. This test evaluates whether the Type 3 SPD can withstand prolonged overvoltage conditions without catastrophic failure or unsafe operation.