SPD parameters Uc, In, Up (Source: SurgePV): Golden Rule: Uc based on low-temperature Voc (Source: LSP); Core Standard: IEC 61643-31 (Source: Thor); Note: Up < 80% Uimp (Source: Synode).
I. Maximum Continuous Operating Voltage (Uc)
Formula: Uc ≥ Voc × 1.1 × Temperature Coefficient (Source: SurgePV);
Low Temperature: Voc increases by 0.3%/°C at low temperatures (Source: Portlandia); Safety: Safety factor of 1.1–1.2 (Source: JUTRION); Common Error: 900V string voltage exceeds 1000V on cold mornings (Source: SurgePV); Voltage Ratings: 600V, 1000V, 1500V (Source: LSP) — Uc: Formula + Low-temperature adjustment + Voltage rating (three key points).
II.
Discharge Current (In/Imax)
In: Nominal discharge current (8/20µs waveform) (Source: LSP); Imax: Maximum discharge current, 1.5–2 times In (Source: LSP); 20kA: In = 20kA is the commercial standard (Source: Thor); 40kA: Imax = 40kA for lightning-prone areas (Source: Thor); Iimp: Iimp = 25kA (10/350µs waveform) (Source: Synode) — Current: In + Imax + Iimp (three indicators).
III. Voltage Protection Level (Up)
Definition: Surge clamping voltage (Source: Synode); Coordination: Up < 80% of equipment Uimp (Source: Synode); 1500V: Up ≤ 4.8 kV for 1500V inverters (Source: Synode); String: Up ≤ 4.0 kV for string inverters (Source: Synode); Cascading: T1 ≤ 4.0, T2 ≤ 2.5, T3 ≤ 1.5 kV (Source: Kuangya)—Up: Coordination + 1500V + Cascading (Three Principles).
IV.
Lightning Protection Type
Type 1: Coarse protection against direct lightning strikes (Source: Kuangya); Type 2: Intermediate protection (Source: Kuangya); Type 3: Fine protection (Source: Kuangya); T1+T2: Commonly used combined type (Source: Prosurge); Installation: Combiner box and inverter side (Source: Kuangya)—Type: T1+T2+T3 (Three-stage cascading).
V.
Standards and Certification
IEC: IEC 61643-31 DC standard (Source: Thor); TÜV: TÜV PV certification (Source: Prosurge); Waveform: 8/20µs, 10/350µs (Source: Kuangya); Testing: 15-impulse test (Source: Thor); Trip: Thermal trip safety protection (Source: JUTRION)—Standards: IEC + TÜV + Testing (Three Certifications).
VI. Selection Criteria
Matching: Uc matched to Voc-max (Source: LSP); Region: Choose 40kA for high-lightning areas (Source: Suntree); Pole Configuration: 3-pole L+/L-/PE (Source: Synode); Service Life: Low Up values may necessitate frequent replacement (Source: Kuangya);
System: 600V system paired with 600V/800V rating (Source: JUTRION)—Selection: Matching + Region + Poles (Three-point check).
VII. Procurement Recommendations
First, calculate Uc (Low-temp Voc × 1.1); second, determine In (starting at 20kA); third, check Up (<4.8kV); fourth, select type (T1+T2);
fifth, verify certification (IEC 61643-31)—Surge Protection Device: Uc + In + Up (Three key parameters).
