SPD (Surge Protective Device) Selection
Select SPD type, Uc, In/Imax, and Up from system voltage, grounding system, installation location, and equipment withstand; check lead length.
Key points
SPD (Surge Protective Device) Selection: Select SPD type, Uc, In/Imax, and Up from system voltage, grounding system, installation location, and equipment withstand; check lead length. Formula: U_c ≥ 1.1·U₀ (1.5·U₀ for TT) | U_p,eff = U_p + L·1kV/m | U_p,eff ≤ U_w. Enter parameters on the DD-CAT IDE online tool page to get results instantly, with a calculation-model diagram that updates with the inputs. SPD Uc must exceed the highest sustained system voltage (including tolerance and harmonics), otherwise it ages faster or misoperates. Effective residual voltage = SPD Up + inductive drop in the connecting leads; longer leads raise it, so keep them short, straight, and Kelvin-connected.
Inputs
U_c ≥ 1.1·U₀ (1.5·U₀ for TT) | U_p,eff = U_p + L·1kV/m | U_p,eff ≤ U_wCalculation model (updates with parameters)
| Recommended SPD type | Type 1 | 总进线，泄放雷current |
| Minimum continuous voltage U_c | ≥ 254 V | 按 1.1×U₀ |
| Recommended nominal discharge current | 12.5 kA (10/350µs) | 按Installation locationand雷暴日 / 暴露程度复核 |
| SPD voltage protection level U_p | 1.50 kV | 厂家铭牌Value |
| Lead additional residual voltage | 0.50 kV | 按 1 kV/m 估算 |
| Effective residual voltage at equipment U_p,eff | 2.00 kV | U_p + L×1kV/m |
| Equipment withstand check | 通过 ✓ | U_p,eff ≤ U_w = 2.50 kV |
| Backup protection | 按厂家推荐配熔断器 / 断路器 | SPD 短路失效时需要Backup protection，不能仅依赖主Switch |
Engineering notes
- SPD Uc must exceed the highest sustained system voltage (including tolerance and harmonics), otherwise it ages faster or misoperates.
- Effective residual voltage = SPD Up + inductive drop in the connecting leads; longer leads raise it, so keep them short, straight, and Kelvin-connected.
- Type 1 / 2 / 3 correspond to main incoming, sub-distribution, and equipment end; energy coordination is required between stages, and backup protection per the manufacturer.
FAQ
- What is SPD (Surge Protective Device) Selection for?
- Select SPD type, Uc, In/Imax, and Up from system voltage, grounding system, installation location, and equipment withstand; check lead length.
- What is the formula for SPD (Surge Protective Device) Selection?
- Core formula: U_c ≥ 1.1·U₀ (1.5·U₀ for TT) | U_p,eff = U_p + L·1kV/m | U_p,eff ≤ U_w. The tool returns results instantly using this formula and the selected parameters.
- What engineering notes should I keep in mind when using SPD (Surge Protective Device) Selection?
- SPD Uc must exceed the highest sustained system voltage (including tolerance and harmonics), otherwise it ages faster or misoperates. Effective residual voltage = SPD Up + inductive drop in the connecting leads; longer leads raise it, so keep them short, straight, and Kelvin-connected. Type 1 / 2 / 3 correspond to main incoming, sub-distribution, and equipment end; energy coordination is required between stages, and backup protection per the manufacturer.