What diodes are commonly used for surge current protection in distribution networks?

一, TVS diode: precision protection core with millisecond level response
1. Device characteristics and working principle
TVS (Transient Voltage Suppressor) diodes are designed based on avalanche breakdown effect, and their core advantages lie in nanosecond response speed (≤ 1 × 10 ⁻¹ ² seconds) and precise clamping voltage control. When the transient voltage exceeds its breakdown voltage (VBR), the device quickly transitions from a high resistance state to a low resistance state, and clamps the voltage within a safe range (VC value) by diverting large currents. The typical clamping coefficient (VC/VBR) is 1.2-1.4. For example, the P0640SC series TVS tube can withstand peak currents of thousands of amperes and clamp voltages as low as hundreds of volts, making it suitable for protection in 600V/800V high-voltage distribution networks.

2. Key parameters for selection
Reverse Cut off Voltage (VRMM): It should be 1.1-1.2 times higher than the normal operating voltage of the circuit. For example, a 120V system requires the use of devices with VRMM ≥ 132V.
Peak Pulse Power (PPP): Calculated based on surge energy, such as PPP ≥ E (surge energy)/VC under 8/20 μ s waveform.
Junction capacitance (CJ): Low capacitance devices (such as 0.1-10pF) should be selected for high-frequency signal lines to avoid signal attenuation. For example, the USB 3.0 interface requires the use of TVS tubes with CJ ≤ 0.3pF.
3. Typical application scenarios
Data center power inlet: SMBJ series TVS tubes are used to construct three-level protection. The first level uses high-power devices (such as 1500W) to absorb large energy surges, and the third level uses low capacitance devices (such as 500W) to protect sensitive chips.
Photovoltaic inverter DC side: Parallel TVS tubes are connected in a DC 1000V system to suppress transient overvoltage caused by cloud cover or array switching.
二, Semiconductor Discharge Tube (TSS): Backbone Protection for High Current Capacity
1. Device characteristics and working principle
TSS (Thyristor Surge Suppressors) adopts a PNPN four layer structure, which combines the switching characteristics of thyristors with the unidirectional conductivity of diodes. Its core advantages lie in its extremely high surge tolerance (up to tens of kiloamperes) and low residual voltage characteristics (typical VC value ≤ 2 times VBR). For example, the P0640SC series TSS can withstand a 20kA surge and residual voltage below 800V under an 8/20 μ s waveform, making it suitable for protection of high-voltage distribution network backbone lines.

2. Key parameters for selection
Breakdown voltage (VBO): It needs to match the nominal voltage of the system, such as selecting devices with VBO=12-15kV for a 10kV system.
Current carrying capacity (Ipp): Based on the lightning risk level, devices with Ipp ≥ 50kA should be selected for high thunderstorm areas.
Response time: Typical value ≤ 100ns, requiring coordination with TVS tube to achieve graded protection.
3. Typical application scenarios
Substation incoming end: A composite protection scheme of TSS and MOV in series is adopted, with TSS as the first stage to absorb high-energy surges and MOV as the second stage to limit residual voltage.
Wind farm collection line: parallel TSS at the 35kV cable terminal to suppress overvoltage caused by cable operation.
三, Varistor (MOV): An Economical and Efficient Universal Protection
1. Device characteristics and working principle
MOV (Metal Oxide Varistor) uses zinc oxide as the main material and achieves voltage limiting function through nonlinear volt ampere characteristics. Its core advantages lie in high cost-effectiveness and high current capacity (up to several hundred kiloamperes per chip), but there is an aging effect (performance degradation after long-term use). For example, the 14D471K MOV can withstand a 40kA surge under an 8/20 μ s waveform and is suitable for end protection in low-voltage distribution networks.

2. Key parameters for selection
Voltage sensitive (V1mA): It needs to be higher than the maximum continuous operating voltage of the circuit, such as selecting devices with V1mA ≥ 320V for a 220V system.
Current capacity: According to the lightning risk level, Class C protection requires Iimp ≥ 65kA (10/350 μ s waveform).
Leakage current: Typical value ≤ 20 μ A, regular testing is required to prevent aging and failure.
3. Typical application scenarios
Residential distribution box: Adopting MOV to construct three-level protection, the first level installs high-energy devices (such as 20kA) at the main incoming line end, and the third level installs low-power devices (such as 2kA) in the socket circuit.
Industrial motor control cabinet: parallel MOV at the input end of the frequency converter to suppress transient overvoltage caused by motor start stop.
四, Construction strategy of multi-level protection system
1. Principle of graded protection
Adopting a combination scheme of "coarse protection+fine protection":

Level 1 (coarse protection): Install TSS or high-energy MOV at the system entrance to absorb large energy surges (such as lightning strikes).
Second level (precision protection): Install TVS tubes at the front end of the equipment to limit residual voltage to a safe level (such as below the chip withstand voltage value).
Third level (local protection): Connect low-power TVS tubes in parallel next to sensitive components to provide final protection.
2. Key points for parameter coordination
Energy coordination: Ensure that the front-end devices absorb energy ≥ 80% of the total surge energy to avoid overloading of the back-end devices.
Voltage coordination: The VC value of each level of device needs to be gradually reduced to form "gradient protection". For example, the first level VC is 1500V, the second level VC is 800V, and the third level VC is 400V.
Time coordination: Utilize the difference in device response time (TSS ≈ 100ns, TVS ≈ 1ns) to achieve fast response.