- 1. Voltage and current matching
（1）Three-phase electricity (380V)
Rated voltage selection: The withstand voltage of the thyristor should be at least 1.5 times the working voltage (recommended to be above 600V) to cope with peak voltage and transient overvoltage.
Current calculation: The three-phase load current needs to be calculated based on the total power (such as 48kW), and the recommended rated current is 1.5 times the actual current (such as 73A load, choose 125A-150A thyristor).
Balance control: The three-phase two-control method may cause a decrease in power factor and current fluctuations. Zero-crossing trigger or phase-shift control module needs to be installed to reduce interference with the power grid.
（2）Two-phase electricity (380V)
Voltage adaptation: The two-phase electricity is actually single-phase 380V, and a bidirectional thyristor (such as BTB series) needs to be selected, and the withstand voltage also needs to be above 600V.
Current adjustment: The two-phase current is higher than the three-phase current (such as about 13.6A for a 5kW load), and a larger current margin needs to be selected (such as above 30A).
2. Wiring and triggering methods
（1）Three-phase wiring:
Ensure that the thyristor module is connected in series at the phase line input end, and the trigger signal line must be short and isolated from other lines to avoid interference. If zero-crossing triggering (solid-state relay method) is used, harmonics can be reduced but the power regulation accuracy is required to be high; for phase-shift triggering, attention should be paid to voltage change rate (du/dt) protection, and a resistor-capacitor absorption circuit (such as 0.1μF capacitor + 10Ω resistor) should be installed.
（2）Two-phase wiring:
Bidirectional thyristors must correctly distinguish between T1 and T2 poles, and the control pole (G) trigger signal must be synchronized with the load. It is recommended to use an isolated optocoupler trigger to avoid misconnection.
3. Heat dissipation and protection
（1）Heat dissipation requirements:
When the current exceeds 5A, a heat sink must be installed, and thermal grease must be applied to ensure good contact. The shell temperature must be controlled below 120℃, and forced air cooling should be used when necessary.
（2）Protection measures:
Overvoltage protection: Varistors (such as MYG series) absorb transient high voltage.
Overcurrent protection: fast-blow fuse is connected in series in the anode circuit, and the rated current is 1.25 times that of the thyristor.
Voltage change rate limit: parallel RC damping network (such as 0.022μF/1000V capacitor).
4. Power factor and efficiency
In a three-phase system, phase shift control may cause the power factor to decrease, and compensation capacitors need to be installed on the transformer side.
Two-phase system is prone to harmonics due to load imbalance, so it is recommended to adopt zero-crossing trigger or time-sharing control strategy.
5. Other considerations
Selection recommendation: give priority to modular thyristors (such as Siemens brand), which integrate triggering and protection functions and simplify wiring.
Maintenance inspection: regularly use a multimeter to detect the conduction state of the thyristor to avoid short circuit or open circuit; prohibit the use of megohmmeter to test insulation.
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Post time: Jul-16-2025
