Five Protection Methods of Surge Protectors

Methods for Surge Protection

1. Parallel Surge Protective Devices (SPDs) Connected Across Power Lines

Under normal conditions, the varistors inside the surge protector remain in a high-impedance state. When the power grid is struck by lightning or experiences transient surges due to switching operations, the protector responds within nanoseconds, causing the varistors to switch to a low-impedance state, rapidly clamping the overvoltage to a safe level. If prolonged surges or overvoltages occur, the varistor degrades and heats up, triggering a thermal disconnect mechanism to prevent fires and protect equipment.

2. Series Filter-Type Surge Protectors Connected in Line with Power Circuits

These protectors provide clean and safe power for sensitive electronic equipment. Lightning surges carry not only massive energy but also extremely steep voltage and current rise rates. While parallel SPDs can suppress surge amplitudes, they cannot flatten their sharp wavefronts. Series filter-type SPDs, connected in-line with power circuits, use MOVs (MOV1, MOV2) to clamp overvoltages in nanoseconds. Additionally, an LC filter reduces the steepness of the surge's voltage and current rise rates by nearly 1,000 times and cuts residual voltage by fivefold, safeguarding sensitive devices.

3. Installing Voltage-Clamping Varistors Between Phases and Lines to Limit Surge Overvoltages

This method works well for lighting, elevators, air conditioners, and motors, which have higher surge withstand capabilities. However, it is less effective for modern compact electronics with high integration. For example, in single-phase 220V AC systems, varistors are typically installed between neutral and ground to absorb induced lightning spikes. Protection effectiveness depends entirely on varistor selection and reliability.

The clamping voltage is set based on the grid's peak voltage (310V), accounting for: - 20% grid fluctuations, - 10% component tolerance, - 15% reliability factors (aging, moisture, heat). Thus, typical clamping levels range from 470V to 510V. Surges below 470V pass through unaffected.

While standard electrical equipment (e.g., motors, lighting) can withstand 1,500V AC (2,500V peak), modern electronics operate at plus-minus 5V to plus-minus 15V, with maximum tolerances below 50V. High-frequency spikes below 470V can still couple through parasitic capacitances in transformers and power supplies, damaging ICs. Moreover, due to varistor residual voltage and lead inductance, strong surges may push clamping levels to 800V-1,000V, further endangering electronics.

4. Enhancing Protection with Ultra-Isolation Transformers (Isolation Method)

A shielded isolation transformer is inserted between the power source and load to block high-frequency noise while enabling proper secondary grounding. Common-mode interference, which is relative to ground, couples through inter-winding capacitance. A grounded shield between primary and secondary windings diverts this interference, reducing output noise.

5. Absorption Method

Absorptive components suppress surges by switching from high to low impedance when threshold voltages are exceeded. Common devices include: - Varistors - Limited current-handling capacity. - Gas Discharge Tubes (GDTs) - Slow response. - TVS Diodes / Solid-State Discharge Tubes - Faster but with trade-offs in energy absorption.

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