How to Select Zinc Oxide Arresters? 10kV Distribution Lightning Protection Selection Guide

Zinc oxide arresters (MOA) are the most important overvoltage protection devices in 10kV distribution systems. An appropriately selected arrester can quickly discharge energy during lightning strikes and switching overvoltages, protecting valuable equipment such as transformers and switchgear. However, improper selection may cause the arrester itself to explode, resulting in secondary accidents.

Core Parameters Analyzed One by One

Continuous Operating Voltage (Uc): This is the power frequency voltage RMS value that the arrester can withstand long-term. For 10kV neutral ungrounded systems, Uc is generally selected as 13.6kV; for neutral grounded via arc suppression coil systems, select 12.7kV. Too low a value may cause thermal runaway; too high a value reduces protection effectiveness.

Rated Voltage (Ur): For 10kV systems, Ur is typically selected as 17kV. The ratio of this value to Uc is called the "charge rate," generally 0.75-0.8 for 10kV systems. The lower the charge rate, the longer the arrester life, but the residual voltage will be higher, reducing the protection margin.

Nominal Discharge Current (In): For 10kV distribution systems, generally select 5kA (8/20μs waveform). For substation incoming lines or important transformer outgoing lines, 10kA can be selected. Note: this value does not represent the number of lightning strikes the arrester can withstand, but is the benchmark for determining the residual voltage level.

Residual Voltage (Ures): The peak voltage across the arrester at the nominal discharge current. The lower this value, the more relaxed the insulation requirements for the protected equipment. For 10kV systems, the 5kA residual voltage is generally ≤50kV (peak), with 10kV electrical equipment lightning impulse withstand voltage of 75kV, providing about 50% protection margin, safe and reliable.

Configuration Schemes for Different Installation Locations

Distribution Transformer High Voltage Side: Select HY5WS-17/50 type. Install between the drop-out fuse and the transformer, as close to the transformer bushing as possible, with total lead length controlled within 1 meter.

10kV Overhead Lines: Install one set of line-type arresters (HY5WX-17/50) every 3-5 poles, focusing on protection of sections crossing roads, rivers and important crossings.

Switchgear Incoming Line Side: Select HY5WZ-17/45 type, with lower residual voltage (45kV) and higher overvoltage protection level. Z-type arresters are suitable for substation-type scenarios.

Key Points to Avoid Pitfalls in Installation

Pitfall 1: Grounding Down Conductor Too Long. The arrester grounding down conductor should be short and straight, with length controlled within 0.5 meters if possible. Each additional 1 meter of down conductor increases residual voltage by about 1.5kV, reducing protection effectiveness.

Pitfall 2: Sharing Ground with Transformer. The arrester must be directly connected to the grounding terminal of the protected equipment, not via the "common grounding bus." In practice, use 16mm2 or larger copper wire for a separate down conductor.

Pitfall 3: Ignoring the Disconnector. Outdoor arresters should be equipped with thermal explosion-type disconnectors. Once the arrester fails short-circuit, the disconnector automatically operates to isolate the faulty arrester from the system, preventing line tripping.

Arrester selection is not complicated, but details determine success. With correct parameters and proper installation, a set of arresters can reliably protect equipment for over ten years.