Metal-Oxide Surge Arrester Type Tests & Ratings: KEMA 3-36 kV and GB/T 11032 Reports Explained

A metal-oxide surge arrester is the component that stops a lightning strike or switching surge from destroying a transformer, breaker or cable. It is deceptively simple — a stack of zinc-oxide discs in a polymer housing — but the difference between a 5-year and a 25-year service life is entirely in the type-test evidence. This article explains what an arrester type test proves and lists the as-tested ratings XinNeng holds, from distribution-class 3-36 kV through 220 kV station class.

1. What a Surge Arrester Actually Does

Every overhead and substation system is struck by lightning or experiences switching surges. Without protection, that overvoltage appears across the insulation of expensive plant — transformers, circuit breakers, cables — and punctures it. The surge arrester is connected in parallel with the equipment: one terminal to the phase, the other to earth. In normal operation it passes only micro-amps; when an overvoltage arrives, its zinc-oxide elements turn conductive within microseconds and divert the energy to earth, holding the voltage across the equipment to a safe ‘residual’ level.

Unlike older gapped arresters, a modern metal-oxide (ZnO) arrester has no spark gap. That removes the coordination problem of gap firing and gives a smoother, more repeatable protective characteristic. The cost is that the ZnO stack must be perfectly manufactured — which is exactly what the type test checks.

2. Inside the Arrester: ZnO and the V–I Curve

The active element is a column of zinc-oxide varistor discs. Each disc is a ceramic of ZnO grains in a Bismuth-rich boundary layer; the boundary acts as a voltage-dependent resistor with an extremely non-linear characteristic. Below a ‘knee’ voltage the disc is almost insulating; above it, resistance collapses and current flows freely while the voltage across the disc stays nearly constant.

• The knee sets the protective level — it is referenced to the 1 mA direct current (the DC reference voltage, U1mA).
• The residual voltage is what appears across the arrester at the rated discharge current (e.g. 8/20 µs, 10 kA or 20 kA). It is the number that protects your transformer.
• The housing is a polymer (silicone or EPDM) weathershed moulded over the stack, with a field-grading ring at the line end to control the electric-field concentration.

3. What the Type Test Must Prove

• Residual voltage (lightning, 8/20 µs). Measured at the nominal discharge current and at higher currents (e.g. 5, 10, 20 kA) to confirm the clamping level.
• Steep-current impulse. Residual voltage under a 1/5 µs or 1/20 µs steep front — the worst case for transformer turn-to-turn insulation.
• Switching-current impulse. Residual voltage under a slow 30/60 µs switching surge (e.g. at 0.5 kA / 508 A) — protects against switching overvoltages.
• Long-duration discharge. Energy-handling capability under a 2 ms rectangular current; confirms the stack will not thermally runaway.
• Temporary overvoltage (TOV). Endurance at power-frequency overvoltage to prove the arrester survives a system fault-induced TOV without thermal collapse.
• High-current (100 kA) withstand. A short-line-fault / fault-current conditioning impulse proving the arrester does not explode under the maximum possible current.
• Pollution & ageing. Salt-fog, humidity and accelerated-ageing tests on the housing.

4. Verified Ratings: 3-36 kV to 220 kV

The following ratings are taken from XinNeng type-test certificates. Distribution class (KEMA) and station class (China EPRI / CEPRI under GB/T 11032) are reported separately because they use different standards and discharge currents.

The 66 kV and 220 kV models are railway/substation-class polymer-housed metal-oxide arresters with capacitor grading; both passed the full GB/T 11032-2020 programme including a 40 kA 8/20 µs discharge test, partial-discharge ≤ 10 pC at 1.05 Uc and RIV ≤ 500 µV. Re-test is recommended by the laboratory before 2028-03-31.

5. Choosing Ur, Uc and the Nominal Discharge Current

Three numbers define an arrester for your system:

• Rated voltage Ur. The highest continuous voltage the arrester can withstand plus its TOV duty. Rule of thumb: Ur should be at least ~1.25 × the system’s maximum continuous operating voltage for effectively-earthed systems, and higher for isolated-neutral networks.
• Continuous operating voltage Uc. The actual system voltage the arrester sees continuously — must be below Uc with margin, or the arrester ages prematurely.
• Nominal discharge current In. 10 kA for distribution, 20 kA for most substations, and 40 kA for stations exposed to very high fault levels or direct strokes. Specify In before you request a quotation.

Always pair the arrester protective level (residual voltage) against the equipment’s basic insulation level (BIL). The residual voltage at the rated discharge current must be below the BIL with a suitable coordination margin — typically the protective ratio is specified by the equipment standard.

6. Standards That Govern Arresters

7. Procurement Checklist

1. State the system voltage, earthing arrangement and maximum continuous operating voltage.
2. Confirm Ur ≥ required value and Uc ≥ actual system voltage with margin.
3. State the nominal discharge current In (10 / 20 / 40 kA) per your exposure.
4. Ask for the residual voltage at In and confirm it is below the protected equipment BIL.
5. Require the type-test certificate from a recognised laboratory (KEMA, CEPRI, XIHARI) with stamp and signatures.
6. For 66/220 kV, confirm the 40 kA 8/20 µs discharge test and the re-test date.

Frequently Asked Questions

What does a 10 kA nominal discharge current rating mean?

It is the class current at which the arrester’s residual voltages are measured and coordinated with the equipment insulation, not the current the arrester can only survive once. The KEMA-tested family in this article is a 10 kA class distribution arrester covering 3\u201336 kV.

What is residual voltage and why does it matter?

Residual voltage is the voltage that appears across the arrester terminals while it is discharging a surge current \u2014 the clamping level your transformer or cable actually sees. The tested unit clamps at 7.61 kV under a 5 kA lightning impulse and only rises to 9.02 kV at 20 kA, a barely 1 kV spread that is the hallmark of a good ZnO varistor.

Does the arrester need a grading ring?

On polymer-housed arresters at distribution voltages a grading ring evens the electric field at the live end, improving the voltage distribution along the varistor column and the pollution flashover behaviour. The construction shown in Figure 1 includes one at the line end.

How is a surge arrester different from a fuse or a disconnector?

A surge arrester protects insulation by diverting transient overvoltages to earth and then returns to an insulating state; it never interrupts load or fault current. A fuse interrupts fault current and must be replaced, and a disconnector only provides visible isolation when the circuit is already de-energised.

Summary

• Pain point: a wrongly specified or poorly made arrester either fails to protect or fails itself — the type test is the only proof.
• Verified data: distribution 3-36 kV at 10 kA (IEC 60099-4, KEMA) with residual 8.19 kV at 10 kA; 66 kV YH10WR(Z)-90/236 (Ur 90 / Uc 72.5) and 220 kV YH10W-216/562 (Ur 216 / Uc 168.5) at 40 kA 8/20 µs, GB/T 11032-2020.
• Selection: size by Ur, Uc and In; coordinate residual voltage against equipment BIL.
• Verification flag: 10/35/110 kV CEPRI model numbers come from scanned certificates and must be confirmed visually before publication.
• Action: buy against the certificate — confirm Ur/Uc/In, residual voltage and the issuing laboratory.