Generator & Motor Arresters
3–20 kV · Ultra-Low Residual · Rotating Machine Protection

Specially designed for rotating machines — generator stator windings and large motor terminals have significantly lower impulse withstand (BIL) than static equipment. Standard distribution arresters won’t protect them adequately. These arresters deliver ultra-low residual voltage specifically matched to rotating machine insulation levels.

3–20 kVGenerator Voltage

5 kADischarge Current

Ultra-LowResidual Voltage

HY5WZ / HY5WDTwo Installation Types

10Standard Models

Request a Quote → See Specifications ↓

Product Gallery

HY5WZ Series — Busbar / Feeder Side

Installed at the power plant busbar or feeder side — the first line of defence before surges reach the generator. HY5WZ-17/45 = HY Polymer ZnO · 5 5 kA · W Gapless · Z Station/Plant type · 17 Rated kV · 45 Lightning residual ≤kV.

Model	Sys. kV	Ur kV	Uc kV	DC 1mA ≥kV	Lightning ≤kV	Switching ≤kV	Steep ≤kV	2ms A
HY5WZ-5/13.5	3	5	4.0	7.5	13.5	11.5	15.5	150
HY5WZ-10/27	6	10	8.0	15.0	27.0	23.0	31.0	150
HY5WZ-17/45	10	17	13.6	24.0	45.0	38.3	51.8	150
HY5WZ-51/134	35	51	40.8	73.0	134	114	154	400
HY5WZ-84/221	66	84	67.2	121	221	188	254	400
HY5WZ-90/235	66	90	72.5	130	235	201	270	600

HY5WD Series — Direct Generator/Motor Terminal

Mounted directly at the generator or large motor terminals — the last line of defence, right where the rotating machine connects. Ultra-low residual voltage because generator winding BIL is the most sensitive in the power system. HY5WD-13.5/31 protects a 10.5 kV generator with lightning residual ≤31 kV.

Model	Generator kV	Ur kV	Lightning ≤kV	Application Example
HY5WD-4(3.8)/9.5	3.15	4 (3.8)	9.5	Small hydro generators, 3.15 kV
HY5WD-8(7.6)/18.7	6.3	8 (7.6)	18.7	Industrial motors, 6.3 kV
HY5WD-13.5(12.7)/31	10.5	13.5 (12.7)	31	Thermal power generators, 10.5 kV
HY5WD-20/45	15.75	20	45	Large generators, 15.75 kV
HY5WD-23/51	18	23	51	Gas turbine generators, 18 kV
HY5WD-25/56.2	20	25	56.2	Large steam turbine, 20 kV

📄 Need a Datasheet?Full specs with terminal connection details for your generator rating. Get Datasheet →

Why Standard Arresters Don’t Work for Generators

The Problem	Generator stator winding BIL (Basic Impulse Insulation Level) is typically only 1.25× the rated voltage — much lower than the 3–4× margin that transformers and switchgear are designed to. A 10.5 kV generator may have a BIL of only ~30 kV. A standard YH5W-12 arrester has a residual voltage of 36 kV — too high to protect the winding.
The Solution	Generator-class arresters use specially selected ZnO blocks with a steeper non-linear curve at low currents — producing a residual voltage up to 30% lower than standard distribution arresters at the same rated voltage. This brings the protection level below the generator’s actual BIL.
HY5WZ vs HY5WD	HY5WZ — bus/feeder side: broader voltage range (3–110 kV), moderate residual reduction. HY5WD — direct terminal: generator voltage only (3–20 kV), maximum residual reduction, closest to the machine.
Associated Standard	JB/T 8952 (Chinese standard for gapless metal oxide arresters for AC power systems). IEC 60099-4 testing adapted for lower residual voltage verification.

Where These Are Used

🏭 Thermal & Hydro Power Plants

HY5WZ at the generator busbar, HY5WD at each generator terminal — layered protection for the most expensive rotating asset in a power station.

⚙️ Large Industrial Motors

HY5WD directly at motor terminals for critical drives — pumps, compressors, fans in refineries, steel mills and mining operations where motor downtime costs exceed the motor itself.

🔌 Generator Step-Up (GSU) Transformer LV Side

HY5WZ on the low-voltage side of GSU transformers — the interface between generator and transformer where reflected waves from HV switching can damage the LV winding.

🌬️ Wind Turbine Generators

Compact HY5WD arresters integrated in wind turbine nacelle switchgear — protecting the generator from lightning surges via the blade and tower.

Frequently Asked Questions

Can I just use a standard distribution arrester for my generator?

No. Standard distribution arresters (e.g. YH5W-12 with 36 kV residual) have too high a clamping voltage for generator insulation. Your generator winding could fail before the arrester even activates. Generator-class arresters are specifically designed for the lower BIL of rotating machines.

What generator information do you need to recommend the right model?

Rated voltage (kV), rated power (MW or MVA), BIL if known, earthing type (solid/resistance/isolated), and whether it’s a new installation or retrofit.

What’s the difference between HY5WZ and HY5WD in practice?

HY5WZ — install at the busbar/feeder in the plant switchgear room (easier access, upstream protection). HY5WD — install at the generator terminal box itself (closest protection, lowest residual). Many plants use both in series for layered protection.

Are these only for large utility generators?

No — they are sized for any generator or motor from 3 kV to 20 kV. Small hydro (3.15 kV), industrial CHP, standby diesel generators, and large mining motors all benefit from proper rotating-machine-grade arresters.