Korea Ever-Power · YB2 Series · Wastewater Treatment Drive Guide

Anaerobic digester building interiors, biogas storage balloon interiors, biogas pipe galleries, and areas within 1 m of biogas valve and fitting clusters. Biogas is primarily methane (60 to 70%) with CO₂ and traces of H₂S. Methane is classified IIA (auto-ignition 537°C). The combined biogas mixture is classified IIB due to the H₂S content. All motors in Zone 1 digester areas must be YB2 Ex d IIB T4. This includes biogas compressor motor drives, digester mixing pump motors, and any electrical equipment mounted in the digester building.

The area outside the digester building within 3 m of any ventilation outlet, access hatch, or pipe entry is typically Zone 2. Biogas may be present in this perimeter zone during maintenance activities, ventilation system anomalies, or minor gas leakage from flanged joints. Outdoor motors in Zone 2 perimeter areas must be YB2 Ex d IIB T4 or equivalent Zone 2 certified motors — standard Y2 motors are not acceptable even in outdoor Zone 2 areas.

Hydrogen sulphide is released from sludge in concentrations that are typically below the explosive range (LEL 4% in air) but above the toxic odour threshold and above the level that aggressively attacks copper, silver, and iron-based coatings. Sludge thickening areas, dewatering buildings, and sludge drying beds may not be classified as hazardous zones for explosion risk (if H₂S concentrations remain below 25% LEL), but all motors in these areas must be specified with H₂S-resistant coatings and sealed terminal boxes to prevent rapid corrosion of electrical components.

A covered digester building (common in cold climates where the digester must be protected from freezing) is classified as Zone 1 throughout its interior because biogas can accumulate within the building envelope at explosive concentrations if ventilation fails or during maintenance access to the digester. All motors inside the digester building — sludge recirculation pumps, mixing pump drives, gas compressor drives, and heat exchanger pump drives — must be YB2 Ex d IIB T4. The electrical classification applies even to motors in corridors and service areas within the building boundary.

Egg-shaped or cylindrical digesters with a floating gas cover have Zone 1 above the gas cover and within 1 m of the gas relief valve, gas outlet connection, and level measurement connections. Zone 2 extends from 1 to 3 m beyond the Zone 1 boundary. Any external mixer motor mounted on the digester wall or roof within the Zone 1 boundary must be YB2 Ex d IIB T4. External agitator drives on the digester wall may be in Zone 2 if their mounting position is more than 1 m from any gas outlet; confirm with the hazardous area classification drawing for the specific digester design.

Sludge pump stations, thickener drives, dewatering press drives, and centrifuge drives in outdoor sludge handling areas require IP55 as a minimum. Hose-down cleaning of concrete surfaces and equipment regularly directs water jets toward motor enclosures. IP55 protection against water jets prevents water ingress that would cause insulation deterioration in the H₂S atmosphere.

Cast iron frames (standard on YB2 Ex d series in IEC 112 and above) are more resistant to H₂S corrosion than painted aluminium frames used on standard Y2 motors up to IEC 100. When the paint coating is breached — by mechanical impact or UV degradation — the exposed aluminium oxidises and H₂S accelerates the corrosion. The YB2 cast iron frame with marine-grade epoxy primer and polyurethane topcoat provides superior longevity in H₂S environments.

H₂S attacks copper cable terminations and brass cable gland bodies rapidly — copper sulphide deposits form on terminal surfaces, increasing contact resistance and potentially causing connection overheating. The YB2 sealed IP55 terminal box prevents H₂S from entering and attacking the terminals. Specify tinned copper or stainless steel terminal inserts where H₂S concentrations above 10 ppm are expected.

The Korea Ever-Power YB2 Ex d IIB T4 provides a single motor specification that covers both Zone 1/2 explosion protection for biogas areas and the superior corrosion resistance needed in H₂S sludge handling areas. The cast iron IP55 enclosure resists H₂S corrosion for service lives exceeding 10 years in wastewater environments. The Ex d IIB T4 certification covers both methane (IIA) and hydrogen sulphide (IIB) gas groups with a single motor type, simplifying the motor specification and spare parts inventory across the entire wastewater plant. The complete YB2 range is in the explosion-proof motor section. For large wastewater plant pump and blower motor specifications above 75 kW, contact Korea Ever-Power.

Biogas combined heat and power (CHP) engine cooling water pump drives and engine room ventilation fans. Engine room is Zone 1 inside biogas engine enclosure and Zone 2 in engine room area. YB2 1.5 to 11 kW for cooling pump and fan drives within engine room boundary.

Biomethane upgrading plants (pressure swing absorption or membrane separation) compress biogas to grid injection quality. Compressor motor drives and all auxiliary pump and fan drives within the gas processing building are Zone 1. YB2 5.5 to 55 kW for compressor auxiliary drives.

Industrial wastewater treatment handling VOC-contaminated effluent from chemical, food, or pharmaceutical plants. Where effluent contains flammable VOC above 25% LEL in the treatment vessel headspace, Zone 1 or Zone 2 classification applies. YB2 IIB T4 for all motors in classified zones.

Screen conveyor drives, grit classifier motors, and screening compactor drives at the plant inlet works. Exposed to H₂S from incoming sewage; non-classified for explosion but corrosive environment. YB2 0.55 to 3.0 kW for inlet works drives in place of standard Y2 for extended service life.