WEG DWE-3 Electronic Motor Protection Relay Class 20 High Inertia

The WEG DWE-3-S3-MT-CLS20 is the Class 20 trip class variant of the DWE-3 electronic motor protection relay, designed for three-phase induction motors driving high-inertia loads that require extended starting times before reaching rated speed. In Saudi industrial applications, high-inertia loads include large centrifugal fans (cooling tower fans, induced draft fans in furnaces and boilers), ball mill drives in cement plants at Yanbu and Jubail, large centrifugal pumps with significant flywheel effect, and conveyor systems with high belt mass.

Class 20 Trip Characteristic

The IEC 60947-4-1 Class 20 trip characteristic allows the motor starter to tolerate up to 7.2× FLC starting current for a longer period than Class 10 (20 seconds at 7.2× FLC vs. 10 seconds), enabling high-inertia motors to accelerate fully before the thermal element trips. Without Class 20 protection, a Class 10 relay would trip during the starting period of high-inertia loads, causing nuisance trip complaints and requiring manual intervention in Saudi industrial control rooms. The DWE-3-S3-MT-CLS20 eliminates these nuisance trips while maintaining full overload protection during running.

Saudi Industrial High-Inertia Motor Applications

Saudi Aramco's large induced draft fans in crude oil heaters at refineries typically have moment of inertia values (GD² values) requiring 15–25 second starting times. SABIC's large stirrer and agitator motors in polymer production require Class 20 or Class 30 protection to accommodate soft starting behaviour. Cement industry motors at Saudi Yanbu Cement, City Cement, and SAFCO's large granulation fans all require extended starting time protection available with the DWE-3-S3-MT-CLS20. Razz Middle East provides motor starting time calculations and relay class selection guidance as part of the DWE-3 technical support package.