The UBZ-304 Universal Electric Motor Protection Device is designed for protection of asynchronous electric motors having power of 2.5 to 315 kW, with the use of external standard current transformers having output current of 5 amperes.

The UBZ-304 can operate in the mains with isolated neural as well as with solidly-grounded neutral.

The device is equipped with the panel.

The UBZ-304 provides continuous control of the mains voltage parameters and RMS phase (line) currents of the three-phase electric equipment of 380V 50Hz, as well as the electric motor insulation resistance test.

The UBZ provides electric motor protection in the following cases:

• when the mains voltage is of poor quality (unacceptable voltage fluctuations, phase interruption,  violation of phase sequence and phase coincidence, phase/line voltage imbalance, decrease of mains frequency below the specified one and (or) increase of mains frequency above the set one)
• when mechanical overloads (symmetrical phase/line current overloads) occur
• when reverse sequence of the current threshold occurs
• when phase current imbalance (without overload) occurs that is induced by the insulation fault inside the motor and/or the lead cable (comparison of current imbalance factor with voltage imbalance factor based on negative sequence)
• when motor torque is lost (“dry run” for pumps) – protection based on the minimum inrush and/or operating current
• when start delays or locked rotor occurs
• when insulation level between the fixed coil (stator) and frame is abnormally low (test before motor start).
• when stator winding ground fault takes place during operation – ground leakage current protection
• when motor thermal overload occurs
• when winding overheating occurs (winding temperature is measured by the integrated temperature sensors, or frame temperature is measured by the external temperature sensors).