The UBZ-304 is designed to protect asynchronous motors with power from 2.5 to 315 kW when using external standard current transformers with an output current of 5 A.

The UBZ-304 can operate in networks with both isolated and solidly grounded neutral.

The device is designed as a panel device.

UBZ provides continuous monitoring of the mains voltage parameters, current values of phase (line) currents of three-phase electrical equipment 400 V 50 Hz and checking the insulation resistance of electric motors

UBZ-304 provides protection of electric motors in the following cases:

• Low-quality mains voltage (unacceptable voltage fluctuations, phase breakage, phase alternation and phase sticking, asymmetry of phase / line voltages, lowering the mains frequency below the specified one and (or) increasing the mains frequency above the specified one).
• Mechanical overloads (symmetrical increase in phase/line currents).
• Threshold exceeding by reverse sequence current.
• Asymmetry of phase currents without overloading due to insulation failure inside the motor and/or power supply cable (comparison of the reverse current asymmetry factor with the reverse voltage asymmetry factor).
• Loss of torque on the motor shaft (‘dry running’ - for pumps) - protection by minimum starting and/or operating current.
• Delayed motor start or rotor blockage.
• Unacceptably low insulation resistance between the stator and motor housing (check before switching on).
• Stator winding earth fault during operation - earth leakage current protection.
• Thermal overload of the motor.
• Overheating of windings (winding temperature is determined when using temperature sensors built into the motor or the temperature of the housing when using external temperature sensors).