The universal motor protection unit UBZ-302-02 is designed for continuous monitoring of 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-302-02 provides protection for asynchronous motors with power from 0.25 kW to 3.3 kW when
when using built-in transformers and up to 315 kW when using external current transformers, including in networks with an insulated neutral.

UBZ provides protection for electric motors in the following cases:

• low-quality mains voltage (unacceptable voltage surges, phase breaks, violations of
• alternating and sticking phases, unbalanced line voltages)
• mechanical overloads (symmetrical overload by phase/line currents)
• exceeding the reverse sequence current threshold
• asymmetry of phase currents without overloading, associated with insulation failure inside the motor or
• insulation inside the motor or supply cable (comparison of the reverse current unbalance factor with the reverse voltage unbalance 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 level of insulation between the stator and the motor housing (check before switching on)
• stator winding short-circuiting to earth during operation - earth leakage current protection
• thermal overload of the motor
• overheating of the windings (the temperature of the windings is determined when using the built-in
• temperature sensors or the temperature of the housing when using external temperature sensors)