The universal motor protection unit UBZ-301 (5-50A) is designed for continuous monitoring of the mains voltage parameters and the current values of phase/line currents of three-phase equipment 380 V / 50 Hz, primarily induction motors (EM) with power from 2.5 kW to 25 kW, including in networks with an isolated neutral.

Three versions of the device are available by current ratings:

• UBZ-301 5-50A
• UBZ-301 10-100A
• UBZ-301 63-630A

The device provides complete and effective protection of electrical equipment by disconnecting it from the mains and/or blocking its start in the following cases:

• low-quality mains voltage (unacceptable voltage surges, phase breaks, phase alternation and phase sticking, phase/line voltage imbalance)
• mechanical overloads (symmetrical overloads in terms of phase/line currents) - overload protection with time-dependent delay
• asymmetric overloads in phase/line currents associated with damage inside the motor - protection against phase current distortions with subsequent reclosing prohibition
• asymmetry of phase currents without overload associated with insulation failure inside the motor and/or supply cable
• loss of torque on the ED shaft (‘dry running’ - for pumps) - protection by minimum starting and/or operating current
• unacceptably low level of insulation on the casing - check before switching on with start blocking in case of poor insulation
• stator winding earth fault during operation - protection against earth leakage currents
• The unit provides protection of electrical equipment by controlling the magnetic starter coil (contactor)

It performs the following functions:

• simple and accurate setting of the rated current of the ED, using a standard scale of rated currents
• Setting the operating current of the motor, which differs from the standard values, taking into account the long-term permissible overload
• overload tripping with a dependent time delay
• The current-time characteristic is built for a conditionally cold motor
• (In the process of operation, the differential equation of the heat balance of the motor is solved, this approach allows taking into account the previous state of the motor and making the most reliable decision on the presence of thermal overload, this method also allows taking into account the heating of the motor during starts and limiting (at the request of the customer) their number per unit of time)
• the ability to shift the current-time characteristic both along the current axis and the time axis
• setting of trip thresholds for minimum/maximum voltage, line voltage and phase current unbalance, as well as automatic reclosing time at the customer's discretion
• indication of the type of fault, availability of mains voltage, current range for which the unit is configured and load switching on
• via the exchange unit BO-01 allows the exchange and transfer of information via the RS-485 protocol (BO-01 is available on request)