UBZ-302 has been designed for protection of asynchronous induction motors ranging from 2.5 kW to 30 kW that use of integrated current transformers and 30 kW to 315 kW through use of external current trnsformers, including in circuits with insulated neutral.
UBZ-302 provides for electric motor protection in case of:
- poor quality supply voltage (unacceptable voltage surges, phase loss, incorrect phase sequence and phase coincidence, phase/line voltage imbalance);
- mechanical overloads (symmetrical phase/line current overload);
- exceeding the negative sequence current threshold;
- phase current imbalance without overload, induced by the insulation fault inside the motor and/or the lead cable (the current imbalance factor is compared to the voltage imbalance factor using negative sequence);
- loss of motor torque (“dry stroke” for pumps) – protection based on the minimal starting and/or operating current;
- delayed motor start or rotor locking;
- abnormally low insulation level between the fixed coil and frame (testing before motor startup);
- ground fault of the stator coil during operation – protection against ground leakage current;
- motor thermal overload;
- coil overheating (measuring the coil temperature with integrated temperature sensors, or the body temperature with external temperature sensors).
For each protection type, automatic reclosing (ARC) can be enabled or disabled.
The device provides for electric equipment protection by means of controlling a magnetic starter (contactor) coil.
The device detects the presence of load currents when the load relay is open (when the load relay is open and the functional relay is in the star-delta mode). In this case the Unit initiates the alarm of external Magnetic Starter (further in text as MS), which starts the engine, until the unit or the control of engine currents are switched off while the load relay is deactivated.
