UBZ-301 universal electromotor protection unit (further referred to as the unit) is designed for continuous monitoring of the circuit voltage parameters and phase/line RMS currents of three-phase 380V/50Hz electrical equipment, primarily, of induction asynchronous motors (EM) with wattage rating from 2.5kW up to 315kW, as well as those with isolated neutral line.
Three device versions are manufactured, with differentiation by current ratings:
- UBZ-301 5-50A;
- UBZ-301 10-100A;
- UBZ-301 63-630A.
The unit provides full and effective protection of electrical equipment by de-energizing and/or disabling its start in the following cases:
- when the mains voltage is of poor quality (unallowable voltage surges, phase loss, incorrect phase sequence and phase “coincidence”, phase/line voltage imbalance);
- when mechanical overloads (symmetrical phase/line current overload) take place. The unit performs overload protection with a dependent time delay;
- when phase/line current asymmetrical overloads induced by faults inside the motor occur. The unit provides protection against phase current imbalance and further disables an automatic reset;
- when phase current asymmetry without overload occurs, as induced by the insulation fault inside the motor and/or the power cable;
- when the EM shaft torque is lost (“dry stroke” for pumps).
- the unit provides protection based on the minimum starting and/or operating current;
- when insulation level to frame is abnormally low, a prestart check is performed, with start disabling in case the insulation is low;
- when stator winding ground-to-fault takes place during operation, the ground leak current protection is activated.
The unit provides for electric equipment protection by means of a magnetic starter (contactor) coil control.
The device performs the following functions:
- simple and accurate EM rated current setting with use of rated currents standard scale;
- setting the EM operating current that differs from standard values, considering allowable continuous overload;
- tripping in case of overload with a dependent time delay.
- the current-time characteristic is given in figure 2. This characteristic curve is described for a conventionally cold motor.
- EM heat balance differential equation is being solved in the operation process.
- This approach allows taking account of the preceding status of the EM and making a most valid decision on heat overload presence.
- This method also allows accounting for EM heating during startup and to restrict (at the customer’s option) amount of starts per unit of time;
- possibility to shift the current-time characteristic curve both along the current-axis (potentiometers 1,2) and along time-axis (potentiometer 3 – tripping time in case of double overload);
- setting trip thresholds for the minimum/the maximum voltage, line voltage & phase current imbalance, and for automatic reset delay time at the client’s discretion;
- fault type indication, the mains voltage presence indication, current range indication the unit is adjusted to, and load energization indication;
- allows for data exchange and transfer through the BO-01 exchange unit according to RS-485 protocol (BO-01 is supplied optionally).