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Three Phase Overcurrent Protection

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We designed this three phase overcurrent protection to provide reliable operation of three phase loads like motors, transformers and power supplies in critical conditions. Using of singlechip microcontroller from PIC12C family of MICROCHIP permits to add additional functions. We use current-to-voltage transformers like current sensors. Using of programmable microcontroller permits software adjustment of starting current ignoring and the time of overload or phase missing, short response time and smooth adjustment of operating current in a wide range. This overcurrent protection unit permits the next additional functions: protection against phase missing, overvoltage, undervoltage or phase unbalance.

There are available two main versions - with three relays 10A/240 VAC for direct switching of the load and with one relay 10A/240 VAC for starting contactor switching. The second version has three modifications with maximum operating current 10A, 16A and 25A.Optionally we offer load short circuit protection.


Supply voltage V 220, 50Hz 220, 50Hz 220, 50Hz
Power consumption VA 2,0 1,35 1,35
Current adjustment range A 2-10 3-16 5-25
Max. starting current A 40 64 100
Response time ms 15 15 15
Time of overload adjustment range s 0,1 0,1 0,1
Overvoltage level V 255 255 255
Undervoltage level V 175 175 175
Level accuracy % 5 5 5

The action of the three phase overcurrent protection is the next: after turn-on the supply voltage the output settles in a "switch off" state. For about 100 ms it tests the presence of the three phases and the voltage level of each phase. If everything is OK, the output settles in a "switch on" state and for the time of overload the starting overcurrent do not cause switch off the load. After end of this time if the current of one of the three phases is bigger of the adjusted working current, the output settles in a "switch off" state and remains in this state. The phase missing, overvoltage, undervoltage or phase unbalance causes switch off the unit too. When the overcurrent protection switches off, it lights up a red LED. The repetitive switch on of the load is possible only after turning off and repetitive turning on the power voltage of the unit.

The three phase overcurrent protection offers in a plastic's case with overall dimensions 86x70x58 mm with clamp for mounting on a Eurobus. The electric mounting is made by clamps, serial to the three phases and "zero".

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