Siemens MICROMASTER 440 Operating Instructions Manual

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3 Functions Issue 10/03MICROMASTER 440 Operating Instructions142 6SE6400-5AW00-0BP0voltage lies above the chopper switch-in threshold VDC chopper . This means that thebraking module is not active in normal operation when motoring.The chopper resistor is only designed for a specific power and a certain load dutycycle and can only absorb a limited amount of braking energy within a specific timeperiod. The chopper resistors, specified in MICROMASTER Catalog DA51.2, havethe following load duty cycle.Power0.05 t [s]12240PDB1P100PDBP100= continuous power= permissable power for 12 s every 240 sDBP20= ⋅Fig. 3-57 Load duty cycle – chopper resistors (MICROMASTER Catalog DA51.2)This load duty cycle (P1237 = 1 → 5 %) is saved in MICROMASTER. If the valuesare exceeded due to the load required, then when the maximum acceptablebraking energy is reached, the load duty cycle monitoring controls the chopper sothat the value is reduced to the value entered in parameter P1237. This means thatthe energy to be dissipated in the chopper resistor is reduced which means that theDC link voltage quickly increases due to the regenerative energy available and thedrive inverter is shutdown (tripped) due to a DC link overvoltage condition.If the continuous power or the load duty cycle for a resistor is too high, then thecontinuous rating can be quadrupled using 4 resistors in a bridge circuitconfiguration. In this case, in addition, the load duty cycle must be increased usingparameter P1237 from P1237 = 1 (→ 5 %) to P1237 = 3 (→ 20 %). When usingthe bridge circuit, the overtemperature switch of the resistors should be connectedin series and incorporated in the fault circuit. This guarantees, that when a resistoroverheats, the complete system / drive inverter is shut down.ChoppercontrolB-B+RP1237 = 1(5 %)ChoppercontrolB-B+RP1237 = 3(20 %)RR RFig. 3-58 Increasing the level of braking energy which can be absorbedThe continuous power and the load duty cycle are modified using parameter P1237(setting values, refer to Fig. 3-59a). If the load duty cycle monitoring switches fromthe peak power (100%) to the continuous power, then this is dissipated for anunlimited length of time in the braking resistor (refer to Fig. 3-59b). Contrary to the