The starting of the motor is supervised by monitoring the TRMS magnitude of all thephase currents or by monitoring the status of the circuit breaker connected to themotor.During the start-up period of the motor, STTPMSU calculates the integral of the I²tvalue. If the calculated value exceeds the set value, the operate signal is activated.STTPMSU has the provision to check the locked rotor condition of the motor using thespeed switch, which means checking if the rotor is able to rotate or not. This featureoperates after a predefined operating time.STTPMSU also protects the motor from an excessive number of start-ups. Uponexceeding the specified number of start-ups within certain duration, STTPMSUblocks further starts. The restart of the motor is also inhibited after each start andcontinues to be inhibited for a set duration. When the lock of start of motor is enabled,STTPMSU gives the time remaining until the restart of the motor.STTPMSU contains a blocking functionality. It is possible to block function outputs,timer or the function itself.4.10.4 Analog input configurationSTTPMSU has one analog group input which must be properly configured.Table 933:Analog inputsInput DescriptionI3P Three-phase currentsSee the preprocessing function blocks in this document for thepossible signal sources.Improper analog channel configuration causes a validation error if the analogchannels are not completely configured or they do not match with certain settings. Fortroubleshooting, check the contents of this chapter and also the preprocessing blocksin this document. The configuration can be written to the protection relay once themismatch is corrected.4.10.5 Operation principleThe function can be enabled and disabled with the Operation setting. Thecorresponding parameter values are "On" and "Off".The operation of STTPMSU can be described with a module diagram. All the modulesin the diagram are explained in the next sections.1MRS759142 C Section 4Protection functionsREX640 993Technical Manual
