Regarding the feedback signal for the motor start/stop status in MCC, the display issue in DCS – what is the difference from hardwired connections?
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As the title suggests: Currently, the start/stop signals of many motors (especially variable-frequency motors) cannot be displayed in the DCS; it seems that they are displayed using one of the following two methods. As for the start/stop signals of pumps in the current DCS systems, I have come across two approaches: 1) Using the auxiliary contacts DI of the KM switches to send signals to the instruments (DCS) via RS485 communication; 2) Using soft connections within the MCC. What is the difference between these two methods? Why is the start/stop status of variable frequency motors displayed inaccurately in the DCS? (For example, the on-site control panel shows that the motor is in the on state, but the DCS indicates that it is stopped.) How can the start/stop status shown in the DCS (using red and green colors) be made consistent with the status indicated by the on-site control panel? That is, how are red and green used to indicate whether the motor is stopped or running? Through what soft connections in the MCC is the display of the start/stop status achieved? What is the actual role of the MCC?
Here, we only need one normally open contact; by default it is red (normally closed). When the motor is running, this normally open contact closes, sending a passive closed signal to the DCS
As for how to configure it in DCS, I can’t help with that; I don’t know how either
The only method I know is the first one: using KM’s auxiliary contact DI to connect to the instrument (DCS) via RS485 communication; there shouldn’t be any problems with that!
Your soft connection is also a form of communication. As for ensuring that the DCS shows the same values as the on-site signals, this can be done during the DCS configuration; it’s still a matter of communication configuration in the end.
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At least one thing is clear: the frequency converter is working, but the PV frequency is 0HZ; therefore, the motor on site is also stopped, even though the power supply is connected. The operating status displayed on the DCS should not be based solely on DI signals – it would be better to have a comparison, such as displaying a value when the operating frequency is greater than 1HZ
There is a fault in the communication between the MCC cards. The low-voltage frequency converters used are of the Shengnuo STDVFD P series, and the communication messages sent are corrupted, resulting in interference between the electrical communication signals. This prevents normal communication with Dongfang Electronics’ 1910 communication device; as a result, the status information of the pumps transmitted to the DCS cabinet and the main transformer control cabinet via the 1910 communication device is incorrect. The production facility cannot obtain accurate status information, and the main transformer control system is unable to record various details related to the low-voltage frequency converters