Pump motor failure, operation signal
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Where are the fault and operation signals for the pump motor sent from MCC to DCS, and under what circumstances do fault signals appear? Under what circumstances does a operation signal appear? Additionally, if the DCS receives a pump failure signal, does that mean the motor has stopped? In other words, is the fault signal related to the motor being in a stopped state?
The pump fault signals sent to the instrument via electrical means can be roughly divided into two categories: one of them is actually a pump shutdown signal. Because in chemical processing, there are some pumps that cannot be stopped; if they do stop, corresponding interlock measures must be taken. At the same time, normal operations are carried out through the DCS; therefore, any shutdown of the pump that is not caused by a DCS command, including shutdowns that occur without the use of the DCS, is considered an abnormal shutdown, and the DCS must be notified. Such fault signals often carry no other information. It means the pump has stopped. However, unlike the normal operating condition (pump shutdown) signal, it is not a feedback signal of the control room’s operational commands. Another approach is to transmit the key parameters of the pump, such as current, temperature, vibration, speed, and return flow, to the control room, where the DCS determines whether it is necessary to stop the pump. These parameters are not actually the objects being operated; they are used merely to determine whether the pump is functioning properly. So it is also called a fault signal. Strictly speaking, this is just a signal used to determine whether there is a fault. In fact, its function for DCS is merely to generate alarm or pump-stop messages. The most common types of fault signals in this category are current signals and the related over-limit settings.
There is a comprehensive motor protection system; does sending a fault signal to the DCS mean that the motor has stopped?
The motor operation signal is sent to the DCS via the auxiliary normally open contact (dry contact) of the closing relay. For industrial-frequency motors, our company generally does not transmit fault signals to the DCS; if such transmission is necessary, the fault signal is obtained from the motor’s comprehensive protection device and sent to the DCS, or in the absence of such a protection device, the auxiliary normally open contact (dry contact) of the thermal relay is used to send the signal to the DCS. Personal opinion; welcome to discuss
The fault signal can be the dry contact of the thermal relay. The operation signal should be the normally open contact of the contactor, right?