Photo courtesy of astgroup.ca
In conventional applications, pumps or fan should be run at full speed, then pressure or flow should be controlled with a control valves hence some energy will be wasted when you throttling control valves. One of the major usages of VFD is cost saving through energy saving.
But we want to look from different angle of cost saving which is capital saving through removing some instrumentation and control valves and utilize WEG VFD with built-in PLC.
If you can replace one VFD with built-in PLC, you can remove control valve, independent PLC for throttling, additional sensors/ transmitters for motor speed, torque, flow element / transmitters, cabling, Junction boxes, installation stands for the transmitters and sensor.
In addition, some other parameters such as motor speed, motor torque, motor current which are freely available when SoftPLC code is used.
There is a SIL2 IEC 61508 STO relays that can stop WEG VFD in case of requirement for Shutdown command, from safety sensors such as vibration protection system.flow element / transmitters, cabling, Junction boxes, installation stands for the transmitters and sensor.
Below are few applications that can utilize built-in SoftPLC with WEG VFD solution:
Header pressure control with Multi Pump Control:
In traditional method, N+1 pump will be connected to the same header, and header pressure to be controlled with control valve downstream of header or flow control valve on each individual pump discharge. In addition, zero or no-flow sensor (transmitter or switch) at down stream of each pump required, as well as pressure monitoring of upstream and down stream of each pump. Flow or pressure will protect the pump by tripping the pump on PAHH, FALL or PALL.
It can be done with one or more WEG VFD, as per below schematic diagram:
WEG Pump Genius Multiplex application for four pumps in parallel controlled by CAN communication interface
For zero flow control, you just need to set a protection in SoftPLC code if the torque percentage is less than a value (e.g. 20%) and motor is at certain speed. All of the auxiliary pumps such as lube oil pump can be programmed in VFC softPLC. Hence costly control valves, flow transmitters can be removed and the same for additional hook-up, cables, JB, tray, etc.
WEG Pump Genius Multipump floating control for five pumps in parallel
Power connection of the WEG Pump Genius Multipump floating control for five pumps in parallel
Control of air flow/ pressure with Fan
Control of air flow/ pressure with Fan | Photo courtesy of astgroup.ca
If built-in SoftPLC with WEG VFD is used, you can connect the pressure or flow sensor to WEG VFD and set internal PID controller to control the fan speed with respect to the set pressure or flow rate. As WEG VFD has DI, AI, you can have many interlocks for safety and similar to pump application, you can detect the fault with the internal parameters of WEG VFD, which could be more effective in compare to some vibration protection sensors.
Differential pressure of filters can be connected to WEG VFD with SoftPLC and get respective alarm or fault trip as required set pressure or flow rate. Traditionally, damper can be used for airflow or pressure control, and for fan protection you should be using the vibration sensor and run the fan on full speed.
By Elmir Rahimpour, Automation & Integration Specialist, WEG / V.J. Pamensky