Constant Water Pressure setup using Multiple Drives
SCENARIO
Use a Pressure Transmitter to measure water pressure in a pipe (use 4-20 mA Pressure Transmitter) and control the speed of 4 separate Drives based on a set Target Pressure – the Drives should start in sequence (and should only start if the first motor/s in the sequency already running are not able to achieve the target pressure). For example (see image later on) – the Leader Drive will be the first Drive to start running, and when it reaches 50hz and the pressure is still below the target pressure, the Follower 1 Drive will start running, then the Follower 2 Drive and then the Follower 3 Drive.
Please note that for Solar Drives this logic is somewhat adjusted – instead of using 50hz, the Start signal is set on a lower Frequency Reached value, thus, instead of triggering the next drive in the sequence when reaching full speed, the relay is set to trigger at a lower speed for the first drive (trigger frequency is increased slightly for each drive in the sequence). This is to allow for sudden drops in voltage (typically caused by sudden cloud cover) which might cause the drives to slow down momentarily (and would thus otherwise have caused all the Follower Drives to switch off because the Leader Drive slowed down momentarily). In addition to this the Solar Drives’ sensitivity (to PV input) is also adjusted (reduced for first the Drive and increased for each drive in the sequence).
When the measured water pressure (Pressure Transmitter Feedback) reaches the target pressure, the last Drive to start running will be the first to slow down (reduce Frequency) and keep slowing down until it reaches its Sleep Frequency (Hz) or until the pressure drops again. If the last running Drive reaches its Sleep Frequency and the pressure is still too high, the next Drive in the sequence should start slowing down. For example (see image later on) – if all 4 Drives are running and the target pressure is reached, the Follower 3 Drive will be the first Drive to start slowing down, and when it reaches its Sleep Frequency and the pressure is still above the target pressure, the Follower 2 Drive will start slowing down, then the Follower 1 Drive and then the Leader Drive. For this it is however important that the target pressures for the various drives are not all set the same (it’s important for the last Drive in the sequence to start slowing down first) – the Leader Drive should have the highest Target Pressure setting with the Target Pressure set somewhat less for each Follower Drive in the sequence. For example – set the Target Pressure for the Leader Drive = 4 bar, the Target Pressure for the Follower 1 Drive = 3.8 bar, the Target Pressure for the Follower 2 Drive = 3.6 bar and for the Follower 3 Drive = 3.4 bar.
To set the Drives to stop (Sleep) before reaching a speed of Zero Hz, a Sleep Frequency (and WakeUp Pressure) will be specified. When a Drive slows its speed down to the specified sleep Frequency, the Drive will continue to slow down to a complete stop. Once the pressure drops to below the WakeUp Pressure, the Drive will automatically start again. Set the WakeUp Pressure of the Leader Drive the highest and then reduce it for each Follower Drive, with the last Follower Drive having the lowest WakeUp Pressure.
It is also important that the Sleep Delay Time for the various Follower Drives are set to be relatively short (to prevent multiple Drives from starting to slow down simultaneously) – Set the Sleep Delay Time of the Leader Drive the longest and then reduce it for each Follower Drive, with the last Follower Drive having the shortest Sleep Delay Time.
Please note that for Solar Drives there are also PV Sleep/WakeUp Frequency parameters (and Delay Times) which can be used (the first Sleep function and last WakeUp function to be triggered will force the Solar Drive into Sleep Mode or WakeUp Mode.
WIRING
- Pressure Transmitter Wiring
The Pressure Transmitter will be wired to the Leader Drive (ensure AI2 input Jumper default position is set for mA), and then the Leader Drive’s Analog Output (0-10V) will be used to relay the Pressure Transmitter reading to all the Follower Drives’ AI1 inputs (ensure AI1 input Jumpers’ default position is set for V).
As an alternative, each drive can use its own Pressure Transmitter, in which case the reading does not need to be relayed from the Leader Drive to all the other Follower Drives.
- Digital Input and Relay Wiring
To ensure each Follower Drive can only activate (will then still only start depending on actual and target pressure settings) once the Drive before it in the sequence has reached full speed (50Hz) or Set Frequency Reached (for Solar Drives), each Follower Drive’s digital input (used for Run Command – Terminal Control Mode) will be connected to the Drive before its Relay Output (which is set to switch on once the drive before it reaches the required speed).
The Leader Drive will have a manual On/Off switch to start the system (the example includes a Intermediate Relay as well in order to quickly switch off the system during power failure to prevent Power Failure Errors and also to protect the Drives – this would not be applicable for Solar Drives).
PARAMETER SETTINGS
Please download the Excel File from HERE for all the parameter settings as used for this example (different sheets for VSDs and Solar Drives).
OTHER PROTECTION SETTINGS
The following protection feature should ideally also be set up:
* End of Curve Settings at least on the first drive – for VSDs, see FAQ Entry HERE, for Solar Drives, see FAQ And HERE.
* Dry Run on all Drives – for VSDs, see FAQ Entry HERE, for Solar Drives, see FAQ HERE.
