Variable Frequency Drive Package
for Tulsa's Haikey Creek Waste Water Treatment Plant Project

This project was with the City of Tulsa, Oklahoma. Due to increased demand on their systems, the City of Tulsa decided to expand its Haikey Creek Waste Water Treatment Plant. In all, OSCO provided 9 variable frequency drives. Three of these were 25 HP units controlling thickened sludge vortex pumps. These units were designated TSP-1, TSP-2 and TSP-3. Eaton Cutler-Hammer AF-5000+ Variable Torque Drives (P/N AF-502507-0480) were used for these. Three 15 HP units powered progressing cavity sludge feed pumps, and were designated SFP-1, SFP-2 and SFP-3. Eaton Cutler-Hammer AF-5000+ Constant Torque Drives (P/N AF-501508-0480) were used for these. Three smaller 2 HP units were provided for control of polymer feed equipment, and were designated PFP-2, PFP-2 and PFP-3. Eaton Cutler-Hammer AF93 Variable Torque Drives (P/N AF93AG0C002D) In addition, we provided 2 master control systems for signal and drive selection for the PFP series and the SFP series. More on that below.

We used enclosures with outer and inner doors to house the VFDs. For each of the series, the engineers wanted room to add a fourth drive in the future. From left to right, the five cabinets house: TSP-1 and TSP-2; TSP-3 and (future) TSP-4; SFP-1 and SFP-2; SFP-3 and (future) SFP-4; PFP-1, PFP-2, PFP-3 and (future) PFP-4.

As is common with most of our variable frequency drive packages, all drives were equipped with a Hand-Off-Auto (HOA) selector circuit. In hand mode, an operator could start the drive and set speed points through the Softouch Operator Panel or the Manual Speed pot. In Automatic Mode, the drive could be switched on remotely via a relay contact, and would follow a 4-20mA signal for speed control.

Not as common was the necessity that the drives produce a 4-20mA signal based on the drive's ACTUAL speed for monitoring purposes. This was an easy addition to the AF-5000+ Drives. An optional Universal I/O board was added to each drive and simply wired in. This provided the 4-20mA output to the controller and power for the Softouch Operator Panel. No extra power supply board was necessary. The AF93 drives, however, only provided a 0-10V signal out... not a 4-20mA signal as required. To overcome this problem, we added an analog data transmitter. We used this as a current repeater/converter to isolate and convert the 0-10V output from the drive to the required 4-20mA signal for monitoring.

These are the three Polymer Feed Pump (PFP) Drives. The open space in the bottom could house a future PFP-4. Below that is the relaying for the Polymer Feed Pump Master Control (PFP-MC). These were built into the enclosures to eliminate the need for additional cabinets.

In addition to the above, all drives also featured an Elapsed Time meter, Drive Running indication and LOR Tripped (fault) indication.

On the Polymer Feed Pumps (PFP-x) and Sludge Feed Pumps (SFP-x) the engineers wanted to be able to enable any two drives at one time. The Master Control Cicuits were added for this reason. In each of the two Master Controls (PFP-MC and SFP-MC) were incorporated two selector switches. One switch selected between pumps 1 and 2, the other between pumps 2 and 3. Then, simple relaying was used to route the speed signals between the the control systems and the drives.

This cabinet houses two of the three Sludge Feed Pump (SFP) Drives. You can see the Sludge Feed Pump Master Control (SFP-MC) below the bottom drive. By using plexiglass windows installed in the outer doors, a level of security and convenience was provided. Un-authorized tampering can be averted by keeping the door locked. Yet an operator could still check the status of the drive by viewing the Softouch Operator Panel through the window.

Last modified: April 07, 2010

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