from wye-delta to INVERTER

hi! i am planning to upgrade our existing system by using an inverter. I'm wondering if someone can help me. We have two pumps and we are using the conventional method which is wye-delta. The specifications of each pump: 100Hp, 440 volts, 3 phase. I'm planning to use the Omron model 3G3RV, 75KW, 440volts, 3 phase inverter. My problem is:
1. I have to maintain a 100psi pressure of the pump. In the conventional method, I am encountering less pressure of the pump. What will i do is to slightly open the switch to maintain the 100psi pressure again. If i will use inverter, is there a parameter that will detect less pressure and make automatic adjustments to maintain the 100psi pressure.
2. "The first pump is active, the second pump is reserve." If the first pump has trouble, can i program the inverter to switch to the 2nd pump?

Or if you can give me other suggestions in upgrading my system like different brand or specifications.

Also, can u send me the operation manual of your suggested inverter.

Thanks in advance for ur help...

Regards,
Abby

I know that Siemens Micromaster VFDs can work completely standalone in pump applications. It manages the starting/stopping and pressure regulation etc. by itself by means of the built-in digital and analog i/o - you have to add overload protection and contactors.
It can also handle applications with several pumps controlled by one VFD.

Being that this is one of the most important market segments in the VFD business, I guess that most other VFDs manufacturers have the same feature.

Not knowing much about your system as a whole.... I would say that the proposed inverter/pump setup sound kinda complicated. My 1st impression would be to replace the Y-D starter with a 6 wire Soft start setup, run the motor & pump at a constant speed, and use a pressure relief/bypass valve on the pump output to regulate pressure/flow. Choosing the right pressure releif valve would depend on weather or not it's a water or oil system. (what your pumping)

Dear invisible Guest, If you have your local inverter reps give you a visit they will tell you how fantastic there products are.

They can in a stand-alone setup control almost anything but the space shuttle.

Give them a try and you will be amazed how them Inverters are smart.

BUT ... ask them to give you 2 references where they are used in that fashion in your area, so you can visit the sites to have a feel for the technologie.

You might find that its often snake oil.

I always prefer to have a PLC doing the maths.

Pierre said:

I always prefer to have a PLC doing the maths.

Click to expand...

Pierre, Your giving me flashbacks. There are so many drives that are so smart these days, I cant think of a reason not to use them to their full capabilities. But then again it all depends on your application I guess...

I don't know about other VFD, but the AB Flex700 will work in PI mode.
Add a 4-20MA or 0-10V pressure transducer and feed the output back to VFD. Use this input to your PI feedback. Adjust your set point till you get 100PSI. The drive will maintain 100PSI thereafter.

A word of caution:
Make sure the feedback sensor won't get stopped up or rust. In other words have postive circulation and drain in the sensor path.
The 100hp drive will require extra protection, E-Stop, Isolation contactor, and control power. Your questions lead me to think that you may want an experienced person to do the job.

You can choose an ABB model ACS550 which has Pump/Fan Sequential Control standard. That software macro is similar to the Siemens macro mentioned above.

All you will need to add is a 4-20ma pressure transmitter connected to some point in the discharge side piping. The ABB drive internal +24VDC power supply will power the 4-20ma loop. Retain the existing starters for use as drive-controlled motor contactors.

With this system, you set a desired discharge pressure and the drive manages motor speed so that the pressure holds steady while the flow changes. You typically save significant energy over pressure regulating bypass valves and get a nice predictable pressure too.

I'm not certain what YOU mean by wye-delta, but if you have 6 phases (two sets of 120-degree 3 phase separated by 30 degrees from another set of 120-degree 3 phase; i.e. a dual secondary, one wye and one delta) available, then I'd consider a dual rectifier set up with some interphase reactors between them to insure current sharing.

Follow up this dual rectifier with the inverter (motor controller). Most VFD manufacturers offer an isolated inverter without the rectifier (together they're termed a VFD). Use the DC from the interphase reactors to feed the inverter. This whole process is done to lessen the harmonic impact of the VFD on the line.

Of course, if you DON'T have the dual transformer already, then the above approach is overkill. On a 100 Hp system, the benefits aren't worth the additional cost.

Most VFDs have built-in process control algorithms that you can use, but I suggest you go with a PLC, for more system-wide control, letting the VFD's inherent program just take care of the VFD. The PLC would be used for contactor control, system annunciations, panel drivers, etc. The VFD controls would just take care of keeping the motor at the speed determined by the PLC. The PID is done by the PLC, keeping the pressure (or whatever process variable you're controlling) constant.

I have to side with Pierre on this one. Let the VFD run the motor. Let the PLC run the application.