Variable Speed Drives

<...ensure that the VSD can be used for...constant flow...>

What will be needed is a flowmeter and a proportional+integral controller.

VFD's are happy running at a constant speed.

If you are really serious about this, contact three suppliers here Search GlobalSpec and tell them what you need.

Use their experience to help you.

How does keeping the flow constant ensure optimum efficiency, especially if pressure conditions change? The VFD part of all this is fine, but the main concept seems questionable.

Dear Mr. Akram Khan,

In addition to the CR4 MEMBERS SUGGESTIONS, I want to SUPPLEMENT that

1. Pl. Specify the Percentage of Hormonics, for 5th, 7th, 11th and 13th in terms of Voltage and Current. If not specified, VFD manufacturers adopt their own Standards which will be a problem, if it is not with in the Standards.

2. Find out from the offers the Level of Heat to be DISSIPATED by VFD while working on Full-Load.

Thanks,

DHAYANANDHAN.S

Sir,

Please note that whenever you chop the waveform your power factor gets affected.

For such a large load You may end up more charges to utility supplier. Please put variable capacitor bank to adjust the power factor.

Dear Mr. Kiranwawathe,

It is OK. Where do you suggest to add the capacitor bank.?

Thanks,

DHAYANANYDHAN.S

Horrible horrible answer, please refrain from posting things that you have no clue about. If someone were to take your suggestion seriously without very specific engineering, they could blow up a VERY expensive VFD!

VFDs inherently present a near unity power factor to the supply already, there is NO NEED for variable capacitors or any sort of capacitors, unless they are part of a specifically engineered harmonic filter solution designed for a specific drive in a specific installation where existing harmonics have been measured and accounted for in the design.

What JRaef says here is important. I'll add that the engineered harmonic filters I am familiar with also include inductors, to form a tuned LC circuit that is very effective at trapping the specified and unwanted harmonics before they get reflected back to the power line.

Another post has mentioned the question of whether the motor is designed for application with a VFD. This is because the windings within the motor present a very different impedance than the feeder to the motor, so the higher frequency harmonics in the VFD output get reflected, thus (approximately) doubling the voltage in the first few turns of the winding. Motors designed for VFD use have insulation on their windings that is with a higher voltage rating, to withstand this higher effective voltage. There are methods for minimizing or eliminating this problem, so a VFD can be applied to a motor not rated for VFD use, but this must be part of the overall design from the beginning of the project.

--JMM

You may want to look into a Magnetic drive to solve this issue. One company I am somewhat familiar with is Magnadrive. http://www.magnadrive.com/ You can control your flow with this type of device.

what type of pump are you using?

what is the OR of that pump at different frequencies?

Is the motor rated for a VSD/VFD application?

What is your required flow rate, and can the pump match your requirements at the various frequencies? What does the pump curve tell you?

If your motor is a DOL started motor using 60Hz then the RPM of the motor & pump will be constant, ( plus or minus) therefore the flow will be constant. As for inrush current.. have you thought about a "soft-starter"?

1. VFD is costly equipment. However its higher cost can be justified if the driven pump needs variable flow. Power drawn by the motor at reduced speed will be less, thus ensuring energy saving.

2. I n a retrofit application the existing motor may not be suitable for VFD application, because of presence of harmonics. Harmonics is having influence on increased core loss and shaft current which may find a path through the bearing to earth and back unless the bearing is insulated.

3. The motor will require cooling independent of motor speed with the help of separate fans fed from an independent power supply.

4. In case of high inertia of driven equipment use of VFD has an added advantage that it can deliver rated torque at lesser speed during starting with very low starting inrush current. Low starting current therefore doesn't cause any stress on the system particularly where the supply network is weak with low fault level

In your case there is no apparent reason for adopting VFD drive as there is no need for variable flow. Moreover the driven equipment i.e. pump being a low inertia equipment doesn't call for VFD for starting purpose. The motor is 3.3 kV, 500 kW motor, so starting current with DOL starting will be approximately 600A.

important point here.. not all VSD's are rated for high voltage, therefore they will require as "step down" & "step up" transformer.

More cost, more hardware, more harmonics, more losses.. more headache!!

ps: I don't know of VSD's rated at 3.3Kv... always willing to learn something new!!