Frequency Converter

How come motors for 50Hz were selected, if the grid supply is 60Hz?

It was lack of information from the client at proposal stage...

Please suggest if there is any solution?

There are plenty of solutions, depending on the numbers and sizes of motors, which information is missing from the original post.

Pretty basic information. Did you get lucky on the voltage guess?

To be fair, I am currently working with a client that is in the process of converting 1/3 of their paper mill from 50 Hz to 60 Hz.

The mill is just over 100 years old. When it was built 50 Hz was standard. They put in a dam and ran their own generators.

Over the following years the utility companies standardized on 60Hz, leaving this small pocket of 50Hz.

The plant expanded and the new machines went on a 60Hz grid.

The mill could make money selling power to the now established utility company so they installed a frequency converter - rotating style, so they could swap power back and forth.

90 years later, the hydro power plant was sold off to raise capital.

Another few years later the 50 HZ turbine goes up in smoke and the power agreement with the new owners of the hydro electric plant has lapsed, so now the mill uses the freq converter to run the remaining pocket - but the AC machines are now getting long in the tooth, about 50 years old, and starting to have issues.

So - my project is to see what is required to change the remaining pocket from 50 Hz to 60 Hz -- but it is not going anywhere because the $ involved are too much for a newsprint machine. (I suspect they will shut down the machine first.)

he's the best / simplest/ most reliable/ most efficent frequency converter:

take a 60 hz prime mover, use it to power a 50 hz generator on a straight shaft.

what are the alternate solutions? get 60 hz motors?

no, no use synchronous machines! 10 and 12 pole machines.

You're wasting your time.

The OP has no concept of what you just said.

One look at his previous posts will show that he is not qualified to work with electricity. Especially high voltage.

He's a candidate for a Darwin award.

I would use synchronous machines for the freq conversion - then the frequency conversion is dead nuts on.

10 pole and 12 pole synch motors.

I agree with the 60HZ prime mover driving a 50 HZ generator - but you must choose the correct number of poles for the machines. Typically synchronous machines are used and the 60HZ machine will have twelve poles, and the 50HZ machine will have 10 poles. The connecting shaft speed will be 600 RPM, and the frequency conversion is exact.

Consider changing jobs.

You don't seem to be well suited for working with electricity.

Adjust the transformer tap to 480V so that V/f is same(400/50 &480/60).

Navneet,

Why do not you install VFD (Variable Frequency Drives). You will have to install one VFD for each motor.

VFD are easily available in the market. Not only 50HZ, you can set each motor to desired speed to optimize output.

Advantage of VFD shall be:

1. Better efficiency than a large common frequency convertor (say motor generator set).

2. Better reliability.

3. Easy to find (ABB, Siemens, Rockwell Automation, Mitsubishi, Hitachi and many more brands at competitive prices are available).

4. It may be possible that even after going to common 50Hz frequency convertor some of drives may not produce the desired output - but if you are using individual VFDs, you can set the speed of each auxiliary anywhere upto 60HZ to get desired output from the plant.

Only disadvantage will be:

1. Lot of Harmonics in Power Supply from VFDs. To minimize harmonics, when you select VFD, ensure that these are with 12 pulse rectifiers.

2. get information on harmonics from VFD manufacturer or use standard IEEE curve for 12 pulse rectifier, depending upon maximum load current of all motors and value of Direct Axis Sub-Transient Reactance (Xd"), calculate distortion at Terminals of alternator. If it below 7% - no problem. It it works out to more than 7% Install Harmonic Filters to limit distortion.

As these Filters are generally capacitive will improve PF and thus efficiency of your power plant up to 2%.

Additionally you may have to order a 3 phase low pass filter (will not cost more that $100) in the sensing supply of AVR of the alternator for stable operation of AVR.

Best of luck

Ramesh

Re: putting VFDs on everything.

A). This concept is assuming all of the loads are AC induction motors

B). No VFD is better than 97% efficient. So unless there is some other energy saving advantage to running at varying speeds (such as process control in centrifugal machines), using a VFD solely as a frequency converter will cost a MINIMUM of 3% more in energy consumption, PERMANENTLY, as in forever. That adds up to a LOT of money over time.

What do you think is the efficiency of a motor generator set (Frequency converter of the rating of few MW for a Paper Mill)? Best efficiency of motor is 96% and of alternator of another 96%.

Hence the net Efficiency of converter is .96 x .96 = 92%.

Which is better, a frequency converter of 92% or using VFD or 97%?

Above efficiency is at load between 75% and 100% which may not be the situation always - so overall efficiency of power source by using frequency converter can be still poorer.

Further when you are running a plant which was designed for 60HZ straight at 50% you may not be able to balance or achieve an equilibrium as efficiency and performance of all auxiliaries will not be in same proportional as 60HZ.

Then to achieve balance and steady unattended operation, the Plant engineer may end up in adding either orifices or regulating valves to match the performance of device in series with that of one behind it and another upstream.

To avoid all above and achieve efficient operation - VFD is a better option than Frequency Converter.

I have seen many power plants saving power by using VFD for Feed water Pumps and Induce and Forced Draft fans for boilers than waisting power in throttling of pump flow by orifice or increasing restriction in dampers.

Thus in all respect a VFD is better answer that Frequency Converter.

Intention is not to heart anyone but to express my experience in front of forum, it may benefit somebody.

While taken at face value, it would seem a VFD (Variable Frequency Drive) would be the solution, but its a drive that varies the Hz to control the motor RPM. As stated this will cost lots of money over time and NEVER give any ROI, if the correct calculations are done now it will be proven to be to expensive over time and not to be cost effective.

That is just for the drive... what about the effect the drive will have on the motors, are the motors VFD rated? What about harmonics? what about run life of the motor.

Here is a solution... sack the guy that did the design and get someone who knows what he is doing!

According to this, the supply in India is 50Hz.