Voltage Problem Solution

[Sazirul]

Hello Engineers! Hope you guys are doing well but I am not. Let me explain.
Last couple of month we are having imbalance voltage problem. We got the main power connection from our national grid. Our line voltage is 33KV. We are using two step down transformer. First one is 33/11KV second one is 11/0.415KV. Both transformer has individual auto tap changing panel. It automatically adjust the rated voltage 380-400V according to our machinery. But sometime our main line voltage drop at 26KV. Yes, transformer can adjust the output voltage by changing its tap position. It takes 30 seconds for each tap changing. But if there is a sudden voltage drop or up like 30 to 25 or 27 to 31 in a second then all machines inside the factory go offline and sometime electronic components like PLC, Inverter goes damage by this sudden millisecond voltage fluctuation. We tried a lot for solving this problem but failed. So guys, can you tell me how we can save our machines from this sudden voltage fluctuation?
Thanks in advance!

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[waross]

A motor-generator?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

There are a verity of facility sized power conditioner solutions available. All it takes is money. How often, how long are your sags?

 

[Sazirul]

Yes, we have plane to buy three gas generator 1500KW each but it will come within a year. We want a solution for this moment that we can save our machinery. Is there any system in HT side the we can control main line voltage. Our Supplier told us don't use too much control system in HT side.

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[waross]

You may try supplying the control circuits of the machines from un-interuptible power supplies with surge protection.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

What machines are in the factory?

If it's motor loads, then what Bill posted will work. Use a UPS system on the control circuits. Keep the controls alive and the motors connected to the grid and they will ride-through a voltage dip that is under 1 second.

Any system to regulate the line voltage to ride through transients will be expensive.

 

[waross]

Another solution may be to feed the control circuits with constant voltage transformers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Sazirul]

Our demand load from the government is 3MW. Now its like 1.7MW we are using. Because our machine is running at low speed for adjusting the performance and quality of product. Its a spinning mill where we are making 100% export quality yarn. 90% of load in my factory is for various types of motor and adjusted VFD with PLC. So if there is any voltage fluctuation then all machine goes offline at once. We planed for backup power by using a online UPS and we calculate it required lot of money and most important thing is that we are having less space inside our factory for installing UPS for individual machine. That's why I am looking for a solution that we can control voltage from substation. Our generator will come after 6-10 month. But now it just like hell to us.

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[Sazirul]

If the constant voltage transformers input voltage has fluctuation then will it maintain constant voltage at output side? @waross

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[waross]

I am most concerned with the voltage Jumps when the primary voltage goes from 25 kV to 33 kV.
This unit from Hammond, if set to receive 30 kV will handle 10% over voltage. That lets you handle 33 kV at the top end.
This unit will handle minus 25%. From 30 kV that is a low of 22.5 kV, or
Set for 33 kV supply this will go down to 24.75 kV.
That looks as if it will handle your range of voltage fluctuations.
I am not recommending this line. I am showing this as an example of what is available.
There are other manufacturers and similar units are available for 50 Hz.
Link
Link
There are three ways to go;
One, break out each control circuit and power each control circuit with a single small Constant Voltage Transformer.
Two, break out each control circuit and power all the control circuits with a single, larger, Constant Voltage Transformer.
Three, feed each machine or each VFD with three Constant Voltage Transformers connected in delta.
Google is your friend.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[waross]

Another option may be to work with the grid operators to mitigate the voltage issues at the source. I do understand that this is not always possible.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

UPS on the control circuits likely won't work if your motors are all VFD driven. Check the VFD specs and see if they will operate with a 25% under-voltage.

You describe them as running at a low speed. Typically, with a VFD you don't need rated voltage to run the motor at a lower speed. For example, the motor could be run continually just fine up to 75% speed with 25kV input.

However, the VFD might have a fixed low voltage trip built-in that you can't bypass or adjust and that will trip when the voltage drops to 25kV. So, you have to check into it to see if the VFD can keep operating with such a line voltage dip.

 

[bacon4life]

This won't fix your instantaneous trips, but a couple of settings changes might recover the voltage fast enough for some of your VFDs to stay online:
-Some LTC controllers have an inverse time curve available to speed up LTC steps for large voltage variations. This might be able to reduce your time from the voltage reduction to the first step down to a couple of seconds. This can have detrimental impacts to the overall transmission network during a voltage collapse scenario, so talking with your transmission provider before implementing this is a good idea.
-Tap changers can be set to either operate continuously until the voltage returns within bandwidth, or they can be programmed for non-sequential operation where each tap change has a delay. Changing your mode of operation may allow the voltage to be returned to normal within 30 seconds total instead of 30 seconds per tap.

 

[Sazirul]

This is sample of motor and we are having 73 motor with 73 ring machine and this motor is driving by ABB ACS880 inverter. We are also having Trutzschler, Murata machinery. I already mention we don't have enough space in our factory floor. Consider if we go with individual UPS then there will big challenge to keep safe UPS from micro dust. In our factory it's too much. Again, is there any way to control from our substation?

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