Electrical Problem in Our Factory

1. -best way is to get motor-generator for 33kVA. the motor inercia will keep your

generator stable output.

2. is this is cost prohibited - then consider to locate most sensible device to protect and use selective protection for each.

Dear Susheel1225,

As this is international forum for discussion will you mind informing rated voltage and other details of your electrical system. any way

Pl. check voltage fluctuation at the source from which you receive power. If it not from Utility you hace to check your system which include,

1. Check proper size incoming cable is selected.
2. Identify if any load is drawing heavy current causing drop in line.

Sir

We require 415 +- 5% for our euipments. Incoming cable is not a problem. Let make it clear, the supply to 33KVA sub station has a problem. There are few furnaces / boilers which draws high current and whenever these are started or switched off, we get fluctuations from the power house supply to our sub station. We feel these things are happening for a fraction of a seconds and thus forming packets of high / low current volts. OLTC cann't control such patterns as its responce time is late and this amplitude is very short. Can we have a system for our entire plant, which ensures no fluctuations, DG set is expensive.

It sounds as though the supply is undersized for the load. It's the cabling, or the upstream transformer, or perhaps both.

Have a qualified Electrical Engineer that specialises in high voltage installations check it over. Pay for it, if necessary.

First of all, is it 33kV or 33kVA?

susheel1225:

It seems to me that there is no way to settle this down internally because the voltage fluctuation is caused by your neighbours.

Could you let us know the operation schedule of such equipments? The way you will do is to let your neighbours know about this and if they could adjust the operation schedule to when the power is strongest.

Then you need to report to the Power company who is selling power for you about the consequence you are dealing with. Then, seek for the alternative power supply method if possible. For our case, we have disconnected our line from the big consumer like cement plant.

But I think that the thing you also need to pay attention, is about your substation information. Is that 30kVA substation because as my understanding, there is not OLTC for such a "SMALL" transformer. 30kVA is a very very small in term of power consumer, you know? Could you please check that and come back here with more exact information?

Earlier we had a power supply from the dedicated line for agriculture fields from the surrouding areas, recently we have connected to industrial line as there are more power cuts for the ealier agri line. Now, we do not have the option of changing from existing line and dedicated line for our industry will be very expensive affair. Can we have a system which can detect / restrict such abnormalities. We have 33KV line.There is any system like for a particular range of voltage , system run or else it trips

Firstly, you need to have or rent a device which can measure and record the fluctuation in power system in term of numbers and waves. Put it there for a couple of days...

Check how much is the fluctuation? Determine how much is the worst one. If it falls within the tolerance in which the transformer can cover. Adjust your No-load tap changer on your transformer (a bit higher than the rated voltage which it is providing you). Could you let us know the voltage at either sides and the capacity of your transformer? But please note before doing so, remember to ask the transformer supplier for appropriated approval of this action because this may cause dangerous to the transformer.

We used to have our transformer designed at 22/6.6kV but when we inspected the site condition we came up with transformer of 22/6.9kV. The reason, I think you know.

For protection, you can look for the under voltage relays which could be the other topic to be discussed.

Sir

I would like to know what device will measure such fluctuations? But our fluctuations are very small like we may not be able to see these in the display ( for each phase ) in our incoming panels near the machines. It is absolutely like a flash. We can see our light getting off and on. Tap changer is operated when voltage remains high or low for some time ( if i am not mistaken ), again we have auto tap changer so we really don't need to look at that angle. We have seen faults in the VFD's as incoming voltage problem and moreover some small components on MPC not functioning thereafter.

You can go for complete study of your voltage profile for 24 hours study using a power quality analyzer , observe the trend and then go for suitable SCVS with 1% regulation for your protection of your equipment since OLTC will operate from 10% regulation with 1 minute interval .

B.Nagarajan

9394043970

Sir

What is power quality analyser, are there any agencies which can take up such study and what SCVS and how different it is from SVC. Pl elaborate.

Sir

Can you provide more information on SVC and you say this has to be connected to the same bus, please explain. Do we need any sort of permission for such device and do they withstand small to big fluctuations. What will be appx. cost.

An SVC has combination of thyristor controlled reactor [TCR] and several fixed capacitors [FC] tuned to different harmonics.

The combination of the thyristor controlled Reactor and capacitor provide reactive power control to virtually any size of the load. 0 MVAR to say 250 MVAR per large load is also possible.

Since TCR generates characteristic harmonics and the load whose reactive power is compensated may also have harmonic contents, the FC are tuned to filter these harmonics at the load bus itself.

The combination of TCR and FC measures the Reactive power drawn by the load and the control circuits determine the exact MVAR compensation needed to meet the load MVAR. Accordingly the TCR firing angles are controlled to provide desired MVAR compensation. The arrangement is fast so that external grid network will not experience MVAR fluctuations and consequent voltage fluctuations.

ABB, Siemens all provide SVC's

Since I am a consultant, your company can contact me if needed for the solution outside this forum.

Please give some values like transformer MVA,furnace MVA,Boiler KW,whether you have PFCC,cable sizes,types of starters used etc

With this,

It is clear that you are facing the problems of switching surges. Not the voltage levels. SVCs are very costly. May not be econimically suitable for your kind of load. Another option is you may install SPDs - Surge Protecting deivices of suitable class.

Class B - near Panel Bus

Class C - near VFds / Electronic panel to protect.

Further, you may also need to protect the electronics from the static charges generated due to cloud effect.

May be this case needs site visit, inspection and discussions

Somewhere, an arc furnace load is mentioned in the discussion. An arc furnace load may need random reactive power support, measurements will clarify the same.

Is the problem occuring only during switching on disturbing loads? or the problem continues even after switching on the disturbing loads in the network for a long time? The answer to this question will say whether this is a switching problem or a problem due to randomly varying reactive power load.

Dear sir

Power Quality Analyzer is a device which can measure the voltage , current , power energy , THD , individual harmonics , inrush current , peaks , max , min values , power quality parameters like CF, K-factor , PST etc.. The Instrument can store data's for 1S Interval for defined time period (30-120 days ).

SCVS is a Servo Controlled Voltage Stabliser which will be having 1% regulation and can stabilise your voltage from (310V-500V ) to a constant output (user settable)with all the protection like under voltage / over voltage , overload , Spike & surge Supression , short circuit etc..

feel free to contact us , we will be providing these services ,

B.Nagarajan

9394043970

Well I never thought about small loads as my experience was with large loads. Voltage stabilizer solution may be considered for small loads.

No other way except to get sanction for separate line...becoz in your situation your neighbour will not agree for cooperation and hence it's better to have separate your separet line...I understand it's tedious and not economical way but it's necessary for QUALITY POWER SUPPLY!!