SELECTION OF RIGHT TRANSFORMERS (PART 1)

The distribution/ power transformer is a equipment which works as back bone of a industry and, proper selection of transformer rating & type having the extensive effect on the industry growth. Therefore its adequate rating selection is must. This blog aims at recommending a policy for transformers rating selection considering technical and economic factors. Proper rating & selection of transformers depends upon so many factors i.e. Load, Voltage, Losses, accessories etc.

The most important factor for transformer selection is the connected load as well as loading of transformer, In an industry loading of transformer could be change time to time.

Loading of transformer is not same during whole of the day, therefore proper selection of transformer as per required loading is most important factor, as transformer is a capital equipment for on industry. Now there are so many models for transformer are available in market which will design as per customer loading requirement. Here we are giving some technical parameters which will help us in deciding the proper transformer as per the requirement:

A) KVA RATING , VOLTAGE CLASS (PRIMARY & SECONDARY) :

1.  Voltage required by load.

2.  Amperes or KVA required by load.

3.  Frequency in Hz (cycles per second).

4.  Verify load is designed to operate on three phase.

All the above information is standard data normally obtained from equipment nameplates or instruction manuals.

B) WHY TRANSFORMER NO LOAD & LOAD LOSSES ARE IMPORTANT ?

As we describe above that loading on transformer is not constant throughout the day therefore according to loading cycle we can select the suitable transformer through which we can save the energy as well as also save on our energy charges including demand and capacitor surcharge/ KVAH units.

For more illustrative purpose we can categorize the industries as below based on its loading cycle:

Category 1: In this category we can select the industry where energy consumption is 1% or 2% of manufacturing cost of our final product.

Category 2: In this category we can select the industry where transformer loading is continuous around 75%.

Category 3: In this category we can select the industry where transformer loading is varied between no load to 100%. For example no load at night and 50% to 100% load during a day.

Category 4: In this category we can select the industry where energy cost is 50% to 90% of final product.

Now suppose we have an industry of category 3 type where loading of transformer is varied between no load to 100% loading, so we can select the transformer which are having low no load losses due to which energy consumption is on lower side during no load hours and also power factor is more than 0.5.

Now we consider the industry where cost of final product is depends upon the cost of energy so we can select the transformer which are having lowest no load losses as well as lowest load losses.

So with the help of above we can ask about the suitable transformer from transformer manufacturer Now a day’s Star Rating & ECBC transformer which are manufactured as per guidelines issued by Bureau of Energy Efficiency.

C) WHAT IS THE FLUX DENSITY AND WHY IT IS IMPORTANT ?

We can describe the flux density as the amount of magnetic flux passing through lamination of transformer.

Value of flux density is most important factor for any transformer we can take a example of a transformer which are designed on 1.7 T and now suppose if the voltage increase by 10% i.e. 12 KV instead of 11 KV, than flux density also get increased by 10% and its value will reach about 1.87 T which is near the saturation point of CRGO core and in this condition core get overheated due to which temperature of winding, structural parts and oil will be increased abnormally and transformer may damage.

D) WHY TAP CHANGERS IS REQUIRED ?

As we know the voltage situation in India is very critical and it will be changed on daily basis so for getting the constant output voltage on output side tap changer mechanism is required. In India voltage condition changed frequently on daily basis therefore we suggest that automatic tap changer with computer controlled mechanism should be used.

E) WHY PROTECTION IS REQUIRED ?

Since we know transformer is an electrical equipment which are under operation on regular basis and its also faces various environment factors, therefore proper protections is mandatory for transformers, due to any fault transformer could be break down and we will face the following problems:

a) Production will be stopped.

b) Product quality may be affected.

c) Due to fault our machines & equipment could be damaged.

d) Heavy financial losses could be there as transformer is capital asset of an industry.

F) WHICH PROTECTION IS REQUIRED IN TRANSFORMER ?

Some of the important protections are as below:

a) Winding/ Oil Temperature Indicator: This device gives the temperature rise values of oil and winding and these devices also having the alarm and trip contact which can be operate if the temperature will go beyond the predefined limits. Excess temperature deteriorates the life of transformer.

b) Buchholz Relay: This device will gives the alarm and trip facility if is there any abnormal gas formation in a transformer oil due to any fault. The fault conditions in most of the cases are insulation failure or overheating.

c) Magnetic Oil Level Gauge: This device will gives the idea of oil level in transformer and gives the facility of alarm & trip if oil level goes down by specified level.

Besides of above various online condition monitoring equipment are also available in market through which we can do the real time monitoring of important parameters which are important for a transformer, some of the parameters are as below:

a) H2 PPM Level

b) Ambient, Oil & Winding Temperature

c) Voltage & Current in all three phases.

d) Active/ Reactive apparent energy and power

e) Maximum demand/ Demand forecasting

f) Time bound & stamped data for KVAH/KWH/KVAR

So with the help of real time monitoring of above parameters we can increase the reliability of transformer and also plan the maintenance or replacement plan.

In case any query free feel to contact us at info@saielectricals.com