Name plate of Transformer

Name plate of a machine is like a ID card which play a very important role. It tells about the working characteristics & safe limits of the machine. Name plate also provides details of the manufacturer along with its serial number.
In this post, Name plate of Transformer is going to be discussed.
There are many types of Transformer like Step up & step down transformers, power transformers, distribution transformers, instrumental transformers & Special purpose transformers. By name plate of Transformer ; Its rating voltage or current & type can easily be distinguished.
Before discussing the name plate of  Transformer , We should study a bit about the Transformer first.

Distribution Transformer 500KVA- 11KV/400V
Distribution Transformer 500KVA- 11KV/400V

 

Transformer

Transformer is a static electrical machine which carry no rotating part. Transformer transfer electrical power from one circuit to another circuit at a same frequency.
 
Transformer works on the principle of faraday law of electromagnetic induction. Generally, there are two types of windings in transformer, Primary winding & secondary winding.
Both the windings are separated from each other. No electrical link exist between both the windings Accept a changing magnetic field links both the windings with common silicon steel stamping.
 
Power always remain the same on both the sides of the Transformer . It is the voltage & current which varies on both the sides of the Transformer As explained below:
Taking an example of  300kVA distribution transformer with voltage ratio 11kV/415V.
Primary Voltage=11000             
Primary Current= 15.75
Apparent Power Primary= √3 *11000*15.75= 300077.8≅300KVA
 
Secondary Voltage=433
Secondary Current=400
Apparent Power Secondary= √3*433*400= 299991.2≅300KVA
 

Distribution Transformers 11KV/415V
Distribution Transformers | Voltage ratio 11KV/415V
 


What is the need of transformer ?

Reason 1. To change the Voltage level
Since power generating stations are at remote places far away from consumers. This distance may be in thousands of kilometers. If generated voltage directly transferred to consumers  through that much long distance than this power drops down in the way, totally. Because power loss is equal to I²R. When voltage is low, Current is high Which makes the power loss high.
 
That’s why to transfer power, voltage should be higher at Generating station. To step up the voltage, Step-up Transformer are needed. Now, at consumer end; for Electricity utilization low Voltage is required Which can be achieved through step down transformer.
Now the question is Why are we using Transformer to change the voltage ?
 
Answer is, Transformer are static machines without any moving part, Makes the Transformer the most efficient device to change the voltage. That’s Why used widely.
 
Reason 2. Instrumentation

Since high voltage & high current can not be measured directly. We need instrument transformers which convert high voltage & high current to low measurable level, directly.

 

Reason 3. For Special purposes
There are some Transformer which are made for special purposes like an Auto transformers which provide variable voltage by just rotating its variac.

Reason 4. Isolation

 Isolation transformers are utilized to isolate one circuit from another. In isolation transformers, Voltage remains the same on both the sides. These are used to eliminate the impact of harmonics & distortion from one circuit to another.

 

Name Plate of Transformer

Lots of details are mentioned on transformer’s name plate Which entirely depend upon the type of Transformer whether it is power transformer, distribution transformer, instrumental transformer or special purpose transformer.
 
For further discussion, The name plate of 300KVA distribution Transformer is going to be discussed which is having a voltage ratio of 11kV/415V.

Name plate of 300KVA Transformer(11KV/415)
300 KVA, 11KV/415V, DISTRIBUTION TRANSFORMER

List of transformer attributes are discussed below :

1. Manufacturer’s name-address & serial number

 
Manufacturer details are always given at front. As shown in an image above; Transformer makers are Elite transformer from Jalandhar city, Punjab.
Top manufacturers are available in every field. These companies sets benchmark for other companies behind them. A logo of top manufacturer, is a sign of reliability & believe. 
      

2. Rating

Transformer rating is 300 KVA. Transformer are rated in kVA (APPARENT POWER) Not in kW, Because Transformer are power transforming device that transfer power from one circuit to another. Transformers are not power consumers; Rather it is the load connected on secondary Which consumes power.
 
3phase Real power =√3 V I cos¢
Where,
√3VI= Apparent power (Voltage ×Amperes(VA/KVA))
cos¢= Power factor
 
It means if cos¢ is eliminated from real power than it becomes apparent power (VA/KVA)
If load is inductive than power factor is lagging. If load is capacitive than power factor is leading. The value of power factor varies from 0 to 1 which is fully depend upon the type of load which is connected across the secondary of Transformer . It means ‘power factor is load dependent.’
 
Since, Transformer has no link with the power factor that’s why Transformer are rated in KVA rather than KW.
 

3. Voltage on HV & LV side

Both the sides HV and LV side voltages are mentioned in this parameter. In general, distribution transformer shown above HV voltage is 11KV & LV voltage is 415 Volts.
 

4. Rated Current

It is the safe level of rated working current; under some specified condition; In which machine works precisely without getting excessive ‘Mechanical & Electrical’ stress.
As shown in an image :
  • HV current= 15.75 Amps
  • LV current= 400 Amps
 

 5. Winding connections

It tells about the connection type on both the winding sides whether it is ‘star‘ or ‘delta‘. In distribution transformer above, primary is delta & secondary in star. 
 

6. No load loss

It is the value of core loss occurring in open circuit or at no load conditions. 
In our name plate no load loss=716 Watt.(see image )
 

7. Load loss

It is the value of copper loss occurring in the winding under the full load conditions at some specified temperature,
In our name plate load loss at 75°C is 4243 Watt.(see image )
 

8. Type of cooling

This term tell about the type of cooling. In an image above, Transformer is ONAN type which means oil & air both are cooled naturally.
 
ONAN stands for- oil natural air natural
In ONAN system hot oil continuously rotate in fins without any external force & a Natural air passes through fins naturally.
 
There are much more types of cooling but all these types depend upon the rating & type of Transformer .
For example;
ONAF– Oil natural air forced
In this system oil naturally flow through the fins but air is forced with the cooling fan.
 
OFAF- Oil forced air forced
In this type, oil flows with the help of pump & air is blown with cooling fan.
 

9. Frequency

The frequency remains constant on both the sides of Transformer . In India, frequency standard is 50Hz+-3%.
 

10. Impedance volts

It generally listed in percentage which tells about the voltage drop in Transformer under short circuit conditions.
This value also tell about highest current flow when Transformer get short circuited.
The formula of short circuit current= (100/impedance volts)× full load rated current.
In an image; impedance volts is 4.3%
which mean short circuit current is; [(100/4.3)*400]= 9302.3 Amps
  

 11. Vector Grouping

This term is the standard set by international Electrotechnical commission (IEC) which tells about the winding configuration on HV & LV side. This term generally tells about the phase shift between primary & secondary voltage.
 
For example 
In Image, vector grouping is DYn11.
Since our transformer is distribution transformer. Primary HV winding is Delta & secondary LV winding is Star. 
NOW
DYn11
D- Primary side which is Delta
Y- Secondary side which is wye or star
n- stands for neutral brought out on Secondary side
11- This terms shows the  30° lead in phase shift. LV phase leads the HV phase by 30°.
This 11 is taken off from clock Since in our clock of full circle there are total 12 numbers.
(1full circle = 360°)
One number in terms of degree equals to ;360°÷12= 30°
Since 11 is Infront of 12 in the left; that’s why taken as 30° lead. LV winding leads HV by 30°.
 

12. Mass of oil in kgs

It is the total weight of Transformer oil Which is 310 Kgs. (See image)
 

13. Total weight of transformer

Total weight of Transformer includes Transformer oil. As shown in image, total weight of 300kVA Transformer is 1500KG.
 

14. Volume of oil (liters)

370 liters
 

15. Year of manufacturing

2007
 

SUMMARY

  • Transformer is a static electrical machine which carry no rotating part. Transformer transfer electrical power from one circuit to another circuit at a same frequency.
  • Transformer works on the principle of faraday law of electromagnetic induction. Generally, there are two types of windings in Transformer , Primary winding & secondary winding.
  • Name plate of Transformer tells about its important credential like its rated voltage & rated current, its type & much more. According to these parameters safe limits can be set around the transformer.

Transformer Name Plate – Q & A (Bijliwala)

Q1. What is a transformer nameplate?

A transformer nameplate is a metal plate fixed on the transformer body that provides important technical information such as rating, voltage levels, current, and connection details. It helps users understand how the transformer should be used safely.

Q2. Why is a transformer rated in kVA instead of kW?

Transformers are rated in kVA because they handle voltage and current, not the power factor. The power factor depends on the connected load, not on the transformer itself.

Q3. Where is the transformer nameplate fixed?

The nameplate is usually fixed on the side wall of the transformer tank, where it is clearly visible for inspection, maintenance, and identification.

Q4. What does the kVA rating on the nameplate indicate?

The kVA rating shows the maximum load capacity of the transformer that it can handle continuously without overheating under rated conditions.

Q5. What information does the voltage rating on the nameplate provide?

The voltage rating indicates the primary (HV) and secondary (LV) voltages for which the transformer is designed. Operating the transformer beyond these values can damage insulation.

Q6. Why is frequency mentioned on the transformer nameplate?

Frequency (usually 50 Hz) shows the supply frequency the transformer is designed for. Operating at a different frequency can cause excessive heating and reduced efficiency.

Q7. What does the vector group mentioned on the nameplate mean?

The vector group explains the winding connection type and the phase difference between primary and secondary voltages, which is important for parallel operation and system compatibility.

Q8. What is the importance of impedance value on the nameplate?

Impedance value helps in estimating short-circuit current and voltage drop. It plays a key role in protection system design.

Q9. Why is cooling method written on the transformer nameplate?

The cooling method indicates how heat is removed from the transformer. Proper cooling ensures safe operation and long transformer life.

Q10. Can a transformer be operated without checking the nameplate details?

No. Ignoring nameplate details can lead to overloading, overheating, and insulation failure. The nameplate should always be checked before installation or load extension.

Q11. Does the nameplate help during maintenance and troubleshooting?

Yes. Nameplate data helps technicians verify ratings, select protection devices, and diagnose issues related to loading and overheating.

Q12. Are nameplate details same for all transformers?

No. Nameplate details vary based on transformer type, capacity, voltage level, and application.

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