How Do You Calculate Transformer kVA Rating Based on Site Measurements?

In summary, the speaker is a student seeking help with an electrical engineering question. They have visited a site and recorded current readings and voltage measurements. They are looking for help in calculating the kVA rating of a transformer based on the given information. The speaker also notes that the voltage measurements may be inconsistent with world standards.
  • #1
engnr.in.trng
1
0
Hi,

I've just got into my electrical engineering course and I need some help with a question of mine here.

During a site visit, we were shown a main LT panel which has switchgears, ammeters and different kinds of relays and the distribution network from that panel. In the main LT panel I've noted down the current readings as Ir - 163A, Iy - 150A and Ib - 147A. The Line to Line voltage is 415 V at 50 Hz and Line to Neutral voltage is 230V at 50 Hz.

From the above details, how would I calculate the kVA rating of transformer? The primary side voltage of the transformer is 11 kV and the secondary side voltage is 415V and the frequency is 50 Hz.
 
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  • #2
Welcome.

You have recorded inconsistent voltages. The voltage between phases will be √3 = 1.732 times the neutral to phase.

World standards have moved to 230V and 400V for single phase and three phase respectively.
The 415V you report suggests distribution is still 240V.

The transformer rating will need to be greater than the KVA observed.
 

1. How do you determine the appropriate size of a transformer for a specific application?

The size of a transformer is determined by calculating the load requirements of the system it will be supplying. This calculation takes into consideration the voltage, current, and power requirements of the system. Additionally, factors such as the load type, load duration, and ambient temperature must also be considered in order to select the correct size transformer.

2. What is the formula for calculating transformer size?

The formula for calculating transformer size is P = VI, where P is the power in watts, V is the voltage in volts, and I is the current in amps. This formula can be used to determine the required kVA (kilovolt-ampere) rating of the transformer.

3. How does the type of load affect transformer sizing?

The type of load being supplied by the transformer can greatly affect its size. Resistive loads, such as lighting or heating systems, typically require a smaller transformer compared to inductive or reactive loads, such as motors or transformers. The power factor of the load must also be taken into consideration when sizing a transformer.

4. Can a transformer be oversized for a specific application?

While it is possible to oversize a transformer, it is not recommended. Oversizing a transformer can result in wasted energy and increased costs. It is important to carefully calculate the required size of a transformer to ensure optimal performance and efficiency.

5. Are there any safety precautions to consider when sizing a transformer?

Yes, there are several safety precautions to consider when sizing a transformer. It is important to select a transformer with the correct voltage and current ratings to avoid overloading and potential hazards. Additionally, transformers should be installed and grounded properly according to manufacturer guidelines to ensure safe operation.

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