Ultimate Guide to Transformer Sizing and Selection

Table of Contents

1. Introduction
2. Step 1: Calculate Total Connected Load
3. Step 2: Add 10% Load for Future Consideration
4. Step 3: Calculate Maximum Demand Load
5. Step 4: Convert Maximum Demand Load to kVA
6. Step 5: Calculate Transformer Capacity with 90% Efficiency
7. Step 6: Select Transformer Size from Selection Chart
8. Conclusion

Article

Introduction

Welcome to my channel! In this video, we will be discussing how to calculate the transformer size for a commercial building or industry. Before we dive into the steps, make sure to subscribe to my channel and hit the bell icon to receive notifications for my upcoming videos. Let's get started!

Step 1: Calculate Total Connected Load

The first step in determining the transformer size is to calculate the total connected load of the building or industry. For example, let's consider a hotel building. Assume the following loads for this building: 80 kW for raw power, 100 kW for lighting, 110 kW for plumbing, 40 kW for elevators, and 3 kW for the DG auxiliary. By summing these loads, we get a total connected load of 333 kW.

Step 2: Add 10% Load for Future Consideration

In the second step, we need to add a 10% safety factor to the final calculated total connected load. This extra load accounts for any potential increase in load in the future. By calculating 10% of the total connected load (333 kW), we get an extra load of 33.3 kW. Adding this to the total connected load gives us a final calculated total connected load of 366.3 kW.

Step 3: Calculate Maximum Demand Load

In step three, we calculate the maximum demand load based on a demand factor. For commercial buildings, a demand factor of 80% is often considered. This means that only 80% of the total connected load will be switched on at a given time, while the remaining 20% will be switched off. Taking the final calculated total connected load (366.3 kW) and applying the demand factor of 80%, we get a maximum demand load of 293.04 kW.

Step 4: Convert Maximum Demand Load to kVA

Step four involves converting the maximum demand load from kilowatts (kW) to kilovolt-amperes (kVA). To do this, we divide the maximum demand load (293.04 kW) by the power factor, which is assumed to be 0.8 in this case. Dividing 293.04 kW by 0.8 gives us a maximum demand load of 366.3 kVA.

Step 5: Calculate Transformer Capacity with 90% Efficiency

Next, in step five, we calculate the transformer capacity or size with a 90% efficiency or a 0.9 derating factor. This means that we only connect loads up to 90% of the transformer's rated capacity. Taking the calculated maximum demand load of 366.3 kVA, we divide it by the derating factor of 0.9. The result is a transformer capacity of 407 kVA.

Step 6: Select Transformer Size from Selection Chart

In the final step, we need to select the actual transformer size from a selection chart. Since we may not find an exact size in the market, we typically choose a transformer size that is larger than the calculated value. In this case, the calculated transformer capacity is 407 kVA, so we can select a transformer size of 500 kVA from the available options.

Conclusion

By following these steps, you can easily calculate the transformer size for any commercial building or industry. It is important to consider the total connected load, add a safety factor, calculate the maximum demand load, convert it to kVA, and determine the transformer capacity considering efficiency. Selecting the right transformer size ensures efficient operation and avoids oversizing or wasting money. Thank you for watching this video, and be sure to like, share, subscribe, and hit the bell icon for more informative content. See you in the next video!

Highlights

• Learn how to calculate the transformer size for a building or industry
• Understand the steps involved in sizing a transformer
• Considerations for future load increase and efficiency rating
• Selecting the appropriate transformer size from a selection chart

FAQ

Q: What is the first step in sizing a transformer? A: The first step is to calculate the total connected load of the building or industry.

Q: Why do we add a 10% load to the calculated total connected load? A: Adding a 10% load accounts for potential future increases in load.

Q: How is the maximum demand load calculated? A: The maximum demand load is calculated based on a demand factor, which is often a percentage of the total connected load.

Q: Why do we convert the maximum demand load from kilowatts to kilovolt-amperes (kVA)? A: Transformers are rated in kVA, so the maximum demand load needs to be converted to the appropriate unit for sizing purposes.

Q: Why is it important to consider efficiency when calculating the transformer capacity? A: Efficiency affects the actual load that can be connected to the transformer, so it is crucial to factor it in during the calculation process.

Q: How do we select the final transformer size? A: The final transformer size is selected from a selection chart, typically choosing a size larger than the calculated value to ensure optimal operation.