---
title: "T/F: rural design, transformer size first"
subject: "Transmission and Distribution System Design"
chapter: 7
key: "semester_8/transmission_and_distribution_system_design:tf-rural-transformer-size-first"
source: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/tf-rural-transformer-size-first
site: BCT Engineering
---

# T/F: rural design, transformer size first

Transmission and Distribution System Design · Chapter 7: Distribution System Design

- Asked in: 2073 Magh, 1+3 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/tf-rural-transformer-size-first
- Whole chapter: https://www.bctengineer.com/md/semester_8/transmission_and_distribution_system_design/chapter-7

## Question

State whether the following statement is TRUE or FALSE. Justify your answer with a brief explanation: For design of rural distribution first select the transformer size and then size of the load centre.

## Short answer

False. Rural loads are clustered at settlements; the load centre location is fixed first. Transformer size is then selected to match that cluster's demand, followed by LT conductor and feeder length.

## Answer

**FALSE.**

#### Justification
In rural areas the loads are not uniform; they appear as **clusters** (villages, settlements, market centres) separated by empty land. The design must therefore start from the **load centre**, not from the transformer size.

Correct sequence for rural distribution design:
1. Survey the area and identify the settlements (load clusters) and the number and type of consumers.
2. Estimate the present and forecast demand of each cluster (e.g. 0.3–0.5 kW per household with diversity, plus small industries, irrigation pumps).
3. **Locate the load centre** (centre of gravity of the loads) of each cluster:
$$
x = \frac{\sum P_ix_i}{\sum P_i},\quad y = \frac{\sum P_iy_i}{\sum P_i}
$$
4. **Then select the transformer size** (standard 25, 50, 100 kVA) to match the forecast demand of that load centre, keeping reserve for growth.
5. Choose LT conductor and length so that voltage drop and loss at the farthest consumer stay within limits; extend the 11 kV line to the transformer.

| Point | Reason |
|---|---|
| Load fixed by village location | Engineer cannot move the load |
| Transformer serves one cluster | Its size depends on that cluster's demand |
| Low load density | LT lines long; drop decides spacing |

So the load centre is chosen first and the transformer is sized to it. Selecting a transformer size first and then "sizing the load centre" reverses cause and effect.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. The statement is:
   A. True
   B. False; load centre comes first
   C. True for large loads
   D. False; conductor first
   Answer: B. Rural design starts from load clusters. (Key point: Truth value)

2. Why locate the load centre first in rural areas?
   A. Loads are clustered in villages; engineer cannot move load
   B. Loads are uniform
   C. Transformers are standard
   D. Cost
   Answer: A. Loads are fixed by settlement location. (Key point: Why)

3. Load centre is:
   A. Sum(Pi xi)/Sum(Pi)
   B. Sum(xi)/n
   C. Sum(Pi)/Sum(xi)
   D. Max xi
   Answer: A. Centre of gravity weighted by load. (Key point: Load centre formula)

4. After the load centre:
   A. Select transformer size to match forecast demand
   B. Choose voltage
   C. Skip survey
   D. Remove growth
   Answer: A. Transformer is sized to the cluster's forecast demand. (Key point: Next step)

## Related in Transmission and Distribution System Design

- [T/F: urban design, transformer location first](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-urban-transformer-location-first) — Transmission and Distribution System Design, chapter 7
- [Selecting load centre and transformer, rural/urban](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Aload-centre-transformer-rural-urban) — Transmission and Distribution System Design, chapter 7, asked 3×
- [T/F: under-loaded distribution transformer losses](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-underloaded-distribution-transformer) — Transmission and Distribution System Design, chapter 7
- [T/F: higher primary voltage in rural distribution](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-rural-higher-primary-voltage) — Transmission and Distribution System Design, chapter 7, asked 2×
- [T/F: thermal limit design urban, losses rural](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-thermal-limit-urban-loss-rural) — Transmission and Distribution System Design, chapter 7, asked 3×
- [T/F: X/R ratio, transmission vs distribution](https://www.bctengineer.com/question.md?key=semester_8%2Ftransmission_and_distribution_system_design%3Atf-xr-ratio-transmission-distribution) — Transmission and Distribution System Design, chapter 1

## Related in other subjects

- [True/false: series motor started at no load](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machine%3Atf-dc-series-motor-start-noload) — Electrical Machine, chapter 4
- [DC series motor started at no load: true/false](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines%3Adc-series-no-load-true-false) — Electrical Machines, chapter 4
- [True/false: load rejection raises terminal voltage](https://www.bctengineer.com/question.md?key=semester_8%2Fhigh_voltage_engineering%3Atf-load-rejection-voltage-rise) — High Voltage Engineering, chapter 3
- [True/false: derivative controllers always used with others](https://www.bctengineer.com/question.md?key=semester_3%2Fcontrol_systems%3Aderivative-always-with-others) — Control Systems, chapter 7, asked 3×