---
title: "EMF of long shunt compound generator"
subject: "Electrical Machines I"
chapter: 3
key: "semester_4/electrical_machines_i:long-shunt-compound-40a-200v"
source: https://www.bctengineer.com/q/semester_4/electrical_machines_i/long-shunt-compound-40a-200v
site: BCT Engineering
---

# EMF of long shunt compound generator

Electrical Machines I · Chapter 3: DC Generator

- Asked in: 2073 Bhadra, 8 marks
- Video: [long shunt compound generators](https://www.youtube.com/watch?v=CWJjNBdG8ow) — Stephen Mutale
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/electrical_machines_i/long-shunt-compound-40a-200v
- Whole chapter: https://www.bctengineer.com/md/semester_4/electrical_machines_i/chapter-3

## Question

A dc long shunt compound dc generator has armature winding resistance of 0.4 ohm, series field winding resistance of 0.5 ohm and shunt-field winding resistance of 100 ohms. The generator delivers a current of 40 A to the load at 200 volt. Calculate the emf generated by the armature.

## Short answer

Shunt current is 200/100 = 2 A, so armature and series current is 42 A. Generated emf = V + I_a(R_a + R_se) = 200 + 42×0.9 = 237.8 V.

## Answer

**Given:** $I_L = 40$ A, $V = 200$ V, $R_a = 0.4\ \Omega$, $R_{se} = 0.5\ \Omega$, $R_{sh} = 100\ \Omega$; long-shunt connection.

```text
     +--Ra--Rse--+-----------+
     |           |           |
    (Eg)        Rsh        Load 200 V
     |           |           |
     +-----------+-----------+
```

In long shunt, the shunt field is across the terminals and the series field carries the armature current.

#### Step 1: Shunt field current
$$
I_{sh} = \frac{V}{R_{sh}} = \frac{200}{100} = 2\ \text{A}
$$

#### Step 2: Armature (and series field) current
$$
I_a = I_{se} = I_L + I_{sh} = 40 + 2 = 42\ \text{A}
$$

#### Step 3: Generated emf
$$
\begin{aligned}
E_g &= V + I_a (R_a + R_{se}) \\
&= 200 + 42 \times (0.4 + 0.5) \\
&= 200 + 37.8 = 237.8\ \text{V}
\end{aligned}
$$

Brush drop is neglected as it is not given.

**Answer:** EMF generated $E_g = 237.8$ V.

## Check yourself

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

1. What is I_sh?
   A. (200 + 40 x 0.5)/100 = 2.2 A
   B. 200/100 = 2 A
   C. 200/0.4 = 500 A
   D. 40/100 = 0.4 A
   Answer: B. In long shunt the shunt field is across the terminals so it sees V = 200 V. (Key point: Shunt field current in long shunt)

2. What current does the series field carry?
   A. I_L = 40 A
   B. I_sh = 2 A
   C. I_a = I_L + I_sh = 42 A
   D. I_L - I_sh = 38 A
   Answer: C. Series field is in series with the armature, so it carries I_a = 42 A. (Key point: Series field current)

3. What is E_g?
   A. 200 + 40 x 0.9 = 236 V
   B. 200 + 42 x 0.4 = 216.8 V
   C. 200 + 42 x 0.9 = 237.8 V
   D. 200 - 42 x 0.9 = 162.2 V
   Answer: C. E_g = V + I_a(R_a + R_se) = 200 + 37.8 = 237.8 V. (Key point: Generated emf)

## Close variants set in other exams

- [EMF of short shunt compound generator (0.5 Ω armature)](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Ashort-shunt-compound-50a-200v-0p5ohm) — Electrical Machines I, chapter 3, asked 2×

## Related in Electrical Machines I

- [Compound generator EMF in long and short shunt](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Acompound-gen-120a-120v-long-short) — Electrical Machines I, chapter 3, asked 2×
- [EMF and load resistance of short shunt compound generator](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Ashort-shunt-7p5kw-230v-emf-load) — Electrical Machines I, chapter 3
- [Short shunt vs long shunt generated voltage (150 A, 230 V)](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Ashort-shunt-150a-230v-long-shunt) — Electrical Machines I, chapter 3
- [EMF and efficiency of short shunt compound generator (50 A, 200 V)](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Ashort-shunt-compound-50a-200v) — Electrical Machines I, chapter 3, asked 2×
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- [EMF of short shunt compound generator (6 kW, 250 V)](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Ashort-shunt-compound-6kw-250v) — Electrical Machines I, chapter 3

## Related in other subjects

- [Long shunt compound generator emf, 40 A at 200 V](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines%3Agen-long-shunt-40a-200v) — Electrical Machines, chapter 3
- [Long shunt compound generator emf, 80 A at 230 V](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines%3Agen-long-shunt-80a-230v) — Electrical Machines, chapter 3, asked 2×
- [Compound generator emf, long and short shunt](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines%3Agen-compound-50a-500v-long-short) — Electrical Machines, chapter 3
- [Short shunt compound generator emf, 80 A at 220 V](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines%3Agen-short-shunt-80a-220v) — Electrical Machines, chapter 3, asked 2×