---
title: "Long shunt compound generator speed"
subject: "Electrical Machine"
chapter: 3
key: "semester_4/electrical_machine:long-shunt-compound-300-conductors-speed"
source: https://www.bctengineer.com/q/semester_4/electrical_machine/long-shunt-compound-300-conductors-speed
site: BCT Engineering
---

# Long shunt compound generator speed

Electrical Machine · Chapter 3: DC Generator

- Asked in: 2070 Bhadra, 8 marks
- Video: [Problems on DC Generators, shunt and compound generators](https://www.youtube.com/watch?v=69kUeAA1dYk) — Electrical and Electronics engg classes made easy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/electrical_machine/long-shunt-compound-300-conductors-speed
- Whole chapter: https://www.bctengineer.com/md/semester_4/electrical_machine/chapter-3

## Question

A 4 pole, 250 V long shunt dc compound generator supplies a load of 10 kW at the rated voltage. The armature, series and shunt field resistances are 0.1 Ω, 0.15 Ω and 250 Ω respectively. The armature is lap wound with 300 conductors. If the flux per pole is 50 mWb, calculate the speed of the generator.

## Short answer

Load current 40 A, Ish = 1 A, Ia = 41 A, E = 260.25 V. For lap winding, speed N = 60 A E / (P Φ Z) = 1041 rpm.

## Answer

For a long shunt machine the series field is in the armature circuit, and the shunt field is across the output terminals. The speed follows from E = PΦZN / 60A. Brush drop is not given, so it is ignored.

#### Equivalent circuit
```text
 Ia --[Ra=0.1]--[Rse=0.15]--+--> IL
 (E)                        |
                      Rsh=250 ohm, V=250 V
```

#### Currents
- Load current I_L = 10 000 / 250 = 40 A
- Shunt current I_sh = 250 / 250 = 1 A
- Armature (and series) current I_a = 40 + 1 = 41 A

#### Generated emf
E = V + I_a(R_a + R_se) = 250 + 41 × (0.1 + 0.15)
= 250 + 10.25 = **260.25 V**

#### Speed
Lap winding: A = P = 4, Z = 300, Φ = 50 mWb = 0.05 Wb.

E = PΦZN / (60A), so N = 60 A E / (P Φ Z)

N = (60 × 4 × 260.25) / (4 × 0.05 × 300)
= 62 460 / 60
= **1041 rpm**

| Quantity | Value |
|---|---|
| I_L | 40 A |
| I_sh | 1 A |
| I_a | 41 A |
| E | 260.25 V |
| N | 1041 rpm |

**Answer: speed of the generator = 1041 rpm.**

## Check yourself

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

1. In a long shunt machine, what is I_a here?
   A. 41 A (40 A load + 1 A shunt)
   B. 40 A
   C. 39 A
   D. 1 A
   Answer: A. I_L = 10000/250 = 40 A; I_sh = 250/250 = 1 A; I_a = 41 A. (Key point: Armature current)

2. What is the generated emf?
   A. 250 V
   B. 260.25 V
   C. 239.75 V
   D. 271.5 V
   Answer: B. E = 250 + 41 x (0.1 + 0.15) = 260.25 V. (Key point: Generated emf)

3. What is the speed using lap winding?
   A. 520 rpm
   B. 2082 rpm
   C. 1041 rpm
   D. 1250 rpm
   Answer: C. N = 60AE/(PΦZ) = 60 x 4 x 260.25/(4 x 0.05 x 300) = 1041 rpm. (Key point: Speed)

## Related in Electrical Machine

- [Long shunt compound generator speed, 300 conductors](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines%3Agen-long-shunt-10kw-300-conductors) — Electrical Machines, chapter 3, asked 2×
- [Long shunt compound generator speed, lap and wave](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines%3Agen-long-shunt-10kw-lap-wave) — Electrical Machines, chapter 3, asked 2×
- [Short shunt to long shunt compound generator (10 kW, 220 V)](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Ashort-shunt-cumulative-10kw-220v-long) — Electrical Machines I, chapter 3
- [4-pole shunt generator, wave wound, 3 kW](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines%3Agen-wave-wound-3kw-120v) — Electrical Machines, chapter 3, asked 3×
- [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
- [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×

## Related in other subjects

- [Armature dimensions of 50 kW shunt generator](https://www.bctengineer.com/question.md?key=semester_5%2Felectric_machine_design%3Adc-generator-50kw-armature) — Electric Machine Design, chapter 5
- [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×
- [EMF of long shunt compound generator](https://www.bctengineer.com/question.md?key=semester_4%2Felectrical_machines_i%3Along-shunt-compound-40a-200v) — Electrical Machines I, chapter 3, asked 2×
- [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