--- title: "DC series and shunt generator characteristics" subject: "Electrical Machine" chapter: 3 key: "semester_4/electrical_machine:shunt-series-generator-characteristics" source: https://www.bctengineer.com/q/semester_4/electrical_machine/shunt-series-generator-characteristics site: BCT Engineering --- # DC series and shunt generator characteristics Electrical Machine · Chapter 3: DC Generator - Asked in: 2073 Bhadra, 8 marks - Video: [Characteristics and applications of DC shunt generators.](https://www.youtube.com/watch?v=35wisVc70PM) — EEE Tutorials - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/electrical_machine/shunt-series-generator-characteristics - Whole chapter: https://www.bctengineer.com/md/semester_4/electrical_machine/chapter-3 ## Question Using circuit diagram and graphical representation, explain the characteristics of DC series generator and DC shunt generator. Also mention their applications. ## Short answer DC shunt generator terminal voltage drops moderately with load due to armature drop and field weakening; used for constant-voltage supply. Series generator voltage rises with load then falls after saturation; used for boosters and arc lamps. ## Answer The characteristics of a generator show how terminal voltage V varies with load current I_L (external characteristic). V = E − I_aR_a (− series drop). #### DC shunt generator ```text Ia = IL + Ish +--(Ia)--+------+-----> IL | Ra | | (G) Rsh [LOAD] | | | +--------+------+ ``` **External characteristic** (V against I_L): ```text V ^ |***** | *** | *** | ** | * <- turning back +------------------> IL ``` - V falls gradually with load because of (i) the armature drop I_aR_a, (ii) armature reaction, and (iii) the fall of field current as V falls (a cumulative effect). - Beyond the maximum current the curve bends back; at a short-circuit only a small current flows (due to residual flux). - Voltage regulation is moderate (about 5 to 10 %). - **Applications**: battery charging, lighting, general power supply, excitation of alternators. #### DC series generator ```text +--[Rse]--(Ia = Ise = IL)--> [LOAD] (G) ``` **External characteristic**: ```text V ^ *** | *** *** | ** ** | * | * +--------------------> IL ``` - The field current equals the load current. At no load only the residual emf appears. - As I_L increases, flux and emf increase, so V rises (almost linearly in the unsaturated region), then flattens due to magnetic saturation, and finally falls because of the I(R_a + R_se) drop and armature reaction. - **Applications**: boosters in feeders, arc lamps (constant current), series lighting. | Point | Shunt generator | Series generator | |---|---|---| | Field current | nearly constant | equals load current | | V with load | falls | rises, then falls | | Use | constant-voltage supply | boosters, special lines | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why does the terminal voltage of a shunt generator fall with load? A. Because speed increases B. Because series field opposes C. Armature drop, armature reaction, and fall of field current as V falls D. Because the residual flux grows Answer: C. All three effects reduce V, and lower V reduces field current further. (Key point: Shunt droop) 2. Which is an application of the shunt generator? A. Boosters in feeders B. Arc lamps in series C. Traction at no load D. Battery charging and lighting Answer: D. Its nearly constant voltage suits charging and lighting. (Key point: Shunt applications) 3. Why does the voltage of a series generator rise with load initially? A. Field current equals load current, so flux and emf rise B. Armature resistance falls C. Speed rises with load D. Residual flux disappears Answer: A. Φ proportional to I_L in the unsaturated region. (Key point: Series rise) 4. Why does the series generator voltage finally fall? A. Field current stops B. Saturation then I(R_a + R_se) drop and armature reaction C. The brushes lift D. Speed doubles Answer: B. After saturation, flux stops rising while drops continue to increase. 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