DC Generator obj

Comprehensive vocabulary flashcards covering key definitions, principles, formulas, and operating characteristics of D.C. generators from lecture notes.

Basic Requirement of a D.C. Armature Winding

A closed one

Reentrancy Requirement of a Wave Winding

Twice

Armature Winding Type with Coil Sides a Pole Pitch Apart

Full-pitch

Back Pitch Condition for Full-Pitch Armature Winding

Commutator bars per pole

Primary Reason for Making Coil Span Equal to Pole Pitch

Ensure the addition of e.m.fs. of consecutive turns

Slot Occupation for $180^\circ$ Electrical Coil Span ($4\text{-pole}$, $35\text{-slot}$ Armature)

1 and 9

Minimum Commutator Bars Required ($72\text{-slot}$, 2-Layer Lap, 6 Conductors/Slot)

$$216$$

Sole Purpose of a Commutator in a D.C. Generator

Convert the induced a.c. into d.c.

Number of Commutator Bars ($4\text{-pole}$, 20-Slot, 2-Layer Lap)

$$20$$

Back Pitch ($4\text{-pole}$, 12-Slot Progressive Lap-Wound Armature)

$$7$$

Winding Type when Commutator Segments Differ from Slot Count by One

Wave

Suitable Voltage and Current Conditions for Lap Winding

High current, low voltage

Current Exciting the Series Field of a Short-Shunt D.C. Generator

Load

Factor Directly Proportional to Generated E.M.F. in a D.C. Generator

Pole flux

Rated Current of Armature ($12\text{-pole}$ Triplex Lap, $100\,\text{A}$ per Conductor)

$$3600\,\text{A}$$

Loss Type Equal to Variable Loss for Maximum Commercial Efficiency

Constant

Results of Skewing Armature Slots in Small D.C. Machines

Quieter operation and slight decrease in losses

Circuit Associated with the Critical Resistance of a D.C. Generator

Field

Actual Cause of Armature Reaction in D.C. Generators

Load current in armature

Effect of Armature Reaction on Main Pole Flux

Reduce and distort main pole flux

Direction of Brush Shift in Clockwise-Rotating Loaded Generator

Clockwise

Primary Reason for Providing Compensating Windings

Neutralize cross-magnetising flux

Main Function of Interpoles in a Loaded D.C. Machine

Minimize sparking between brushes and commutator

Electrical Degrees Corresponding to $90^\circ$ Mechanical in a $6\text{-pole}$ Machine

$$270^\circ$$

Most Likely Causes of Brush Sparking in a D.C. Machine

Open coil in armature, defective interpoles, or incorrect brush spring pressure

Required Compensating Conductors per Pole ($10\text{-pole}$, 50 Active Conductors/Pole)

$$5$$

Basic Definition of Commutation Process in D.C. Generator

Reversal of current in an armature coil as it crosses MNA

Methods to Improve Commutation in D.C. Generators

Using interpoles, using carbon brushes, and shifting brush axis in direction of rotation

Incorrect Statement Regarding Interpoles

They are connected in parallel with the armature

Voltage Characteristic Making Shunt Generators Suited for Parallel Operation

Dropping

Conditions for Proportional Load Sharing in Parallel Shunt Generators

Same rated voltage and same voltage regulation

Main Function of an Equalizer Bar

Make parallel operation of over-compounded generators stable

Essential Characteristic Condition for Stable Parallel Operation

Dropping voltage characteristics

Main Factor Causing Unstable Parallel Operation in Over-Compound Generators

Their rising voltage characteristics

Simplest Way to Shift Load Between Parallel Shunt Generators

Adjust their field rheostats

Compound Generator Type Exempt from Needing Equalizer Bars

Under-compound

Characteristic Used to Directly Obtain External Characteristic of Shunt Generator

Open-circuit characteristic

Relationship Shown by Load Saturation Characteristic

$V$ and $I_f$

Cause of Slight Curvature at Lower End of O.C.C.

Residual pole flux

Non-Essential Condition for Self-Excited Voltage Build-Up

Armature speed must be very high

Nature of Voltage Build-Up Process in a D.C. Generator

Cumulative

D.C. Generator Type Unable to Build Up Voltage on Open Circuit

Series

First Action if Installed Self-Excited Generator Fails to Build Up

Reverse field connections

Method to Restore Accidentally Destroyed Residual Magnetism

To a d.c. source

Three Factors Causing Terminal Voltage Drop in a Shunt Generator

Armature resistance, armature reaction, and reduction in field current

Consequence of Increasing Field Resistance Beyond Critical Value

Will not build up

Voltage Regulation Value of an Ideal D.C. Generator

Zero

D.C. Generator Type with Poorest Voltage Regulation

Series

Sign of Voltage Regulation for Over-Compound Generator

Negative

Reason Commercial Compound Generators are Supplied as Over-Compound

Degree of compounding can be adjusted by using a divertor across series field