Advantages, Disadvantages, Solved Example Problems | Testing of D.C. Machines
Subject and UNIT: Electrical Machines: Unit III: b.Testing of D.C. Machines
Another method of testing the d.c. motor is brake test method. This is a direct method of testing the motor. In this method, the motor is put on the direct load by means of a belt and pulley arrangement.
Advantages, Disadvantages, Solved Example Problems | Testing of D.C. Machines
Subject and UNIT: Electrical Machines: Unit III: b.Testing of D.C. Machines
This is indirect method of testing d.c. motors in which flux remains practically constant i.e. specially in case of shunt and compound motors. Without actually loading the motor the losses and hence efficiency at different loads can be found out.
Direct and Indirect Method
Subject and UNIT: Electrical Machines: Unit III: b.Testing of D.C. Machines
The efficiency of a d.c. motor is given by, Efficiency = Power output / Power input = Power input - Losses / Power input
Subject and UNIT: Electrical Machines: Unit III: b.Testing of D.C. Machines
Condition for Maximum Efficiency - Current at Maximum Efficiency• In case of a d.c. generator, following three efficiencies are defined.
Subject and UNIT: Electrical Machines: Unit III: b.Testing of D.C. Machines
• The various losses in a d.c. machine whether it is a motor or a generator are classified into three groups as: 1. Copper losses 2. Iron or core losses 3. Mechanical losses.
Testing of D.C. Machines
Subject and UNIT: Electrical Machines: Unit III: b.Testing of D.C. Machines
For any d.c. machine whether it is a generator or a motor, its efficiency is important. It should work efficiently.
Subject and UNIT: Electrical Machines: Unit III: b.Testing of D.C. Machines
Electrical Machines: Unit III: b.Testing of D.C. Machines : Syllabus, Contents
D.C. Motors | Electrical Machines
Subject and UNIT: Electrical Machines: Unit III: a. D.C. Motors
Electrical Machines: Unit III: D.C. Motors : Two Marks Questions with Answers
Advantages and Disadvantages | D.C. Motors
Subject and UNIT: Electrical Machines: Unit III: a. D.C. Motors
• When it is desired to have wide and very sensitive speed control then this system is more generally used. The system is as shown in the Fig. 4.22.1.
Subject and UNIT: Electrical Machines: Unit III: a. D.C. Motors
• The flux produced by the winding depends on the m.m.f. i.e. magnetomotive force which is the product of current and the number of turns of the winding through which current is passing. So flux can be changed either by changing the current by adding a resistance or by changing the number of turns of the winding. Let us study the various methods based on this principle.
Subject and UNIT: Electrical Machines: Unit III: a. D.C. Motors
• Out of the three methods, let us study flux control method.
Subject and UNIT: Electrical Machines: Unit III: a. D.C. Motors
• According to the speed equation of a d.c. motor we can write, N α Eb / ϕ ∞ V-IaRa / ϕ