How do you determine the polarity of a voltage?

The polarity of the voltage drop across any resistive component is determined by the direction of current flow through it: positive entering, and negative exiting.

How can the terminal voltage of a separately excited DC generator be regulated?

In separately excited DC generators, the terminal voltage as the load increases and the load current started to flow. There is slight drop in the terminal voltage due to armature reaction and IR drop but these drop can be eliminated by increasing field excitation and then we can get constant terminal voltage.

How can the polarity of a DC generator be reversed?

The polarity of induced e.m.f. in a generator can be reversed by reversing either the direction of rotation or field winding connection.

What is polarity of voltage?

Voltage Polarity Voltage is an energy level difference between two points, and the polarity of the voltage simply indicates which point has the higher energy level. Voltage polarities are typically indicated on circuit diagrams by “+” and “-” signs, as shown in Fig. 1.

What are two ways of changing the polarity of the circuit on a direct current machine?

You can reverse the direction of your DC motor in two ways. You can change the polarity of the circuit at supply or in the field windings. Or you can change the polarity in the armature winding.

What are the different types of generator according to the way of their fields are excited draw their figures?

DC generators are categorized into three main types based on the methods of field excitation: Permanent Magnet, Separately Excited, and Self-Excited DC generators. The first type excites the field coils by using Permanent magnets, while the separately excited one includes an external force for excitation.

Which determines the polarity of induced emf in DC shunt generator?

The polarity of induced emf depends upon the direction of the magnetic field and the direction of rotation. In a motor, the induced emf is called Back Emf (Eb) because it acts opposite to the supply voltage.

What polarity do Interpoles take in a DC motor?

Interpoles are narrow poles placed at the GNA and fitted to the Yoke and also known as Commutating Poles or Compoles. For generator, the polarity of Interpoles must be same as that of main Pole ahead of it in the direction of rotation. For Motor, the polarity of Interpole must be same as that of Main Pole behind it.

What are the two types of dc generators?

Types of DC Generators (Diagrams Included)

• Permanent Magnet DC Generators – Field coils excited by permanent magnets.
• Separately Excited DC Generators – Field coils excited by some external source.
• Self Excited DC Generators – Field coils excited by the generator itself.

How to control the voltage of a separately-excited DC generator?

The voltage of a separately-excited DC generator can be controlled by controlling generator speed, by using a variable field supply, or by a combination of both. A self-excited dc generator can be controlled by generator speed or by a rheostat or electronic circuit that reduces the field current. A combination could also be used.

How do you change the polarity of a generator?

In order to change the polarity at the generator terminals, either the direction of rotation of the generator has to be reversed or the direction of magnetic field has to be reversed (this can be done by reversing the current in the separately excited field coil) but not both together.

What is magnetic or open circuit characteristic of a DC generator?

Magnetic or Open Circuit Characteristic of Separately Excited DC Generator. The curve which gives the relation between field current (I f) and the generated voltage (E 0) in the armature on no load is called magnetic or open circuit characteristic of a DC generator.

How does voltage affect the speed of an excited DC motor?

The speed of a separate excited DC motor will change in proportion to armature voltage. Moreover, changing the polarity of the armature voltage will change its direction of rotation. That is basically the method which was, until fairly recently, used to control elevators in large buildings.