What is the OCC characteristics of DC shunt generator?
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What is the OCC characteristics of DC shunt generator?
The open circuit characteristics (O.C.C) or magnetization characteristics is the curve that shows the relationship between the generated EMF at no-load (E0) and the field current (If) at constant speed. It is also known as no-load saturation curve.
What is self excitation in DC shunt generator?
What is Self-excitation in DC shunt generator? Explanation: Rather than arranging a separate dc source for excitation purposes, practical generators are always excited from their own armature terminals, this method of excitation being known as self-excitation.
What are the characteristics of a separately excited DC generator?
The external characteristic of the separately excited DC generator is obtained by subtracting the drops due to ohmic loss (Ia Ra) in the armature from generated voltage (Eg). Terminal voltage(V) = Eg – Ia Ra. This curve gives the relation between the terminal voltage (V) and load current.
What is self excitation in DC shunt motor?
What is self excitation in case of a dc machine? Ans. The process of generating a magnetic field by means of an electric current is called excitation. Modern generators with field coils are self-excited, where some of the power output from the rotor is used to power the field coils.
Why the OCC of a DC shunt generator is not a straight line?
Characteristics of DC Series Generator The curve AB in above figure identical to open circuit characteristic (O.C.C.) curve. This is because in DC series generators field winding is connected in series with armature and load.
Why OCC is also known as magnetization characteristics?
A typical Magnetization Characteristics is shown in Fig. 7.20. It is known as open-circuit characteristic (OCC) because of the method by which it is determined. It exhibits all the important characteristics of the magnetization curve of iron, modified by the presence of an air-gap in the magnetic circuit.
Why the OCC for the self excited generator does not start from the origin?
In shunt DC Generator, there is a residual magnetism in the poles. Because of this, some emf is induced in the generator even before field current If = 0. It is called Residual emf and is shown in the above graph as OA. Hence the curve starts little way up, instead of starting from the origin.
What are the characteristics of DC shunt motor?
Characteristics of a DC Shunt Motor:
- Speed-Armature Current Characteristic:
- Torque-Armature Current Characteristic:
- Speed-Torque Characteristic:
- Break in Field Circuit of a DC Motor:
What is the difference between OCC external and internal characteristics curve of DC generator?
An external characteristic curve shows the relation between terminal voltage (V) and the load current (IL). Terminal voltage V is less than the generated emf Eg due to voltage drop in the armature circuit. Therefore, external characteristic curve lies below the internal characteristic curve.
What is the purpose of OCC test?
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Why is OCC not on Origin?
In an OCC at If =0, graph starts from origin. Explanation: As the machine would have been previously subjected to magnetization, a small residual voltage would be present with field unexcited. As will be seen practically, this is necessary for generator to self-excite.
Why the OCC of DC shunt generator not starts from the origin?
The curve does not start from the origin but from the point above the Y-axis, slightly above the origin. This is due to the residual magnetism in the poles of generator at low value of field current. draw the O.C.C.
Why OCC is called as no load magnetization characteristics?
It is known as open-circuit characteristic (OCC) because of the method by which it is determined. It exhibits all the important characteristics of the magnetization curve of iron, modified by the presence of an air-gap in the magnetic circuit.
What are the types of characteristics in DC motor?
Generally, three characteristic curves are considered important for DC motors which are, (i) Torque vs. armature current, (ii) Speed vs. armature current and (iii) Speed vs. torque.
What is the difference between self excited and separately excited generators?
In a separately excited (S.E.) machine, the field winding is connected to a separate voltage source while, in a self excited generator field winding is connected across the armature terminals (provides its exciting current) .
What is external characteristics of DC shunt generator?
AC curve is showing the external characteristic of the shunt wound DC generators. It is showing the variation of terminal voltage with the load current. Ohmic drop due to armature resistance gives lesser terminal voltage the generated voltage. That is why the curve lies below the internal characteristic curve.
What is OCC of synchronous generator?
Open-circuit characteristic (OCC) of a generator The OCC follows a straight-line relation as long as the magnetic circuit of the synchronous generator does not saturate. Since, in the linear region, most of the applied mmf is consumed by the air-gap, the straight line is appropriately called the air-gap line.
Why the OCC curve starts from a point above the origin?
This curve starts from a point which is slightly higher than the origin representing that there is some flux produced by the field poles even no current is passed through the field windings.
