What is an Open Circuit ?
Definition
Open Circuit Characteristics (O.C.C) refer to the relationship between the generated voltage (EMF) and the field current in a generator (especially a DC generator), when the armature is running at a constant speed and no load is connected.
This is also called the no-load characteristic of a generator.
Open Circuit Characteristics
This curve shows the relation between the generated e.m.f at no load (Eo) and the field current (Ip) at constant speed.
1. When the field current is zore (0), the generator field , the generator still gives some small voltage.
- This happens because of residual magnetism (leftover magnetism in poles).
2. In the beginning part of the curve (up to point B) the Curve is straight (linear)
- This is because the iron does not resist magnetism much , and the air gap is the main resistance.
3. After point B, the curve starts to bend
- This is because the iron starts to resist magnetism (iron saturation starts ).
4. After point c the curve becomes almost flat
- This means the generator can’t increase voltage much more, even if we increase field current.
This happens due to magnetic saturation . The poles are already fully magnetizer.