DC network analysis
Choice of the supposed direction.
First of all, the supposed direction of the current must be clearly determinated before starting calculation. Here is a way which works without ambiguity.
The direction of electrons flow in an ammeter is like the direction of blood into lungs. Black venous blood flows into lungs and red arterial blood flows out of lungs. When the real electrons current flows in this direction, the ammeter will indicate positive value for both volt and ampere.
The diagram has not been drawn in the traditional manner just in order to show you the arrangement of ammeter.
Branch current method ( or “nodal analysis”) with Kirchoff’s current law.
The sum of all ampere values toward a node is 0. There must be a negative value somewhere.
An unknown value can be calculated.
Mesh analysis ( or “loop analysis”) with Kirchoff’s voltage law.
The sum of all volt values in a loop is 0. There must be a negative value somewhere.
A part of the current from E1 may get into the Loop2 and mix with the current I2. In that case a part of the current from E2 must get into the Loop1 and mix with the current I1. The result will be the same.
An unknown value can be calculated.
Superposition theorem is the easiest way when loads have been simply arranged.
Open circuit voltage, OCV
When a dry cell is providing electricity, sometimes it gets warm. It means the cell has its own resistance. That is internal resistance. Internal resistance can be simply schematized like this diagram. When a load is connected to the cell, the potential energy, voltage, will be divided between the resistance of that load and the internal resistance of the cell. This cell is laveled as 1.5 volt. 1.5 volt is its open circuit voltage. That is its potential energy without any circuit connection.
Millman’s theorem, Thevenin theorem and Norton theorem are all the same.
Millman’s theorem makes calculation of open circuit voltage easy.
Utilisation of conductance G makes the forlmulae simple.
Wye-delta transformation.
A delta circuit can be easily calculated as changeing values as if it were a wye circuit.
