Malla Reddy College of Engineering and Technology (MRCET)
Department of EEE ( 2017-18 )
Electrical Circuits EEE
Cut-set:
It is that set of elements or branches of a graph that separates
two main parts of a
network. If any branch of the cut-set is not removed the network remains connected. The term
cut-set is derived from the property by which the network can be divided into two parts.
A cut-set is shown on a graph by a dashed line which passes through the branches defining the
cutest. A graph should have at least one cutest though there can be more than one cut-set in any
graph.
Fundamental cut-set:
A fundamental cut set of a graph with respect to a tree is a cut set formed by one and only one
twig and a set of links.
Thus in a graph ,for
each twig of a chosen tree ,there would be a
fundamental cut-set. For a graph having N nodes there will be (N-1) fundamental cut-sets ( i.e.
equal to the number of twigs).
As a convention, the orientation of cutest is so chosen that it coincides with the orientation of it’s
twig.
Cut-set Matrix:
This matrix provides a compact and effective means of writing all the algebraic
equations giving branch voltages in terms of the tree branches.
Procedure for forming the fundamental Cut-set Matrix:
1. A tree is selected arbitrarily in the graph.
2. Fundamental cut-sets are formed (i.e. The network is divided into two parts) with each twig in
the graph for the entire tree.
3. Directions of the cut-sets are oriented in the same direction as that of concerned twig.
4. Fundamental cut-set matrix [Qkj] is formed where
Qkj = 1 when branch bj has same orientation as that of the cut-set k
Qkj = -1 when branch bj has opposite orientation to that of the cu-set k
Qkj = 0 when branch bj is not in the cut-set k
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