You should avoid building electric circuits that are inconsistent. The following section illustrates inconsistent circuits.
In Figure 14.1: Voltage Generators Forming a Loop monitoring Kirchhoff's loop equation on the lower loop, what is the voltage between node 1 and 2? If V1 and V2 are not equal, the voltage forces are inconsistent. Note in that figure that voltage generators form a loop . Even if V1 and V2 were consistent, numerical solution difficulties would occur.
The circuit in Figure 14.2: Voltage Generators in Parallel With Resistors is more complicated than that shown in Figure 14.1: Voltage Generators Forming a Loop, yet the main topological inconsistency is still present. The voltage generators form a loop.
Figure 14.3: Voltage Generators in Parallel With Other Circuit Components is even more complex. But you can easily identify the inconsistent loop of voltage generators.
In Figure 14.4: Current Generators in Parallel, monitoring Kirchhoff's nodal equation of node 1, what is the balance? If I1 ≠ I2, then the balance is not zero, the current forces are inconsistent. Even if I1 = I2 numerical solution difficulties would occur.
The circuit in Figure 14.5: Circuit Generators and a Supernode is more complex. Here, the current generators have no common node. Kirchhoff's nodal law is violated on a "super-node" in that figure. The "super-node" is called a cut. Current generators cannot form cuts; that is, there should be no super-node such that only current generators are entering it.
In a transient analysis, at t = 0, a capacitor can be represented by a voltage generator having the same voltage as the initial voltage of the capacitor. See Figure 14.6: Voltage Generator and Capacitor Equivalence.
In Figure 14.7: Velocity Generators Forming a Loop, right after closure of the switch, the initial current distribution can be computed by the equivalent circuit shown on the right-hand side. This is an inconsistent circuit (producing infinite current) because the voltage generators form a loop. Thus, the DC/harmonic rule that voltage generators should not form a loop should be applied such that the capacitors are considered as voltage generators.
In a transient analysis, at t = 0, an inductor can be represented by a current generator having the same current as the initial current of the inductor. See Figure 14.8: Current Generator and Inductor Equivalence.
In Figure 14.9: Current Generators Forming a Cut, right after the closure of the switch, the initial voltage distribution can be computed by the equivalent circuit shown on the right-hand side. This is an inconsistent circuit (producing infinite voltage) because the current generators form a cut. Thus, the DC/harmonic rule that the current generators should not form a cut should be applied such that the inductors are considered as current generators.
These circuits are contradictory, and they do not have physical meanings. Therefore, the program cannot detect them.