We found that voltage sources of different terminal voltages cannot be
placed in parallel because of a violation of Kirchhoff's voltage law.
current sources of different values cannot be placed in series due to a
violation of Kirchhoff's current law.
However, current sources can be placed in parallel just as voltage
sources can be placed in series. In general,
two or more current sources in parallel can be replaced by a single
current source having a magnitude determined by the difference of
the sum of the currents in one direction and the sum in the opposite
direction. The new parallel internal resistance is the total resistance
of the resulting parallel resistive elements.
Consider the following example.
Reduce the parallel current sources in Fig.no.1 to a
single current source.
Fig.no.1: Parallel current sources for Example 1.
The net source current is
$$I = 10 A - 6 A = 4 A$$
with the direction being that of the larger source.
The net internal resistance is the parallel combination of resistances,
R1 and R2:
$$R_p = 3 Ω || 6 Ω = 2 Ω$$
The reduced equivalent appears in Fig.no.2.
Fig.no.2: Reduced equivalent for the configuration of Fig.no.1.