Page 638 - Basic Electrical Engineering

Since I R is very small as compared to V, change of (V − I R ) with change
a
a
a
a
of I will be very small.
a
Thus, N will remain constant as I , which is proportional to load, increases
a
as has been shown in Fig. 7.20 (bi).
By knowing the variation of T and N against the load current, I , the
a
relationship of T versus N can be drawn as shown in Fig. 7.20 (bii).

It can be seen that dc shunt motors are approximately constant speed
motors and can be used in applications like lathe machines, drilling machines,

milling machines, in printing press, paper mills, etc.

7.12.2 Characteristics of DC Series Motors

In a dc series motor the field winding is connected in series with the armature

so that same current flows through the field and armature windings. The flux
produced, ϕ is proportional to the field current which is equal to I . The
a
relevant equations are written as

Figure 7.21 (a) Circuit diagram of a series motor; (b) characteristics of a dc series motor

Therefore,