# The Short Line (up to 80 km, 50 miles)

The equivalent circuit is shown in Figure 3.26 and it will be noticed that both shunt capacitance and leakage resistance have been neglected. The four-terminal network constants are (see Section 2.7):

The *regulation* of a circuit is defined as:

received voltage on no load (Vs) — received voltage on load (V_{R}) received voltage on load (V_{r})

It should be noted that if I leads V_{R} in phase, that is a capacitive load, then *V _{R} > V_{S}, *as shown in Figure 3.27.

**Figure 3.25 **Distributed constant representation of a line: *L =* inductance of line to neutral per unit length; *r =* a.c. resistance per unit length; C = capacitance line to neutral per unit length; *R =* leakage resistance per unit length

**Figure 3.26 **Equivalent circuit of a short line - representation under balanced three phase conditions

# Medium-Length Lines (up to 240 km, 150 miles)

Owing to the increased length, the shunt capacitance is now included to form either a p or a T network. The circuits are shown in Figure 3.28. Of these two versions the p representation tends to be in more general use but there is little difference in accuracy between the two. For the p network:

from which Vs and Is are obtained in terms of V_{R} and I_{R} giving the following constants:

**Figure 3.27 **Phasor diagram for short line on leading power factor load

**Figure 3.28 **(a) Medium-length line - p equivalent circuit, (b) Medium-length line - T equivalent circuit

Similarly, for the T network: giving