Page 205 - Practical Power System and Protective Relays Commissioning

Protection Relays Chapter | 18 205

The angle by which the current applied to the relay is displaced from the
voltage applied to the relay at the unit power factor is called the relay con-
nection, for example, 90 degrees connection between I R and V Y-B .
The relay angle which produces maximum torque is the maximum torque
angle (MTA).
As shown in Fig. 18.5.6, the relay connection is 90 degrees between
polarizing voltage V Y-B and current input to the relay I R and the MTA is 45
degrees between the maximum torque line and the reference polarizing
voltage V Y-B (Table 18.5.1).
As shown in Fig. 18.5.7, the relay connection is 90 degrees between
polarizing voltage V Y-B and the current input to the relay I R and the MTA is
30 degrees between the maximum torque line and the reference polarizing
voltage V Y-B (Table 18.5.2).
As shown in Fig. 18.5.8, the relay connection is 30 degrees between
polarizing voltage V R-B and current input to the relay I R and the MTA is
0 degree between the maximum torque line and reference polarizing voltage
V R-B (Table 18.5.3).

FIGURE 18.5.6 90 Degrees connection 45 degrees maximum torque angle.