Question

The positive-sequence line impedance as well as CT and VT ratios at B1 for the 33 kV system as shown in Table 1 and Table 2 below :

Table 1

Line	Positive Sequence Impedance
1-2	4+j30
2-3	4+j40
3-4	4+j50

Table 2

Breaker	CT Ratio	VT Ratio
B1	100/5 A	33000/5 V

Zone 1 reaches 90% of the protected line while zone 2 extend beyond the protected line up to 50% of the adjacent line and Zone 3 covers the protected line up to 25%. Determine the settings Zr1, Zr2 and Zr3 for the B1 three-zone, directional impedance relays. Draw its MHO relay diagram and impedance relay diagram.

Answer 1

Transmission line impedence transferred to relay side is given as  

So,

  

  

The impedence relays setting of B1 is following,

​​​​​​​

The impedence relay diagram is shown in followin figure in which Z1, Z2, Z3 represents the zone 1,2,and 3 protection impedence setting

For Mho Relay,

here MTA(Maximum Torque Axis is not provided so taken as 90 degree.

So,

Similarly,

The mho diagram is drawn following.