Carrier Aided Protection Scheme

PUTT (Permissive Underreach Transfer Trip):

• Carrier Send = Zone 1 pickup
• Carrier Receive + Zone 2 Pickup = Instantaneous Trip

POTT (Permissive Overreach Transfer Trip):

·????????Applicable for only series compensated transmission line.

·????????Carrier Send = Zone 2 pickup

·????????Carrier Receive + Zone 2 Pickup = Instantaneous Trip

BOP (Blocking Overreach Protection) / DCB (Direction Comparison Blocking):

·????????Carrier Send = Zone 4 pickup

·????????Carrier Not Receive + Zone 2 Pickup = Trip @ T2 time (Zone - 2 time)

For a fault (F1):

CB1=Zone -2 pickup ( Forward Zone )

CB2=Zone -4 pickup ( Reverse Zone )

CB3=Zone -1 pickup ( Forward Zone )

CB4=Zone -2 pickup ( Forward Zone )

CB2 send carrier to CB1?So CB1 Tripping is blocked. (Unnecessary Tripping is eliminated)

DCUB (Direction Comparison Unblocking):

·????????It is accompanied with POTT Scheme.

·????????For implementing Unblocking logic in a system , FSK ( Frequency Shift Keying ) feature is needed.

·????????It uses two frequency to maintain the protection system . They are

1.??????Guard Signal (Blocking Frequency)

2.??????Permissive Signal ( Trip Frequency)

Frequency Shift Keying under Normal condition – Guard Frequency is send/received.

Frequency Shift Keying under Abnormal condition – Unblock or Trip Frequency is send/received.

When a relay on both ends of the line shifts to unblocking frequency from blocking frequency then only tripped (DCUB Employed)

Guard/Trip Frequencies are specified by the utilities such that no two lines in the system has the same frequency.

Case 1:

·????????CB1 is in guard mode.

·????????Abnormal condition because of F1.

·????????Trips in Z1 Time.

·????????CB2 is in guard mode

·????????Abnormal condition because of F1.

·????????Trips in Z1 Time.

Case 2:

·????????Source impedance of line is high. SIR > 4.

·????????Zone fault impedance will be very less than actual impedance, overreach occurs.(POTT Employed )

·????????CB1 is in guard mode

·????????Abnormal condition sensed because of F1.

·????????FSK removes guard signal

·????????POTT Enabled

·????????Zone -2 Pickup = Carrier Send

·????????CB2 Unblocking Frequency received

·????????Similarly for CB2.

Case 3:

·????????CB1 is in guard mode

·????????Communication Channel got failed

·????????Guard Signal removed automatically

·????????Unblocking window enabled

·????????Internal Permissive Receive Enabled.

Case 1: (Within 150 ms) if a Fault F1 experienced, the below logic employed.

·????????Case 2: (After 150 ms) if a Fault F1 experienced, Zone -2 Operates in Zone 2 Time delay.

Similarly for CB2.

The main advantage of DCUB is Carrier aided scheme remains active for certain few milliseconds even after the communication channel got failed.

Weak Infeed & Echo Logic:

Weak Infeed Trip Condition:

Echo Logic: