ohmega305 protection_schemes

7/29/2019 Ohmega305 Protection_Schemes

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PROTECTION SCHEMES 3

Contents

1 TIME STEPPED DISTANCE .....................2

2 PERMISSIVE UNDERREACH...................3

3 PERMISSIVE OVERREACH.....................4


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1 TIME STEPPED DISTANCE

A system diagram for a typical TIMESTEPPED DISTANCE SCHEME is shownin Figure 1 with typical time delays forfaults at various points along the line

length as shown in Figure 1(c).

Typically the Zone 1 is set to 80% of theline length, Zone 2 to 120% of the linelength and Zone 3 as delayed back upprotection to cover at least the longestadjacent line.

A STEPPED DISTANCE SCHEME isnormally applied when there is nosignalling available between relays and asshown in the timing diagram givesinstantaneous Zone 1 coverage up to 80%

of the line length and Zone 2 time delay forthe remaining 20%. In this case the Zone3 time delay is available as back upprotection but this would not normally tripthe CB as the Zone 1 or Zone 2 of the nextfeeder would operate faster.

Z1A INST

Z2A DELAY

Z3A DELAY

Z2B DELAY

Z3B DELAY

DISTANCE

TIME

(b)

Z3A(R) Z1A Z2A Z3A(F)

Z1B Z2B

RELAY

'B'

RELAY

'A'

(a)

A) SYSTEM DIAGRAM

STEPPED DISTANCE PROTECTION

FOR 3 PHASE TRIPPING SCHEMES

Z1B INST

Z3B(R)

C) TIMING DIAGRAM

B) ZONE DIAGRAM

(c)

Z3A

Z1A

Z2A

Z1B

Z2B

Z3B

Figure 1


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2 PERMISSIVE UNDERREACH

A system diagram for a typicalPERMISSIVE UNDERREACH SCHEME isshown in figure 2 (a). Figure 2(b) showsthe set-up of the zones. Typical trip delays

for faults at various points along the linelength as shown in figure 2(c).

Typically the Zone 1 is set to 80% of theline length, Zone 2 to 120% of the linelength and Zone 3 as delayed back upprotection to cover at least the longestadjacent line.

A PERMISSIVE UNDERREACH SCHEMErequires signalling between two distanceprotection relays at each end of a line withthe VTs and CTs connected so that the

two relays are looking towards the sectionof line being protected as illustrated infigure 2(a). If a system fault occurs on theline at point x, the relay at end A trips theCB at end A in Zone 1 time and the relayat end B trips the CB at end B in Zone 1

time. If a system fault occurs on the line atpoint Y (outside the zone 1 reach of therelay at end A), the relay at end B trips theCB at end B in Zone 1 time and the Zone 1element at end B sends a signal (SS) toend A which informs end A that there is afault on the protected line. When end Areceives this signal the Zone 3 element atend A is allowed to trip the CB at end Ainstantaneously. If for any reason thesignal link fails system faults at Y will becleared at end A, in Zone 2 time as for thetime stepped distance scheme.

C) TIMING DIAGRAM

A) SYSTEM DIAGRAM

PERMISSIVE UNDERREACH


RELAY

'A'

RELAY

'B'

Z3B(R)

Z2A Z3A(F)

SIGNALLINGLINK

SSSS

SR SR

Z1B

Z1A

YX

Z3A(R)

Z2BZ3B(F)

Z3B DELAY

Z2B DELAY

Z1A/B INST

Z2A DELAY

Z3A DELAY

Z3B.SR Z3A.SR

DISTANCE

(a)

(c)

TIME

---- FAULT CLEARANCE TIME IF

SIGNALLING LINK FAILS

B) ZONE DIAGRAM

(b)

Z3A

Z1A

Z1B

Z2B

Z3B

Figure 2


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3 PERMISSIVE OVERREACH

A system diagram for a typicalPERMISSIVE OVERREACH SCHEME isshown in 3 below.

In this case, the Zone 1 is set to overreachat approximately 120% of the line sectionbeing protected but cannot tripinstantaneously until it receives permissionfrom the other end. If the signal link failsfault clearance will take place in Zone 2time delay as shown in fig 1(c). ThisPermissive Overreach Scheme shouldtherefore only be used with high reliabilitysignalling equipment.

An alternative PERMISSIVE OVERREACH

SCHEME is shown in Error! Referencesource not found. with the Zone 1 set tounderreach and the Zone 2 is used as theoverreach element. In this case the Zone

1 is independent of the signalling channeland gives instantaneous tripping for faultswithin Zone 1 setting (80%) even if thesignal channel fails.

The signal send (SS) output is enabled byoperation of any operation of any zone 2element in figure 4.

C) TIMING DIAGRAM

A) SYSTEM DIAGRAM

PERMISSIVE OVERREACH FOR 3 PHASE

TRIPPING SCHEMES (SCHEME 1)

Z3B

Z3B DELAY

Z2B

DELAY

Z2A

DELAY

Z3A DELAY

Z1A/Z1B

DISTANCE

(a)

(b)

TIME



RELAY

'A'

RELAY

'B'

Z3B(R)

Z1A Z3A

SSSS

Z3A(R)

Z2B

SRSR

B) ZONE DIAGRAM

Z3A

Z1A

Z2A

Z2B

Z1B

Z3B

(c)

Z1B

Z2A

Figure 3


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C) TIMING DIAGRAM

A) SYSTEM DIAGRAM

PERMISSIVE OVERREACH FOR 3 PHASE

TRIPPING SCHEMES (SCHEME 2)

Z3 B

Z3B DELAY

Z2 B

DELAY

Z2 A

DELAY

Z3A DELAY

DISTANCE

(a)

(b )

TIME



RELAY

'A '

RELAY

'B '

Z3B(R)

Z1 A Z3 A

SSSS

Z3A(R)

Z2 B

SRSR

B) ZONE DIAGRAM

Z3A

Z1 A

Z2 A

Z2B

Z1B

Z3 B

(c )

Z1 B

Z2 A

Z1A/Z1B Z2A.SRZ2B.SR

Figure 4


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ACCELERATED UNDERREACH

A system diagram for a typical ZONE 2ACCELERATED UNDERREACHSCHEME is shown in Figure 5(a) with

typical trip times for faults at various pointsalong the line length as shown in Figure5(b). This scheme is similar to thepermissive underreach scheme but usesthe Zone 2 element in conjunction with SR(signal receive) for aided tripping. Thus thereceipt of an SR signal will remove thetime delay for Zone 2.

Typically the Zone 1 is set to 80% of theline length, Zone 2 to 120% of the linelength and Zone 3 as delayed back upprotection to cover at least the longest

adjacent line.

An ACCELERATED UNDERREACHSCHEME requires signalling between two

distance protection relays at each end of aline with the VTs and CTs connected sothat the two relays are looking towards thesection of line being protected asillustrated in Figure 5 (a).

If a system fault occurs on the line at pointx, the relay at end A trips the CB at end Ain Zone 1 time and the relay at end B tripsthe CB at end B in Zone 1 time. If asystem fault occurs on the line at point Y,the relay at end B trips the CB at end B inZone 1 time and the Zone 1 element atend B sends a signal (SS) to end A whichinforms end A that there is a fault on theprotected line. When end A receives thissignal the Zone 2 element at end A isallowed to trip the CB at end Ainstantaneously. If for any reason the

signal link fails system faults at Y will becleared at end A in Zone 2 time delay asillustrated in the timing diagram.

C) TIMING DIAGRAM

A SYSTEM DIAGRAM

ZONE 2 ACCELERATED UNDERREACH


RELAY

'A'

RELAY

'B'

Z3B(R)

Z2A Z3A(F)

SSSS

Z1B

Z1A

YX

Z3A(R)

Z2BZ3B(F)

Z3B DELAY

Z2B DELAY

Z1A/B INST

Z2A DELAY

Z3A DELAY

Z2B.SR Z2A.SR

DISTANCE

(a)

(c)

TIME



B) ZONE DIAGRAM

Z3A

Z1A

Z2A

Z1B

Z2B

Z3B

(b)

SR SR

SIGNALLING

LINK

Figure 5

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