Areva MiCOM P441, Техническое руководство

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P44x/EN AP/E33 Application Notes
Page 28/220 MiCOM P441/P442 & P444
Z1 G/F (Optional)
Z1 G/F (Normal)
ZMO
P3048ENa
FIGURE 5 - ZONE 1 REACH CONSIDERATIONS
2.7.10 Effect of Mutual Coupling on Zone 2 Setting
If the double circuit line to be protected is long and there is a relatively short adjacent line, it
is difficult to set the reach of the zone 2 elements to cover 120% of the protected line
impedance for all faults, but not more than 50% of the adjacent line. This problem can be
exacerbated when a significant additional allowance has to be made for the zero-sequence
mutual impedance in the case of earth faults (see Section 2.4.6). For parallel circuit
operation the relay Zone 2 earth fault elements will tend to underreach. Therefore, it is
desirable to boost the setting of the earth fault elements such that they will have a
comparable reach to the phase fault elements. Increasing the residual compensation factor
kZ2 for zone 2 will ensure adequate fault coverage.
Under single circuit operation, no mutual coupling exists, and the zone 2 earth fault elements
may overreach beyond 50% of the adjacent line, necessitating time discrimination with other
Zone 2 elements. Therefore, it is desirable to reduce the earth fault settings to that of the
phase fault elements for single circuit operation, as shown in Figure 5. Changing between
appropriate settings can be achieved by using the alternative setting groups available in the
relay series relays.
Z2 ' Boost ' G/F
Z2 ' Reduced ' G/F
(i) Group 1
(ii) Group 2
Z2 PH
Z2 PH
ZMO
P3049ENa
FIGURE 6 - MUTUAL COUPLING EXAMPLE - ZONE 2 REACH CONSIDERATIONS