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Blocking of Zone Z1
If the main protection functions - differential protection and distance protection - operate in parallel, the distance
protection of Zone Z1 may pick up before the differential protection (e.g. in the case of close-up faults). If this
is desired, the distance protection works as a „booster" stage for fast tripping. If the fast tripping acts on one
end of the line only, accelerated tripping of zone Z1 is not desired (see also Section 2.5.1.4).
There are two ways of blocking Z1. If the device operates in differential protection mode, zone Z1 can be
blocked by setting a parameter (address 1533 Z1 blkd by diff). Another way of blocking the zone is to
set a binary input (No 3610 „>BLOCK Z1-Trip").
Controlled zone Z1B
The overreaching zone Z1B is a controlled zone. It does not influence the normal zones Z1 to Z6. There is no
zone switching, but rather the overreaching zone is activated or deactivated by the corresponding criteria. It
can also be set in address 1751 Op. mode Z1B to Forward or Reverse. If this stage is not required, it is set
to Inactive (address 1751). The setting options are similar to those of zone Z1: Address 1752 ZR(Z1B).
The delay times for single-phase and multiple-phase faults can again be set separately: T1B-1phase (address
1655) and T1B-multi-phase (address 1656).
Zone Z1B is often used in combination with automatic reclosure and/or teleprotection schemes. It can be acti-
vated internally by the teleprotection functions (see also Section 2.7) or the integrated automatic reclosure (if
available, see also Section 2.17), or externally by a binary input. It is generally set to at least 120 % of the line
length. On three-terminal lines („teed feeders"), it must be set to securely reach beyond the longest line section,
even when there is additional infeed via the tee-off point. The delay times are set in accordance with the type
of application, usually to zero or a very small delay. When used in conjunction with teleprotection comparison
schemes, the dependence on the fault detection must be considered (refer to margin heading „Distance Pro-
tection Prerequisites" in Section 2.7.14.
If the distance protection is used in conjunction with the internal or an automatic recloser, it may be determined
in address 1657 1st AR -> Z1B which distance zone is released prior to starting the AR. Usually the over-
reaching zone Z1B is used for the first cycle (1st AR -> Z1B = YES). This may be suppressed by changing
the setting of 1st AR -> Z1B to NO. In this case, overreaching zone Z1B is not released before and during
the first automatic reclose cycle. Zone Z1 is always released. When using an external automatic reclose device,
the setting only has an effect if the readiness of the automatic recloser is signalled via binary input „>Enable
ARzones" (No. 383).
Polarization
The degree of polarization with a fault-accurate memory voltage can be set in address 1771
Mem.Polariz.PhE for phase-to-earth loops, and in address 1773 Mem.Polariz.P-P for phase-to-phase
loops. For polarization with an unfaulted valid voltage (cross-polarization), the evaluation factor can be set sep-
arately for phase-to-earth and phase-to-phase loops under address 1772 CrossPolarizPhE and 1774
CrossPolarizP-P. This setting can only be changed using DIGSI at Additional Settings.
These parameters have an impact on the expansion of the characteristics dependent on the source impedance.
If these parameters are set to zero, the basic characteristic is displayed without any expansion.
Minimum Current of Zone Z1
In earthed systems with parallel lines without zero-sequence system infeed at the opposite line end, it may be
necessary to allow a tripping of Z1 only when exceeding an increased phase current threshold. For this pur-
pose, you can define a separate minimum current for the zone Z1 in address 1608 Iph>(Z1). A pickup of
zone Z1 is only possible if the phase currents have exceeded this threshold value. This parameter is only avail-
able if address 119 Iph>(Z1) is set to Enabled.
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
Functions
2.5 Distance Protection
173
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