Zone 1 Extension Scheme - GE MiCOM P40 Agile Technical Manual

Application Notes
MiCOM P40 Agile P442, P444
• The zone 3 elements would usually be used to provide overall back-up protection for
adjacent circuits. The zone 3 reach (Z3) is therefore set to approximately 120% of the
combined impedance of the protected line plus the longest adjacent line. A higher
apparent impedance of the adjacent line may need to be allowed where fault current
can be fed from multiple sources or flow via parallel paths.
• Zones p and q are reversible directional zones. The setting chosen for zone p (q), if
used at all, will depend upon its application. Typical applications include its use as an
additional time delayed zone or as a reverse back-up protection zone for busbars and
transformers. Use of zone p(q) as an additional forward zone of protection may be
required by some users to line up with any existing practice of using more than three
forward zones of distance protection. Zone p(q) may also be useful for dealing with
some mutual coupling effects when protecting a double circuit line, which will be
discussed in section 3.1.2.1.2
• The zone 4 elements would typically provide back-up protection for the local busbar,
where the offset reach is set to 25% of the zone 1 reach of the relay for short lines
(<30km) or 10% of the zone 1 reach for long lines. Setting zone 4 in this way would
also satisfy the requirements for Switch on to Fault, and Trip on Reclose protection, as
described in later sections. Where zone 4 is used to provide reverse directional
decisions for Blocking or Permissive Overreach schemes, zone 4 must reach further
behind the relay than zone 2 for the remote relay. This can be achieved by setting:
Z4 ≥ ((Remote zone 2 reach) x 120%) minus the protected line impedance.
To understand the distance zones interactions, it should be considered:
• If Zp is a forward zone:
 Z1  Z2 < Zp < Z3
 T1 < T2 < tZp < T3 (
 R1G < R2G < RpG < R3G = R4G
 R1Ph < R1extPh < R2Ph < RpPh < R3Ph
• If Zp is a reverse zone:
 Z1 < Z2 < Z3
 Zp > Z4
 T1 < T2 < T3
 tZp < T4
 R1G < R2G < R3G
 RpG < R3G = R4G
 R1Ph < R2Ph < R3Ph
 RpPh < R3Ph = R4Ph
 R3G < U
 R3Ph < U
Note:
3.1.2.1.2

Zone 1 Extension Scheme

Auto-reclosure is widely used on radial overhead line circuits to re-establish supply following
a transient fault. A Zone 1 extension scheme may therefore be applied to a radial overhead
feeder to provide high speed protection for transient faults along the whole of the protected
line. Figure 17 shows the alternative reach selections for zone 1: Z1 or the extended reach
Z1X.
/ (1.2 X √3 I
)
N N
/ (1.2 X √3 I
)
N N
1. If Z3 is disabled, the forward limit element becomes the smaller zone Z2 (or
Zp if selected forward)
2. If Z4 is disabled, the directional limit for the forward zone is 30°.
P44x/EN AP/Hb6
(AP) 5-37