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2 CALCULATION OF SETTINGS
2.
Compensated Lines:
a) Series compensated line, no capacitor at the relay end of the line.
Set the NT_OFSET per the uncompensated line procedure.
b) Series compensated line, Bus-side Potential
NT_OFFSET = (0.0055)·( Z
c) Series compensated line, Line-side Potential
NT_OFFSET = (0.022)·( X
where : Z
= positive sequence impedance of protected line (in secondary ohms)
1
X
= total series capacitive reactance connected between the bus-side source of potential and the source
t
of potential of the relays located at the remote end of the line (in secondary ohms)
X
= series capacitive reactance (in secondary ohms) of capacitor located between line-side potential source
c
and bus directly behind relay ( X
I
= Magnetics Module CT rating (1A or 5A)
n
507: UNBALALARM - Unbalanced Current Alarm
The ALPS system is supervised by a fault detector (FD) that uses the following operating quantity:
I ∆
FD
=
I
I
+
+
op
1
2
0
Tripping will not be permitted unless there is a concurrent output from the fault detector, therefore an increase in security is
obtained. The ALPS monitors the output of the fault detector, and if it produces an output that lasts for more than 60 sec-
onds, then it is an indication:
1.
That there is an unbalance in the current on the system as indicated by the presence of negative sequence current ( I
and/or zero sequence current ( I
2.
The fault detector has failed (unlikely).
If either of these conditions is detected, then an UNBALARM signal is produced. This signal can be routed via the Xpres-
sion Builder program to drive one of the programmable outputs, or it may be used as an input to one of the programmable
outputs that may already have been selected for alarm duty.
601: 50 - Phase Instantaneous Overcurrent
The 50 function can be used in many applications to provide high speed, direct tripping for heavy close in faults. To use the
phase instantaneous overcurrent trip function, set 50 = YES, otherwise set 50 = NO. See Protection Settings 602 and 603
for further discussion on use of 50 function. Also, Protection Setting 201: Z2PHASE must be set to YES.
602: 50_DIRCNL - Directional Control Of 50
The 50 function can be set to directional or nondirectional. Directionality is obtained with the Zone 2 phase distance func-
tions. Protection Setting 201 must be set to Z2PHASE = YES to make the 50 function directional.
If 50 is made directional, the setting to be made on the function is based on the maximum fault current for a fault at the
remote end of the line. When 50 is made non-directional, then the setting is based on the maximum fault current for a fault
at either end of the line. If the maximum fault current for a fault at either end of the line is approximately the same, then it is
proposed that the 50 function be made non-directional.
603: 50PICKUP - 50 Pickup Setting
50 provides direct tripping for multiphase faults, and it operates on the highest of the three delta currents, IA-IB, IB-IC, or
IC-IA. This permits 50 to have the same response for all multiphase faults at the same location. If 50PICKUP is non-direc-
tional, then it should be set at least 25% greater than the maximum delta three-phase fault current for a fault at either termi-
nal of the line. If 50PICKUP is directional, then it should be set at least 25% greater than the maximum delta three-phase
fault current for a fault at the remote terminal of the line. The setting is calculated on the basis of the delta current which for
a three phase fault is equal to the square root of three times the phase current.
GE Power Management
- X
)·( I
)
1
t
n
)·( I
)
c
n
above in Figure 2–11: NT/NB FUNCTIONS).
c
).
0
ALPS Advanced Line Protection System
2.3 PROTECTION SETTINGS
2.3.7 OVERCURRNT
2-25
2
)
2
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