Broken Conductor Detection - GE MiCOM P40 Agile Technical Manual

Application Notes
MiCOM P40 Agile P442, P444
Selective fault clearance of the protection for forward faults is provided by the power
measurement combined with a time-delay inversely proportional to the measured power.
This protection function does not issue any trip command for reverse faults.
In compliance with sign conventions (the zero-sequence power flows from the fault towards
the sources) and with a mean characteristic angle of the zero-sequence source impedances
of the equal to 75°, the measured power is determined by the following formula:
Where:
ϕ
=
ϕ
=
0
Vr , Ir =
r.m.s r.m.s
The Vr and Ir values are filtered to eliminate the effect of the 3
Figure 69: Zero sequence power logic
3-pole trip is sent out when the residual power threshold "Residual Power" is overshot, after
a time-delay ('Basis Time Delay') and an IDMT time-delay adjusted by the "K" time delay
factor.
The basis time-delay is set at a value greater than the second stage time of the distance
protection of the concerned feeder if the 3-pole trip is active, or at a value greater than the
single-phase cycle time if single-pole autorecloser shots are active.
Ta time-delay is fixed (200 ms) and starts with residual current.
The IDMT time-delay is determined by the following formula:
Where:
K =
S =
ref
S =
r
4.6

Broken conductor detection

The majority of faults on a power system occur between one phase and ground or two
phases and ground. These are known as shunt faults and arise from lightning discharges
and other overvoltages which initiate flashovers. Alternatively, they may arise from other
causes such as birds on overhead lines or mechanical damage to cables etc. Such faults
result in an appreciable increase in current and hence in the majority of applications are
easily detectable.
Sr = Vr
Phase shift between Vr and Ir
255° or – 75°
R.M.S values of the residual voltage and current
Adjustable time constant from 0 to 2sec ('K Time Delay Factor' setting)
Reference residual power, depending on the CT:
10 VA for In = 1A
50 VA for In = 5A
Residual power generated by the fault
× cos(ϕ - ϕ
× Ir )
r.m.s r.m.s 0
t = K × (S /S )
ref r
P44x/EN AP/Hb6
(AP) 5-99
rd th
and 5 harmonics.