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Understanding L60 Oscillography; Overview - GE L60 Instruction Manual

Line phase comparison system, ur series.
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10 APPLICATION OF SETTINGS

10.5UNDERSTANDING L60 OSCILLOGRAPHY

The L60 oscillography feature is a powerful tool for tuning, commissioning, and troubleshooting. It also helps to understand
the theory of phase-comparison and how the L60 relay incorporates standard analog phase comparison principles. The
L60 oscillography allows customer to observe not only AC waveforms and 87PC operate signals, but all details of compos-
ite signal forming, fault detector operation, input and output processing, squares forming, coincidence detection, and inte-
gration of the signal. All currents are processed per CT breaker on breaker-and-a-half applications (applies to composite
signal, fault detectors, etc.).
As explained in the Theory of Operation chapter, the phase comparison operating current is either mixed from all three
phase currents into one composite quantity using the I_2 – K × I_1 formula, or it is just 3I_0. In contrast to phase current
waveforms, where raw samples are captured and displayed, the operating current is digitally filtered with the DC compo-
nent and harmonics removed. During no-fault conditions, the operating current is relatively small and dictated mostly by the
load positive sequence current (FDL and FDH detectors drop off). However, the
power cycle and the
local pulses at the negative half of the power cycle are present in oscillography once the operating
NEG
current is greater than 0.02 pu. When the
exceeds the FDL pickup setting, the
fault condition and thus initiating transmitting squares on the positive (
wave. At this moment, the logic is preparing to process the phase comparison algorithms according to the selected
schemes and setting values.
The next step is to adjust pulses according to channel asymmetry and channel delay. The received pulse is adjusted in
accordance to the
CHANNEL ASYMMETRY
, etc.) are also delayed to properly align with a local pulse. The local aligned signals (
ALIGNED
) are derived from either one CT current or from two CTs current and are delayed as per channel delay setting.
ALIGNED
Even when FDL and FDH operate, the scheme will not produce until the
FDH delayed by the channel delay until received signal arrives. The scheme is now ready to produce a trip.
GE Multilin
Composite signal
Coincidence integrator
Trip output
Net positive squares
BRK1 positive squares
BRK1 FDL
Trip sent to I/O module
Pos. sq. delayed (Ch. Del)
FDH delayed (Ch. Del)
Figure 10–10: MAIN L60 OSCILLOGRAPHY SIGNALS
operating current (or
87PC BRK1
(and
BRK1 FDL
BRK2 FDL
setting. If this setting is quite high, then the adjusted signals (
L60 Line Phase Comparison System
10.5 UNDERSTANDING L60 OSCILLOGRAPHY
BRK1 negative squares
Neg. sq. delayed (Ch. Del)
local pulses at the positive half of the
POS
current for two-breaker applications)
87PC BRK2
for two breaker applications) flags are asserted, indicating a
) and negative (
Tx POS
flag is asserted, which represents the
FDH ALIGNED

10.5.1 OVERVIEW

FDH operand
Raw received signal
Net negative squares
BRK1 FDH
Rx adjusted (asymm.)
Integrator input
831796A1.CDR
) halves of the sine-
Tx NEG
,
RX1P ALIGNED
RX1N
and
POS ALIGNED
NEG
10-13
10

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