Page 32 - Basic PD Theory

PD Data Types

The Q m, or Peak Magnitude, is the magnitude of the pulses
for one fundamental (directly measured) pulse category
that has a repetition rate of 10 pulses per second, and
corresponds to the peak PD activity. Q m is an indicator
of how severe the PD is at the most deteriorated part of
the winding. Positive and negative Q m refers to the peak
PD activity from the positive and negative PD pulses,
respectively.
For our purposes, Q m and NQN are derived from the test
results and are valuable for comparisons amongst

Trend Analysis Plot
Figure 31: PD Summary Variables
machines or trending over time. The Trend Plot 200 Mach. Qm+ Mach. Qm- Noise Qm+ Noise Qm-
represents the trend in partial discharge summary 175
numbers, specifically NQN and Q m, and thus provides 150
a graphical representation of the progression in 125
insulation ageing. The Trend Plot provided in the 100 75Y Axis
PDView software may display trends of up to 10 50
parameters for a given selection of data sets, including 25
±NQN and ±Q m, load, and temperature (Figure 32). 0
The summary variables available for the report depend 2001 Dec Jan 2002 Feb Mar Apr May X Axis Jun Jul Aug Sep Oct Nov
on the Iris instrument (see Section E. Zone of Coverage).
It some cases, the polarity of the pulses are reversed Figure 32: Trend Plot
from these “classic” positions, see Appendix F. Prime
Numbers) Pulse Phase Analysis Plot
Meas: 146, Absolute C1
280.0
4.3 Phase Resolved Plots
During data collection using a Portable, Guard or GuardII
instrument, each cycle is divided into 100 phase windows to 1000
enable the display of data relative to the specific phase-to-
ground voltage reference, or 24 phase windows for a Trac or 100
TracII monitor. Experience has indicated that such pulse phase 250
500
analysis is useful to help identify what the deterioration Pulse Count Rate [PPS] 750 Pulse Magnitude [mV]
mechanisms are and if multiple mechanisms are occurring. 10 1000
The Pulse Phase Analysis (Figure 33 - 3D or PPA) displays the 1250
PD pattern in 3D with the horizontal axis the AC reference, the 1 0
vertical axis the pulse count rate and the emanating axis as the 45 90 1500
magnitude. The Linear Pulse Density Plot (Figure 34 - LPD or 135 180 225
referred to as PRPD by some in the industry [12] ) is the most Phase Angle [deg] 270 315
commonly used graph type for display of phase-resolved partial 360
discharge data [12]. This two-dimensional plot displays the Figure 33: Phase-resolved PPA
partial discharge magnitude (vertical axis) as a function of the
phase angle of the reference 50/60 Hz sine wave (horizontal axis). A colour-coding scheme provides information on the pulse
repetition rate for a given combination of phase-angle and magnitude.

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