# PARTIAL DISCHARGE LOCATION Selected

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```					PARTIAL DISCHARGE LOCATION
Selected Topics

M.S. Mashikian
IMCORP

ICC Meeting - Fall 2000
TOPICS
   TESTING PHILOSOPHY
• Excitation Voltage
• Test Voltage Level
 METHOD OF REFLECTOMETRY
 METHOD OF ARRIVAL TIME
 TESTING
• Branched Circuits
• On-line - Discussion of ON and OFF-Line
   Major Concerns - Answers                    1
TESTING PHILOSOPHY
   PURPOSE:
• Reduce Service Failures - Improve Reliability
• Reduce Cost or Delay Capital Expenditure
   TEST GOALS:
• Identify defects that may cause near-term service
failures
• Characterize severity of defects to help prioritize
corrective actions
• Constraint: Minimize likelihood of test-produced damage
• Other
2
TESTING PHILOSOPHY
EXCITATION VOLTAGE
 Use 50/60Hz produced by resonant test
set
 Ramp voltage slowly until PD is
detected or max. test voltage is reached
 Dwell approx. 2 seconds (will be
reduced to ~ 10 cycles).
 Reduce voltage to zero very rapidly.

3
RESONANT TRANSFORMER
Inductor
1. Variable air-gap inductor
L               2. Fixed inductor

C       Cable

U1                                              Resonance:
wL = 1/wC
1. U1 is 50/60 Hz
2. U1 is variable frequency
L
w
4
PARTIAL WAVE - 50/60HZ
1/4 or 1/2-cycle
50/60Hz

dc
0°   90°    180° 270°   360°

PD is detectable only in the quadrants shown

5
OSCILLATING WAVE (OSW)
• Frequency dictated
by cable capacitance
• Attenuation depends
dc           on cable

6
APDAC
50/60 Hz

+
dc

-

ALTERNATING POLARITY DC-BIASED AC

7
TEST VOLTAGE LEVEL
 Decide after discussing with client
 Minimum: 2U0 recommended
 Maximum: 2.5 - 3.0U0

   Rationale
Consider maximum transient voltage that
may exist on system: geographic location
and system protection.
8
CUMULATIVE PD PROBABILITY,
2500km, EXTRUDED CABLE
Cumulative PD Probability, %
100

80

60

40

20

0
1.0   1.3     1.7      2.5   3.0
PDIV Range, U0

DATA BASED ON 960 PD EVENTS IN CABLES
At 1.0 U0, less than 3% of PD events can be identified.
9
TEST VOLTAGE LEVEL
   PDIV varies with type of excitation
voltage:
With sinusoidal VLF, PDIV may be as high
as 2.5 times that at 50/60Hz.
   Where PD is detected with 50/60Hz
voltage, no PD may seem to exist at the
same voltage level in PD tests with
other types of excitation voltage.
10
PRINCIPLES OF PD TESTING
PD Site Location
 Reflectometry     (off-line)
 Arrival-Time
IMCORP
• Non-branched (2-termination) system   Technologies

– Off-Line
– On-Line
• Branched system:
– Off-Line
– On-Line
   Frequency-Domain Testing                     11
REFLECTOMETRY
25
t2                 A                                 C      B
20                 ~                                          x
t1
PD Site
Amplitude, mV

15                                    Estimator

10                                                       t1
AC =        x AB
t2
5

0

-5
0   2             4               6                 8           10
Time, ms

12
TEST REPORT
Joint and PD Locations

PD

Joint

13
TEST REPORT
Joint and PD Locations

PD

Joint

14
PHASE RESOLVED PD DISPLAY
PD in Termination

15
ARRIVAL-TIME
NON-BRANCHED CABLE
Principle                   sensor 2
sensor 1
x

t1                 x                        L-x             t2

x = 1/2[v(t1-t2)+L]

Sensor 1                  Actual                      Sensor 2
~
Signal
Conditioner
From SDCT                                SDCT
Multi-Channel
Estimator                            SDCT = Signal detection - conditioning - transmission

16
ARRIVAL-TIME
BRANCHED CABLES

Remote #2

SDCT
Test
Transformer                                                   Remote #3
Sensor          Branched Cable

Signal
conditioner
From                                       SDCT
Estimator       #1,2,3               SDCT
Multi-Channel                 Remote #1

17
TESTING 4-TERMINAL
CIRCUIT

18
PD-LOCATION

19
PD TESTING - Major Concerns
   Is PD test able to locate water trees?
• All trees?
• Some trees?
See McBride et al.
 Does PD testing unduly deteriorate or fail
• Good cables?
• Defective cables? - Effect of high dc or thumping
   How effective is ON-LINE testing?
   How effective is PD testing of PILC cables?
   Are PD test results obtained by different 20
methods identical?
McBride et al. (Georgia Power Res., and
EPRI) - IEEE Trans. on Power Del. 4/94
70mils

70mils

35x48-mil void

21
McBride et al. (Georgia Power Res., and
EPRI) - IEEE Trans. on Power Del. 4/94
   Inspection of these wafers revealed a large
void (35 mils wide and 48 mils high) in the
center of the (70 mils diameter and 70 mils
high) water tree.
   There was significant evidence of PD within
the interior of the water tree, with darkened
areas near the tips of the tree. This was
clearly the site of the PD activity.
   Cable failures near large water trees have
occurred in ac breakdown tests…
22
McBride et al. (Georgia Power Res., and
EPRI) - IEEE Trans. on Power Del. 4/94
   Seven cables failed while active PD sites were
monitored (at higher voltage than PDIV).
   With the exception of two samples (out of the
remaining 7 samples with PD) all other cable failures
occurred at the PD inception voltage while (PD site)
locations were being performed… Failures were
associated with the PD sites.
   The duration of sustained PD ranged from 2 to 80
minutes prior to failure.
   The theory that PD above operating voltage results in
failure at operating voltage is not supported by this
data.
23
McBride et al. (Georgia Power Res., and
EPRI) - IEEE Trans. on Power Del. 4/94
   Very few cables contained active PD sites
near operating voltage. No PD above 1-3pC
was detected in any of the test cables (61
samples) when energized at operating
voltage. (PDIV = 8 - 35kV).
   Most PD sites were detected at twice
operating voltage or higher.
   The (pC) level of the PD at a site could not be
correlated with the likelihood of a failure at or
near the site.
24
BREAKDOWN AT PD SITE
THROUGH VENTED WATER TREE

25
IMPROVED RELIABILITY
Peter Daly, San Francisco, Jan. 20, 2000
0.60
BEFORE UPTI   AFTER UPTI
TESTING      TESTING

0.50

241 Feeder Cables
0.40

SAIFI   0.30

0.20

0.10

554 Feeder Cables
0.00
1992    1993    1994   1995   1996   1997   1998    1999    2000

Year
26
NOTE: Only 40% of Recommended Repair Was Completed

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