ICC Educational Program Spring 2001.
Tan Delta / Dissipation Factor As An
Effective Tool In Determining The
Insulation Condition Of Power Cables
Using The BAUR PHG VLF System.
Craig Goodwin, HV Diagnostics Inc. GA, USA
e-mail: [email protected]
ICC Educational Program Spring 2001.
Summary of Presentation
• Theory / Background
• Description of Diagnostic Method/s
• Field Examples
ICC Educational Program Spring 2001.
Benefits of Voltage Testing with VLF
Sinusoidal Waveforms in the field.
„ Low Power Requirement for on site testing.
„ Compact portable design of test equipment.
„ Easier diagnosis of water tree deteriorated
insulation at low frequencies compared to
higher frequencies such as 60Hz using TD.
„ Easier to integrate Cable diagnostic interfaces
such as TD and PD etc.
ICC Educational Program Spring 2001.
"WATER TREEING" in polymeric insulation
(schematic layout)
electrical field
● water
● disturbance field
● time
●
conditions for possible
development of
"water trees"
"bow-tie trees"
outer semiconducting
layer
insulation
inner semiconducting
layer
conductor
"vented trees"
ICC Educational Program Spring 2001.
Vented- tree growing from the inner semicon
layer of a 30 kV- PE- cable
ICC Educational Program Spring 2001.
Dielectric Failure of insulation originating from a water
tree
ICC Educational Program Spring 2001.
What is Dissipation Factor ( tan δ) ??
voltage
current
0
time/sec
dissipation factor tan δ=
true power
U² / R
1
=
=
reactive power U².ωC ωC.R
10
ICC Educational Program Spring 2001.
Simplified Dielectric Equivalent Circuit of a
Water Tree
wt
R2
C1
C2
>>
R1
ICC Educational Program Spring 2001.
AC Pure Sinewave Output Voltage and
Current.
ICC Educational Program Spring 2001.
Q&A
Do I have a DF dependancy regarding the
total length or the amount of joints in a
cable?
NO!
ICC Educational Program Spring 2001.
Voltage Dependence of 0,1 Hz Tan Delta on New
and Service-aged XLPE-insulated Medium Voltage
Cables.
-3
T a nD e lta . (1 0 )
0 .1 H z D i s s ip a ti o n F a c
10
9
8
7
6
5
4
3
2
1
0
0
0 .5
1
1 .5
2
2 .5
3
V /V 0 (A p p lie d V o lta g e )
G o o d c a b le
S lig h tly s e r vic e -a g e d ( 1 )
M o d e r a te ly s e r vic e -a g e d (3 )
S tr o n g ly s e rv ic e - a g e d ( 4 )
M o d e r a te ly s e r vic e -a g e d (2 )
ICC Educational Program Spring 2001.
Criteria For tan δ – for PE or XLPE
Cables are still in good condition, if :
tan δ (2 Uo) < 1,2 ‰ and
[tan δ (2 Uo) - tan δ (Uo)] < 0,6 ‰
Cables in bad condition (or to be replaced immediately ) if :
tan δ (2 Uo) ≥ 2,2 ‰ or
[tan δ (2 Uo) - tan δ (Uo)] ≥ 1,0 ‰
EPR and TR - XLPE cables have higher absolute values of Tan
Delta than the above XLPE values, however the change in Tan
Delta is still the important criteria to take note of.
ICC Educational Program Spring 2001.
Field Test Result for an 1974 XLPE Cable
Good Result
for an old
Cable.
ICC Educational Program Spring 2001.
Field Test Result for an 1984 XLPE Cable
Nominal Operating
Voltage: Vo = 14kV
PDIV: only at 19kV
Note: TD values are
poor even at Vo.
ICC Educational Program Spring 2001.
Comparison of Cable Diagnostic Systems
IR C
R e c o v e ry
D is s . F a c t o r
S p e c tr o s c o p y
A n a ly s is
V o lt a g e
V L F ta n d
V L F ta n d
D i a g n o s is s t r o n g ly a g e d c a b le s
0
-
+
+
I n f lu e n c e o f d is tu r b a n c e s
-
0
+
+
R e p r o d u c ib ility o f m e a s u r e m e n ts
-
+
+
+
D i a g n o s t ic t e s t t im e
-
-
+
+
I n f lu e n c e o f T e m p e r a tu r e
+
-
+
-
R E F .:
S I N T E F R e p o r t, N 7 4 6 5 T r o n d h e im
S . H v id s te n , J .T . B e n ja m in s e n
T R A 5 0 7 2 , A ug . 2 0 0 0
R E F .:
D r . I n g . R . P la th
P ro f . D r. W . K a lk n e r
D ip l. I n g . I . K r a g e
I P H B e r lin
T U B e r lin
VEW EURO TEST
Key:
0 OK
+ Pos.
- Neg.
ICC Educational Program Spring 2001.
Other Applications and Techniques available using the
Tan Delta measurement:
●
Measurement of TD and Capacitance with respect to
Frequency ( Dielectric Spectroscopy).
Application of TD as a reference signature and
method
●
for determining moisture ingress for PILC cables.
ICC Educational Program Spring 2001.
Conclusions of Tan Delta Diagnostics
A TD cable assessment system can clearly
distinguish
between new, medium and strongly aged extruded
cable insulation.
●
●
●
●
Water trees which are a major original source of
insulation failures in aged extruded cables can be
detected in a non-destructive manner.
Excellent Field Results.
To detect singular defects, a combined assessment
system including the application of partial discharge
measurement and location in addition to TD is
necessary.