Test of Cable installations  
Purpose of the Test:
 
Purpose of the Test:
To find existing fault spots which are critical for a further safe operation and to break them down without any additional negative influence on the quality or ageing of the good parts of the cable!
Questioning:
Questioning:
1. s the test procedure non destructive and reduces the cable failures in operation
". #oes the technology permits it to shift the possible breakdown of a cable into an uncritical time window
$. %ow small is the possibility for a breakdown of a successful tested cable after the test& eventual required repair of local weak spots included
 
outer semiconductor 
Structural Changes
Mechanical Stress and contact
corrosion at the conductor  
Test voltage level is above the normal operating voltage
 Test on insulation breakdown or high leakage current
)ote:
The operating voltage *o is the phase to ground voltage
U =o Ph-PhU
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What is a usable or tyical !oltage form testing different ob"ects# 
Voltage test 
DC- voltage
 testable object:
PILC segments
/ #
t a n δ
C a b l e " o i n t C a b l e e n d
/ e r m i n a t i o n
H o m o g e n i o u s a g e d
C a b l e s e g m e n t
i n t e g r a l) o c a l
/ e s t i n g m e t h o d s
I 0 C
1 i a g n o s t i c m e t h o d s
M a i n gM e a s u r i n g
2 $ + 3 $ $ H ' $ % & H ' 4 a r t i a l d i s c h a r g e +
o s ' i l 5 I m u l s
W e a 6 s o t
- $ H '
able ;: %eavily water tree damaged
1. n both cables -76 test leads to flash over< no differentiation possible
". +valuation of damage is possible only by means of dielectric diagnostics
$iagnosis and testing of PE%&'PE ( cable
 
+ decomosition of the aer 
+ driing out
sheath
isolator 
  oil
nsulation Procedure -oltage Type -oltage 7evel #uration
P+ , =7P+ -76/cos/sq. .1 %3 4 1&>/ '&" x *o&5?8 10/2 min
P+ , =7P+ -76/sine .1 %3 4 1&>/ '&" x *o&5?8 10/2 min
P+ , =7P+ -76/sine .1 / .1 %3 4 1&>/ x *o&5?8 10/ min
P+ , =7P+ 5esonance& 9- $ @ $ %3 4 "/ x *o&5?8 $/ min
Paper& P- # # 0.2 / A x *o 10 @ $ min
 
 A-tual Test P)ocedu)es acc to V$E ./012
Test of Ene)g* dist)ibution cables ,ith e#t)uded Insulation fo) nominal
 
5?8
-76 &1 %3 #uration 2 min ac to experiences
2 min
medium "oltages acc to 6a)t 1/7
 
fo) &'PE Cables+ because2
down after the application of relatively high voltages for several
hours. This procedure causes damage and accelerated ageing
to undamaged segments of the cable.
The long lasting exposure to the high voltage causes residual
space charges& which can be considered like 5 components
with a time constant of several hours up to days.
These space charges decline very slowly.
5esulting they can multiply with the electrical
fields of the normal 4 operating voltage after re/energisation
and cause an uncontrolled breakdown in operation.
 
C/
The negative # test voltage inDects electrons into dielectric and builds up
space charge around the defect. 4fter testing& every positive wave of the
nominal 4 voltage causes large voltage gradients between the defect and
its negative residual space charge.
The cable can be damaged by an uncontrolled breakdown.
 
Testing with operating frequency is certainly the most effective
test method. The polarity change with operation frequency causes
a fast growth of faults. This positive behaviour has a disadvantage&
since it causes a fast rising gas pressure inside the fault void&
reducing the overall growth rate and causing the generation
of Ebush like treesF.
 4 and 5esonance 8ystems are due to the extremely high reactive
load very large& heavy and expensive and require a high energy.
Their use for the medium voltage net is accordingly limited.
5esonance 8ystems are specified up to $ %3& in the practical
application their frequency is more in the range of $ %3 and
following not in the operation frequency range.
 
8ome manufacturers offer frequencies of .0& &" and .1 %3
This is only to compensate for the described lack of test power.
t is marketed as an advantage by combining these frequencies
with a high testable cable capacity.
There is not scientific base for the application of these frequencies.
+xisting research activities show& the these frequencies are rather
useless for a reliable test.
The reduction of the frequency causes in the most positive view
an proportional increase of the test duration& extending the time
to several hours.
The 8eba G?T $%& ()F H' Cosine S*uare Wa!e
Technology is momentarily the only existing Technology
on the market which provides a test
/ (ith operational 6requency&
but still
and Terminations including 8witch gear.
 
Technology is since almost "
scientific investigations as well as in practical
field trials.
as recommended Test -oltage Technology !
The .+7 9: V' Cosine S<ua)e Wa"e
&;< + 2$$2
du)ing a 8. 9: test 
 
 
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0esearches sho, that the gro,th !elocity of electrical tree !oids ,ith $%$&
H' is ar5 &$= slo,er as a comarable $%& H' test at the same test !oltage
le!el
$5$& H' sin
   G   r  o   ,    t   h   s      e   e    d    i  n   m   m    7   h
/ree gro,ing !elocity as function of 
test !oltage for four different testing
se*uences
" . 0
) e e d l e w t / d a m a g e
. 1 % 3 / 8 i n u s
. 1 % 3 / o s i n u s "
0 % 3 / 8 i n u s
9 s c i l l a t i n g v o l t a g e s
. 0 ~~
P$ ince6tion "oltage at diffe)ent test se<uences no)med 
 4t 0 %3 operation frequency the measurable P# inception voltage *e is the
lowest for artificial needle faults& as for (T ageing
 
k V
%
;reakdown voltage of cable samples with and without fault spots at
different frequencies. +. ockenbach& 8chering/nstitut
•  (ithout faults
Reliable detection of ,ea- s6ots in the insulation=
 
nverse Power 7aw J>K
n: nsulation condition =7P+ Ln app. 0 for water trees& n app.1 at good
insulation& ?odel ableM
t: #uration of the 6ield influence
)log(~ k 
6equency dependency at model cables JAK
5esults of -oltage tests with different frequencies cannot be compared& without
adDustment of voltage level and duration.
 
@ )eedle / Plate
(ithout faults
?echanical #amage
(ater trees
If for $%& H' and intact insulation the according standing !oltage
9rdinate in @B is t,ice as hight as for -$ H'% than this is less
re damage at $%& H'5 0esulting the consumtion of lifetime at
$%& H' is the lo,est5
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ms1 " $ ' 0 2 > A B 1 11 1" 1$ 1' 10 12 1> 1A 1B "
k-
/ 0
/ 2
Similar to the -$ H' 9eration !oltage the change o!er of
the $%& H' Cosine S*uare Wa!e (oltage from one olarity
haens !ery fast5 /he fast changing sloe ro!ides a fast
changing of a ,ater tree into an electrical tree5
 
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A significant difference of the sinusoidal test !oltage in comarison to the
$%& H' Cosine S*uare Wa!e (oltage is the &%< times higher load to the cable
insulation% "oints% terminations etc5
/est !oltage le!els as stated in (1E or other standards are in 0MS
5 10 15 20 s
70kV b) Change-over slopes   expanded view
30 1 2 4 5 6s
63kV 70kV
20 1
0 1 1 0 " t J s K
P r N f s p a n n u n g * p
J k - K

 
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()F Cosine S*uare Wa!e Q 6ield load if the dielectric d*,dt is
comparable to the nominal load
Q The period has an ending point
Q ?easurement of leakage current
Q +fficient power use. 1,1 of a -76
8inusoidal Test 8et
Q 6ield load if the dielectric d*,dt during the
phase change is ,0 of the nominal load
Q )o measurement of 7eakage urrent
possible
during the polarity change
&$sec
()F+ Sinusoidal
2
10sec
V
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/he technical usability for on sot testing of 4lastic or aer 
insulated cables is !ery high% since si'e% ,eight and o,er
re*uirements are comarati!ely lo,5
$
test methods
8ystem $ k-
**5?85?8 !!!!
 
Breakdowns during the test 
per 1 km
 
>)ea-do,ns o"e) the test time
22 R of the breakdowns during the first 1 minutes22 R of the breakdowns during the first 1 minutes
>0 R of the breakdowns during the first $ minutes>0 R of the breakdowns during the first $ minutes
The experience shows that the -76 voltage test does not cause new faults inThe experience shows that the -76 voltage test does not cause new faults in
service aged cables and their equipment and the time when it came to breakdownservice aged cables and their equipment and the time when it came to breakdown
during test.during test.
$
-$
&$$
&-$
 
   4   a      e   r
   4   a      e   r    K   o    i  n    t
   8    )    4    E    K   o    i  n    t
   /   r   a   n   s    i   t   i  o   n    "  o    i  n    t
 Anal*sis of faults
 
The breakdown properties of plastic insulated and paper insulatedThe breakdown properties of plastic insulated and paper insulated
cables is comparable. > R of all faults come to breakdown withincables is comparable. > R of all faults come to breakdown within
the first $ minutes& most of them L2$ RM within the first 1 minutes.the first $ minutes& most of them L2$ RM within the first 1 minutes.
#espite of the lower -76 test voltage in comparison to the # test#espite of the lower -76 test voltage in comparison to the # test
voltage faults in paper insulated cables come to breakdown within shortvoltage faults in paper insulated cables come to breakdown within short
time& so that this voltage test is well suited for paper insulated cablestime& so that this voltage test is well suited for paper insulated cables
+xisting water trees in the =7P+ insulation in a significant number of cases+xisting water trees in the =7P+ insulation in a significant number of cases
lead to breakdown only shortly before the completion of the one hour testlead to breakdown only shortly before the completion of the one hour test
time. That means that the test duration of one hour is correct.time. That means that the test duration of one hour is correct.
 
AC + /est System ,ith -$ H'
 
%- Test 8et
 
Test Voltage VLF 0...27 kV / 0,1 Hz
Testable Capacity 5 F / 0... 27 kV
pera(ional 'epera(.re -20 o C /// 40
o C
115 V 50 60
#eig't ( 50 kg, po)table
Cosi*s +*a)e #a-e
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ma=5 testable line
max. Test apacity
ma=5 /est lengths
 4 O 0 mmU
 4 O "' mmU
 4 O 0 mmU
ma=5 /est lengths
 4 O "' mmU
 
-76 Test 8ystem
   )   e   a    6   c   u   r   r   e   n    t
Lm4M 7eak
 
Q  4utomatic 5ecording of
7eakage urrent and Test Parameters Q Protocol of #ate and Time&
Test 5esult
4arameters
Q Pre/setting of Test Time Q Pre/setting of Test -oltage Q  4utomatic setting of Test Parameters
  5eadable via P @ 4dapter and
comfortable (indows 8oftware
     .     a     r     d
    e      .
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Recommendations for the VLF Test Voltage levels at new installed and aged Cable installations
/est (oltage le!el at ne, installed cables
Test 7evel: $ x *o
Test Time: 2 min
 Test 7evel : 1&> ... $ x *o
 Test Time : 2 min