Epoxy Resin Impregnated
Paper Bushings
17.5 kV to 800 kV
up to 31,500 A
BS EN ISO 9001
TRENCH (UK) LTD - The site at Hebburn in the north east of England has pioneered the design and
manufacture of bushings for transformers and switchgear since 1929 and is a worldwide supplier to
equipment manufacturers and utility companies. In the early 1970's we developed Epoxy Resin Impregnated
Paper bushings for use in a wide range of applications and have become the international specialist for this
type of product, which accounts for over 40% of production. Epoxy resin is superior to resin-bonded paper
by offering lower partial discharge activity, a lower power factor and better thermal stability. Our products
are designed and manufactured to BS EN ISO 9001 as well as IEC and ANSI where appropriate.
Facilities Include
● Products designed and manufactured to customer requirements.
● All bushings impulse tested as standard.
● Unique high voltage testing.
● Research and development and dielectric type testing to all national and international standards
up to 4MV impulse, 2MV AC, lMV DC in wet and dry conditions.
● Insulation studies and large-scale simulations.
Transformer Bushings
● Full range of designs for outdoor or indoor use.
● Oil and SF6 connections.
● Insulation types include ERIP, OIP and RBP.
● OIP condenser bushings (type OTA) for medium/high power transformers
Switchgear Bushings
● Solid insulation system for SF6 insulated switchgear giving unrivaled mechanical and electrical
performance up to 550kV.
Insulation Components
● Total design and manufacture to customer requirements using epoxy resin, glass fibre and
composites for all types of electrical insulators.
After Sales Service
● Comprehensive refurbishment facilities.
● Loan of steel transit frames for 300kV and 420kV bushings.
● Check testing
● Full reporting service
● Re-gasketing.
● Major refurbishment.
● Re-certification included.
● Covers bushings manufactured by other companies including English Electric, Ferranti, Micanite,
Reyrolle and VA Tech.
Epoxy Resin Impregnated Paper Bushings
17.5kV to 800kV up to 31,500A
The epoxy resin impregnated paper range provides the very highest standard in
bushing technology. Every product is impulse tested as a routine so you can be
assured of high reliability and a low cost. With over 30 years experience in the field
of oil free bushing applications our engineers can support all your through life
needs.
CONTENTS
Type HETA Voltage Range 17.5kV to 36kV
3-6
High current bushings for transformer to phase
busbar isolated connections
Type ETG Voltage Range 72.5kV to 800kV
7-8
Bushings for transformer to gas insulated
switchgear connections
Type EGA Voltage Range 145kV to 525kV
9-10
Condenser bushings for direct connection between
metalclad SF6 switchgear and outdoor equipment
TRENCH (UK) LTD
is a quality registered
company.
Its management
systems have been
assessed and comply
with BS EN ISO 9001.
Type HETA Voltage Range 17.5kV to 36kV
High current bushings for transformer to phase
busbar isolated connections
Features
● Central aluminium conductor cast in one piece without joints.
● Main insulation : vacuum impregnated epoxy condenser.
● Solid filling available : permits mounting at any angle.
● Thermal stability : excellent.
● Partial discharge : less than 10pC at 1.5Un.
● Freedom from oil leakage from the transformer in the event of
porcelain breakage.
● Current transformer accommodation can be provided on request.
● Test tapping : standard.
● Designs available to cover IEC, ANSI and other International
Specifications.
● Voltages from 17.5kV to 36kV and current from 6300A to 31500A
The bushing flange dimensions and design of
bushing terminals can be adapted to specific
requirements of the transformer
manufacturer or to provide interchangeability
with existing bushings.
Type HETA Voltage Range 17.5kV to 36kV
High current bushings for transformer to phase
busbar isolated connections
Figure 1
d
L
L7
5
L1
L2
L6
20
90°
D3
D2
D4
24
95
54
1.4
4
5
895
905
340
460
470
100
250
80
90
130 165
20
290
650
240
185
480
545
555
100
335
80
90
130 165
20
185
565
100
615
760
125
180
300 220
25
375
870
320
D2
255
300
340
410
470
560
255
300
340
410
470
560
255
300
340
410
470
560
670
830
D3
290
350
400
450
535
620
290
350
400
450
535
620
290
350
400
450
535
620
720
930
D4 D5
335 445
400 500
450 545
500 625
590 685
680 780
335 445
400 500
450 545
500 625
590 685
680 780
335 445
400 500
450 545
500 625
590 685
680 780
780 900
980 1070
D6
300
350
395
470
535
630
300
350
395
470
535
630
300
350
395
470
535
630
750
920
d
15
20
n2
12
22
16
15
20
12
22
16
15
20
12
22
16
24
WEIGHT (kg)
D1
250
290
330
400
460
550
250
290
330
400
460
550
250
290
330
400
460
550
660
820
NUMBER OF FLANGE BOLT HOLES
160
FLANGE BOLT HOLE DIAMETER
430
FLANGE DIAMETER
L8
205
LINE METAL (Air end)
FLANGE LENGTH
L7
20
185
395
955
1135 375
PROTECTED CREEPAGE
320
MINIMUM CREEPAGE
865
875
STRING LENGTH
325
FLANGE PLATE THICKNESS
795
805
LINE METAL (Transf. end)
305
L5 L6
130 165
TOP PLATE DIAMETER
5
765
775
L4
80
90
MAX. PORCELAIN DIAMETER
4
310
L3
165
FLANGE BOLT CIRCLE DIAMETER
1.4
695
705
L2
375
385
FLANGE GASKET SEAT DIAMETER
36
L1
290
TRANSFORMER END DIAMETER
70
L
665
675
PORCELAIN LENGTH
4
AIR END LENGTH
1.4
TRANSFORMER END LENGTH
26
5
24
L8
PORCELAIN
TOTAL LENGTH
CANTILEVER WITHSTAND (kN)
Mechanical
TIGHTNESS TEST 24 HOURS (barg)
Uy Up
17.5 50
D5
DIMENSIONS (mm)
PARTIAL DISCHARGE (kV)
(10pC Max.)
POWER FREQUENCY
WITHSTAND (kV) - 1 MIN.
MAX. PHASE TO GROUND (kV)
REFERENCE CURRENT (A)
LIGHTNING IMPULSE
WITHSTAND (VOLTS)
RATED VOLTAGE (kV)
Un Up
Ir
17.5 125 6300
8000
10000
12500
16000
20000
24 150 6300
8000
10000
12500
16000
20000
36 200 6300
8000
10000
12500
16000
20000
25000
31500
L5
D6
PERFORMANCE
Voltage
L3
D1
Minimum Oil Level
n2 holes
REFERENCE
L4
69
88
105
133
168
207
85
107
126
161
192
241
101
126
149
185
230
288
364
502
Type HETA Voltage Range 17.5kV to 36kV
High current bushings for transformer to phase
busbar isolated connections
2
3
4
2
3
4
50
25
60
50
60
50
25
60
50
60
50
60
50
60
T1
150
120
150
200
300
350
150
120
150
200
300
350
150
120
150
200
300
350
400
480
T2
75
100
120
140
190
75
100
120
140
190
75
100
120
140
190
220
250
T3
30
25
t
50
60
50
30
25
50
60
50
30
25
50
60
50
30
60
NUMBER OF HOLES
n3
6
4
6
8
4
6
6
4
6
8
4
6
6
4
6
8
4
6
8
8
HOLE PITCH
a
60
THICKNESS
A3
25
SPACING
HOLE PITCH
A2
160
250
290
340
430
530
160
250
290
340
430
530
160
250
290
340
430
530
610
700
WIDTH
200
4
A1
180
120
150
200
120
150
180
120
150
200
120
150
180
120
150
200
120
150
200
240
NUMBER OF HOLES
150
Fig
2
3
Transformer End
THICKNESS
ARRANGEMENT
Ir
6300
8000
10000
12500
16000
20000
6300
8000
10000
12500
16000
20000
6300
8000
10000
12500
16000
20000
25000
31500
SPACING
36
Air End
WIDTH
Un Up
17.5 125
24
TERMINALS (FIGURES 2, 3 & 4)
REFERENCE CURRENT (A)
LIGHTNING IMPULSE
WITHSTAND VOLTS (kVp)
RATED VOLTAGE (kV)
REFERENCE
n4
6
4
6
8
12
14
6
4
6
8
12
14
6
4
6
8
12
14
16
16
Figure 2
85
T3
A2
A3
a/2
85
20
20
t/2
a
A1
t
n4 Holes
n3 Holes
T1
40
40
Figure 3
85
A3
20
A2
T3
85
T2
20
a/2
t/2
A1
a
t
n4 Holes
n3 Holes
40
40
T1
Type HETA Voltage Range 17.5kV to 36kV
High current bushings for transformer to phase
busbar isolated connections
Figure 4
85
A3
A2
T3
85
T2
20
20
t/2
a/2
t
A1
a
T1
n4 Holes
40
n3 Holes
40
To - Ta(K)
Current Rating- Factor ’R’.
Air temperature
TA = 70°C
Max. conductor temperature TC = 120°C
Therefore
TO - TA = 20K
Therefore
TO - TO = 30K
Consequently, the rating factor ‘R’ for these conditions is defined as 1.0. For other
temperature conditions refer to fig. 5 for the appropriate value. Use of this factor in
determining the correct bushing is described below.
1.2
RATING FACTOR 'R'
The bushing nominal current rating Ir is based on one set of temperature conditions
typical of those found in power transformers connected via phase isolated bus-duct
systems. These reference conditions are:
Oil temperature
TO = 90°C
50 40 30 20
10
1.1
0
1.0
0.9
0.8
0.7
0.6
0
10
20
30
40
50
Tc - To(K)
Figure 5. - Rating factor selection chart.
Connections to Bushing - Section SA and SO
Fig. 6 identifies the connections made to the bushing; these are the air end SA and the
transformer end SO. The reference conditions for the bushings are based on defined
values of current density in the copper connections as follows:
SA = 1.5 A/mm2
SO = 2.5 A/mm2
Operating the bushing at higher air temperatures will demand some decrease in the
value SA while restricted conductor temperature rises will demand some decrease in
value SO. When requested we can advise on specific values.
SA
SO
Figure 6. - Connections to bushing.
Selection Procedure
1.
2.
3.
4.
5.
6.
Select voltage class (creepage may influence decision).
Determine (TO - TA) and (TC - TO) : bushings to IEC 137 allow (TC - TO) = 30K. Other
specifications may reduce this to 20K or 10K.
Refer to fig. 5 for rating factor ‘R’.
Divide maximum system current by factor ‘R’. This gives minimum current rating in
terms of the catalogue reference temperatures.
Add any overload and proximity effect.
Select next highest Ir value from catalogue list.
Example
1.
2.
3.
4.
HETA 36/200 class.
(TO - TA) = 10, (TC - TO) = 20
R= 0.82
eg 8650A max, therefore
8650/0.82 = 10550A
5. NOT REQUIRED
6. Therefore Ir = 12500 A
Type ETG Voltage Range 72.5kV to 800kV
Bushings for transformer to gas insulated
switchgear connections
Features
● The design is compatible with the requirements of IEC 1639 for the GIS to
transformer interface. Other dimensions can be provided on request
● The ETG bushing range is provided for a full range of operating ratings to IEC
and ANSI Standards
● Epoxy resin impregnated paper insulation. Vacuum impregnation of the
condenser core gives excellent partial discharge performance
● Oil free solid insulation provides no fire or explosion risk with the bushing
● Design allows for differential expansion across normal operating temperature
range
● lnsulation is gas tight and when combined with an effective sealing ring
system will provide <10-5 torr litres per second Ieakage
● Connecting flange is also gas tight and incorporates a self grounding test
tapping for through life capacitance and tan delta measurement
● Non-standard CT accommodation and corona shields can be provided on request
● All bushings are electrically tested with a simulation of the service arrangement,
preventing oil contamination of the gas side
Description
The epoxy resin impregnated paper range provides the very highest standard in
bushing technology. Every product is impulse tested as a routine so you can be
assured of high reliability and a low cost. With over 30 years experience in the field
of oil free bushing applications our engineers can support all your through life
needs.
The bushings detailed show our product range which is suitable for connecting oil
filled transformers directly to SF6 metalclad switchgear or ducting.
for details
see opposite
Type ETG Voltage Range 72.5kV to 800kV
Bushings for transformer to gas insulated
switchgear connections
contact area
on bushing side
d2
t1
n1xm1
L3
L2
d3
d4
enclosure
flange
n2xm2
L4
sealing surface
Rmax 6.3
S2
S1
d9
bushing
flange
t2
d8
L7
L
L4
L1
L5
E
D1
D2
SF6 END
TRANSFORMER END
n3xm3
D3
750
*
1250 325
98
1120
170
750
*
2000 325
98
1190
245 1050
*
1250 460
142 1560 770
245 1050
*
2000 460
142
TRANSFORMER SIDE TERMINAL
DIAMETER
170
TRANSFORMER SIDE
FLANGE THICKNESS
84
TRANSFORMER SIDE FIXING
HOLES NO. x DIAMETER
2000 275
EXTERNAL DIAMETER OF
TRANSFORMER SIDE FLANGE
*
L5
TRANSFORMER SIDE FLANGE PCD
650
L7
25
TRANSFORMER SIDE DIAMETER
145
n2xm2
MINIMUM EARTH BAND
84
d9
TRANSFORMER SIDE LENGTH
1250 275
d8
315
MOUNTING FLANGE HEIGHT
*
t2
285
GAS SIDE FLANGE THICKNESS
650
GAS SIDE FIXING SCREWS
NO. x DIAMETER
145
260
GAS SIDE FLANGE FIXING
HOLE DIAMETER
71
200
TRANSFORMER SIDE
EXTERNAL DIAMETER OF
GAS SIDE FLANGE
71
2000 230
d4 S1max S2min
200
GAS SIDE FLANGE PCD
1250 230
*
250
EXTERNAL DIAMETER OF
GAS SIDE SEALING FACE
*
550
d3min
INTERNAL DIAMETER OF
GAS SIDE SEALING FACE
550
123
n1x m1 d2
INTERNAL DIAMETER OF
GAS SIDE ENCLOSURE FLANGE
123
t1
INTERNAL DIAMETER OF
GAS SIDE ENCLOSURE
42
L2min L3min
OUTER DIAMETER OF
GAS SIDE TERMINAL
2000 140
GAS SIDE TERMINAL PCD
*
GAS SIDE TERMINAL
THREAD DEPTH
72.5 325
GAS SIDE TERMINAL THICKNESS
MAXIMUM PHASE TO GROUND
VOLTAGE (kV)
330
GAS SIDE LENGTH
POWER FREQUENCY
WITHSTAND VOLTAGE (kV) 1 Min.
L4
740
Us
OVERALL LENGTH
RATED CURRENT (A)
L
42
Up
SWITCHING IMPULSE
WITHSTAND VOLTAGE (kVp)
Uy
1250 140
LIGHTNING IMPULSE
WITHSTAND VOLTAGE (kVp)
Up
*
RATED VOLTAGE (kV)
Ir
72.5 325
Ur
D4
GAS SIDE DIMENSIONS AND TERMINOLOGY AS IEC61639
RATING
NO. OF HOLES x DIAMETER
REFERENCE
L6
L1
E
D1
D3
D4
n3xm3
L6
D2
260
90
110
1010
90
250
290 8x15
18
340
20
70
1050
520
243 2410 1050
525 1550 1175 2000 680
303 2560
800 2050 1500 2000 800
462 3595 1340 125
8xM12
300
4x
M12
30
420 1425 1050 2000 630
99
220
220
280
305
335
30
16
110
150
380
30
145
290
335 12x15
450
22
220
450
450
450
510
535
565
16xM12
30
570
200
400
450 12x20
540
540
540
600
640
690
20 16xM16
33
200 1160 300
329
500
560 12x24
630
500
500
630
720
764
23 28xM20
33
355 1900 600
487
600
660 16x24
175
139
25
110
*
*
1210
*
60
25
200
Type EGA Voltage Range 145kV to 525kV
Condenser bushings for direct connection between metalclad
SF6 switchgear and outdoor equipment
Direct connection between metalclad SF6 switchgear and outdoor equipment
The bushings in the EGA range are suitable for connecting outdoor equipment to
SF6 metalclad switchgear or ducting and may be mounted vertically, horizontally or
at any angle between.
The primary insulation used in this range of bushings is condenser graded, epoxy
resin impregnated paper - ERIP. The bushings are intended as alternatives to
conventional gas- filled porcelain. Use of ERIP provides a compact bushing design
which is completely free of oil. The lack of oil or pressurised gas in the bushing
greatly minimises the risk of fire or explosion.
Used extensively for many years, ERIP has a proven reliability record in many
applications and is virtually free of partial discharges at test voltages.
The cast epoxy insulation has inherent gas tight properties and combined with an
effective sealing ring system provides security for the gas environment and a gas
leakage rate of <10-5 torr litres per second is guaranteed. The design caters for the
effect of differential expansion across the normal operating temperature range.
The connecting flange is impervious to gas and incorporates a self grounding test
tapping for capacitance and tan delta measurement during periodical maintenance.
The bushing flange dimensions and design of the SF6 terminal can be adapted to
suit the specific requirements of the SF6 equipment. The design of the outdoor
terminal can also be adjusted to suit connections to the outdoor equipment or
overhead lines.
Type EGA Voltage Range 145kV to 525kV
Condenser bushings for direct connection between metalclad
SF6 switchgear and outdoor equipment
L
L1
L2
L5
L4
L3
100
d1
d2
D3 D2 D1
Zxi
Terminal and flange dimensions may vary to suit
requirements of both SF6 and outdoor equipment.
REFERENCE
DIMENSIONS
SF6 END INSULATION DIAMETER
FIXING FLANGE P.C.D.
FIXING FLANGE OUTSIDE DIAMETER
OUTDOOR END TERMINAL DIAMETER
SF6 END TERMINAL DIAMETER
FLANGE FIXING
No. OF HOLES x DIAMETER
D3
d1
d2
Zx diam i
290
200 1250 140
290
335
40
160
12x16
2280 1870 410
330
200 1450 160
290
335
40
160
12x16
2000 460
142 3195 2690 505
400
300 2150 220
400
450
40
160
12x23
300 1050 850 2000 460
173 3405 2900 505
400
350 2320 270
532
570
60
170
16x18
420 1425 1050 2000 630
243 4465 3860 605
500
400 3200 329
532
570
60
203
16x18
420 1425 1050 4000 630
243 4465 3860 605
500
400 3200 375
532
570
80
220
16x18
525 1675 1175 4000 740
303 5090 4400 690
585
400 3740 375
532
570
80
220
16x18
525 1800 1300 2000 860
303 5610 4810 800
660
400 4150 375
532
570
80
203
16x18
750
-
245 1050
-
145
650
170
FLANGE HEIGHT
2000 275
Us
SF6 END INSULATION LENGTH
-
Up
SF6 END LENGTH
L
Un
OUTDOOR LENGTH
Uy
SWITCHING IMPULSE
WITHSTAND (VOLTS)
Up
LIGHTNING IMPULSE
WITHSTAND (VOLTS)
In
RATED VOLTAGE (kV)
TOTAL LENGTH
D2
MAXIMUM PHASE TO GROUND
VOLTS (kV)
D1
POWER FREQUENCY
WITHSTAND (kV)
L5
RATED CURRENT (A)
OUTDOOR PORCELAIN CLEARANCE
RATING
L1
L2
L3
L4
84
2040 1670 370
2000 325
98
Trench Facilities
The Trench Group is your
partner of choice for electrical
power transmission and
distribution solutions today;
and for the development of
your new technology solutions
of tomorrow.
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Postfach 13
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Fax: 43-732-671341
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Instrument Transformer Division
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Scarborough, Ontario
Canada M1P 3B5
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200245
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E 322.30
Subject to change without notice (05.2006)
Printed in Canada.