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Siemens Transformer Technology SeminarInsulation & Thermal Design
Customer Technical Meeting Pomona, CA May 24 – 25, 2016
Siemens AG – Transformers
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Insulation & Thermal DesignWinding Selection
Kurt Kaineder - EM TR MPT GTCPage 2
Windings:
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Insulation & Thermal DesignWinding Selection
Conductors: Paper Insulated Flat Conductors
If higher mechanical stability is required:Multiple conductors with Epoxy bonding.In this case, the individual strips are insulatedfrom one another with enamel.
Kurt Kaineder - EM TR MPT GTCPage 3
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Insulation & Thermal DesignWinding Selection
Conductors: Continuously Transposed Conductors (CTC)
CTC Axial twin CTC
If higher mechanical stability is required:• Strands with Epoxy bonding• CTC with intermediate paper layer
Kurt Kaineder - EM TR MPT GTCPage 4
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Insulation & Thermal DesignWinding Selection
Conductors: Conductor Insulation• High electrical breakdown withstand• Thermal stability• Kraft Paper – made of long wood
fibers, purified from resin materialand lignin through a chemical process.
• The Degree of Polymerization (DP)measures the length of the fibers and is a measure for aging
Kurt Kaineder - EM TR MPT GTCPage 5
Density Thermal Class
Cellulose Paper 0.7-0.85 g/cm³ 105
Cellulose Paper, Thermallyupgraded
0.7-0.85 g/cm³ 120
Calendered paper 0.95-1.1 g/cm³ 105
Calendered Paper,Thermally upgraded
0.95-1.1 g/cm³ 120
Meta Aramid (Nomex 410) 1 g/cm³ 220
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Insulation & Thermal DesignWinding Selection
Example: Net Covered CTC for lower winding gradients
Kurt Kaineder - EM TR MPT GTCPage 6
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Insulation & Thermal DesignInsulation Materials
Solid Insulation MaterialsBased on natural cellulose fibers – all materials can be impregnated with oil
Papervery thin material (50 ... 200 mm)electrical +++, mechanical –
Pressboardthickness 0,5 ... 8mmSheet material, angle ringssnout segmentselectrical ++, mechanical +
Kurt Kaineder - EM TR MPT GTCPage 7
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Insulation & Thermal DesignInsulation Materials
Solid Insulation Materials
Laminated PressboardGlued pressboard withCasein or Polyesterthickness 9 .... 120mmelectrical +, mechanical ++
Laminated Woodglued veneer from beech (or birch)with Phenolharzdifferent direction of layersthickness 10 ... 120mmelectrical -, mechanical +++
Kurt Kaineder - EM TR MPT GTCPage 8
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Insulation & Thermal DesignInsulation Materials
Solid Insulation Materials
Synthetic materials – cannot be oil impregnated
• Insulating varnish• Nomex• Glass fiber
Kurt Kaineder - EM TR MPT GTCPage 9
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Insulation & Thermal DesignTypical Insulation Structure
Example
Kurt Kaineder - EM TR MPT GTCPage 10
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Insulation & Thermal DesignTypical Insulation Structure
Field plot of a 123 kV transformer
Test: one phase induced
The green lines areequipotentials – they connectpoints of equal voltage. Theelectric field gradient cutsthese at 90 degrees.
Kurt Kaineder - EM TR MPT GTCPage 11
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Insulation & Thermal DesignPD and breakdown considerations
General cause of partial discharge and/or a breakdown is high electricalstress according the following situations:
Causes can be• Cavity not filled with oil• Contamination (metal)• Design (selection of material, failure in design)• Mechanical damage• Manufacturing outside of tolerance• Sharp edges
Kurt Kaineder - EM TR MPT GTCPage 12
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Insulation & Thermal DesignPD and breakdown considerations
Cavity not filled with oil (inside glue, glass fiber, …)
• Electrical field strength higher than inside the materialEcavity ~ 2 … 5x Ematerial
• Breakdown voltage of cavity < Breakdown voltage of material• Start of partial discharge inside the cavity• Breakdown
Kurt Kaineder - EM TR MPT GTCPage 13
Material with Er > 1
Er ~ 1 air, vacuum
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Insulation & Thermal DesignPD and breakdown considerations
Contamination (metal) inside material (pressboard, laminatedpressboard, KP-wood, paper)
• High field strength at the edges of the metal part, local overload• Partial discharge• Breakdown possible (dependent on the size of the metal part)
Kurt Kaineder - EM TR MPT GTCPage 14
Metal
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Insulation & Thermal DesignPD considerations
Causes of Partial Discharge and Breakdown – ExampleManufacturing outside of tolerance
Kurt Kaineder - EM TR MPT GTCPage 15
Cylinder
High electrical field strength§ partial discharge§ breakdown
≥ 2 mm
HV-
disc
win
ding
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Insulation & Thermal DesignPD considerations
Causes of Partial Discharge and Breakdown - Examples
Kurt Kaineder - EM TR MPT GTCPage 16
Deformed angle ring
Soft paper insulation
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Insulation & Thermal DesignPD considerations
Causes of Partial Discharge and Breakdown - Examples
Kurt Kaineder - EM TR MPT GTCPage 17
Contamination with metal parts Glue in the insulation arrangement
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Insulation & Thermal DesignThermal Design Considerations
Source of conductor and core heatingLoss contribution:
ContributionLoad currentOhmic resistance of winding conductor: I²·R 60-90 %eddy current losses in all metallic parts due
to the magnetic stray flux of the windings < 20 %
No-load voltageMagnetic flux Φ in core 10-30 %core steel ≈ 1 W/kgexciting current < 1 % ofrated current
Kurt Kaineder - EM TR MPT GTCPage 18
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Insulation & Thermal DesignThermal Design Considerations
Cooling types
e.g. ONANor one transformer with several conditions,
e.g.: ONAN, ONAF, OFAFformer ANSI code: OA, FA , FOA since 2006: ANSI = IEC
Kurt Kaineder - EM TR MPT GTCPage 19
Oil Loop Symbol
Oil Natural ON
Oil Forced (pump) OF
Oil Directed (pump, directedflow into main windings) OD
Cooler Type Symbol
Air Natural (radiator) ANAir Forced (radiatorwith fans, or cooler)
AF
Water Forced(cooling by water)
WF
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Insulation & Thermal DesignThermal Design Considerations
Oil flow in core type transformers:
Kurt Kaineder - EM TR MPT GTCPage 20
OF: Oil Forcedoil pumps: flow into tank
ON: Oil Naturaloil flow by heated parts(buoyant force)
OD: Oil Directedoil pumps: flow directedinto windings
pumppumptop
LV HV
Cor
e
Rad
iato
r
bottom
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Insulation & Thermal DesignThermal Design Considerations
Examples
Kurt Kaineder - EM TR MPT GTCPage 21
ONAN / ONAFradiators with fans
ODAF5 Coolers
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Insulation & Thermal DesignThermal Design Considerations
Conventional Limits as per IEEE
Thermally upgraded paper shall be used for insulation components thatdetermine the minimum life expectancy, such as: winding insulation, layer tolayer insulation, lead insulation.• The allowed Hotspot Temperature of thermally upgraded paper insulation is
30+80=110°C.• IEEE C57.91-2012 suggests that the expected lifetime at 110°C could be 15-
20 years.• The lifetime depends strongly on the moisture and oxygen content of the oil
and insulation, therefore an oil preservation system is recommended.
Kurt Kaineder - EM TR MPT GTCPage 22
Limits as per IEEE C57.12.00-2010Top Oil rise above ambient 65 KWinding rise above ambient 65 KHotspot rise above ambient 80 K
Ambient Limit IEEE C57.12.00-2010Range …+40°C
oil: ≥ -20 °C
Daily average 30 °C
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Insulation & Thermal DesignThermal Design Considerations
Standard Model
Kurt Kaineder - EM TR MPT GTCPage 23
A is the top-oil temperature derived as the average ofthe tank outlet oil temperature and the tank oil pockettemperature
B is the mixed oil temperature in the tank at the top ofthe winding (often assumed to be the sametemperature as A)
C is the temperature of the average oil in the tankD is the oil temperature at the bottom of the windingE represents the bottom of the tankgr is the average winding to average oil (in tank)
temperature gradient at rated currentH is the hot-spot factorP is the hot-spot temperatureQ is the average winding temperature determined by
resistance measurementX axis indicates temperature riseY axis indicates relative vertical positions■ measured point; ● calculated point
Win
ding
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Insulation & Thermal DesignThermal Design Considerations
Detailed simulationLoss Distribution in individual partsof the windings can be calculatedwith very high precision
On this basis calculation of theHotspot-Temperature is done, basedon the calculated winding gradients, oilgradients and outer cooling systemsimulation.
Kurt Kaineder - EM TR MPT GTCPage 24
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Insulation & Thermal DesignThermal Design Considerations
Hotspot distribution
Test
Kurt Kaineder - EM TR MPT GTCPage 25
Mineral oil Synthetic Ester Natural Ester
Hot-spot rise 69.8 K Hot-spot rise 77.4 K Hot-spot rise 80.2 K
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Insulation & Thermal DesignThermal Design Considerations
Winding to oil gradient of a CTC
Kurt Kaineder - EM TR MPT GTCPage 26
14,2 K
Interface paper-oil 8,9 K
Paper Insulation3,0 K
Oilfilm 1,5 KEnamel 0,8 K
Loss W/m²
Temp
Distance
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Insulation & Thermal DesignThermal Design Considerations
Oil Flow Concepts for the Windingssuitable for natural or directed oil flow
Test
Kurt Kaineder - EM TR MPT GTCPage 27
Layer Windings withStripsDisc Windings withoutradial cooling ductsbut with axial coolingducts
Disc Windings withradial and axial coolingductsIncreased coolingsurface
Disc Windings withradial cooling ductsThe oil is guided by oilguide washers
Disc Windings withradial and axial coolingductsThe oil is guided by oilguide washers
Very efficient for ON and OD cooling
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ODRecommendable for largertransformersLimit: oil velocity to avoidelectrostatical charging
Insulation & Thermal DesignThermal Design Considerations
Examples of temperature rises in oil and windings(same windings, losses and radiators)
Kurt Kaineder - EM TR MPT GTCPage 28
7855
5739
2323
55
39 78
63
55!
45!
3535
39
37
ONHigh longitudinal rise
59
52
41
38
35
35
39
37
OFCooler top oil: low,but hotspot unchanged
Not recommendable
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Siemens AG – MPT TransformersContact
Kurt KainederHead of EngineeringHead of Electrical Design GlobalTechnology Center MPTSiemens AG Oesterreich
Transformers Linz
Kraussstraße 74020 LinzPhone: +43 (5) 1707-71098Fax: +43 (5) 1707-55391
Mobile: +43 (664) 615 4946Mobile: +43 (664) 80117 71098
E-mail: [email protected]
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Siemens US – TransformersContact
James McIverPrincipal Application EngineerE T TR US6860 Bermuda Road, STE 100Las Vegas NV 89119USA
Mobile: (702) 241-0157
E-mail:[email protected]
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