ABB
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Thermal Considerations when
Condenser Bushings Are
Applied in Bus Duct djr 00/2

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The Thermal Issues
• Heat generated in the conductor tube due to flow of current and the electrical resistance of conductor tube
• Steady state temperature rise at the hot spot is determined by the temperature rise of the hot spot due to the flow of current and by the heat transfer characteristics of the bushing.
• The heat that is generated within the condenser can only leave the bushing by transfer into the oil or into the air at the terminal ends of the bushing.
• The heat dissipated at the terminal ends is determined by the temperature of the connecting bus and the surrounding medium (air side and oil side) djr 00/2

ABB
Anatomy of a
Condenser Bushing djr 00/2

Condenser Bushing Fundamentals
• Field strength between co-axial cylinders:
E ( r )

1 r
 ln (
U r
2
/ r
1
)
• Capacitance of the cylinder configuration: l
C
   ln
2
 
( r
2
/
 l r
1
)
• Capacitances in series:
 r
2
ABB
1
C
 i n 

1
1
C i r
1 djr 00/2

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Anatomy of a Condenser Bushing djr 00/2

ABB
Anatomy of a Condenser Bushing djr 00/2

ABB
Anatomy of a Condenser Bushing
Test Tap Test Tap
Test Tap

450 kV BIL Voltage Tap

450 kV BIL djr 00/2

ABB
C
11
C
12
C
13
C
14
C
1
Anatomy of a
Condenser Bushing
C
2 djr 00/2

Standard Thermal Conditions for Condenser Bushings
ABB
• Defined in IEEE C57.19.00, Requirements and Test
Procedure for Outdoor Power Apparatus Bushings
• Section 4.1: “Usual Service Conditions”
• Ambient air temperature = 40 °C, max; -30°C, min.
• 24 hour average transformer oil temperature = 95 °C
• External bus connection temperature rise = 30 °C max, at rated current.
• Section 5.4.1: ‘Thermal Basis of Rating
• Bushing hot spot temperature rise at rated current = 65 °C, max, over ambient air temperature.
• Hottest spot bushing temperature at rated current
105 °C = 40°C + 65°C djr 00/2

Standard Thermal Conditions for Condenser Bushings
ABB
• Defined in IEEE C57.19.00, Requirements and Test
Procedure for Outdoor Power Apparatus Bushings
• Section 4.1: “Usual Service Conditions”
• Ambient air temperature = 40 °C, max; -30°C, min.
• 24 hour average transformer oil temperature = 95 °C
• External bus connection temperature rise = 30 °C max, at rated current.
• Section 5.4.1: ‘Thermal Basis of Rating
• Bushing hot spot temperature rise at rated current = 65 °C, max, over ambient air temperature.
• Hottest spot bushing temperature at rated current
105 °C = 40°C + 65°C djr 00/2

Standard Thermal
Conditions for Condenser
Bushings
 t = 30°C max
T = 70 °C
 t = 65°C
T
=
105°C
I = Rated Current
40°C
95°C
ABB djr 00/2

95°C
Standard Thermal Conditions
40°C
105°C 70°C
ABB djr 00/2

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Thermal Conditions Inside of
Bus Duct djr 00/2

ABB
Potential Bus Duct Thermal Conditions
• Air side terminal temperature rise can be as much as 65 °C according to IEEE C37.23
• Ambient air temperature inside of bus duct will, most likely, be greater than the 40 °C specified as standard for condenser bushings.
• 24 hour average transformer oil temperature = 95 °C
• The amount of heat generated within the bushing remains the same. djr 00/2

ABB
Potential Bus Duct Thermal Conditions
• Air side terminal temperature rise can be as much as 65 °C according to IEEE C37.23
• Ambient air temperature inside of bus duct will, most likely, be greater than the 40 °C specified as standard for condenser bushings.
• 24 hour average transformer oil temperature = 95 °C
• The amount of heat generated within the bushing remains the same. djr 00/2

Bus Duct
Thermal Conditions
 t = 65°C,
T = 115°C
Hot Spot = ??
95°C
>>40°C  50°C
I = Rated
Current
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95°C
ABB
 t = 65°C
T not =
105°C
T »» 105°C
Bus Duct vs Free Air
»» 40°C  50°C not 70°C but
 t = 65°C
T = 115°C djr 00/2

High Temperature Condenser Bushing
Developed for Bus Duct Applications
• Condenser = Nomex™ (Aramid) insulation + aluminum foils
• All Seals = high temperature Viton™ (Fluorocarbon rubber)
• These materials are suitable for continuous operation at 200 °C
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ABB
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