This is a complete guide on Hollow conductors which are used at Power Plants for AC systems. This is a training report on Bus Ducts. This was presented at Sri Balaji College of engineering and technology by Ajay Meena.

1. A
PRESENTATION
ON BUS DUCTS
P R E S E N T E D BY A J AY M E E N A

2. CONTENTS
• Training site and organization
• Bus Ducts
• Why bus ducts, why not cables
• Types of bus ducts
• Force acting on bus Bars
• Bus ducts accessories
• Ingress protection
• Test performed on bus ducts and their types

3. TRAINING SITE AND ORGANIZATION
• Bharat Heavy Electricals Ltd. (BHEL), Rudrapur, Uttrakhand
• Established in March 1983
• It’s a Component Fabrication Plant (CFP)
• Manufacturing Product is Bus Ducts ( All 3 Types)
• BHEL turn over: Rupees 10,341.58 Crores (2017-2018)
Rupees 10,476.28 Crore (2016-2017)
• Largest Plants: (1) Tiruchipalli (Tamil Nadu)
(2) Bhopal (MP)
• It also have International Customers: Malaysia, Oman, Iraq, UAE, Bhutan, Egypt, New Zealand

4. OTHER
BRANCHES
These are some of the
Manufacturing units(17),
Repair Units(02) and BHEL
Subsidiary(01).
BHEL Manufacturing Units Bangalore Electronics Division
Electronics Systems Division
Electro Porcelain Division
Bhopal Heavy Electrical Plant
Goindwal Industrial Valves Plant
Haridwar Heavy Electrical Equipment Plant
Central Foundry Forge Plant
Hydrabad Heavy Power Equipment Plant
Jagdishpur Insulator Plant
Centralized Stamping Unit
Jhansi Transformer Plant
Rudrapur Component Fabrication Plant
Ranipet Boiler Auxiliaries Plant
Tiruchirappalli High Pressure Boiler Plant
Seamless Steel Tube Plant
Thirumayam Power Plant Piping Unit
Visakhapatnam Heavy Plates and Vessels Plant
BHEL Repair Units Mumbai Electrical Machine Repair Plant
Varanasi Heavy Equipment Repair Plant
BHEL Subsidiary Kasaragod BHEL Electrical Machines

5. BUS DUCTS
J U S T A FA N C Y N A M E F O R C O N D U C TO R S

7. BUS DUCTS
• These are the hollow conductor, used to carry current from generator to transformer.
• These have High current and voltage handling capacity
• Material used may be Copper or Aluminium
• These materials are according to the demand of Customer
• Design either defined by the customer or suggested by Company
• These are according to the ISO standards
• Conductor Shape can be a Bar, Cubical or Cylindrical
• Magnetic field due to the conductor is reduced up to 95% due to this hollow design.
• There are two main part of the Duct which are the Enclosure and Conductor.

8. CONDUCTORS
• Thick and hollow
• Usually made up of Aluminium
• Ends of conductors are silver polished.
• There are some cutting on regular distance on it to make the heat escape.
• outside and inside of the conductor is painted with black color to minimize the heat
reflection.
• Ends of the conductor are angled just to make effective welding with another
conductor.

9. ENCLOSURE
• It is the outer part of the bus duct
• It is used for protection of humans and conductors.
• It also made up of Aluminum
• Aluminum is used because it is non-magnetic and light in weight and easier to
fabricate.
• It is made dust tight to protect the conductor from potential faults.
• It is also painted black from inside for the same purpose.
• Outer color is demanded by the customer.

10. WHY BUS DUCT
WHY NOT
CABLES????
Q U E S T I O N O F T H E E R A …

11. • Cables have very low short circuit current withstand capacity in comparison with Bus
ducts
• More material is used to make cable for such rating.
• Cables become Bulky
• Hard to install
• Repair and maintenance is not easy for cables
• Installation of cables is very difficult and may stress other equipment
• Current carrying capacity of bus duct is much higher than cables
• Voltage drop is bus ducts is much lower than cables
• Insulation is not practical or if possible it is not reliable.
• Connection to electrical equipment like Switch gear and transformers is not easy, its
more stressful.

12. T YPE OF BUS
DUCTS
There are 3 types of
bus ducts which are
also further divided
according to working
and construction.
The adjacent figure
shows the different
categories of Bus
Ducts.
Bus Ducts
Isolated Phase Bus
Ducts
Discontinuous Continuous
Natural Cooled Forced Cooled
Segregated Phase
Bus Ducts
Non-segregated
phase Bus Ducts

13. ISOLATED
PHASE BUS
DUCT
V E R Y H I G H C U R R E N T R AT I N G S

14. I S O L AT E D P H A S E
B U S D U C T
• Abbreviation: IPBD
• Connected between Generator and Generating
Transformer.
• Each phase is separated or isolated
• Thickness and diameter of conductor depend on the
current rating of Duct.
• Rating of the IPBD starts from 1200 Amp to 31000
Amps.
• Classified into three parts according to the connection
schemes: > Main run
> Delta Run
> Tap-off

15. DESIGN ASPECTS AND CRITERIA
• Rated Continuous Current for main bus: 19000 Amps
• Rated Continuous Current for Tap off bus: 1600 Amps
• Rated voltage 21KV
• Short time current for main bus 135 KA RMS for 3 sec
• Short timer current for tap off bus 254KA RMS for 1 sec
• Temperature rise allowed for bus enclosure 30 to 50° Celsius
• Temperature rise allowed for bus conductor 40° for plain bolt joint
50° to 55° for silver plated joint
These are the parameters for 2X500 MW plant at TUTICORIN, Tamil Nadu

16. CONSTRUCTIONAL ASPECTS
• Enclosure is made up of aluminum alloy, this is usually shorter than conductor.
• Additional channel rings are used to fill the gap between two enclosure.
• Conductors are not completely in cylindrical shape it have some cuttings to pass the
heat produced in internal portion.
• Conductor have some holes to mount insulators.
• Coloring schemes.
• Enclosure also have a inspection window for routine checkups.
• These sections also have a hot air blower or HAB.
• There are also some Seal-off bushings at the end of the sections.

17. SEGREGATED
PHASE BUS
DUCT
A L L T H R E E P H A S E I N O N E D U C T

18. S E G R E G AT E D P H A S E
B U S D U C T
• Abbreviation: SPBD
• Generally used for medium voltages.
• These are used to connect equipment like switch
gear from unit aux transformers
• It have common enclosure but separated by Al
sheet
• This provide non-magnitude barrier.
• Conductor may by copper of aluminum.
• Supporting insulators are made up of porcelain or
epoxy resin.
• It may be Bar, Cuboidal or cylindrical in shape.
• Can also be used to form link between LAVT, UAT,
NGC etc.

19. DESIGN ASPECT AND CRITERIAFollowing parameters are given for 500 MW Power Plant

20. CONSTRUCTIONAL ASPECTS
• Enclosure is made up of aluminum alloy, sheet provided is of length of 3.72 meters.
• Barrier plate is of thickness 2mm which provide complete phase segregation.
• Inspection windows are also provided near the joints where is High Resistance is used
to make duct air tight or weather proof.
• Space heater(HAB) are also used here for the same purpose.
• Thermistor is also used which keep track of temperature inside duct.

21. NON-SEGREGATED PHASE BUS DUCT
• The only difference between the SPBD and NSPBD is that there is no separation barrier
between the phases.
• Also the current rating is not so wide.
Difference in current rating of these 3 are given
below>>

22. INGRESS
PROTECTION
P R OT E C T I O N O F C U B I C L E S

24. DESIGN AND
SELECTION
CRITERIA
FA C TO R S D E C I D I N G D E S I G N A N D
S E L E C T I O N

25. DESIGN DEPEND UPON FOLLOWING
FACTORS
• The continuous current rating
• Maximum system voltage
• Maximum dynamic forces it may be subjected to during its life span
• The dielectric requirement of the system
• Climatic conditions

26. SELECTION CRITERIA
• Current carrying capability
• The resistivity required for permissible thermal limits
• Forces between the different conductors in short circuit condition
• Skin effects
• Proximity effects
• Effects of solar radiation on temperature rise
• Seismic condition
Shape and size of the bus ducts is selected considering the following aspects:

27. FORCES ACTING
ON BUS BAR
W H AT B U S D U C T S H AV E TO FA C E

28. • Weight :
Dusts are made from Aluminum, so it light in weight
It is also easier to support the main bus bar inside the enclosure.
Supported using insulators.
• Wind and ice
If bus ducts are outside, forces like wind and ice are also considered.
This is taken into account and the radial thickness should be 9.5 mm.
• Expansion forces
Due to the Temperature rise and fall the conductor, expends and contracts
respectively. So there will be relative motion between the two adjacent bars.

29. BUS DUCT
ACCESSORIES
A U X I L I A R Y PA R T O F B U S D U C T

30. CURRENT
TRANSFORMERS
• It is mounted within the enclosure, suitable for
operation at an ambient temperature.(90° to 100°)
• The CT secondary boxes are brought through the
marshalling boxes.
• Marshalling boxes have the terminal blocks
provide the facility of shorting and grounding.

31. L AV T CUBICLES• VT, SC and LA all three present in one cubicle
• Generally IP 52 protection is used
• Supplied from tap off bus duct.
• Fabricated from cold rolled sheet of Aluminum
(2mm)
• There is a automated shutter mechanism for isolation
when carriage is out.
• Generally the number of VTs are four but it depends
upon the customer.

32. NGT CUBICLES
• It consists of two parts which are NGT and NGR.
• Both are located in separated chambers of cubicle
• Painted with heat resistant paint.
• Lower IP (23)
• NGT is cast epoxy resin type, natural cooled, Single
phase
• Secondary is connected to the NGR.
• This is made from anti-aging, corrosion resistant
punched stainless steel grid.
• This is designed for indoors, for temperature rise as per
IEEE 32

33. OTHER AUXILIARY PARTS
• Seal off bushing: made up of cast resin and used at the equipment termination.
• Rubber Bellow: provided between the sections of the enclosure, provide discontinuous
path to the circulating current.
• Shorting plate: it’s a plate of Aluminum alloy, its used to make IPBD enclosure
continuous. It is used at generator end, GT ends, UT ends.
• Wall frame Assembly: These are the supporting plated used where Bus Ducts need to
penetrate the building walls, it make sure no loads are imposed
the building structure.

34. • Air pressurization system: Since Generator bus duct must be air tight, so the air
leakage rate shall be restricted to the minimum
ie 5% of total air volume per hour.
• HAB: It is used to maintain the moisture content inside the Bus Ducts.
• Silica gel breather: Provided in non-pressurized bus duct to keep it dry. It is used to
maintain the ingress of the duct.

35. TEST
PERFORMED
B E C A U S E Q U A L I T Y I S I M P O R TA N T

36. ROUTINE TEST
• Visual inspection
• Dry power frequency voltage withstand for 1 minute
• Milli-volt drop test
• Water-tightness test
• Insulation resistance

37. TYPE TEST
• Impulse voltage test
• Heat run test
• Milli-volt drop test
• Air leakage test
• Water tightness test
• Temperature rise test

38. ANY QUESTIONS
LEFT????
W H AT ’ S I N Y O U R M I N D

39. THANK
YOU
T H A N K S F O R L I S T E N I N G