Study of Electrical Furnace and West Plant Substation
1. Study of Electrical Furnace in
Heat Treatment Shop and
Power System of West Plant
Substation
- Nishant Ranjan
2. Acknowledgement
I am thankful to the entire TATA STEEL family for having extended full support and co-
operation during the duration of my summer training to help me complete this project as
well as gain valuable information as to how the Iron and Steel industry functions.
This project report would not be complete without the help and cooperation of Mr. M C
Jha (Foreman, Heat Tr. Shop). Every other member of IEM office had extended their
hand of help throughout my course of summer training. I had a very good experience
working with them and the office ambience was very much friendly. In particular, I would
like to express my gratitude towards: Mr. Binay Kumar Agarwal (Manager, Spare
Manufacturing Department) – My benevolent guide who was most helpful throughout my
project.
3. Certification
This is to certify that Nishant Ranjan a student of 3rd year Electrical and Electronics
Engineering from GITAM UNIVERSITY has undergone summer training at Spares
Manufacturing Department of TATA STEEL under my guidance and has successfully
completed the project titled “Study of Electrical Furnace in Heat Treatment Shop and
Power System of West Plant Substation”. The duration of the training was from 3rd June to
28th June, 2014.
He has shown a lot of initiative in learning during his training program and has
enthusiastically completed all the work allotted. I wish all the best for his future
endeavours.
Project Guide:
Mr. Binay Kumar Agarwal
Manager
Spare Manufacturing Department
TATA Steel
4. Overview of TATA STEEL
Tata Iron and Steel Company was established by Dorabji Tata on August 26, 1907, as part of
his father Jamsetji's Tata Group. Jamsetji Tata had started his quest for steel way back in
1882 but it was twenty-five years later, in December 1907 that the explorers found their
way to Sakchi - at the confluence of the rivers Subarnarekha and Kharkai. On 27th February
1908 when the first stake was driven into the soil of Sakchi the dream had come alive. By
1939 it operated the largest steel plant in the British Empire. The company launched a
major modernization and expansion program in 1951. Later, the program was upgraded to
2 MTPA project. In 1990, it started expansion plan and established its subsidiary Tata Inc. in
New York. The company changed its name from TISCO to Tata Steel in 2005.
The last decade has been marked by Tata Steel’s prominent role in the overall development
of the country, even during phases of economic turbulence and its decisive foray into more
and more global territory. Intense strategic thinking about future expansions, plans for
organic growth and initiation of new projects are a few highlights in Tata Steel’s expanding
and more penetrative roles in the larger perspective. The acquisition of NatSteel in 2004
was Tata Steel’s first overseas acquisition and the series of joint ventures and mergers that
followed found a peak when the acquisition of Corus, happened in April 2007. But in every
positive step that the Company has taken towards growth and expansion, involving diverse
cultures and geographies, Tata Steel has never lost sight of its great heritage of social and
community responsibility.
5. Overview of TATA STEEL
Tata Steel is headquartered in Mumbai, Maharashtra, India and has its marketing
headquarters at the Tata Centre in Kolkata, West Bengal. It has a presence in around 50
countries with manufacturing operations in 26 countries including: India, Malaysia,
Vietnam, Thailand, Dubai, Daggaron, Ivory Coast, Mozambique, South Africa, Australia,
United Kingdom, The Netherlands, France and Canada.
Tata Steel primarily serves customers in the automotive, construction, consumer goods,
engineering, packaging, lifting and excavating, energy and power, aerospace, shipbuilding,
rail and defence and security sectors.
Tata Steel has set a target of achieving an annual production capacity of 100 million tons
by 2015; it is planning for capacity expansion to be balanced roughly 50:50 between
greenfield developments and acquisitions. Overseas acquisitions have already added an
additional 21.4 million tonnes of capacity, including Corus (18.2 million tonnes), NatSteel
(2 million tonnes) and Millennium Steel (1.2 million tonnes). Tata plans to add another 29
million tonnes of capacity through acquisitions. Major greenfield steel plant expansion
projects planned by
Tata Steel include:
- A 6 million tonne per annum capacity plant in Kalinganagar, Odisha, India;
6. Overview of TATA STEEL
- An expansion of the capacity of its plant in Jharkhand, India from 6.8 to 10 million tonnes per
annum;
- A 5 million ton per annum capacity plant in Chhattisgarh, India (Tata Steel signed a
memorandum of understanding with the Chhattisgarh government in 2005; the plant is facing
strong protest from tribal people);
- A 3 million ton per annum capacity plant in Iran;
- A 2.4 million ton per annum capacity plant in Bangladesh;
- A 10.5 million ton per annum capacity plant in Vietnam (feasibility studies are underway);
- A 6 million ton per annum capacity plant in Haveri, Karnataka.
Departments of TATA Steel Plant, Jamshedpur:
From raw material to the final product many units work upon the material. These units are
-Blast furnace -LD1
-LD2 -CRM
-HSM -CO MILLS
-SINTER PLANT 1,2,3 -MERCHANT MILL
-SM & SPOS
7. Spares Manufacturing Department
The spares manufacturing department is divided into the following different sections:
• Forge Shop
• Heat Treatment Shop
• Welding Shop
• Fabrication Shop
• Machine Shop
• Segment Shop
Some of the machines available in the above mentioned shops are:
Forge Shop:
Davy Press
Steam Hammer
Pneumatic Hammer
Gear Turning machine
Furnace
8. Spares Manufacturing Department
Machine Shop:
• Skoda conventional horizontal boring machine- M/C #249, #253, #254, #257, #259
• Skoda CNC horizontal boring machine (CNC of Fagor and Kirloskar)- M/C #252, #255, #256,
#258, #260
• Plano miller (CNC of Siemens)- M/C #449
• Grinding machine (CNC of Siemens)- M/C #347
• Conventional lathe machine
-Without turret
-With turret- M/C #172, #180
• CNC lathe machine (CNC of Fagor and Siemens)- M/C #89, #94, #97, #106
• Vertical boring machine (CNC of Fagor)- M/C #178
Fabrication Shop:
• Sheet Bending machine
• Sheet Straight machine
• Sheet Shearing machine
• Profile Gas Cutting machine (CNC of Barny Phantom, Tanaka, Kirloskar)
• Penetrating machine
10. Heat Treatment Process
Heat treating is a group of industrial and metalworking processes used to alter the physical,
and sometimes chemical, properties of a material. The most common application
is metallurgical. Heat treatments are also used in the manufacture of many other materials,
such as glass. Heat treatment involves the use of heating or chilling, normally to extreme
temperatures, to achieve a desired result such as hardening or softening of a material. It is
noteworthy that while the term heat treatment applies only to processes where the heating
and cooling are done for the specific purpose of altering properties intentionally, heating and
cooling often occur incidentally during other manufacturing processes such as hot forming or
welding. Heat treatment techniques include:
• Hardening
• Annealing
• Normalizing
• Tempering
• Surface Hardening
11. Hardening
Case hardening or surface hardening is the process of hardening the surface of a metal object while
allowing the metal deeper underneath to remain soft, thus forming a thin layer of harder metal
(called the "case") at the surface. For steel or iron with low carbon content, which has poor to no
hardenability of its own, the case hardening process involves infusing additional carbon into the case.
Case hardening is usually done after the part has been formed into its final shape, but can also be
done to increase the hardening element content of bars to be used in a pattern welding or similar
process.
The hardened metal is usually more brittle than softer metal, through-hardening (that is, hardening
the metal uniformly throughout the piece) is not always a suitable choice for applications where the
metal part is subject to certain kinds of stress. In such applications, case hardening can provide a part
that will not fracture (because of the soft core that can absorb stresses without cracking) but also
provides adequate wear resistance on the surface.
12. Annealing
Annealing consists of heating a metal to a specific temperature and then cooling at a rate that
will produce a refined microstructure. The rate of cooling is generally slow. Annealing is most
often used to soften a metal for cold working, to improve machinability, or to enhance properties
like electrical conductivity.
In ferrous alloys, annealing is usually accomplished by heating the metal beyond the upper
critical temperature and then cooling very slowly, resulting in the formation of pearlite. In both
pure metals and many alloys that can not be heat treated, annealing is used to remove the
hardness caused by cold working. The metal is heated to a temperature
where recrystallization can occur, thereby repairing the defects caused by plastic deformation. In
these metals, the rate of cooling will usually have little effect
13. Normalizing
Normalizing is a technique used to provide uniformity in grain size and composition
throughout an alloy. The term is often used for ferrous alloys that have been
austenitized and then cooled in open air. Normalizing not only produces pearlite,
but also bainite sometimes martensite, which gives harder and stronger steel, but
with less ductility for the same composition than full annealing.
14. Tempering
Tempering is a process of heat treating, which is used to increase the toughness of iron-based
alloys. Tempering is usually performed after hardening, to reduce some of the excess hardness,
and is done by heating the metal to a much lower temperature than was used for hardening
(which means below critical temperature). The exact temperature determines the amount of
hardness removed, and depends on both the specific composition of the alloy and on the desired
properties in the finished product.
Untempered martensitic steel, while very hard, is too brittle to be useful for most applications. A
method for alleviating this problem is called tempering. Most applications require that quenched
parts be tempered. Tempering consists of heating steel below the lower critical temperature,
(often from 400 to 1105 ˚F or 205 to 595 ˚C, depending on the desired results), to impart
some toughness. Higher tempering temperatures, (may be up to 1,300 ˚F or 700 ˚C, depending
on the alloy and application), are sometimes used to impart further ductility, although some
yield strength is lost.
Tempering may also be performed on normalized steels. Other methods of tempering consist of
quenching to a specific temperature, which is above the martensite start temperature, and then
holding it there until pure bainite can form or internal stresses can be relieved. These
include austempering and martempering.
15. Tempering
Tempering Colours
Steel that has been freshly ground or polished will form oxide layers when heated. At a very specific
temperature, the iron oxide will form a layer with a very specific thickness, causing thin-film interference.
This causes colours to appear on the surface of the steel. As temperature is increased, the iron oxide layer
grows in thickness, changing the colour. These colours, called tempering colours, have been used for
centuries to gauge the temperature of the metal. At around 350˚F (176˚C) the steel will start to take on a
very light, yellowish hue. At 400˚F (204˚C), the steel will become a noticeable light-straw colour, and at
440˚F (226˚C), the colour will become dark-straw. At 500˚F (260˚C), steel will turn brown, while at 540˚F
(282˚C) it will turn purple. At 590˚F (310˚C) the steel turns a very deep blue, but at 640˚F (337˚C) it
becomes a rather light blue.
The tempering colours can be used to judge the final properties of the tempered steel. Very hard tool
steel is often tempered in the light to dark straw range, whereas spring steel is often tempered to the
blue. However, the final hardness of the tempered steel will vary, depending on the composition of the
steel. The oxide film will also increase in thickness over time. Therefore, steel that has been held at 400˚F
for a very long time may turn brown or purple, even though the temperature never exceeded that needed
to produce a light straw colour. Other factors affecting the final outcome are oil films on the surface and
the type of heat source used.
16. Tempering
In Heat Treatment shop of Spares Manufacturing Department the materials which are to be sent
in Machine shop for machining are given required hardness and after machining they are again
brought to Heat Treatment shop for removal of excess hardness i.e. tempering.
17. Carburizing
Carburizing is a heat treatment process in which iron or steel absorbs carbon liberated when the
metal is heated in the presence of a carbon bearing material, such as charcoal or carbon
monoxide, with the intent of giving the metal required hardness. Some types of carburizing
process are- liquid carburizing, gas carburizing, plasma carburizing, salt bath carburizing.
In gas carburizing the surface carbon content as well as the case depth can be accurately
controlled. It also gives uniform case depth. It is much cleaner and efficient method of carburizing.
The main carburizing agent in this process is any carbonaceous gas such as methane, propane or
alcohols. In this process it is necessary that the hydrocarbon gases should be diluted with a carrier
gas to avoid heavy soot formation. In NGC Tempering machine of Heat Treatment shop the carrier
gas is nitrogen
18. Furnace in Heat Treatment Shop
There is basically two types of furnace in Heat Treatment Shop:-
a. Gas Chamber Furnace
b. Electrical Furnace
We have three types of Electrical Furnace
• BOFCO Tempering Machine
• NGC Tempering Machine
• NGC Furnace
19. Gas Chamber Furnace
Short heating times due to the high power are a convincing argument. The chamber furnaces with
powerful gas burners cover a wide variety of these processes. In the basic version the burners are
manually ignited once at the start of the process. The automatic control system then takes over control
of the temperature curve. At program end, the burners are automatically switched off. Depending on
the process, the furnaces can be equipped with automatically controlled fan burners and safety
technology for debinding. Especially in case of larger binder concentrations, gas furnaces have the
advantage that the exhaust quantity can be significantly reduced as the binders are burnt off in the
furnace, providing for downsizing of the exhaust cleaning.
Specifications:-
- Tmax 1300 °C
-Powerful, atmospheric burners for operation with coke gas and water vapour
-Special positioning of the gas burners with flame guide top-down provides for good temperature
uniformity
-Fully automatic temperature control
-Gas fittings with flame control and safety valve in accordance with DVGW (German Technical and
Scientific Association for Gas and Water)
-Multi-layer, reduction-proof insulation with light-weight refractory bricks and special back-up
insulation result in low gas consumption
-Self-supporting and rugged ceiling, bricks laid in arched construction or as fiber insulation
20. Gas Chamber Furnace
-Dual shell housing, side
panels made of stainless
steel (NB 300), for low
outside temperatures
-Solid, dual shell door
-Exhaust hood with 150
mm (NB 300) and 00
mm (NB 400, NB 600)
diameter connection
-Over-temperature
limiter with manual
reset for thermal
protection class 2 in
accordance with
EN 60519-2 as
temperature limiter to
protect the furnace and
load
21. BOFCO Tempering Machine
• It is an Electrical furnace. Rating of the heater is 60kW. Heating element is Nichrome.
• It is a chamber type furnace.
• Dimension: 1550mm (depth) x 1000mm (width) x 450mm (height)
• Temperature Range: 500°C to 1150°C with tolerance from ±5°C to ±10°C
• Charging capacity: per batch is 1 ton.
• Floor is made by ceramic bricks.
• Charge Conveyance: Pushers, Rollers or Walking Beams
• Processes: Hardening, Quench and Tempering, Normalizing, Annealing, Isothermal Annealing,
Spherodize Annealing, Solution Annealing, Stress Relieving, etc.
• Material: Alloy Steels, Stainless Steels.
The charge is loaded into trays or baskets mounted on trays, and conveyed across the hearth using
pushers, rollers or walking beams at a controlled rate. Conveyors and extractors are used to
automate and integrate the heat treatment processes into other manufacturing processes at the
plant.
An easy to use Control Panel provides the interface to setup the automation sequences and heat
treatment parameters. The Control Panel and Process automation is implemented via PID
Controller. Multi-point Digital Temperature Recorders are provided with an option to record various
zone temperatures to a paper based system or to local storage that can subsequently
22. BOFCO Tempering Machine
be interfaced to a PC for long
term record keeping and
analytics.
Hydraulic pushers are used for
pushing the trays into the
heating chamber &
Electromechanical Extractor
Mechanisms are used to
unload the baskets or trays.
Specially designed conveyors
are used for transferring the
baskets or trays from the
Austenitising Furnace to the
Quench elevator and
subsequently to the Tempering
Furnace and discharge station.
23. BOFCO Tempering Machine
Design of Heating Coil:
The heating coils are mounted on both side walls. In each side wall 18 coils are there in 3 sets,
each set having 6 coils. Previously 12 coils of each side walls and the remaining 6+6 coils from
each side were connected in delta. But it was observed that there is a difference of 100°C in the
temperature of the side walls. To overcome this 6 coils from one side and 5 from other side are
taken and they are connected in series. Like this each branch of delta is made. Now there is only
difference of about 10-20°C between the temperature of the sidewalls.
Theory:-
When electric current flows through a conductor some loss occurs and this loss is almost
inevitable, and more the resistance of the conductor, more the loss. This loss due to the electrical
resistance of conductor is mainly responsible for the heating effect of electric current. As some
electric power is converted into heat energy, this phenomenon can be described by Joule's law,
which states that,
Where H is the generated heat in calories, i is the current that is flowing through the wire and it is
measured in amperes, r is the resistance of the conductor in ohm(Ω) and t is the duration of
current flowing in seconds. If we know the time of current flowing, the resistance of wire, and
amount of electric current flow, we can easily find out the generated heat of the circuit. This heat
24. BOFCO Tempering Machine
can be utilized in various ways.
We saw that the more
the electrical resistance of the
wire the more the generated heat
in the circuit, but to know more
accurately about the heating
effect of current, we should know
about it from the atomic level. As
the flow of electric current is
nothing but the flow of electrons
there will always
be resistance from the fixed
atoms of the conductor. The fixed
atoms of the wire resist the flow
of electrons and as a result there
are collisions and as the kinetic
energy converts into heat energy
we see that the wire is getting
hot.
25. BOFCO Tempering Machine
Heating Element: Nichrome
Patented in 1905, it is the oldest documented form of resistance heating alloy. A common alloy is
80% nickel and 20% chromium, by mass, but there are many others to accommodate various
applications. It is silvery-grey in colour, is corrosion-resistant, and has a high melting point of about
1,400 °C (2,550 °F). Due to its resistance to oxidation and stability at high temperatures, it is widely
used in electric heating elements, such as in appliances and tools. Typically, nichrome is wound in
coils to a certain electrical resistance, and current is passed through it to produce heat.
The element will be coiled tube type supported with ceramic tubes, ceramics bobbins. These tubes
will be suitably anchored with SS studs to the wall. The element terminal will be taken to the rear
side of the furnace casing for suitable interconnection. The design of the heating element will be
low watt density for longer life.
26. BOFCO Furnace Controller
PID Controller:
PID controller is used to control the temperature of the furnace. A PID controller calculates an
"error" value as the difference between a measured process variable and a desired set point. The
controller attempts to minimize the error by adjusting the process control inputs.
The PID controller calculation algorithm involves three separate constants parameters, and is
accordingly sometimes called three-term control: the proportional, the integral and derivative
values, denoted P, I and D. Simply put these values can be interpreted in terms of time: P
depends on present error, I on accumulation of past errors, and D is a prediction of future errors,
based on current rate of change. The weighted sum of these three actions is used to adjust the
process via a control element such as the position of a control valve, a damper, or the power
supplied to a heating element.
27. BOFCO Furnace Controller
The output of the PID controller u(t) can be expressed in terms of the input e(t), as:
And the transfer function of the controller is given by:
The terms of the controller are defined as:
Kp= Proportional gain, τd = Derivative time, and τi = Integral time
28. BOFCO Furnace Controller
If the PID controller parameters (the gains of the
proportional, integral and derivative terms) are
chosen incorrectly, the controlled process input can
be unstable, i.e., its output diverges, with or without
oscillation, and is limited only by saturation or
mechanical breakage. Instability is caused by excess
gain, particularly in the presence of significant lag. So
tuning a control loop is required for the adjustment of
its control parameters (proportional band/gain,
integral gain/reset, derivative gain/rate) to the
optimum values for the desired control response.
In the PID controller time and temperature
parameters are set for required for the tempering
process. In certain time interval how much
temperature will rise or it will remain constant, all
these parameters are put in the controller. And the
controller works as per requirement after getting the
temperature feedback from the TC.
30. Drives of BOFCO Tempering Furnace
Incomer:
Feeder no: 0
Feeder Rating: 125 A SDFU
Type of Feeder: SDFU
Control Transformer:
Feeder no: 1
Feeder Rating: 415/220V, 50Hz, 500Va
Type of feeder: Control Supply
Zone -1 Heater:
Feeder no: 2
Feeder rating: 60KW
Type of feeder: Thyristor
Recirculation Fan:
Feeder no: 3
Feeder Rating: 3HP
Type of feeder: DOL
31. Drives of BOFCO Tempering Furnace
Connection diagram of BOFCO Furnace
32. Drives of BOFCO Tempering Furnace
AC Drive internal circuit of control panel
33. Thermocouple (TC)
Thermocouple is used to measure the temperature of the inside wall of the furnace i.e. the
temperature at which the material is being tempered. One end of the thermocouple is inserted
into the furnace.
A thermocouple consists of two dissimilar conductors in contact, which produces a voltage
when heated. The size of the voltage is dependent on the difference of temperature of the
junction to other parts of the circuit. Although the voltage is within the range of millivolts. For
measurement purpose we need to transfer this voltage, but as the amount of voltage is very less,
most of it is lost during transmission. So this voltage is first converted to current by a transmitter.
The output of the transmitter is in the range of 4-20 mA. The minimum current is not zero because
even at lower temperature the voltage produced is not zero, so the current is also not zero. The
temperature scale of the measuring device is calibrated in accordance with the current output of
the transmitter
34. Thermocouple (TC)
Working Principle
The working principle of thermocouple is based on three effects, discovered by Seebeck, Peltier and
Thomson. They are as follows:
1) Seebeck effect: The Seebeck effect states that when two different or unlike metals are joined
together at two junctions, an electromotive force (emf) is generated at the two junctions. The
amount of emf generated is different for different combinations of the metals.
2) Peltier effect: As per the Peltier effect, when two dissimilar metals are joined together to form two
junctions, emf is generated within the circuit due to the different temperatures of the two junctions
of the circuit.
3) Thomson effect: As per the Thomson effect, when two unlike metals are joined together forming
two junctions, the potential exists within the circuit due to temperature gradient along the entire
length of the conductors within the circuit.
35. Thermocouple (TC)
How it Works
The general circuit for the working of thermocouple is shown in the figure 1 above. It comprises of two
dissimilar metals, A and B. These are joined together to form two junctions, p and q, which are
maintained at the temperatures T1 and T2respectively. Remember that the thermocouple cannot be
formed if there are not two junctions. Since the two junctions are maintained at different temperatures
the Peltier emf is generated within the circuit and it is the function of the temperatures of two
junctions.
If the temperature of both the junctions is same, equal and opposite emf will be generated at both
junctions and the net current flowing through the junction is zero. If the junctions are maintained at
different temperatures, the emf’s will not become zero and there will be a net current flowing through
the circuit. The total emf flowing through this circuit depends on the metals used within the circuit as
well as the temperature of the two junctions. The total emf or the current flowing through the circuit
can be measured easily by the suitable device.
The device for measuring the current or emf is connected within the circuit of the thermocouple. It
measures the amount of emf flowing through the circuit due to the two junctions of the two dissimilar
metals maintained at different temperatures. In figure 2 the two junctions of the thermocouple and the
device used for measurement of emf (potentiometer) are shown.
Now, the temperature of the reference junctions is already known, while the temperature of measuring
junction is unknown. The output obtained from the thermocouple circuit is calibrated directly against
the unknown temperature. Thus the voltage or current output obtained from thermocouple circuit gives
the value of unknown temperature directly.
36. YOKOGAWA display unit
The TC output is also connected to the YOKOGAWA display unit. There we can see the
temperature of all the furnaces together.
The function of the circuit is to provide a high accuracy multichannel thermocouple measurement
solution. Achieving a precision thermocouple measurement requires a signal chain of precision
components that amplifies the small thermocouple voltage, reduces noise, corrects nonlinearity,
and provides accurate reference junction compensation (commonly referred to as cold junction
compensation). This circuit addresses all these challenges for measuring thermocouple
temperature with better than ±0.25°C accuracy.
38. DAQLOGGER Software
Daqlogger software which plots
graphs of temperature vs. time.
In the computer display we can
observe heat treatment curve.
The primary purpose of the
DAQLOGGER software package
is to acquire data at fixed
intervals. Data acquisition is the
function whose performance is
considered most important. To
improve the performance, we
have designed the logger
software so that it has the
functions listed below
1. Reading measurement data
at fixed intervals
2. Writing measurement data
to data-sharing memory
3. Converting measurement
data to file
39. Circulatory Fan
There is a circulating fan (3HP,
4 pole, 1440 rpm) with bare
Impeller and hub, mounted
on the top of the furnace.
The SS fabricated
recirculation fan located at
the roof level behind the top
of baffle for circulating the
hot air inside the working the
chamber of the furnace. The
fan shaft will extend through
the roof lining, and be
supported on Plummer Block
bearings. The fan will be
driven by V belt arrangement.
The fan motor will be 3 HP.
The fan shaft will also be of
SS material
40. Quenching
There are basically three type of quenching:-
1. Oil Quenching
2. Water Quenching
3. Plasma Quenching
*In Heat Treatment Shop we have Oil quenching and Water Quenching available
Oil Quenching:
Quench immersion is operated using an Elevator table. Quench operation can be completed within
22 seconds for the first tank and about 35 seconds for the second tank.
The term quenching normally refers to the controlled cooling of steel components in a fluid to
give specified propeties. the hardness and the other physical properties obtained depend up on the
composition of the steel, the dimension of the component, the time and temparature of the heat
treatment and the speed and duration of the quenching process.
A number of quenching mediums such as molten salts, brine solutions and synthetic quenchants cab
be used, but petroleum based quenching media find the widest application due to the following
advantage.
They are easier to control and give uniform hardness.
• Suitable for large scale automation
• These are non-corrosive and non –toxic.
41. Quenching
Here Metaquench oil is used. Metaquench grades have been specially formulated from highly
refined petroleum oils with additives and have the following characteristics.
• Good thermal properties
• Good chemical and oxidation stability
• High boiling points and low volatility
• High flash and fire points
42. NGC Tempering Furnace
It has Electrical Furnace. NGC stands for New Gas Carburizing. The furnace of NGC is pit type. It
has a lid which is opened by hydraulic system. The heating element of the coils of the furnace is
nichrome. It has 3 coils each of 60 KW. The coils are fed from 440V, 50Hz 3 phase AC supply. The
Heating mechanism of this NGC Tempering Furnace is similar to that of the BOFCO Tempering
Furnace.
43. NGC Tempering Furnace
- The basic difference is the design of coils. NGC Tempering furnace has circular coils of diameter of
about 2 inches forming a pair of 3 each. These coils are placed on the inner walls of the Furnace.
- The work pieces are pre-heated and then held for a period of time at an elevated temperature in
the austenitic region of the specific alloy, typically between 820 and 940°C.
During the thermal cycle the components are subject to an enriched carbon atmosphere such
that nascent species of carbon can diffuse into the surface layers of the component. The rate of
diffusion is dependent on the alloy and carbon potential of the atmosphere. Care must be taken
to ensure that only sufficient carbon is available in the atmosphere at any one time to satisfy the
take up rate of the alloy to accept the carbon atoms.
In practice, this is defined in a carbon potential setpoint profile which runs concurrently with
the temperature cycle. The setpoint may give a boost phase where the carbon potential would be
typically set above 1.0% carbon but, as the cycle progresses and the effective case depth increases,
the carbon setpoint will be reduced to complete the diffusion stage.
- It has two fans (3 phase induction motor). They are of 3HP and 5HP. One of them circulates the
hot air inside the furnace uniformly and the other is for cooling purpose.
- There are 4 thermocouple of K-Type used here.
44. NGC Tempering Furnace
From the nameplate of the machines we can know the following things about it
• Maximum operating temperature is 700°C.
• Capacity of the machine is 3 tons per batch.
• Dimension of the machine is 3000mm (depth) x 1500mm (diameter).
• Type of treatment done is tempering.
45. NGC Furnace 1
It has Electrical Furnace. NGC stands for New Gas Carburizing. The furnace of NGC is pit type.
Here in this It has a lid which is opened by hydraulic system. The heating element of the coils of
the furnace is nichrome. It has 5 coils each of 90+90 KW. The coils are fed from 440V, 50Hz 3
phase AC supply. The Heating mechanism of this NGC Furnace-1 is similar to that of the BOFCO
Tempering Furnace.
46. NGC Furnace 1
- NGC Tempering furnace has coils
in U shaped each forming a pair of
five. There are five coils of each
phase and they are short-circuited
into one. These coils are placed on
the inner walls of the Furnace.
- It has one fans (3 phase induction
motor). They are of 3HP.It circulates
the hot air inside the furnace
uniformly.
- It has 3 Thermocouple of K- Type.
Specifications:
Dimension: 1500mm(depth) X
2000mm diameter
Capacity: 2 Ton per batch
Maximum Temp: 1100°C
47. Masibus
The operation of NGF Furnace 1 and NGC
Tempering Furnace is controlled by
Masibus.
Masibus:
This a microprocessor based scanner with
built-in features. The basic scanner is
having a capacity of 20 channels.
The scanner can accept any industrial
grade input like thermocouples, RTD, mV,
mA or voltage or current input. The type of
input is factory settable to any of the
above types. The unit is either operated
by 230V Ac or 110V Ac supply. The setting
of operating power supply is done at
factory only. The instrument is having two
back plates. The first back plate is having
connections for main power inputs and
relay outputs. It is also having connection
for parallel port and serial port
48. Power System of West Plant Substation
Overview of West Plant Substation:
• It is a 3.3kV substation. The substation is installed to supply power to different workshops and
offices of Spares Manufacturing Department of TATA Steel.
• 3.3kV is supplied to the substation from Power House no. 1 and Segment Shop tie.
• The 3.3kV bus is connected to three 1500kVA, 3300V/440V transformers and one 750kVA
rectifier transformer. The 3.3kV bus is also supplying power to Fabrication Shop Substation.
• The 440V bus is connected to the secondary side of the transformers. This bus is feeding
different machines and cranes of the workshops.
• To feed the DC crane at 250V one 750kVA, 3300kV/440V transformer and a rectifier
arrangement are used. The rectifier converts the 3 phase AC voltage to 250V DC.
• In both sides of the transformer (primary and secondary) circuit breakers are connected for
safe operation. In the high voltage side vacuum circuit breakers of Siemens are installed. In
the low voltage side air circuit breakers of Eswaran and Schneider and oil circuit breakers are
connected.
50. West Plant Substation
The above diagram is the single
line diagram of West Plant
Substation. Power House 1 is
feeding the 750kVA rectifier
transformer and one of the
distribution transformers. Segment
shop tie is feeding the rest of the
distribution transformers. These
two high voltage buses are
connected by a bus coupler which
is a VCB. It is kept in OFF position;
if one of the supplies fails the
breaker is put to ON position.
Similarly 440V bus #1 and #2 are
connected by bus coupler, so that
if one the transformer fails the
other transformer supplies both
the feeder.
The SLD of West Plant Substation is
given aside
51. Transformer
West Plant substation has 4 transformers, 3 of them are for distribution purpose and one is for
rectifying the alternating current to direct current. Distribution transformers are 3 phase,
1500kVA, 3.3kV/440V and the rectifier transformer is 3 phase, 750kVA, 3.3kV/440V.
From the nameplate of the distribution transformer we know the following details.
1. Rating of the transformer is 1500kVA; 6300V, 3150V/440V.
2. Max voltage that can be applied to the high voltage side is 6930V.
3. The transformer is designed in such a way that we can get 440V in the secondary side though
we apply different voltages in the primary side. We can apply 10 different voltages starting from
2835V up to 6930V and still get 440V in the secondary side. This is possible by connecting the
high tension leads in different manners.
4. For the distribution purpose in West Plant substation (3300kV/440V) in high tension side
leads 1 and 8; 7 and 14; 3 and 5; 10 and 12 are connected.
5. The vector group of transformer id Dy11. That means secondary line to neutral
voltage leads primary line to virtual neutral voltage by 30°.
52. Transformer
Transformer
6. Leads A2, B2, C2 in the high tension side and a2, b2, c2 in the low tension side are brought out
of the transformer.
7. Operating frequency is 50Hz.
8. Per unit impedance of the transformer #2 is 4.71% and of transformer #3 is 5.25%.
9. Rectifier transformer- 750kVA, 50Hz
former Primary Seconday Tertiary
Rated
Volatage 6300V/3150V 268V 239V
Rated
Current 83.5A/177A 3000A 30A
Phase 3 6 3
53. Transformer
Advantage od using D-y transformer:
We get an advantage of having delta in the primary side. Third harmonic current can flow through
the delta, as the current gets a loop to flow. The origin of the third harmonic current is sinusoidal
magnetic flux. If flux is purely sinusoidal then current required to produce that flux cannot be purely
sinusoidal. So we get a third harmonic component if we do the Fourier series expansion of the
current. And the third harmonic components of all three phase R, Y, B are in same phase. So if both
side of the transformer are star at the star point summation of the currents are not zero if the star
point is not grounded. And the resulting effect is oscillation of neutral point. In we have delta in one
side of the transformer third harmonic current can flow thorough the close loop.
Some Points:
• As the primary side is connected to the high voltage side and it is arranged in delta, the voltage
induced per turn is higher if it was connected in star. So the insulation grade should be better
and it is costly.
• Secondary side bus bars carries huge amount of current, so these bus bars are thick, whereas
the primary bus bars are thin.
• Here in the west plant substation all the transformers are feeding different loads. No two
transformers are operated in parallel to operate a single load. But as the vector groups of the
transformers are same and their voltage ratings are also same they can be operated in parallel
after checking the polarity.
54. Transformer
Maintenance:
• Transformer body temperature should be measured and noted down on regular basis.
• The radiator oil level should be checked. The oil level inside the indicator should not be less
than one half.
• The colour of the silica gel in the breather is to be noticed. It is blue in normal condition. Its
colour changes to pink when it absorbs moisture from the air. Then the silica gel is separated
from the breather and then it is heated to vaporize the moisture.
• Transformer acidic neutrality (TAN) test and tanδ test (for seeing capacitance loss) are to be
done in regular basis.
• The star point is grounded through neutral earthing pit and the transformer body is grounded
through equipment earthing pit. The combined earthing resistance value should be measured
on regular basis; its value should not be more than 1Ω. If it becomes more then saltwater is to
be poured in the pit to reduce the resistance value. The information plate of the neutral
earthing pit has red background and of equipment earthing pit has black background. On this
plate designation of the earthing pit, date of test, earth pit value is to be written.
55. Rectifier
To feed the DC cranes of Spares Manufacturing Department the rectifier is needed. The output
of the rectifier is 250V DC as required for the DC cranes. Rectifier has following parts.
• AC isolator panel (2 nos)
1. Rating: 500V AC, 1250A
2. Continuous operation
3. pole
• Thyristor converter (1 no)
1. 6 phase full controlled rectifier, single way
2. 750kW
3. Output: DC 250V, 3000A
4. Loading: 100% continuously, 125% for 2 hours, 200% for 10seconds
5. No of series path: 1
6. No of parallel path: 3
7. Fuse: 660V, 800A
8. Forced air cooled
56. Rectifier
• Reactor panel
1. Rating 250V, 3750A
2. Continuous duty cycle
3. Air cored
4. Inductance: 0.25mH
5. Provided with blower and forced air cooled
• Control cubicle
1. Constant potential through phase angle control of SCRs
2. Measuring instruments: AC ammeter and voltmeter, DC ammeter and voltmeter, power
factor meter.
3. Natural air cooled
4. DC isolator panel
5. 2 pole
6. 250V DC, 4000A
7. Continuous operation
57. Rectifier
• High speed DC circuit breaker (1 no)
1. Type: GEARAPID; SE-6000
2. Air circuit breaker
3. 4200A at 55°C
4. 750V DC, rated current 5000A
Operation of the rectifier assembly:
The high tension input three phase AC voltage is fed to a double wound step down transformer.
The step-down secondary voltage is in double star configurations connected to hexa phase full
controlled bridge which gives six pulse rectification.
The hexa phase AC output from the rectifier transformer is fed to the six phase full control
thyristor bridge having AC and DC isolators connected at input and output respectively. DC air
cored reactor at the output of the rectifier bridge limits the short circuit fault current level also
provides filtering.
The hexa phase thyristor bridge consists of 3 high power silicon controlled rectifiers in parallel in
each arm. Each SCR is protected by a fast acting fuse and dv/dt circuit. The SCR bridge is
protected against input voltage transients by a suppression network comprising of rectifier
bridges with resistors and capacitors.
58. Rectifier
3 phase full wave rectifier
using thyristor, input
voltage step down by a
double wound
transformer
59. Rectifier
Maintenance:
• Regular lubrication of blower bearing and checking the shaft alignment are to be done.
• The power and control cubicle are to be cleaned regularly with vacuum cleaner to avoid dust
collection on busbars, silicon devices, capacitors. While cleaning the cubicle must be
electrically isolated and the capacitors must be discharged.
• The ventilation of the room where the rectifier assembly is placed has to be good. If the
height of the room is less than 5 metres exhaust fan must be provided.
The sequence of the phase R, Y, B must be maintained in all interconnections. This is very
important.
60. Circuit Breaker
Circuit breaker is a high power switching device which can make, break and carry current under
normal as well as abnormal conditions. Circuit breakers are vital part of a power system for safe
power supply. In West Plant Substation vacuum circuit breakers (VCB) is used in high tension
side and air circuit breakers (ACB) and oil circuit breakers (OCB) are used in low tension side.
As fault occurs, the fault impedance being low the current increases and the relay set actuated.
The moving part of the relay moves because of the increase in the operating torque, the relay
takes some more time to close the contact. Relay contacts close trip circuit of the circuit
breaker closes and the trip coil is energised. The operating mechanism starts operating for the
opening process. The CB contact separates. Arc is drawn between the circuit breaker contacts
and it is extinguished through various mechanism in different types of circuit breakers.
Modern circuit breakers have over load trip, short circuit trip, under voltage trip, shunt trip,
earth fault trip indication and service, test, isolated position indication. As the OCBs installed in
this substation are old they do not have these many indication. Along with it OCB has
maintenance problem. So the old OCBs are being replaced by modern ACBs.
61. Circuit Breaker
Vacuum circuit breaker: 10 VCBs (new) are installed in West Plant Substation
Made by Siemens
• Rated voltage- 12kV, rated current- 1250A
• Short circuit current- 31.5kA for 3 seconds
• Impulse voltage- 75kV
• Connected to the high tension side of the transformers
• Pressure of the vacuum is in the range of 10-7 to 10-3 tor.
Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact
material), so the arc quenches when it is stretched a very small amount.
The vacuum as such is a dielectric medium and arc cannot persist in ideal vacuum. However the
separation of current carrying contacts causes the vapour to be released from the contact giving
rise to plasma. Thus, as the contact separate, the contact space is filled with vapour of positive ion
liberated from contact material. The vapour density depends on the current of the arc. During
decreasing mode of current wave the rate of release of vapour reduces and after the current is zero,
the medium regains dielectric strength provided vapour density around the contact has
substantially reduced. While interrupting the current of the order of few hundred amperes by
separating flat contacts under high vacuum, the arc generally has several parallel paths, each arc
path originating and sinking in hot spot of current.
62. Circuit Breaker
Thus the total current is divided in several arcs. The parallel arcs repel each other so that the arc
tends to spread over the contact surface. Such an arc gets interrupted easily.
The advantages of using VCB are-
• No emission of gases, pollution free.
• Modest maintenance.
• No explosion, silent operation
• Long life
But VCBs are more expensive and requires high technology.
Vacuum circuit breaker: 10 VCBs (new) are installed in West Plant Substation
Made by Siemens
• Rated voltage- 12kV, rated current- 1250A
• Short circuit current- 31.5kA for 3 seconds
• Impulse voltage- 75kV
• Connected to the high tension side of the transformers
• Pressure of the vacuum is in the range of 10-7 to 10-3 tor.
63. Circuit Breaker
Vacuum circuit breakers have minimal arcing (as there is nothing to ionize other than the contact
material), so the arc quenches when it is stretched a very small amount.
The vacuum as such is a dielectric medium and arc cannot persist in ideal vacuum. However the
separation of current carrying contacts causes the vapour to be released from the contact giving
rise to plasma.
Oil circuit breaker: 14 old OCBs are there in this substation connected to the low tension side of
the transformer.
As the current carrying contacts are separated under oil, the heat of the arc cause decomposition of
the oil, the products of the decomposition being hydrogen gas and other gases like acetylene. The
gases formed cause increase in pressure inside the arc-control device. The flow of gases is
influenced by the design of arc-control device speed of contact travel, the energy liberated by the
arc, etc. The high pressure gas in the arc-control device tries to escape through the side vents
towards the top of the interrupter. While doing so, it tries to cool the arc and lengthen it into the
vents. When current goes to zero, the arc diameter is very small and the gas flow is able to
interrupt the arc. The interruption of the arc stops the generation of gas and the contact is filled
with fresh dielectric oil.
64. Circuit Breaker
Disadvantages of using oil-
• The decomposed products of dielectric oil are inflammable and explosive. If the oil circuit
breaker is unable to break the fault current, pressure in the tank may rise above safe limit and
explosion may occur.
• The oil absorbs moisture readily. Dielectric strength reduces by carbonising which occur during
arcing. The oil is needed to be replaced after a certain breaker operation. It needs regular
maintenance.
• Oil is not a suitable medium for breakers which have to operate repeatedly.
Air circuit breaker: West Plant substation has 8 old Eswaran ACBs and 6 new Schneider ACBs. New
ACBs have various trip indication mentioned above and service, test and isolated position
indication.
Trip characteristics are often fully adjustable including configurable trip thresholds and delays.
Usually electronically controlled, though some models are microprocessor controlled via an
integral electronic trip unit.
Every air circuit breaker is fitted with a chamber surrounding the contact. This chamber is called
‘arc chute’. The arc is driven into it. If inside of the arc chute is suitably shaped, and if the arc can be
made conform to the shape, the arc chute wall will help to achieve cooling.
65. Circuit Breaker
The inner walls of the arc chute is shaped in such a way that the arc is not only forced into close
proximity with it but also driven into a serpentine channel projected on the arc chute wall. Thus the
arc path is lengthened.
The main arc chute is divided into numbers of small compartments by using metallic separation
plates. These metallic separation plates are actually the arc splitters and each of the small
compartments behaves as individual mini arc chute. In this system the initial arc is split into a
number of series arcs, each of which will have its own mini arc chute. So each of the split arcs has its
own cooling and lengthening effect due to its won mini arc chute and hence the arc extinguishes.
66. Circuit Breaker
Maintenance:
• It is recommended to grease the breaker after some particular numbers of operation.
• In VCB contact resistance of all three poles are to be measured by CRM meter. According to
TISCO standard its value should be less than 100µΩ.
• In VCB insulation resistance value between phase to phase and phase to neutral should be
greater than (3.3+1)MΩ. For ACB IR value should be greater than 1MΩ.
• Appropriate parts are to be lubricated.
• Contact erosion is to be noticed and checked as per manual.
• Insulators, switching bars should be cleaned with damp cloth.
• OCBs need regular maintenance. Breakdown value of the oil is to be measured. It must not be
less than. DGA(dissolved gas analysis) test are also be carried out. This called blood test of oil.
This is done how much gas is dissolved in the oil. If it is less than the standard value then the OCB
is prone to explosion as the gases formed by decomposing of oil are flammable.
67. Circuit Breaker
Safety precaution during handling High Tension Breaker
• The concerned IEM officer is to be informed before handling the high tension breaker.
• The voltage and current of the breaker which is going to be handled is to be checked. Also the
current level should be zero before putting the breaker off.
• If power shut down job is given to external agency, necessary power clearance is to be taken for
the same.
• The breaker is to be handled with personal protective equipment's (PPE) i.e. hand gloves, cool
coat, power tester, ground rod, link road, fuse puller, barricading tape.
• The breaker is to be switched on/off with the consent of the concerned authority.
• Red tag is to be used for necessary information about the S/D taken for the breaker.
• The HT equipment is to be discharged with the help of discharge rod before starting the work.
• Before putting the breaker into service, insulation resistance value is to be taken through
mugger.
