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ENHANCEMENT OF VAR
MANAGEMENT IN CESC
NETWORK
(Operation of NCGS units asSynchronous Condensers)
A PRESENTATION BY VAR ENHANCEMENT TASK FOCE
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1.Introduction
2.Exercises that have been carried out
3.Path forward to execution
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Introduction
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Q: What is the effect of low system voltage? A:
a) There is a possibility of VAR drawal from SEB.
~ ~CESC SEB
VAR FLOW
V
~ ~CESC SEB
V1 V2
V1 < V2
b) Low system voltage may lead to grid voltage instability and the wholegrid may collapse. Such grid failure at Southern and Western grid tookplace, a few years back due to low voltage.
c) Low voltage may lead to rotor angle instability while overloading agenerator.
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Q: What is the limitation in method 1?
A:
• In the process of increasing excitation, overall MVA delivered by thegenerator increases (provided the active power delivered remains constant).
• This increases the generator current and often crosses the rated limit.
• However increased lagging load can be met at the cost of reduction inactive load.
• Hence contradictory in nature.
• During peak summer evening load, both active and reactive becomesequally important
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Resort to Method 2
(Disadvantages of Cap Banks)
• Several cap banks have been installed. But supply / demand reactive power
is so much impaired, that we are not yet been able to manage the reactive
demand.
• The cap banks are prone to failure due to harmonic overheating andelectrical resonances.
• Switched capacitors are added to the system in steps which can develop
over voltages.
• In addition to abrupt system changes, switched capacitors cause voltage
transients on the electrical system during this switching steps
• Life expectancy of a cap bank can be in the range of 3 – 5 years.
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Resort to method 2(Advantages of Synchronous Condenser)
•Step less smooth control.
•The system produces no switching transients and is not affected by system
electrical harmonics.
•Some harmonics can even be absorbed by synchronous condensers.
•Synchronous condensers will not produce excessive voltage levels and are not
susceptible to electrical resonances.
•Synchronous condensers are also very reliable and require little maintenance.
•Initial cost is comparable to switched capacitors and is considerably less than
static VAR compensators.
•Life expectancy is in the range of 20 – 30 years.
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With a view to the advantages of
synchronous condensers and imminent
retirement of NCGS Units as generators,
conversion of the NCGS units tosynchronous condensers is being thought
of.
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A task force comprising of the following
officers has been formed for the purpose.
1. P.K. Guha (Manager, SGS)
2. J.R. Bhattacharjee (Manager, Testing)
3. S. Samaddar (Manager, CTM)4. P. Dey (Asst. Manager, NCGS)
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What is a Synchronous Condenser?
A synchronous motor designed to run
unloaded and over excited to serve as a
load on the supply system of a very low
leading P.F. is called a synchronouscondenser.
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Typical characteristic of a synchronous condenser
a) Large synchronous reactance (Xs) to minimize active
load on the system
EV Active Load= --------- Sinδ
Xs
b) Large field winding for over excitation
c) Typical P.F. at full load = 0.02
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Exercises that have been carried out
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• As a first step to study the feasibility of conversion of NCGS 30 MW unit, the
capability curve of the machine has been developed.
•To develop the capability curve, an old OCC and SCC characteristic curve has
been retrieved from Testing Department archive. This is required to find out the
synchronous reactance of the machine.
Specification of NCGS 30 MW unit
MW 30
MVA 35.3
Volts 33 KV
Stator Amps 618 A
PF 0.85
Star Connected, 50 Hz 3000 RPMExcitation voltage 300 V
Rotor current 360 A
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NCGS #2 (OCC-SCC)
0
5
10
15
20
25
30
35
0 50 100 150 200
Rotor Current (A)
S t a t o r V o l t s ( K V )
0
100
200
300
400
500
600
700
S t a t o r C u r r e n t
If1 = 100 A
180 A
IG = 618 A
If2 = 180 A
SCR = 100/180 = 5/9 = 0.55
Xs = (1/0.55)x100 % = 180 %
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Capabilty
Chart
Of
NCGS
30 MW
Machine
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Inferences derived from capability curve
•The capability curve reveals that machine can deliver 29 MVAR
(max) at 260 % excitation which corresponds to the maximum
rated current of 260 A of rotor current.
•NCGS data shows that, of late the rotor has handled 210 Awithout any problem.
•Keeping a margin of 20 A rotor current (meaning 240% excitation
or 240 A rotor current) and considering 0.5 MW active power loss
in the machine, it is evident from the capability chart that themachine can deliver around 26 MVAR.
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Speeding up of the machine
Once the reactive capability of the machine is
evaluated, the next greatest challenge is to raisethe machine to synchronous speed and
subsequent decoupling of the prime mover after
synchronisation.
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Some practical means of speeding up the
synchronous condenser
a) Using the steam turbine
b) Using a pony motor (may be a low slip induction motor)
c) Using the existing DC exciter
d) Using another generator
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Mr. S. J. Lishman of Siemens, UK, has answeredseveral questions raised by CESC in connection
to conversion of NCGS generator to synchronous
condenser. The question answer session is shown
in the next few slides.
Note:Mr. Lishman has commented that the following notes are
intended as guidance comments only and do not make any
particular recommendations for which system would be more
suitable for New Cossipore unit 1.
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Q: We intend to remove the LP spindle and fit a dummy shaft, remove enough
HP turbine blading such that the output of HP is limited to running the generator
rotor to speed. Once synchronised the steam supply will cut off leaving the HP
blading to run in the air. Is this option possible? If so,
•How much HP blading needs to be removed to power the machine to speed?
•Is vacuum necessary with the remaining blades or can they run in air?
•Can the condenser take resulting positive pressure?
A: Generally for smaller machines it takes around 6% of the mass flow of steam
to drive a machine up to full speed no load. However, regarding how much of
the existing blading would be required to do this is not a simple calculation as
there are potential windage heating effects etc to be considered. Coupled with
the fact that the HP blading is old design 600 series we believe this would be a
novel approach to the conversion to synchronous condenser operation and
therefore a design study would be required to confirm whether this method ofconversion would be possible. Given that this method also removes the
possibility of the machine ever again operating as a turbine generator it would
be better to consider other less destructive options for the conversion, as
above. In addition, all the reports and literature consulted have indicated that
the steam turbine is mechanically uncoupled from the generator when
operating as a synchronous condenser.
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Q: Is there any clutch available for decoupling the machine from the prime
mover?
A:There is a special type of clutch available commercially called a synchro-
self-shifting clutch (SSS clutch). The clutch is connected between thegenerator and the prime mover. The clutch is an arrangement of fluid-drive
gears which operate automatically by torque reversals. On starting, the
clutch engages both the prime mover and the generator as soon as torque is
applied. When the generator is synchronised to the system, power is cut off
from the prime mover, the clutch disengages and the prime mover slows
down alone. If required the prime mover can be run up again and at thecorrect speed the clutch will engage both machines. This system has been
used on gas turbine generators up to around 100 MVA. The supplier of this
type of clutch is SSS Gears Limited UK.
Note: There should be some form of bound bearing applied to the generatorrotor following disconnection from the turbine. This is to eliminate any axial
movement of the rotor during operation as a synchronous condenser. Also,
for New Cossipore unit 1, the main oil pump is at the governor end,
therefore as the main turbine would be disconnected the auxiliary oil pump
must be in operation during run up and operation of the synchronous
condenser.
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Q: If LP is removed permanently from generator rotor coupling,
can the DC exciter be used as motor and does it have suffcient
drive to run the generator rotor?
A: It is possible for a dc exciter to be used as a motor to run a
generator to full speed no load, however, it is generally the case
that the exciter is designed to take this extra duty. Also, there
requires to be an adequate dc supply available. From the
design files for New Cossipore units 1 and 2 the mechanicallosses (windage and friction) are quoted as 286 kW, the design
rating of the dc exciter is quoted as 225 kW with an output of 90
kW for CMR operation. Although the power required to
overcome the mechanical losses is greater than the rating it may
be possible for the exciter to carry out this duty as it is only
required to run the condenser up to speed, the mechanical
losses will be taken from the generating system once
synchronised.
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Q: If using the DC exciter as a motor is a feasible proposition, then
can the quill shaft also take the torque required to turn thegenerator rotor up to full speed?
A: Another consideration is whether the torsion rod drive will take
the load from the condenser rotor when driven from the dc exciter.
A quick calculation as to the increase in torque applied to the
torsion rod drive when driving the condenser from the dc exciter (as
opposed to driving the dc exciter from the generator) shows an
increase in torque by a factor of approximately 3.6 times. At steady
state conditions, ie, 3000 revs / min, the increased shear stress in
the torsion rod is within the ultimate tensile strength of the material,
however, this does not take account of the initial starting torquerequired to turn the shafts from zero speed. How the application of
current to the dc exciter during starting is carried out is thus
important and should be considered.
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Some precautions which are necessary when
generators are used as synchronous
condensers
1. It must be ensured that in cases where the generator is uncoupled from
the prime mover the lubrication system is still effective.
2. When the rotor is uncoupled it should have no axial play.
3. The synchronous condenser will require protection against over-speeding
and loss of voltage.
4. Overheating is possible when the machine is excited before the rotor is
up to speed, care should be taken to avoid damage to the rotor windings.
5. With small generators coarse synchronising is unavoidable, care must be
taken to choose the most favourable moment to close the synchronising
circuit breaker.
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Mr. Lishman has another proposal for starting
mechanism as commented below
“One area which has not been discussed so far is the use ofanother generator to run up the synchronous condenser to
speed. In this configuration the generator and condenser
armature windings are connected together when both are at
rest or on turning gear via their respective generator
transformers and an isolated route through the station switch
yard. The field circuit breakers of both units are initially
open. The generator and condenser are synchronised at
turning gear speed and run up throughout the speed range as
a synchronous pair. This has been the practice of somecross-compound machines and at least one cross compound
set has been run up, with both generators uncoupled from
their turbines, using a third generator driven by an induction
motor, with all three generators synchronised at turning gear
speed.”
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Some information downloaded from internet and E-mail
correspondence
From Tata Power site
In 1991 Tata Electric Company proposed utilisation of generators of unit-1, 2 &
3 as electrically driven synchronous condensers for P.F. improvement.
From BHEL EDN, Bangalore Site (which supports the above information)
In this page, some landmarks of important achievements in power plant
automation has been listed. One of them is as below
GTO Thyristor controls for starting of 67 MW Synchronous Condenser at TEC-
Trombay Plant, India.
http://www.bheledn.com/acheivments2.htm
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On enquiry from Jojobera power station of Tata Electric the
following information has been received.
•One unit of capacity 62 MW was converted into a synchronouscondenser in the year 1992-93, having capacity of 42/45 MVAR.
•It ran for less than a year before the project was finally
declared failure and shutdown.
•Problems faced were aging, increased maintenance cost.
•Expertise for this project was taken from Tata Consulting
engineers and Tata Power’s own project group.
•Presently no such unit exists in Trombay Power station.
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IEEE Power Engineering SocietyChicago Chapter 1998-1999
Conversion of Two Zion 1220 Mva Generators to Synchronous Condenser Operation
Wednesday, February 10, 1999
Raymond F. Cameron and Thomas W. Kay
Commonwealth Edison Company
About the Topic
During the Spring of 1998, Commonwealth Edison Company successfully modified two retired 1220
Mva nuclear generators for operation as synchronous condensers. This presentation will discuss the
planning studies which identified the need for the synchronous condenser, alternative starting
mechanisms considered, and operational issues and experience with the synchronous condenser.
The justification for the synchronous condenser was demonstrated by planning studies which
showed the critical need for voltage support after the Zion generators were retired. The synchronous
condensers enabled ComEd to maintain voltage stability margins to the same level as before thegenerators were retired.
During the design stage, one of the biggest challenges in the conversion to synchronous condenser
was designing the starting mechanism. Several alternatives were investigated, including utilization of
a starting motor to accelerate the generators to synchronous speed, and utilization of a variable
frequency drive to accelerate the generator from a standstill.
The first synchronous condenser was synchronized ahead of schedule on May 25, 1998. The
second unit was synchronized on June 2, 1998. The synchronous condensers proved to be a very
valuable asset during operation during the summer of 1998. Operation of the synchronous
condensers enabled ComEd to maintain adequate voltage stability margins throughout the summer.
http://www.ece.iit.edu/~flueck/chicago_pes/1998/anb0210.html
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Correspondence with BHEL, Hyderabad
From Mr. STH Rizvi, GM/PED, R&D Engg
Dear Sir,
Your request letter in this forwarded mail is seen and dicussed with our design
engineers, concerned and the following are our comments:
Generator can be in principle operated as synchronous Condenser to improve Power
factor in the system. But if Generator is to be operated as Synchronous Condenser, a starting
motor with a suitable decoupling device is required to bring generator to synchronous speed. At
present BHEL does not have any such equipment (motor with decoupling device) nor the required
experience associated with this.
However you can visit, if desired so, TNEB Basin Bridge GT Power Plant where BHEL
(HYD) has supplied Generator to operate as generator normally and as synchronous condenser
occasionally.
Further we do not have any knowledge or necessary information on GTO thyristor
controls being supplied by BHEL EDn, Bangalore for 67 MW Synchonous Condenser at TEC as
mentioned in your letter. You may further probe in this matter with our Bangalore unit directly.
Lastly, we do not have information whether anybody in India is taking up jobs of
converting old generators to synchronous condensers.
Trust, we may be of help to you in some other occasion.
Regards.
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Path forward to execution
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Phase-1:
(On immediate basis)
•To prove the rotor withstanding capacity, the team feels to operate
the machine as a generator at a very low active power (to the tune of
4 – 5 MW) and maximum lagging MVAR (to the tune of 26 MVAR)
and P.F.=0.2
•To accomplish this, the following are required
-Generator rotor temperature detection system by VI method
already exists
-Generator Low Forward Power protection to be removed – does not
exist at all
-Generator Reverse Power protection to be incorporated –
Requisition made, order being processed
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Phase-2:(Operation as pure synchronous condenser)
•In this phase, conversion to synchronous condenser is being thought of as
long as steam generation is available and active power from NCGS is
required.
•In this proposition one machine will be decoupled from LP coupling.
•Modification for the lubrication of the synchronous condenser with AOP is
required.
•The stator terminals of two machines are connected together.
•The field breakers of both the machines will be made on when both are at
turning gear speed.•One machine will be started as a generator with steam input which
eventually will speed up the second machine synchronously till the rated
speed is achieved.
•Finally the synchronous pair will be synchronised to the 33 KV Bus Bar.
~ ~Synchronous Condenser Synchronous Generator
Synchronising Circuit Breaker
33 KV Bus Bar
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Phase-3:
(When NCGS retires fully and there is no active
demand & steam generation)
•In this phase, NCGS will be considered as pure synchronous condenserstation.
• The exciter will be used as prime mover.
•The electrical supply to the exciter will be provided from a motor generator
set. One such motor generator set exists at Mulajor Generating Station.
• A separate excitation system will be required for the excitation of the
synchronous condenser
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SEEG
M
33 KV Bus Bar
Synchronising Circuit Breaker
Synchronous
Condenser
3 phase AC supply
Induction Motor
DC Generator
JOP Supply
Turning Gear
Arrangement
Lube Supply
From AOP
Existing Exciter
To be used as
DC Motor
Schematic of phase-3
Extra Thrust
Bearing Arrangement
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Once the task force gets the
direction towards the
execution of the three phases,the team will go in for detailed
engineering with the help of a
competent party.
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CONVERSION OF 30 MW
SYNCHRONOUS GENERATOR
TO SYNCHRONOUS
CONDENSER
A PRESENTATION BY VAR ENHANCEMENT TASK FOCE
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RATING OF THE 30 MW GENERATOR
• MW : 30 MW
• MVA : 35.3 MVA
• VOLTS : 33 KV
• STATOR CURRENT : 618 A
• P.F. : 0.85
• RPM : 3000
• EXCITATION VOLTAGE : 300 V
• ROTOR CURRENT : 260 A
O ti f th U it # 1
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Operation of the Unit # 1
Synchronous Generator at low active and high
reactive:To prove the rotor withstanding capacity, the team felt to operate the
machine as a generator at a very low active power (to the tune of 4 –
5 MW) and maximum lagging MVAR (to the tune of 26 MVAR) and
P.F.=0.2
•To accomplish this, the following additional protections are
incorporated
-Generator rotor temperature detection system by VI method
has been calibrated
-Generator Reverse Power protection relay has been procured
and installed-Generator over voltage relay has been procured and installed
-A new calibrated VAR meter has been procured and installed
-Both the air coolers are cleaned
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Results of the test carried out on
24th November, 2006 are shown in
the next slide
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T/A-1 READINGS FOR LOW ACTIVE POWER & HIGH REACTIVE POWER
TEST ------- ON 24.11.06 L=LIMIT
Sl
.
N
o
Start
Time
Pilot
Excitor
output
voltage
Pilot
excitor
output
crt (1-5)
A
Main
excitor
field
voltage
(7-8) V
Gen.
Field
(rotor)
voltage
V
Gen.
Field
(rotor)
current
(L-260 )
A
Stat
or
volta
ge
KV
Deriv
ed
Powe
r
facto
r
Activ
e
power
MW
Rea
ctiv
e
pow
er
MVA
R
Stator
current
(L-550
A)
Rotor
temp
(L-
190 O
F) =
88 o C
Air Air
cooler
temp I/L
(L- 140 O F)
Air
Air
cool
er
tem
p
O/L
(L-
108
O F)
Cond
Temp
opp ex
duct
(L- 198O F)
Back of
core
temp (L-
198 O F)
End
Time
1 10-10 13 6.3 10.32 118 119 34.2 0.781 5 4 100 34 97 87 107.1 106.7
2 10-20 15 7 11.82 138 139 34 0.53 5 8 135 43 101 88 113.3 116.1 10-30
3 10-35 18 8 13.82 162 162 34 0.385 5 12 235 50 102 88 115.2 123.2 10-50
4 10-50 19 8.6 14.99 184 181 33.9 0.298 5 16 295 56 105 89 120 130.1 11-15
5 11-15 22 9.8 17.53 215 210 33.8 0.242 5 20 380 66 108 90 125.7 136.7 11-45
6 11-45 25 10.6 19.3 240 230 33.8 0.204 5 24 405 82 113 92 136 148 12-40
Frequency = 49.45 HZ Bus voltage = 32.4 KV
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A
Gen. Field Ammeter Shunt
Field Switch
Gen. Field
Voltmeter
T/ARotor
Field
M Ex
Ex Field
Ammeter
MainRheostat
M
ai
n
Neg
Fi
el
dP.
Ex
S
h.
Fiel
d
Fi
el
d
Vo
lt
m
eter
42
68
7513
T/A FIELD EXCITATION SYSTEM
Disc
Res
Main
Ex
Field
Dis
Sw
V
V
Rotor
Temp
Shunt
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Results of the test carried out on
12th December, 2006 are shown in
the next slide
T/A-1 READINGS FOR LOW ACTIVE POWER & HIGH REACTIVE POWER TEST -------
ON 12-12-2006
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Freq
= 49.15 Hz Bus Voltage = 33 KV T/A-1 synchronised at 9-40 AM
Sl.
No
Start
Time
Pil
ot
Ex
cit
or
vo
lta
ge
V
Pilo
t
exci
tor
out
put
ct
A
Main
excito
r field
voltag
e
(7-8)
V
Gen.
Field
(rotor)
voltage
V
Gen.
Field
(rotor)
current
A
Stato
r
volta
ge
KV
Powe
r
factor
Ac
tiv
e
po
w
er
M
W
Reactive
power
MVAR
(from
SCADA)
Reac
tive
powe
r
MVA
R
(from
analo
g
meter
)
Stator
curre
nt
(L-
550
A)
Rotor
temp
(L- 84
O C)
Air Air
cooler
temp
I/L
(L- 140
O F)
Air Air
cooler
temp
O/L
(L-
108 O
F)
Cond
Temp
opp
ex
duct
(L-
198 O
F)
Back
of
core
temp
(L-
198 O
F)
End
Time
1 9-50 15 6.9 140 142 33.2 0.96 10 5 5 190 48 93 80 105.5 108.6 10-15
2 10-15 16 7.5 12.6 149 149 33 0.55 5 10 10 195 54 96 81 110 118.2 10-30
3 10-30 19 8.5 15.2 180 179 32.4 0.32 5 14 14 270 64 97 81 113.3 125.3 11-00
4 11-00 22 9.6 16.7 220 210 32.3 0.26 5 20 20 360 72 99 82 118.2 130.9 11-30
5 11-30 25
10.
9 19.3 245 235 32 0.21 5 25 25 455 82 97 86 125.8 138.6 13-00
6 13-00 27
11.
5 21.05 258 235 32.6 0.1 3 25 25 450 84 93 87 124.8 140 14-00
7 14-00 3 25 25 84 93 88 126.9 143.8 15-00
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SINCE IT IS PROVEN THAT THE MACHINE CAN GENERATE 25
MVAR WITH ALL THE RELEVANT PARAMETERS WITHIN LIMIT,
THE NEXT CHALLENGE IS TO SPEED UP THE MACHINE TO 3000
RPM
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• To accomplish this, the team decided touse the main exciter as DC Motor to turn
the generator rotor.• The generator will remain decoupled
from the LP stage of the turbine
• The Lub oil pump will be in service• JOP will be in service
• As an extra precaution a gravity feed
tank for generator bearing oil will beinstalled
R i f h i i k
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Requirements for the main exciter to work as aDC Motor
• The armature of the main exciter will be fed
with the 90 KW transformer rectifier broughtfrom MGS
• The pilot exciter will be electricallydisconnected from the main exciter shunt field.
• It is observed experimentally that the directoutput voltage of the pilot exciter at 3000 rpmis approximately 100 v dc and fixed in nature.
• Since the pilot exciter voltage will not be available,
hence it is decided to make a separate powersupply tailored to our requirement to feed theshunt of the main exciter
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T/A-1 rpm vs Pilot Gen. DC voltage
0
20
4060
80
100
120
0 1000 2000 3000 4000
rpm
P i l o t G e n
D C V
o l ( V )
DC pilot volt (V)
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• Input voltage: 230 V AC
• Output voltage: 100 V DC• Output current capacity: 20 A
• A minimum current sensing device
• In the event of the shunt current going below a
minimum preset value the armature contactor willdrop out
• In the event of armature contactor dropping out, theshunt current will be removed
• The shunt field power supply will be interlocked to
the lube-oil pressure switch
• The schematic of the power supply unit is shown inthe next slide
The features of the external DC Power supply unit
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T/A
Rotor
Field
A
Gen.Field
Ammeter
ShuntField
Switch
Gen.
Field
Volt
mete
r
M Ex
Main
Rheostat
Mai
n
N
eg
Fi
el
d
Fi
el
d
Volt
m
et
er
42
68
7513
T/A FIELD EXCITATION
SYSTEM WITH
EXTERNAL POWER
SUPPLY UNIT
Di
sc
.R
es
Mai
n
Ex
Fiel
dV
V90 KW
Tr.
Rectifier
Armature
Supply
Ext
100 V
Power
Supply
Unit P. Ex
Sh.
Field
Rotor
Temp
Shunt
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•90 KW oil cooled transformer rectifier brought from MGS.
•Output DC current capacity: 300 A
•Output DC voltage (with step less control): 0-300 Vdc
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New 100 V DC power supply to feed the main exciter shunt
field externally
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•DC power contactor of the 90 KW transformer rectifier being mounted
on a separate obsolete panel
•A load test has been carried out for the transformer rectifier with
heater load
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•Front view of the 100 V DC power supply. When the shut current is below
set value, the red lamp will glow and drop out the DC contactor of the
armature supply.
•When the shut current is more than the set value, the green lamp will glow
and enable the armature DC contactor to pick up
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The 100 V DC power supply is being tested for set value
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STEPS TO BE FOLLOWED FOR MOTORING
THE ROTOR WITH MAIN EXCITER
• OCB ISOLATED/ VT DISCONNECTED / UNIT TRANSFORMER ISOLATED & RACKED OUT
• TURBINE DECOUPLED.• AOP IS PUT IN SERVICE AND LUBRCATING OIL PRESSURE O.K.
• JACKING OIL Pp. RUNNING JUST BEFORE THE OPERATION.
• DOUBLE AAF IS PUT IN SERVICE.
• A NEWLY INSTALLED ELECTRONIC RPM METER IS PUT IN SERVICE.
• 300A CFS IS KEPT ON FOR 90 KW RECTIFIER TRANSFORMER.
• A.C. 220 V SOURCE IS AVAILABLE FROM REMOTE.
• EXCITATION RHEOSTAT AT SWITCHBOARD IS KEPT AT ITS MINIMUM PSITION.
• ATA IS RESET TO ENABLE THE AAFS TO RUN.• RECTIFIER TRANSFORMER AT MIN TAP.
• PSU UNIT PUT ON BY PRESSING THE BYPASS SWITCH AND THE POWER CONTACTOR OF MAIN
EXCITER ARMATURE SUPPLY IS MADE ON.
• BYPASS SWITCH IS RELEASED ONLY AFTER THE POWER CONTACTOR OF THE MAIN EXCITER
POWER CONTACTOR IS MADE ON.
• THE RHEOSTAT POSITION IN THE SWITCH BOARD IS SLOWLY INCREASEDUNTILL THE PSU REGISTRS
10 AMPERES.
• IN THE PROCESS IT IS TO BE NOTED THAT THE MINIMUM SET CURRENT VALUE IS REACHED.• AAT THIS STAGE IT IS EXPECTED THAT THE FULL EXCITATION FLUX IS ESTABLISHED.
• THE ARMATURE SUPPLY VOLTAGE IS THEN SLOWLY INCREASED UNTILL THE GENERATOR ROTOR
STARTS ROTATING.
• CONSIDERING THE RATED VOLTAGE AND THE CAPACITY OF THE MAIN EXCITER ARE 300 VOLTS AND
90 KW RESPECTIVELY, IT IS TO BE NOTED THAT IN NO CICUMSTANCES THE MAIN RXCITER OUTPUT
VOLTAGE AND CURRENT EXCEEDS 300 V AND 300 A.
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