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Electronics Engineering
Electronics Engineering is a branch of engineering that deals with practical applications of electronic components, devices, systems, or equipment. Electronics are devices that operate on low voltage sources, as in electron tubes, transistors, integrated circuits, and printed circuit boards and use electricity as part of its driving force.
24,372 Questions
- in DRAM there will be slightly more than 8 billion transistors (one per bit, plus address decode and support circuits)
- in SRAM there will be slightly more than 48 billion transistors (six per bit, plus address decode and support circuits)
Is BJT is a current control device or voltage control device?
transistor is a current controlled device. as the current flows through the base of the transistor , it works like a close switch.
I assume you're referring to an amplifier circuit. In a differential amplifier, there are two inputs. The common mode output voltage is the output voltage that will result from the same voltage being applied to both inputs. Typically this is very low, as the common mode rejection ratio (CMRR) is very high in a differential amplifier. This is an ideal characteristic (high CMRR) as it means unwanted noise will not be amplified and potentially squelch out the desired signal; this is why a differential amplifier is used in high quality sound equipment. Three wires are used - a ground, and two signal wires that are opposite each other. Noise will inherently "hop on" the signal wires, but as they are close to one another, it is likely the noise will be nearly the same magnitude and sign on each wire. Since the amplifier CMRR is high, this noise does not propogate through the amplifier, while the original signal is amplified.
Why high frequency carrier is required for a communication system?
to shift the frequency of information signal ,at the frequency domain to a higher frequency ...so the information can be transmitted to the receiver .
What is the difference between sampling frequency and frequency?
frequency is simply the rate at which something is happening, ie the frequency of Christmas is once a year, the frequency of having breakfast is once a day etc. If frequency is expressed in Hertz, it's how many times something happens during a second.
Sampling is, well, sampling. Usually means testing and measuring something changeable. If you're running a bath and occasionally stick your fingers in to check the temperature, then that's sampling,
Sampling frequency simply describes at which rate you're making whatever test or measurement it is you're talking about.
What is a diode and how does it work?
When varactor diode is reverse biased then the neutral region between P and N layer increases. When reverse biasing decreases then the neutral region also decreases.
How many flip flops are required for divide-by-32 device?
(2^5) = 32
SO, 5 flipflops are required to produce a divide by 32 device
How you increase current by keeping voltage constant?
If you are referring to a simple circuit, you could add resistance throughout it. Increased resistance means decreased current flow yet the same voltage.
The Gain provided by the multistage amplifier is greater than the gain of single stage amplifier.
The gain of the two stage amplifier is the product of the gain of the individual stages.
A: DC couple amplifiers refers to stages of amplifiers where is the biasing is direct without adding capacitors to remove the DC component from amplifier to amplifier
In dc motor, the armature conductors are revolving in the magnetic field and emf is induced in the armature conductors. The direction of the induced emf is in opposite direction to the applied voltage as per Flemings left hand rule. So, the induced emf in motor is called as back emf or counter emf.
Vydehi
When must give a signal either by hand and arm or by a signal device?
You must give a signal either by hand and arm or by a signal device
How does you establish whether or not a source is biased?
-You would look for the wording to see if the information has been set towards one side or not.
-Usually biased information are to do with no one really knowing the truth such as 'Do aliens exist?'.
-You would also look if it is an opinion which means it is unbiased.
-Look for a fair viewpoint for the topic which reasons for good and bad.
-I fancy Georgina Miners.
The main advantage of RADAR, is that it provide superior penetration capability through any type of weather condition, and can be used in the day or night time. Radar uses electromagnetic wave that does not require a medium like Sonar (that uses water) so can be used in space and air. Radar can be long range and the wave propagate at the speed of light rather then sound (like with sonar). It is less susceptible to weather conditions compared with Lasers.And be used at night unlike passive cameras. It does not require target cooperation to emit any signals or emission.
EDIT- Simple fix in spelling and slight expansion to previous answer
Working principle of venturi meter?
The differential producing flowmeter or Venturi has a long history of uses in many applications. Due to its simplicity and dependability, the Venturi is among the most common flowmeters. With no moving parts or abrupt flow restrictions, the Venturi can measure fluid flowrates with a minimal total pressure loss.
The principle behind the operation of the Venturi flowmeter is the Bernoulli effect. The Venturi measures a fluid's flowrate by reducing the cross sectional flow area in the flow path and generating a pressure difference. After the pressure difference is generated, the fluid is passed through a pressure recovery exit section where up to 80% of the differential pressure generated at the throat is recovered. The pressure differential follows Bernoulli's Equation.
Bernoulli's Equation:
The Venturi Principle
In the illustration above, the fluid, either liquid or gaseous, enters the Venturi at the location with a cross-sectional area A1, pressure P1, and velocity v1. These properties form the potential and kinetic energy of the fluid at one location. Energy is conserved in a closed system, that is, the sum of potential and kinetic energy at one location must equal the sum of the potential and kinetic energy at any another location in the system. If potential energy decreases at one location, the kinetic energy must proportionally increase at that location. The fluid now enters the throat of the Venturi with a new area A2, which is smaller than A1. In a closed system mass can be neither created nor destroyed (law of conservation of mass, simply, what goes in, must come out), and as such, the volumetric flowrate at area A1 must equal the volumetric flowrate at area A2. If the area at location A2 is smaller than A1, the fluid must travel faster to maintain the same volumetric flowrate. This increase in velocity results in a decrease in pressure which follows Bernoulli's equation. The result: by knowing the pressure and cross-sectional area at two locations, one can calculate the velocity of the fluid. With the velocity of the fluid and its density, one can calculate the flowrate.
A Venturi requires two pressure and one temperature measurement to accurately determine flow. The first pressure is measured at the Venturi's upstream location, P1. This is used for the density calculation and the high side input to the differential pressure measurement.
The Venturi Flowmeter
The second pressure is measured at the Venturi's throat, P2. This is connected to the low side of the differential pressure gauge to form the DP pressure measurement. The temperature reading is taken several pipe diameters in length upstream of the Venturi so as not to disrupt the uniform flow profile.
With proper instrumentation and flow conditioning, a Venturi's flowrate can be reduced to about 10% of its full scale range without adding multiple transducer configurations. This provides a 10 to 1 turn-down in a Venturi's flow range, For example: If a Venturi is designed for a maximum flow of 50 SCFM, approximately 5 SCFM would be the lowest value readable but there are compromises. See Instrumentation for a detailed discussion on instrumenting venturi flowmeters and how to maximize the measurement accuracy.
Applications:
Installation Requirements for Venturi Flowmeters:
1) 10-20 diameters in length of straight pipe upstream of the Venturi
2) 5 diameters in length of straight pipe downstream of the Venturi
3) Flow conditioning tube before the Venturi, if the flow is non-uniform or swirling
Free Flow System This arrangement is probably the most common, allowing the Venturi to be installed at any point within the flowing system. The location is generally selected for installation convenience and best flow conditioning. Flow conditioning is necessary to minimize swirling and non-uniform flow profiles such as patterns created by fittings, regulators, and any other flow affecting devices.
Pressure Reducing Flow System A Venturi can be installed at several different locations within a pressure reducing flow system. Each location generally has advantages and disadvantages. In the diagram below, two locations are shown for the Venturi's location. Location A is in the high pressure supply line to the system. Location B is after the pressure regulator has substantially reduced the flowing pressure and density. Because of the higher gas density at location A, the Venturi will have a greater flow range than at the lower pressure location B. However, this greater range comes at the cost of lower signal resolution as compared with location B. This would be similar to measuring the accuracy of a clock by timing either the minute hand or the second hand. Both clock hands carry the same accuracy information, the timing of the clock, but it would be much easier to measure the movement of the second hand versus the movement of the minute hand over a small time period. This is because the second hand has higher resolution, that is, it's easier to see a change in movement of the second hand versus a change in movement of the minute hand. If a greater time range is required, then one would need to measure the minute hand. It is the same with the Venturi's location. Some flow systems may only operate over a relatively small range. In that case, location B would be more advantageous than location A, and a properly sized Venturi at that location would provide the best signal resolution and accuracy. However, if measuring the full flow range of the system is required, then location A is the proper configuration. It is tempting to size a Venturi to measure the full air supply flow range, but, if it is only operated over a small flow range, this wide range comes at the cost of lower signal resolution and lower measurement accuracy. Require the Venturi to measure only the range that you need.
Free Standing Inlet System A Venturi can be installed as the inlet component to a flow system. This arrangement is often used as a calibration standard for a CVS (Constant Volume System) flow stand in emissions testing. Venturis used in this application are referred to as SAOs (Smooth Approach Orifice). SAOs have several advantages over LFEs (Laminar Flow Elements), also used in this application. SAOs are calibrated to an accuracy level which is expressed in percent of reading. LFEs are calibrated typically to percent of full scale. This is very advantageous at mid range and lower flow rates, the error being a percent of reading not of full scale. As with Sonic Nozzles, Venturis (SAOs) will retain their original calibration accuracy unless they are physically damaged or abused. The stainless steel or anodized aluminum surface will not erode through normal everyday use with clean air.
many people contributed but the person who developed was Sir Robert Watson-Watt Radar was developed from US naval experiment to build a death ray. they found that although they could not get enough power to produce the death ray of energy that you get to echo off other ships. But the ranges where not great enough to make it practical. and the project was caned. until the magnetron made in the UK and then RADAR became practical
When an electric current flows though a long conductor each free electron moves?
Only a very tiny fraction of an inch before scattering off another electron or atom. This scattering distance is independent of wire length.
What do the colors on a resistor mean?
Most resistors have either 3 or 4 color bands. The fourth, if it is there, only indicates the tolerance, or how accurate the value is. For the first three bands, the following colors may be used: black = 0 or X1 brown = 1 or X10 red = 2 or X100 orange = 3 or X1000 yellow = 4 or X10000 green = 5 or X100000 blue = 6 or X1000000 violet = 7 gray = 8 white = 9 A resistor uses the first two color bands to form a 2 digit number, then a third band to add a multiplier. For instance, suppose you have a resistor that has a red, violet, brown color code. Decoding: red = 2 violet = 7 27 brown = X10 27 * 10 = 270 In this case, you are holding a 270 ohm resistor. How about a 2.2K resistor? Well, K = 1000, so 2.2K is the same as 2200 ohms. Reverse decoding: The first two bands would have to be red, red (22). To get to 2200 from 22 we have to multiply by 100, so the third band would also be red (X100). The last, or fourth band indicates how close to the nominal value the resistor is. The band colors are: none = 20% silver = 10% gold = 5% So, if the 2.2K resistor is red, red, red, silver, it means the actual resistance can be as much as 10% (or 220 ohms) higher or lower than 2.2K, or anywhere from 1980 ohms to 2420 ohms. You can get resistors with better accuracy than 5%, such as 2%, 1%, 0.1%. Some use three number bands and a fourth multiplier band, others have no bands at all, just the actual resistance printed as a number on the body. If in doubt, measure the resistor with an ohmmeter to be sure.
light dependent resistors are those whose resistivity increases with decrease in the amount of light being exposed on them. The darker the environment, the higher the resistivity.
What are the characteristics of an ideal transformer?
1. Effect of primary voltage= there is no wide variation of supply voltage to which primary winding of pt is connected .therefore the study of variation of ratio nd phase angles wd supply voltage is nt important.....
How governing system of steam turbine is being done?
(pictures insert is not being allowed by wiki. i am sorry)
TOPICS OF DISCUSSION
CONCEPT OF GOVERNING SYSTEM
FEATURES OF KWU GOVERNING SYSTEM
OVERVIEW OF GOVERNING RACK
FUNCTIONING OF EHC CIRCUITS
FREE GOVERNOR MODE OPERATION
BEST PRACTICES IN GOVERNING SYSTEM
EMERGENCIES IN GOVERNING SYSTEM
WHAT IS GOVERNING SYSTEM ?
n Turbine Governing system is meant for regulation of turbine speed under no load and varying load condition.
n It helps in precise control of grid frequency under normal operation and protects the machine as well as grid during emergency situation.
KWU GOVERNING SYSTEM-FEATURES
n ELECTRO-HYDRAULIC GOVERNING SYSTEM WITH HYDRAULIC BACKUP
n OPERATION OF STOP VALVES BY STARTING & LOAD LIMITING DEVICE (HYDRAULIC)
n ROLLING, SYNCHRONIZATION & LOAD OPERATION BY HYDRAULIC / ELECTRO- HYDRAULIC SYSTEM
n ELECTRO- HYDRAULIC SPEED GOVERNOR WITH HYDRAULIC BACK UP
n SAFE SHUTDOWN BY HYDRAULIC / ELECTRO- HYDRAULIC SYSTEM
n ELECTRICAL AND HYDRAULIC PROTECTION SYSTEM ALONG WITH TEST FACILITIES
FEATURES OF EHC
n AUTO ROLLING & SYNCHRONIZATION THROUGH SPEED CONTROLLER UNDER INFLUENCE OF TSE
n CONSTANT LOAD OPERATION BY LOAD CONTR. WITH PRESSURE CONTR. AS BACKUP
n RUNBACK OPERATION THROUGH PRESSURE CONTR.
n EMERGENCY OPERATION THROUGH SPEED CONTR.
n AUTO GRID FREQUENCY CONTROL THROUGH EXTERNAL FREQUENCY INFLUENCE
n AUTO UNLOADING AT HIGH FREQUENCY THROUGH INTERNAL FREQUENCY INFLUENCE
n CONTROL DURING AUTOMATIC TURBINE TESTING,
ISOLATED GRID CONDITION & LSR OPERATION
SPEED CONTROLLER CIRCUIT
L - Raise & Lower command from UCB :
nr - Speed Reference :
nr limit - Delayed Speed Reference :
NLC - No Load Correction (Ensures required Speed controller O/P for Rolling even when Speed reference n r matches n act.)
n act - Actual Speed :
hr nc - Speed Controller O/P with DROOP of + / - 10.0 V for nr lim ~ n act = 150 RPM ( GAIN = 22
LOAD SET POINT GENERATION CIRCUIT
1 - SET POINT FOLLOW UP when Automatic Grid Control or CMC In service
(Other Raise / Lower commands get blocked)
2 -- TSE ENABLING when
A) GCB is closed AND
B) Load controller (L C) not OFF AND
C) Fast calibration signal 6 absent AND
D) I) Load controller (L C) in control
OR ii) Pressure controller with initial pressure in action
OR iii) Turbine follow mode in service
This helps to bring manually adjusted gradient and stress effect in service.
+/- 10 V gradient => +/- 25 MW / MIN for 200 MW units
OR +/- 50 MW / MIN for 500 MW units.
PRESSURE CONTROLLER CIRCUIT
EHC TRANSFER CIRCUIT
FGMO - BACKGROUND
n Unique frequency band of 49.0 Hz to 50.5 Hz, as specified by IEGC
n Scheduling & dispatch by RLDCs/SLDCs is based on day ahead demand & availability
n Frequency control by load-generation balance in every 15 mins time block
n Wide frequency variation during Grid disturbance, Unit outage, change in demand, etc.
n No primary response by generators to maintain frequency under such system contingency
n Emergencies caused due to frequency control only through importing /cutting load by system operator
n
FGMO - GRID CODES
n All generating units should have their speed governors in normal operation at all times to enable Grid frequency control by loading / unloading
n Droop characteristic for primary response should be within 3% to 6%
n Each unit shall be capable of instantaneously picking up at least 5% extra load for a minimum of 5 mins (up to 105%MCR), during fall in frequency
n No dead bands and/or time delays shall be deliberately introduced
n Facilities like load limiters, CMC, etc. shall not be used to suppress the normal governor action
IMPLEMENTATION OF FGMO
In line with clause Clause 1.6 of IEGC and CERC order dated 30-10-99, date of FGMO implementation, as decided by REBs are :-
n Western Region - 19-05-03 ( ABT - 01-07-02 )
n Southern Region - 01-08-03 ( ABT - 01-01-03 )
n Northern Region - 01-10-03 ( ABT - 01-12-02 )
n Nor-East Region - 22-12-03 ( ABT - 01-11-03 )
n Eastern Region - 02-01-04 ( ABT - 01-04-03 )
FGMO CHARACTERISTIC FOR KWU M/C
MAJOR ISSUES WITH FGMO IN 2004
Ø Wide and frequent variation of freq.
Ø Perpetual oscillations in critical parameters due to Boiler response time
Ø M/C subjected to cyclic loading and fatigue stresses
Ø Frequent HP/LP Bypass valve operation
Ø Continuous manual interventions
Ø Self-defeating feature(Unloading when freq. improving towards 50 Hz)
Ø Conflict with ABT(Offsetting freq. correction)
TRANSIENTS IN GOVERNING SYSTEM
n FAILURE OF POWER PACKS OF CONTROLLER RACKS IN EHC PANEL
n POWER SUPPLY FAILURE IN ATRS PANEL
n SIGNAL ACQUISITION PROBLEM
n FAILURE IN TURBINE SYSTEM
n ELECTRICAL SYSTEM FAILURE
n COMPONENT FAILURE IN GOVERNING RACK
n OPERATIONAL EMERGENCY
1 CONTROL RACK SUPPLY FAILURE
n M/C is on EHC. Power supply fails in Load control/Pressure control / transfer circuit rack. Starting device becomes off automatically due to EHC fault.
Observation: EHC output is minimum/zero and load minimum/ zero with EHC fault alarm. Machine on bar with ESV & IV open (Turbine not tripped).
Action: Confirm HP/LP bypass opening, isolate EHC from governing rack and parallely adjust starting device position from UCB. Reduce boiler firing to restrict rise in boiler pressure.
2) SUPPLY FAILURE IN ATRS PANEL(ATRS=Automatic Turbine Rolling & Synchronisation)
n M/C is on EHC. Power supply fails in CCA panels only.
Observation: All indication lamps in ATRS consoles will go off. EHC output and Load will become zero due loss of GCB close feedback. All ATRS drives will become inoperative.
Action: Confirm HP/LP bypass opening , isolate EHC. Reduce boiler firing. Adjust starting device position from local. Normalize power supply in CCA panels at the earliest.
3) SIGNAL ACQUISITION PROBLEM
n Loss of speed signal occurs due to Hall Probe / card failure.
Observation: Speed indication will become zero. M/C will be loaded through speed controller. Subsequently Pressure controller will come in service. AOP & JOP will take auto start & Barring Gear valve Will open on auto.
Action: Isolate EHC and adjust Starting device position. If pressure oil pressure is normal, make SLC of AOP, JOP and Barring Gear vlv OFF and stop AOP, JOP and close Barring Gear vlv.
4)FAILURE IN TURBINE SYSTEM
n Loss of speed signal occurs due to breakage of MOP shaft.
Observation: Speed indication and pressure oil pressure will come down. M/C will be loaded through speed controller and Pressure controller will come in service. Subsequently, AOP & JOP will take auto start &Barring Gear valve. will open on auto.
Action: Safe shutdown of M/C is to be ensured.
5) ELECTRICAL SYSTEM FAILURE
n M/C is on EHC with Tracking on. Starting device becomes inoperative due to Electrical module trouble/motor failure/overload.
Observation: During increase in boiler firing, Boiler pressure will increase due to load restriction by Starting device. EHC output will go to 100%.
Action: Switch off the electrical module of Starting device and increase Starting device position from local so that EHC can take control.
6) FAILURE IN GOVRRNING RACK
n EHC Plunger coil failure
n EHC Pilot valve bearing failure
Observation: EHC starts hunting
Action: Isolate EHC and take Hydraulic mode in service. Replace the failed omponent. Governing characteristic checking should be done before EHC is put in service
n Speeder Gear spring tension gets altered.
Observation: M/C may get unloaded at frequency lower than recommended value.
Action: Speeder Gear spring tension may be adjusted to increase the start of unloading.Testing for proper setting should be checked during suitable opportunity.
LOGICS
A SPEED CONTROLLER LOGICS
1 Command for slow rate at nr > 2850 RPM to facilitate easy synchronisation
2 TSE Influence ON, when min of all the upper stress margins comes into picture to control gradient of nr lim and hence, acceleration of Rolling speed. Upper stress margin = 30 deg C => 10.0 V => 600 RPM ~ (Acceleration < 108 RPM ~ causes dn / dt tripping)
B LOAD SET POINT GENERATION LOGICS
1 Stopping of nr lim when
a) GCB open AND
b) n act is < nr lim by approx. 45 RPM.
This restricts hr nc up to around 30 % during Rolling to avoid wide v/v opening.
2 Stopping speed set point control when,
a) n act > 2850 RPM AND
b) nr raised ( I.e, nr > nr lim) AND
c) I) TSE ON and faulted in GCB open condition
OR ii) Stop command from SGC in SGC ON condition.
3 Tracking in synchronized condition if
a) Frequency within limit (adjustable, say 48.5 to 51.5 Hz.) AND
b) Load controller O/P , hr PC > hr nc AND
c) I) Load controller (L C) in control
OR ii)Pressure controller in action
4 Set Point Follow Up (Fast Calibration) during
a) Tracking condition 5 ( nr = n act + 21 RPM ) OR
b) Turbine Trip ( nr = n act - 120 RPM ). Simultaneously nr lim immediately equals to nr
Condition (a) ensures certain speed controller O/P during emergency to keep machine in rolled condition along with some load.
Condition (b) ensures negative speed controller O/P during Trip condition.
LOAD CONTROLLER (L C) IN CONTROL CONDITIONS -
a) Speed OR Pressure Controller not in action AND
b) Isolated Grid condition absent AND
c) Both Load Controller OFF and Schedule OFF absent (I.e, L C ON)
LOAD CONTROLLER SCHEDULE OFF - L C can be made OFF if Speed controller is in action and hrnc > hr PC. Otherwise, with OFF command OFF lamp blinks - called Schedule OFF
C .LOAD SET POINT GENERATION LOGICS
1TSE ON AND NOT FAULTED
This helps to keep stress effect for gradient control in service.
2-- LOAD GRADIENT ON
This helps to keep manual gradient control in service
3-- STOP POWER SET POINT CONTROL when
a) TSE ON and Faulted OR
b) Stop command from SGC OR
c) Pr raised when Pressure controller is in action with CMC ON OR Limit pressure mode selected OR Boiler follow mode selected
In above conditions Pr lim stops, I.e,Set point can not be increased.
4-- FAST CALIBRATION when
a) Pressure controller is in action OR
b) Follow above (h v0) condition present
Under this condition MW error (ep) is selected and Pr lim immediately equals to Actual load (P act) without any gradient .
5 -- FREQUENCY INFLUENCE ON
This is made ON from ATRS panel to put EXTERNAL FREQUENCY EFFECT in service for
loading / unloading w.r.t. 50 Hz ( with 2.5 % to 8 % Frequency Droop)
6 TSE TEST RELEASE : TSE TEST (For checking healthiness of TSE Margins) can be done when
a) TSE Influence is OFF OR
b) Both Pr, Pr lim and hr, hr lim are balanced, I.e, Speed and Power set point controls are not in action.
D .LOAD CONTROLLER LOGICS
FOLLOW ABOVE ( h v0 ) --
a) GCB closed and load < 10 % (station load) OR
b) GCB open OR
c) Load controller OFF
Absence of these conditions help Load controller output to track above Pressure controller output when Pressure controller is in service.
FOLLOW LOW ( h vu ) - GCB CLOSED AND Speed controller in action.
This helps Load controller output to track below Speed controller output.
8 -- Either a) Initial pressure mode selected OR
b) Turbine follow mode in action OR
c) CMC Runback active
This ensures Load controller output above pressure controller output
9 -- Load controller OFF
This defeats transmission of Load Controller output to Transfer circuit.
R & L - Raise & Lower command from UCB :
nr - Speed Reference :
nr limit - Delayed Speed Reference :
NLC - No Load Correction (Ensures required Speed controller O/P for Rolling even when Speed reference n r matches n act.)
n act - Actual Speed :
hr nc - Speed Controller O/P with DROOP of + / - 10.0 V for nr lim ~ n act = 150 RPM ( GAIN = 22
LOAD SET POINT GENERATION CIRCUIT
1 - SET POINT FOLLOW UP when Automatic Grid Control or CMC In service
(Other Raise / Lower commands get blocked)
2 -- TSE ENABLING when
A) GCB is closed AND
B) Load controller (L C) not OFF AND
C) Fast calibration signal 6 absent AND
D) I) Load controller (L C) in control
OR ii) Pressure controller with initial pressure in action
OR iii) Turbine follow mode in service
This helps to bring manually adjusted gradient and stress effect in service.
+/- 10 V gradient => +/- 25 MW / MIN for 200 MW units
OR +/- 50 MW / MIN for 500 MW units.
PRESSURE CONTROLLER CIRCUIT
EHC TRANSFER CIRCUIT
FGMO - BACKGROUND
n Unique frequency band of 49.0 Hz to 50.5 Hz, as specified by IEGC
n Scheduling & dispatch by RLDCs/SLDCs is based on day ahead demand & availability
n Frequency control by load-generation balance in every 15 mins time block
n Wide frequency variation during Grid disturbance, Unit outage, change in demand, etc.
n No primary response by generators to maintain frequency under such system contingency
n Emergencies caused due to frequency control only through importing /cutting load by system operator
n
FGMO - GRID CODES
n All generating units should have their speed governors in normal operation at all times to enable Grid frequency control by loading / unloading
n Droop characteristic for primary response should be within 3% to 6%
n Each unit shall be capable of instantaneously picking up at least 5% extra load for a minimum of 5 mins (up to 105%MCR), during fall in frequency
n No dead bands and/or time delays shall be deliberately introduced
n Facilities like load limiters, CMC, etc. shall not be used to suppress the normal governor action
IMPLEMENTATION OF FGMO
In line with clause Clause 1.6 of IEGC and CERC order dated 30-10-99, date of FGMO implementation, as decided by REBs are :-
n Western Region - 19-05-03 ( ABT - 01-07-02 )
n Southern Region - 01-08-03 ( ABT - 01-01-03 )
n Northern Region - 01-10-03 ( ABT - 01-12-02 )
n Nor-East Region - 22-12-03 ( ABT - 01-11-03 )
n Eastern Region - 02-01-04 ( ABT - 01-04-03 )
FGMO CHARACTERISTIC FOR KWU M/C
MAJOR ISSUES WITH FGMO IN 2004
Ø Wide and frequent variation of freq.
Ø Perpetual oscillations in critical parameters due to Boiler response time
Ø M/C subjected to cyclic loading and fatigue stresses
Ø Frequent HP/LP Bypass valve operation
Ø Continuous manual interventions
Ø Self-defeating feature(Unloading when freq. improving towards 50 Hz)
Ø Conflict with ABT(Offsetting freq. correction)
TRANSIENTS IN GOVERNING SYSTEM
n FAILURE OF POWER PACKS OF CONTROLLER RACKS IN EHC PANEL
n POWER SUPPLY FAILURE IN ATRS PANEL
n SIGNAL ACQUISITION PROBLEM
n FAILURE IN TURBINE SYSTEM
n ELECTRICAL SYSTEM FAILURE
n COMPONENT FAILURE IN GOVERNING RACK
n OPERATIONAL EMERGENCY
1 CONTROL RACK SUPPLY FAILURE
n M/C is on EHC. Power supply fails in Load control/Pressure control / transfer circuit rack. Starting device becomes off automatically due to EHC fault.
Observation: EHC output is minimum/zero and load minimum/ zero with EHC fault alarm. Machine on bar with ESV & IV open (Turbine not tripped).
Action: Confirm HP/LP bypass opening, isolate EHC from governing rack and parallely adjust starting device position from UCB. Reduce boiler firing to restrict rise in boiler pressure.
2) SUPPLY FAILURE IN ATRS PANEL(ATRS=Automatic Turbine Rolling & Synchronisation)
n M/C is on EHC. Power supply fails in CCA panels only.
Observation: All indication lamps in ATRS consoles will go off. EHC output and Load will become zero due loss of GCB close feedback. All ATRS drives will become inoperative.
Action: Confirm HP/LP bypass opening , isolate EHC. Reduce boiler firing. Adjust starting device position from local. Normalize power supply in CCA panels at the earliest.
3) SIGNAL ACQUISITION PROBLEM
n Loss of speed signal occurs due to Hall Probe / card failure.
Observation: Speed indication will become zero. M/C will be loaded through speed controller. Subsequently Pressure controller will come in service. AOP & JOP will take auto start & Barring Gear valve Will open on auto.
Action: Isolate EHC and adjust Starting device position. If pressure oil pressure is normal, make SLC of AOP, JOP and Barring Gear vlv OFF and stop AOP, JOP and close Barring Gear vlv.
4)FAILURE IN TURBINE SYSTEM
n Loss of speed signal occurs due to breakage of MOP shaft.
Observation: Speed indication and pressure oil pressure will come down. M/C will be loaded through speed controller and Pressure controller will come in service. Subsequently, AOP & JOP will take auto start &Barring Gear valve. will open on auto.
Action: Safe shutdown of M/C is to be ensured.
5) ELECTRICAL SYSTEM FAILURE
n M/C is on EHC with Tracking on. Starting device becomes inoperative due to Electrical module trouble/motor failure/overload.
Observation: During increase in boiler firing, Boiler pressure will increase due to load restriction by Starting device. EHC output will go to 100%.
Action: Switch off the electrical module of Starting device and increase Starting device position from local so that EHC can take control.
6) FAILURE IN GOVRRNING RACK
n EHC Plunger coil failure
n EHC Pilot valve bearing failure
Observation: EHC starts hunting
Action: Isolate EHC and take Hydraulic mode in service. Replace the failed omponent. Governing characteristic checking should be done before EHC is put in service
n Speeder Gear spring tension gets altered.
Observation: M/C may get unloaded at frequency lower than recommended value.
Action: Speeder Gear spring tension may be adjusted to increase the start of unloading.Testing for proper setting should be checked during suitable opportunity.
LOGICS
A SPEED CONTROLLER LOGICS
1 Command for slow rate at nr > 2850 RPM to facilitate easy synchronisation
2 TSE Influence ON, when min of all the upper stress margins comes into picture to control gradient of nr lim and hence, acceleration of Rolling speed. Upper stress margin = 30 deg C => 10.0 V => 600 RPM ~ (Acceleration < 108 RPM ~ causes dn / dt tripping)
B LOAD SET POINT GENERATION LOGICS
1 Stopping of nr lim when
a) GCB open AND
b) n act is < nr lim by approx. 45 RPM.
This restricts hr nc up to around 30 % during Rolling to avoid wide v/v opening.
2 Stopping speed set point control when,
a) n act > 2850 RPM AND
b) nr raised ( I.e, nr > nr lim) AND
c) I) TSE ON and faulted in GCB open condition
OR ii) Stop command from SGC in SGC ON condition.
3 Tracking in synchronized condition if
a) Frequency within limit (adjustable, say 48.5 to 51.5 Hz.) AND
b) Load controller O/P , hr PC > hr nc AND
c) I) Load controller (L C) in control
OR ii)Pressure controller in action
4 Set Point Follow Up (Fast Calibration) during
a) Tracking condition 5 ( nr = n act + 21 RPM ) OR
b) Turbine Trip ( nr = n act - 120 RPM ). Simultaneously nr lim immediately equals to nr
Condition (a) ensures certain speed controller O/P during emergency to keep machine in rolled condition along with some load.
Condition (b) ensures negative speed controller O/P during Trip condition.
LOAD CONTROLLER (L C) IN CONTROL CONDITIONS -
a) Speed OR Pressure Controller not in action AND
b) Isolated Grid condition absent AND
c) Both Load Controller OFF and Schedule OFF absent (I.e, L C ON)
LOAD CONTROLLER SCHEDULE OFF - L C can be made OFF if Speed controller is in action and hrnc > hr PC. Otherwise, with OFF command OFF lamp blinks - called Schedule OFF
C .LOAD SET POINT GENERATION LOGICS
1TSE ON AND NOT FAULTED
This helps to keep stress effect for gradient control in service.
2-- LOAD GRADIENT ON
This helps to keep manual gradient control in service
3-- STOP POWER SET POINT CONTROL when
a) TSE ON and Faulted OR
b) Stop command from SGC OR
c) Pr raised when Pressure controller is in action with CMC ON OR Limit pressure mode selected OR Boiler follow mode selected
In above conditions Pr lim stops, I.e,Set point can not be increased.
4-- FAST CALIBRATION when
a) Pressure controller is in action OR
b) Follow above (h v0) condition present
Under this condition MW error (ep) is selected and Pr lim immediately equals to Actual load (P act) without any gradient .
5 -- FREQUENCY INFLUENCE ON
This is made ON from ATRS panel to put EXTERNAL FREQUENCY EFFECT in service for
loading / unloading w.r.t. 50 Hz ( with 2.5 % to 8 % Frequency Droop)
6 TSE TEST RELEASE : TSE TEST (For checking healthiness of TSE Margins) can be done when
a) TSE Influence is OFF OR
b) Both Pr, Pr lim and hr, hr lim are balanced, I.e, Speed and Power set point controls are not in action.
D .LOAD CONTROLLER LOGICS
FOLLOW ABOVE ( h v0 ) --
a) GCB closed and load < 10 % (station load) OR
b) GCB open OR
c) Load controller OFF
Absence of these conditions help Load controller output to track above Pressure controller output when Pressure controller is in service.
FOLLOW LOW ( h vu ) - GCB CLOSED AND Speed controller in action.
This helps Load controller output to track below Speed controller output.
8 -- Either a) Initial pressure mode selected OR
b) Turbine follow mode in action OR
c) CMC Runback active
This ensures Load controller output above pressure controller output
9 -- Load controller OFF
This defeats transmission of Load Controller output to Transfer circuit.
