Procedure for Boiler Gauge glass line up & Flushing

Boiler Gauge glass: is a transparent glass of shape tubular, flat or square blocks fitted to the boiler steam drum to facilitate a visual indication of the water level of a steam drum. These types of glasses are manufactured by borosilicate glass which is robust, temperature & chemical resistant.

 



Line up of Gauge glass:

  • Ensure all tools & required PPEs are taken to operate the valves (Hand gloves, Safety goggles, “F” rods etc)
  • Ensure steam & water side valve of gauge glass are healthy & operating properly
  • Ensure there are no any leakages
  • Ensure steam side & water side valves are closed
  • Ensure gauge glass drain valve is open & drain is connected/extended to safe location
  • Now crack open the steam valve & check for any leakages in gauge glass. Wait for some times until system heats uniformly.
  • Then crack open the water side valve, wait for some time for stabilization
  • Then close the drain valve
  • Open the steam valve & water valve fully
  • Observe water collected in glass & showing the level
  • Cross check the level glass with other side level glass or control room transmitter reading or with Hydra step

Factors considered for Boiler Engineering

Flushing of gauge glass

Ensure all tools & required PPEs are taken to operate the valves (Hand gloves, Safety goggles, “F” rods etc)

Step-I

  • Close the water side valve & open the drain valve for flushing, wait for some time
  • Then close the drain valve & open the water side valve

Note: After opening the water side valve, water level should retain its normal operating level, if not then there might be blockages in valve or line

Step-II

  • Close the steam side valve & open the drain valve for flushing, wait for some time
  • Then close the drain valve & open the steam side valve

Note: After opening the steam side valve, water level should retain its normal operating level, if not then there might be blockages in valve or line

Questions & Answers on AFBC Boiler





10-tips to reduce LOI/unburnt in Boilers

 

 1-Optimization of fuel moisture in the fuel:

Higher moisture in the fuel leads to unbalanced draft in the furnace or combustion chamber. Which ultimately results into poor mixture of air & fuel, higher moisture fuel demands more excess air. So optimization of fuel moisture will help to reduction in LOI.

2-Maintaining balanced draft in furnace:

Unbalanced draft is nothing but more FD air/less ID draft or less FD air /More ID Draft.

More FD & less ID causes back fire & improper mixing of air & fuel.

More ID & less FD causes escape of fuel particles from furnace without proper combustion

3-Maintaining 3Ts of combustion:

3Ts of combustions are: Temperature, Time & Turbulence

Temperature: For proper combustion temperature of the furnace must be sufficient enough to burn the fuel completely.

Time: There must be sufficient time for combustion

Turbulence: There should be proper turbulence in furnace for proper mixing of air & fuel

4-Increasing the secondary air quantity & pressure:

This will help to increase the residence time of fuel in furnace resulting into complete combustion

5-Maintaining the required excess air:

Lesser excess air than required will lead to incomplete combustion that is conversion of carbon into carbon monoxide instead of carbon di-oxide. So sufficient air is required to achieve complete combustion.

6-Using correct or designed GCV of a fuel:

Lesser GCV fuel requires more air for combustion, even may not achieve the designed parameters of Boilers like flow, pressure & temperature.

7-Ultimate & Proximate analysis of fuel:

In order to achieve proper combustion, we must know the contents of fuel properly. Need to operate the Boilers at designed parameters of fuel. For example if FC of the fuel increases, then need to increase air & combustion time and need to reduce turbulence.

So it is very important to know the fuel contents.

8-Operating the Boilers at stable loads:

Stable loaded Boilers will not lead into much LOI, as air & fuel mixture is constant & will not vary frequently. LOI cannot be reduced in variable load boilers.

9-Operating the Boiler at little positive draught:

Operation of Boiler at positive draught will help for complete combustion. If boiler is operated at more negative draught, then there will be more chances of escaping of unburnt fuel particles from the furnace & causing secondary combustion at super heaters & other convective zones.

10-Reusing unburnt or cinder:

Generally unburnt/cinder from Boiler Bank & economiser zones are re-injected into furnace by using “Cinder re-injection” system. This will help in re-burning of cinder & reduction in LOI

 Procedure for Boiler Gauge glass line up

 

Viva Questions & answers for preparation of BOE exam & interview


 

 

-

16-Perfect reasons for more fuel consumption of Boilers

Following are the 16-reasons for increase in Boilers fuel consumption

1. Decreased economiser inlet feed water temperature:

On every 6-8 deg C decrease in Economiser inlet feed water temperature causes the rise in Boiler fuel consumption by 1%.

2. Increased Boiler outlet  flue gas  temperature:

On every 22 deg C increase in flue gas temperature causes the reduction in Boiler efficiency by 1% & hence boiler fuel consumption increases for generating same steam.

3. Increased moisture content in the fuel

Boilers fuel consumption increases as the moisture in the fuel increases. As it requires more excess air & reduces combustion efficiency leading to unburnt losses

4. Increased excess air

10-Tips to reduce LOI in Boilers

Increase in excess air causes dry flue gas loss & hence more fuel consumption. And also leads to more auxiliary power consumption.

5. Increased unburnt loss

Unburnt fuel or incomplete combustion of fuel leads to increased consumption of fuel. Unburnt is due to improper air fuel mixture or unbalanced draught or variation in the fuel quality

6. Higher blow down

Blow down water carries saturated water/steam through it, so leads into more fuel consumption. Maximum acceptable blow down rate for normal Boiler operation is 0.5 to 1%.

7. Operating the Boiler at lower or partial loads

Operating the Boilers on partial load requires more excess air & leads to incomplete combustion forming unburnts.

Calculated reasons for for SSC of Turbine

Boiler calculations for Boiler operation engineer (BOE) exam

Viva Questions & answers for preparation of BOE exam & interview

8. Operating the boiler at non-standard operating parameters

Operating the Boilers at non standard parameters like pressure, temperatures, flow etc will lead to the higher fuel consumption

9. Leakage into & out of the Boilers

Air & flue gas leakages into the Boiler & out of the Boiler will reduce the working efficiency there by increasing the boiler fuel consumption

10. Steam leakage

It is a direct cause for higher steam consumption. Generally steam leakage is from vent & drains valves, welding & flange joints

11. Boiler heating surfaces internal scaling

Pressure parts namely water wall tubes, economiser tubes & super heater coils internal & external scaling will result into poor heat transfer, which increases fuel input to produce required amount of steam.

Pressure parts internal scaling can damage the pressure parts by over heating

12. Radiation & Convection losses

Radiation & convection losses in the boiler causes increased fuel consumption. These losses may be due to uninsulated or unlagged surfaces of boiler

13. Lower combustion air temperature

On every 20 Deg C decrease in combustion air temperature leads to Boiler efficiency reduction by 1%

14. More ash content in the fuel

More ash content in the fuel takes away heat associated with it during discharging through hoppers. Especially bed ash is having more temperature. Also higher ash fuel are having lower GCV

Guide for Boilers troubleshooting


Why does Boilers main steam temperature increases more than design?

15. More Volatile matters (VM) in the fuel

Calorific value of the fuel reduces as the VM increases. Boilers using Lower GCV fuel consume more fuel

16. Other potential reasons for increased fuel consumption of a Boiler are;

Boiler design related issuers

Wrong selection of auxiliaries like fans & fuel feeding system

Low quality of Bed materials

Defects in fuel burners & fuel spreaders

Over refractory on internal heating surfaces

Faulty field instruments

Factors considered for Boiler Engineering

Also read Why & How these in Boilers???



Calculated reasons for increase in Turbine specific steam consumption

1. Lower vacuum

Turbine consumes more steam, if vacuum in condenser is maintained on lower side.

Example:  Consider a 20 MW Steam Turbine having Inlet steam parameters 65 kg/cm2 & 490 Deg C & Vacuum maintained in condenser is -0.9 kg/cm2.

Calculate the steam consumption of turbine at vacuum -0.9 kg/cm2 & -0.85 kg/cm2

A-Steam consumption Q at -0.9 kg/cm2 to develop 20 MW power

P =Steam flow X( Enthalpy of inlet steam-Enthalpy of exhaust steam)/ 860

Enthalpy of inlet steam at inlet steam parameters =810 kcal/kg

Exhaust steam enthalpy at -0.9 kg/cm2 vacuum = 619 kcal/kg

Then, 20 = Q X (810-619)/860

Q1 = 90 MT

B- Steam consumption Q at -0.85 kg/cm2 to develop 20 MW power

Exhaust steam enthalpy at -0.85 kg/cm2 vacuum= 623 kcal/kg

Then, 20 = Q X (810-623)/860

Q 2= 90.9 MT

It is clear that, Turbine operating at -0.9 kg/cm2 vacuum consumes lesser steam as compared to turbine operating at vacuum-0.85 kg/cm2

2. Lower inlet main stream pressure& temperature

Turbine operating at higher main steam pressure consumes lesser steam as compared to turbines operating at lower pressure

Example: Consider a 20 MW Steam Turbine having Inlet steam temperature 490 Deg C & Vacuum maintained in condenser is -0.9 kg/cm2.

A-Inlet steam parameters: Pressure: 65 kg/cm2 & temperature 490 deg C , Enthalpy = 810 kcal/kg

Exhaust steam parameters P = 0.9 kg/cm2 & Enthalpy = 619 kcal/kg

Steam consumption of Turbine Q = P X 860 / (Enthalpy of inlet steam-Enthalpy of exhaust steam)

Q = 20 X 860 / (810-619)

Q1 = 90.05 MT

B-Inlet steam parameters: Pressure: 87 kg/cm2 & temperature 515 deg C , , Enthalpy = 818 kcal/kg

 

Steam consumption of Turbine Q = P X 860 / (Enthalpy of inlet steam-Enthalpy of exhaust steam)

Q = 20 X 860 / (818-619)

Q2 = 86.43 MT

It is clear that, Turbine operating at pressure 65 kg/cm2 & temperature 490 deg C consumes more steam as compared to turbine operating at 87 kg/cm2 & temperature 515 deg C

3. Higher extraction/bleed steam flow

Steam turbines consume more steam to develop same power on higher steam extraction as compared to lower extraction.

Example: A condensing & extraction steam turbine having Inlet steam flow 105 TPH at pressure 65 kg/cm2 & 490 Deg C & Vacuum maintained in condenser is -0.9 kg/cm2.

Here we can cross check the power generation by steam turbine by increasing the extraction flow keeping inlet steam constant.

A-Extraction pressure = 2 Kg/cm2 & Temperature = 150 Deg C, flow = 75 TPH, Exhaust steam to condenser = 30 TPH

Enthalpy of inlet steam, H1 = 810 kcal/kg

Main steam flow Q1 = 105 TPH

Enthalpy of extraction steam = H2 =660 kcal/kg

Extraction steam flow Q2 = 75 TPH

Enthalpy of exhaust team = 620 kcal/kg

Exhaust steam flow Q3 = 30 TPH

Power developed by steam Turbine P = (Q2 X (H1-H2) / 860) + (Q3 X (H1-H3) / 860 )

P = (75 X (810-660) / 860) + (30 X (810-620) / 860) = 19.7 MW

B- Extraction pressure = 2 Kg/cm2 & Temperature = 150 Deg C, flow = 65 TPH, Exhaust steam to condenser = 40 TPH

Enthalpy of inlet steam, H1 = 810 kcal/kg

Main steam flow Q1 = 105 TPH

Enthalpy of extraction steam = H2 =660 kcal/kg

Extraction steam flow Q2 = 65 TPH

Enthalpy of exhaust team = 620 kcal/kg

Exhaust steam flow Q3 = 40 TPH

Power developed by steam Turbine P = (Q2 X (H1-H2) / 860) + (Q3 X (H1-H3) / 860 )

P = (65 X (810-660) / 860) + (40 X (810-620) / 860) = 20.16 MW

It is clear that, Turbine power generation at same inlet main steam flow will increase as extraction flow gets decrease & vice versa

4. Higher pressure/temperature of extraction & bleed steam

Higher pressure/temperature of extraction & bleed steam leads to increased steam consumption to generate same power or power consumption reduces at same inlet flow.

Example: A condensing , extraction & bleed steam turbine having Inlet steam flow 105 TPH at pressure 65 kg/cm2 & 490 Deg C & Vacuum maintained in condenser is -0.9 kg/cm2

 A-Bleed steam 10 kg/cm2 & Temperature 200 Deg C, flow =25 TPH, Extraction pressure = 2 Kg/cm2 & Temperature = 150 Deg C, flow = 60 TPH, Exhaust steam to condenser = 25 TPH

Enthalpy of inlet steam, H1 = 810 kcal/kg

Main steam flow Q1 = 105 TPH

Enthalpy of bleed steam = H2 =674 kcal/kg

Bleed steam flow Q2 = 25 TPH

Enthalpy of extraction steam = H3 =660 kcal/kg

Extraction steam flow Q3 = 60 TPH

Enthalpy of exhaust team H4= 620 kcal/kg

Exhaust steam flow Q4 = 20 TPH

Power developed by steam Turbine P = (Q2 X (H1-H2) / 860) + (Q3 X (H1-H3) / 860 ) +(Q4 X (H1-H4)/860)

P = (25 X (810-674) / 860) + (60 X (810-660)/860) + (20 X (810-620)/860)

P = 18.82 MW

B-Bleed steam 14 kg/cm2 & Temperature 260 Deg C, flow =25 TPH, Extraction pressure = 2.5 Kg/cm2 & Temperature = 170 Deg C, flow = 60 TPH, Exhaust steam to condenser = 25 TPH

Enthalpy of inlet steam, H1 = 810 kcal/kg

Main steam flow Q1 = 105 TPH

Enthalpy of bleed steam = H2 =704 kcal/kg

Bleed steam flow Q2 = 25 TPH

Enthalpy of extraction steam = H3 =669 kcal/kg

Extraction steam flow Q3 = 60 TPH

Enthalpy of exhaust team H4= 620 kcal/kg

Exhaust steam flow Q4 = 20 TPH

Power developed by steam Turbine P = (Q2 X (H1-H2) / 860) + (Q3 X (H1-H3) / 860) + (Q4 X (H1-H4)/860)

P = (25 X (810-704) / 860) + (60 X (810-669)/860) + (25 X (810-620)/860)

P = 18.43 MW

It is clear that, Turbine power generation reduces at higher extraction or bleed steam pressure &temperature

Note: Steam consumption of turbine increases if,

1-Bleed steam & extraction steam pressure increases

2-Bleed steam & extraction steam temperature increases

3-Bleed steam flow & extraction steam flow increases

4. Increase of exhaust steam temperature due to more clearance in labyrinth seals

Turbine steam consumption increases if exhaust steam temperature to condenser increases

Also read 16-Perfect reasons for increasing the fuel consumption of Boilers

Turbine oil and transformer oil standard testing parameters




Why do the Boilers explode???

 



Now days, we are hearing more on explosion in Boilers & related auxiliaries. This is harming man, machines & system and creating unrecoverable situations in power plant. Upon thinking on this following major causes or reasons come into picture.

The main reasons for Boiler explosions are;

  • Operating the Boiler more than the design pressure for long time
  • Operating the Boilers at lower water level in drum
  • High furnace pressure
  • Poor water quality
  • Poor maintenance of Boilers in shutdowns
  • Ignoring the aging factors of Boiler parts
  • Operating the Boilers at higher main steam or metal temperature

1-What are the reasons for operating the Boilers at more than operating pressure?

  • Malfunction of pressure transmitter or leakages in its impulse line
  • Faulty local pressure gauges
  • Faulty safety valves or safety valves set at higher pressure
  • Improper control of combustion system
  • Operating the Boiler at higher pressure set point
  • Varying fuel quantity & quality
  • Frequent load fluctuation on Boiler
  • Leakages
  • Improper spreading of fuel or no control on fuel feeding system

2-What are the potential reasons for low or no water level in the boilers?

  • Feed water pump is not running, but showing running indication in DCS
  • Mis-operation of feed water control valve or control valve is not opened as per requirement
  • False reading from feed water or steam flow meters
  • Malfunction of drum level transmitters/controllers
  • Low water level in Deaerator or mal function of Deaerator level sensors
  • Feed water discharge pump is closed
  • More load on Boiler than design
  • Under capacity feed water pumps
  • Cavitation or steaming in feed water pumps
  • Steaming in Economizers
  • Long time lifting of Boilers safety valves-(Higher blow down of Safety valves)
  • Wrongly set Boiler safety valves (Super heater line safety valve should be set at lower pressure than drum safety valves)
  • Heavy passing in blow down valves
  • Bypassing the instrument process interlocks like alarm value, low level trips etc

3-How does no water in pressure parts lead to explosion?

No water in pressure parts for long time leads into overheating of pressure parts & eventually failure.

Sudden entry of cold water into no water operating parts leads to flashing of water resulting into high volume steam. This high volume steam suddenly lead to explosion, as there is no sufficient space for steam to expand.

4-How do wrongly set Boiler safety valves lead to explosion?


POWER PLANT PROTECTIONS & INTERLOCKS

Requirement is SH outlet Steam line safety valve is to be set at lower pressure than steam drum safety valves.

If drum safety valves set at lower pressure, on lifting of drum safety valves before lifting of SH line safety valves lead to starvation of super heater coils leading to overheat & eventually explosion.

Questions & Answers on AFBC Boilers

5-What are the reasons for high furnace pressure?

  • High furnace pressure is due to;
  • No control on FD fans
  • Bypassing or not working of Fans interlocks
  • Sudden closure or miss-operation of ID fans dampers
  • Variation of fuel moisture
  • Improper spreading of fuel into furnace
  • Wrongly set over fired air
  • Draught transmitter malfunction & its impulse pipe leakages
  • Choke up of open portion transmitter

6-How the Boiler does lead into explosion due to high furnace pressure

Boiler calculations for Boiler operation engineer (BOE) exam

High furnace pressure leads into damages to the sealing, buck stay & membranes if exceeds leads to furnace & duct explosion.

7-How does the poor quality of feed water lead into Boiler explosion?

Poor quality of feed water leads to scaling & corrosion of pressure parts.

Scaling will lead into poor heat transfer & overheating of tubes, this over heating of tubes cause failure of pressure parts followed by explosions.

8-What are the reasons for overheating of pressure parts?

  • Low water level
  • Continuous flame impingement on particular area of pressure parts
  • Localized heating
  • Fuel (Coal) deposition on pressure parts area
  • Pressure parts choke up
  • Poor material quality
  • More Excess air than requirement
  • Internal scaling
  • Lower feed water temperature at economizer inlet

9-What is the significance of shutdown maintenance of Boilers to avoid explosions?

  • In order to take proper care on Boilers to avoid damages & explosion, need to concentrate on following listed areas of maintenance
  • Thorough cleaning of pressure parts
  •  Inspection of pressure parts thickness & replacement of less thickness
  • Proper setting of air & gas nozzles
  • Proper setting of mechanical spreaders to avoid direct hitting of coal particles to rear wall tubes
  • Inspection of steam line spring hangers
  • Cleaning & inspection of buck stays
  • Safety valves maintenance & proper floating
  • Removing all obstacles & temporary supports in boilers for boilers free expansion
  • Proper setting of burners & air nozzles to avoid localized heating & flame impingement
  •  Cleaning & inspection of ducts
  • Overhauling of steam drum gauge glasses
  • Maintenance & calibration of pressure & level transmitters, pressure gauges & temperature gauges
  • Proper maintenance of soot blowers 
Note:Bend lance tube inside the furnace/SH zone/Economiser can harm the pressure parts
Lance tubes if not rotating may damage the pressure parts by continuous impingement of steam jet.

Why & How these in Boilers???

10-What are the reasons for Boiler back end flue gas ducts explosion?



It is due to secondary combustion & formation of carbon monoxide at ducts such as APH & ESP.

During start up or abnormal operation of Boilers, fuel will carry through flue gas  & settle into APH & ESP ducts, where its incomplete combustion starts & form CO gas.CO is very explosive gas, when external Oxygen combines with this gas results into explosion.


Also read 16-Perfect reasons for increasing the fuel consumption of Boilers

11-What precautions can be taken to avoid high metal temperature operation?

  • Installation of metal skin temperature sensors for Super heater coils
  • Avoiding wet fuel intake into the furnace
  • Avoiding more excess air than design for long time
  • Maintain required or designed feed water temperature at economizer inlet
  • Operate boilers more than 50% of its MCR

  

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Protections & Interlocks in power plants

 Interlocks: Are the programmed or hardwired control systems to protect systems and improve the operation reliability.

Protections: Are the programmed or hardwired control systems to protect the equipments, man power and systems from failure/harm.

The interlock and protection system is used to ensure safety of equipment and personnel as well as smooth & trouble free operation of the plant

This system initiates automatic corrective actions to stabilize the unit quickly. The protection scheme is developed to trip the equipment automatically with or Class A trip involves a serious electrical fault like differential, stator earth fault etc. and is considered to be the most dangerous in terms of the shock on the unit. Since it involves serious electrical faults, connections from both generator and the HV bus is immediately switched off to limit the damage at the fault point and also to isolate the healthy system. Hence the unit (turbine, generator and boiler) has to be tripped without time delay. Alarm & buzzers are generally used to alert the operator.

POWER PLANT PROTECTIONS & INTERLOCKS AND THEIR SIGNIFICANCE

Sl No.

Interlock description

Significance

A

Boiler

 

1

FD & SA fan trip/stop on tripping of ID fans

To avoid furnace pressurizing

2

Fuel feeding system trip/stop on trip/stop of SA fans

To avoid jamming of fuel feeding system due to no spreading air

3

FD fans trip/stop on high furnace pressure (>25 MMWC)

1-To avoid furnace leakage

2-To avoid furnace explosion

3-To avoid buck stay damage

4

ID fans trip/stop on low furnace pressure (-25 MMWC)

1-To avoid carryover of fuel at secondary combustion zone

2-To avoid back end flue gas ducts explosion due to accumulation of unburnt (Unburnt results into formation of CO gas)

5

FD fan trips on low drum level (On tripping ID fans, boiler all systems like FD,SA & fuel feeding system trip)

To avoid boiler pressure parts over heating & failure

B

Steam Turbine

 

1

Turbine trips on high main steam pressure

To protect turbine internals & casing from high pressure damage

2

Turbine trips on low main steam pressure

To protect turbine internals from  saturated  steam (water particles in steam)

3

Turbine trips on high main steam temperature

To protect Turbine internals from creep failure (Turbine internals fail on prolonged exposure to temperature more than recommended)

4

Turbine trips on low temperature

1-To protect Turbine from uneven expansion

2-To protect Turbine internals from water particles in steam (Low pressure & temperature steam will have water particles in it)

5

Turbine trips on high bearing temperature (>110 deg C)

To protect turbine bearing failure & other secondary system/operation interruption for long time

6

Turbine trips on high vibration (>5 mm/sec or >110 microns)

To protect turbine bearing failure & other secondary system/operation interruption for long time

7

Turbine trips on high axial displacement

To protect turbine internals from rubbing & damages

8

Turbine trips on high differential expansion

To protect turbine internals uniform thermal expansion & from rubbing & damages

9

Turbine trips on low control oil pressure

To ensure reliable operation of HP & LP actuators

10

Turbine trips on low lube oil pressure

To avoid damages to the bearings

11

Turbine trips on low trip oil pressure

 

12

Turbine trips on low vacuum or high exhaust pressure

To avoid damages to the rotor blades

Note: High back pressure on rotor creates reaction force to rotation of turbine rotor

13

Turbine trips on high back pressure

 

14

Vacuum breaker valve opens on activation of trip interlocks like

To reduce the speed of rotor within minimum time to avoid damages to the bearings & internal parts.

1.High bearing temperature

Note: High back pressure on rotor creates reaction force to rotation of turbine rotor

2-High bearing vibration

 

3-High axial displacement

 

4-High differential expansion

 

5-Low lube oil pressure

 

15

High hot well level

To avoid entry of water into Turbine

C

Fuel handling

 

1

Belt conveyor trips on operation of Zero speed switch (ZSS)

1-To avoid the further damage to the belt conveyor

2-To avoid system disturbance & major damages to the conveyor structure

Note: ZSS operates when belt gets cut or slips on pulley

2

Belt conveyor trips on operation of belt sway switch (BSS)

1-To avoid swaying of belt

2-To avoid belt side edges damage

3-To avoid fuel spillage

3

Belt Pull cord Switch (PCS)

To stop the belt conveyor during emergency situations to avoid damages to the man & system

D

Boiler feed pumps

 

1

Pump trips on high bearing temperature

To avoid bearing damage & secondary system damage/disturbance

2

Pump trips on high bearing vibrations

To avoid bearing damage & secondary system damage/disturbance

3

Pump trips on low suction pressure

To avoid pump cavitation

4

Pump trips on high differential pressure

To avoid pump cavitation

5

Pump trips on high balance leak off pressure

To avoid further damages to the balance & counter balance discs

6

Pump trips on lower cooling water temperature

To avoid failure of pump's bearings & seal

7

Pumps trips on over load

To avoid damages to the pump internals

8

BFP trips on Deaerator level low

 

E

Boiler fans

 

1

Fan trips on high bearing temperature

To avoid bearing damage & secondary system damage/disturbance

2

Fan trips on high bearing vibrations

To avoid bearing damage & secondary system damage/disturbance

F

Motor

 

1

Motor trips on higher bearing temperature

To avoid bearing damage & secondary system damage/disturbance

2

Motor trips on higher winding temperature

To protect winding

3

Motor trips on over load

To protect winding

G

Generator

 

1

Over current protection

Protects the generator from over load, short circuit & earth faults

2

Earth Fault Protection

To protect the generator from earth faults & short circuits

3

Generator Differential Protection

To protect the generator from winding faults or unbalance currents in winding

4

Reverse Power Protection

To avoid motoring of generator during reverse flow of power to generator from other source

5

Low Forward Power Protection

To protect the generator running under load

6

High bearing temperature

To avoid bearing damage & secondary system damage/disturbance

7

High bearing vibrations

To avoid bearing damage & secondary system damage/disturbance

8

Higher winding temperature

To protect winding

9

Higher core temperature

To protect core

10

High air temperature

To limit winding temperature

 

Other protections

 

11

High & Low voltage protections

 

12

High & low frequency protection

 

13

Rotor earth fault protection

 

14

Loss of excitation

 


 Classes of STG Trips:

Class A trip

This involves serious electrical faults and is considered to be the most dangerous in terms of the shock on the unit. Since it involves serious electrical faults, connections from both generator and the EHV bus is immediately switched off to limit the damage at the fault point and also to isolate the healthy system. Hence the whole unit need to be tripped.

Class B trip

Class B primarily relates to mechanical problems. This results in tripping of turbine followed by generator.

Class C

Class C involves basically external system related problems like frequency, overvoltage etc. This does not involve instant tripping of the unit. CPP unit operates on house load

Classes of Generator protections

SL NO.

CLASS A

CLASS B

CLASS C

1

Generator Differential Protection

Loss of Excitation

Under Frequency

2

100% Stator Earth Fault Protection

Rotor Earth Fault

 Over Frequency

3

Generator Over Voltage Protection

Over excitation

Pole Slipping Protection

4

95% Stator Earth Fault Protection

 

Tripping of unit transformer

5

Starting Over Current Protection

 

 

6

Over fluxing Protection of Generator

 

 

7

  Differential Protection of GT

 

 

8

Buchholz Relay of GT

 

 

9

Trip from oil & winding temperature of generator transformer

 

 

 

These protection when operated initiate tripping of Generator Circuit Breaker, Field Circuit Breaker, Generator Transformer Circuit Breakers & Unit Transformer LV Circuit Breakers and turbine.

This results in tripping of turbine followed by generator.

Class C involves basically external system related problems like frequency, over voltage etc. This does not involve instant tripping of the unit. 


 Why do the Boilers explode


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