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Wednesday, September 28, 2011
express: The Diesel generator set.
express: The Diesel generator set.: The packaged combination of a diesel engine, a generator and various ancillary devices (such as base, canopy, sound attenuation, control sys...
The Diesel generator set.
The packaged combination of a diesel engine, a generator and various ancillary devices (such as base, canopy, sound attenuation, control systems, circuit breakers, jacket water heaters and starting system) is referred to as a "generating set" or a "genset" for short.
Set sizes range from 8 to 30 kW (also 8 to 30 kVA single phase) for homes, small shops & offices with the larger industrial generators from 8 kW (11 kVA) up to 2,000 kW (2500 kVA three phase) used for large office complexes, factories. A 2,000 kW set can be housed in a 40 ft ISO container with fuel tank, controls, power distribution equipment and all other equipment needed to operate as a standalone power station or as a standby backup to grid power. These units, referred to as power modules are gensets on large triple axle trailers weighing 85,000 pounds (38,555 kg) or more. A combination of these modules are used for small power stations and these may use from one to 20 units per power section and these sections can be combined to involve hundreds of power modules. In these larger sizes the power module (engine and generator) are brought to site on trailers separately and are connected together with large cables and a control cable to form a complete synchronized power plant.
Diesel generators, sometimes as small as 200 kW (250 kVA) are widely used not only for emergency power, but also many have a secondary function of feeding power to utility grids either during peak periods, or periods when there is a shortage of large power generators.
Ships often also employ diesel generators, sometimes not only to provide auxiliary power for lights, fans, and winches, etc. but also indirectly for main propulsion. With electric propulsion the generators can be placed in a convenient position, to allow more cargo to be carried. Electric drives for ships were developed prior to WW I. Electric drives were specified in many warships built during WW II because manufacturing capacity for large reduction gears was in short supply, compared to capacity for manufacture of electrical equipment.[1] Such a diesel-electric arrangement is also used in some very large land vehicles such as railroad locomotives.
[edit] Generator Size
Generating sets are selected based on the Electrical load they are intended to supply, the electrical loads total characteristics (kWe, kVA, var's and Harmonic Content including starting currents (normally from motors) and non-linear loads. The expected duty, for example, emergency, prime or continuous power as well as environmental conditions such as altitude, temperature and emissions regulations must be taken into account as well.
[edit] Power plants – electrical "island" mode
One or more diesel generators operating without a connection to an electrical grid are referred to as operating in "Island Mode". In island mode, several parallel generators provide the advantages of redundancy and better efficiency at partial loads. The plant brings generator sets online and takes them off line depending on the demands of the system at a given time. An islanded power plant intended for primary power source of an isolated community ("Prime Power") will often have at least three diesel generators, any two of which are rated to carry the required load. Groups of up to 20 are not uncommon.
Generators can be electrically connected together through the process of synchronization. Synchronization involves matching voltage, frequency, and phase before connecting the generator to the system. Failure to synchronize before connection could cause a high current short-circuit or wear and tear on the generator and/or its switchgear. The synchronization process can be done automatically by an auto-synchronizer module. The auto-synchronizer will read the voltage, frequency and phase parameters from the generator and bus-bar voltages, while regulating the speed through the engine governor or ECM (Engine Control Module).
Load can be shared among parallel running generators through load sharing. Load sharing can be achieved by using droop speed control controlled by the frequency at the generator, while it constantly adjusts the engine fuel control to shift load to and from the remaining power sources. A diesel generator will take more load when the fuel supply to its combustion system is increased, while load is released if fuel supply is decreased.
[edit] Supporting main utility grids
In addition to their well known role as power supplies during power failures, diesel generator sets also routinely support main power grids worldwide in two distinct ways:
[edit] Peak lopping
Maximum demand tariffs in many areas encourage the use of diesels to come on at times of maximum demand. In Europe this is typically on winter weekdays early evening peak when cooking and lights are on as people come home—around 5:30–7:00 PM, whereas in the United States this is often in the summer to meet the air conditioning load.
[edit] Grid support
Emergency standby diesel generators, for example such as those used in hospitals, water plant, are, as a secondary function, widely used in the US and the UK (Short Term Operating Reserve) to support the respective national grids at times for a variety of reasons. In the UK for example, some 0.5 GWe of diesels are routinely used to support the National Grid, whose peak load is about 60 GW. These are sets in the size range 200 kW to 2 MW. This usually occurs during, for example, the sudden loss of a large conventional 660 MW plant, or a sudden unexpected rise in power demand eroding the normal spinning reserve available.[2]
This is extremely beneficial for both parties - the diesels have already been purchased for other reasons; but to be reliable need to be fully load tested. Grid paralleling is a convenient way of doing this. This method of operation is normally undertaken by a third party aggregator who manages the operation of the generators and the interaction with the system operator.
In this way the UK National Grid can call on about 2 GW of plant which is up and running in parallel as quickly as two minutes in some cases. This is far quicker than a base load power station which can take 12 hours from cold, and faster than a gas turbine, which can take several minutes. Whilst diesels are very expensive in fuel terms, they are only used a few hundred hours per year in this duty, and their availability can prevent the need for base load station running inefficiently at part load continuously. The diesel fuel used is fuel that would have been used in testing anyway. See Control of the National Grid, National Grid Reserve Service[3][4]
A similar system operates in France known as EJP, where at times of grid extrema special tariffs can mobilize at least 5 GW of diesel generating sets to become available.In this case, the diesels prime function is to feed power into the grid.[5]
During normal operation in synchronization with the electricity net powerplants are governed with a five percent droop speed control. This means the full load speed is 100% and the no load speed is 105%. This is required for the stable operation of the net without hunting and dropouts of power plants. Normally the changes in speed are minor. Adjustments in power output are made by slowly raising the droop curve by increasing the spring pressure on a centrifugal governor. Generally this is a basic system requirement for all powerplants because the older and newer plants have to be compatible in response to the instantaneous changes in frequency without depending on outside communication.[6]
[edit] Cost of generating electricity
See: Relative cost of electricity generated by different sources
[edit] Typical operating costs
Fuel consumption is the major portion of diesel plant owning and operating cost for power applications, whereas capital cost is the primary concern for backup generators. Specific consumption varies, but a modern diesel plant will consume between 0.28 and 0.4 litres[7][8] of fuel per kilowatt hour at the generator terminals.
However diesel engines can operate on a variety of different fuels, depending on configuration, though the eponymous diesel fuel derived from crude oil is most common. The engines can work with the full spectrum of crude oil distillates, from natural gas, alcohols, gasoline, wood gas to the fuel oils from diesel oil to residual fuels.[9] This is implemented by introducing gas with the intake air and using a small amount of diesel fuel for ignition. Conversion to 100% diesel fuel operation can be achieved instantaneously.[10]
* Fuel cost 11p - 16p/kWh (using red diesel at 40p/litre)
* lifetime engine maintenance about is 0.5p/kWh - 1.0p/kWh[4]
[edit] Typical costs of conversion to paralleling for grid operation
To be able to operate in parallel with the mains certain modifications are necessary which include the following:
* Approx. £3k to fit a PLC / Genest Controller to the set
* Paralleling and synchronising gear and G59 equipment including switchgear modifications (this allows grid connection) Approx £10k
* Tidying up set (noise, larger fuel tank) Approx another £5k
* So for a 1MW set…£13/kW
* 50 kW…maybe £260/kW
This capital cost of £13/kW - £260/kW is low compared to combined cycle gas turbines that cost £350/kW.[4]
[edit] Generator sizing and rating
[edit] Rating
Generators must be capable of delivering the power required for the hours per year anticipated by the designer to allow reliable operation and prevent damage. Typically a given set can deliver more power for fewer hours per year, or less power continuously. That is a standby set is only expected to give its peak output for a few hours per year, whereas a continuously running set, would be expected to give a somewhat lower output, but literally continuously, and both to have reasonable maintenance and reliability.
To meet the above criteria manufactures give each set a rating based on internationally agreed definitions.
These standard rating definitions are designed to allow correct machine selection and valid comparisons between manufacturers to prevent them from misstating the performance of their machines, and to guide designers.
Generator Rating Definitions[11]
Standby Rating based on Applicable for supplying emergency power for the duration of normal power interruption. No sustained overload capability is available for this rating. (Equivalent to Fuel Stop Power in accordance with ISO3046, AS2789, DIN6271 and BS5514). Nominally rated.
Typical application - emergency power plant in hospitals, offices, factories etc. Not connected to grid.
Prime (Unlimited Running Time) Rating: Should not be used for Construction Power applications. Output available with varying load for an unlimited time. Average power output is 70% of the prime rating. Typical peak demand 100% of prime-rated ekW with 10% of overload capability for emergency use for a maximum of 1 hour in 12. A 10% overload capability is available for limited time. (Equivalent to Prime Power in accordance with ISO8528 and Overload Power in accordance with ISO3046, AS2789, DIN6271, and BS5514). This rating is not applicable to all generator set models.
Typical application - where the generator is the sole source of power for say a remote mining or construction site, fairground, festival etc.
Base Load (Continuous) Rating based on: Applicable for supplying power continuously to a constant load up to the full output rating for unlimited hours. No sustained overload capability is available for this rating. Consult authorized distributor for rating. (Equivalent to Continuous Power in accordance with ISO8528, ISO3046, AS2789, DIN6271, and BS5514). This rating is not applicable to all generator set models
Typical application - a generator running a continuous unvarying load, or paralleled with the mains and continuously feeding power at the maximum permissible level 8760 hours per year. This also applies to sets used for peak shaving /grid support even though this may only occur for say 200 hour per year.
As an example if in a particular set the Standby Rating were 1000 kW, then a Prime Power rating might be 850 kW, and the Continuous Rating 800 kW. However these ratings vary according to manufacturer and should be taken from the manufacturer's data sheet.
Often a set might be given all three ratings stamped on the data plate, but sometimes it may have only a standby rating, or only a prime rating.
[edit] Sizing
Typically however it is the size of the maximum load that has to be connected and the acceptable maximum voltage drop which determines the set size, not the ratings themselves. If the set is required to start motors, then the set will have to be at least 3 times the largest motor, which is normally started first. This means it will be unlikely to operate at anywhere near the ratings of the chosen set.
Manufactures have sophisticated software that enables the correct choice of set for any given load combination. Sizing is based on what type of appliances, equipment, and devices that will be serviced by the generator.[12]
[edit] Correct Generator Installation
To ensure correct functioning, reliability and low maintenance costs generators must be installed correctly. To this end manufacturers provide detailed installation guidelines[13][14] covering such things as:
* Sizing and selection
* Electrical factors
* Cooling
Types of cooling
1. air cooling
2. water cooling
* Ventilation
* Fuel storage
* Noise
* Exhaust
* Starting systems
These are frequently ignored causing problems for users
[edit] Diesel engine damage due to misapplication or misuse of generating set
Diesel engines can suffer damage as a result of misapplication or misuse - namely internal glazing (occasionally referred to as bore glazing or piling) and carbon buildup. This is a common problem in generator sets caused by failure to follow application and operating guidelines. Ideally, diesel engines should be run at least 60-75% of their maximum rated load. Short periods of low load running are permissible providing the set is brought up to full load, or close to full load on a regular basis.
Internal glazing and carbon buildup is due to prolonged periods of running at low speeds and/or low loads. Such conditions may occur when an engine is left idling as a 'standby' generating unit, ready to run up when needed, (misuse); if the engine powering the set is over-powered (misapplication) for the load applied to it, causing the diesel unit to be under-loaded, or as is very often the case, when sets are started and run off load as a test (misuse).
Running an engine under low loads causes low cylinder pressures and consequent poor piston ring sealing since this relies on the gas pressure to force them against the oil film on the bores to form the seal. Low cylinder pressures causes poor combustion and resultant low combustion pressures and temperatures.
This poor combustion leads to soot formation and unburnt fuel residues which clogs and gums piston rings, which causes a further drop in sealing efficiency and exacerbates the initial low pressure. Glazing occurs when hot combustion gases blow past the now poorly-sealing piston rings, causing the lubricating oil on the cylinder walls to 'flash burn', creating an enamel-like glaze which smooths the bore and removes the effect of the intricate pattern of honing marks machined into the bore surface which are there to hold oil and return it to the crankcase via the scraper ring.
Hard carbon also forms from poor combustion and this is highly abrasive and scrapes the honing marks on the bores leading to bore polishing, which then leads to increased oil consumption (blue smoking) and yet further loss of pressure, since the oil film trapped in the honing marks is intended to maintain the piston seal and pressures.
Unburnt fuel then leaks past the piston rings and contaminates the lubricating oil. Poor combustion causes the injectors to become clogged with soot, causing further deterioration in combustion and black smoking.
The problem is increased further with the formation of acids in the engine oil caused by condensed water and combustion by-products which would normally boil off at higher temperatures. This acidic build-up in the lubricating oil causes slow but ultimately damaging wear to bearing surfaces.
This cycle of degradation means that the engine soon becomes irreversibly damaged and may not start at all and will no longer be able to reach full power when required.
Under-loaded running inevitably causes not only white smoke from unburnt fuel but over time will be joined by blue smoke of burnt lubricating oil leaking past the damaged piston rings, and black smoke caused by damaged injectors. This pollution is unacceptable to the authorities and neighbors.
Once glazing or carbon build up has occurred, it can only be cured by stripping down the engine and re-boring the cylinder bores, machining new honing marks and stripping, cleaning and de-cooking combustion chambers, fuel injector nozzles and valves. If detected in the early stages, running an engine at maximum load to raise the internal pressures and temperatures allows the piston rings to scrape glaze off the bores and allows carbon buildup to be burnt off. However, if glazing has progressed to the stage where the piston rings have seized into their grooves, this will not have any effect.
The situation can be prevented by carefully selecting the generator set in accordance with manufacturers printed guidelines.
For emergency only sets which are islanded, the emergency load is often only about 1/4 of the sets standby rating, this apparent over size being necessitated to be able to meet starting loads and minimizing starting voltage drop. Hence the available load is not usually enough for load testing and again engine damage will result if this us used as the weekly or monthly load test. This situation can be dealt with by hiring in a load bank for regular testing, or installing a permanent load bank. Both these options cost money in terms of engine wear and fuel use but are better than the alternative of under loading the engine. For remote locations a Salt water rheostat can be readily constructed.
Often the best solution in these cases will be to convert the set to parallel running and feed power into the grid, if available, once a month on load test, and or enrolling the set in utility Reserve Service type schemes, thereby gaining revenue from the fuel burnt.
Set sizes range from 8 to 30 kW (also 8 to 30 kVA single phase) for homes, small shops & offices with the larger industrial generators from 8 kW (11 kVA) up to 2,000 kW (2500 kVA three phase) used for large office complexes, factories. A 2,000 kW set can be housed in a 40 ft ISO container with fuel tank, controls, power distribution equipment and all other equipment needed to operate as a standalone power station or as a standby backup to grid power. These units, referred to as power modules are gensets on large triple axle trailers weighing 85,000 pounds (38,555 kg) or more. A combination of these modules are used for small power stations and these may use from one to 20 units per power section and these sections can be combined to involve hundreds of power modules. In these larger sizes the power module (engine and generator) are brought to site on trailers separately and are connected together with large cables and a control cable to form a complete synchronized power plant.
Diesel generators, sometimes as small as 200 kW (250 kVA) are widely used not only for emergency power, but also many have a secondary function of feeding power to utility grids either during peak periods, or periods when there is a shortage of large power generators.
Ships often also employ diesel generators, sometimes not only to provide auxiliary power for lights, fans, and winches, etc. but also indirectly for main propulsion. With electric propulsion the generators can be placed in a convenient position, to allow more cargo to be carried. Electric drives for ships were developed prior to WW I. Electric drives were specified in many warships built during WW II because manufacturing capacity for large reduction gears was in short supply, compared to capacity for manufacture of electrical equipment.[1] Such a diesel-electric arrangement is also used in some very large land vehicles such as railroad locomotives.
[edit] Generator Size
Generating sets are selected based on the Electrical load they are intended to supply, the electrical loads total characteristics (kWe, kVA, var's and Harmonic Content including starting currents (normally from motors) and non-linear loads. The expected duty, for example, emergency, prime or continuous power as well as environmental conditions such as altitude, temperature and emissions regulations must be taken into account as well.
[edit] Power plants – electrical "island" mode
One or more diesel generators operating without a connection to an electrical grid are referred to as operating in "Island Mode". In island mode, several parallel generators provide the advantages of redundancy and better efficiency at partial loads. The plant brings generator sets online and takes them off line depending on the demands of the system at a given time. An islanded power plant intended for primary power source of an isolated community ("Prime Power") will often have at least three diesel generators, any two of which are rated to carry the required load. Groups of up to 20 are not uncommon.
Generators can be electrically connected together through the process of synchronization. Synchronization involves matching voltage, frequency, and phase before connecting the generator to the system. Failure to synchronize before connection could cause a high current short-circuit or wear and tear on the generator and/or its switchgear. The synchronization process can be done automatically by an auto-synchronizer module. The auto-synchronizer will read the voltage, frequency and phase parameters from the generator and bus-bar voltages, while regulating the speed through the engine governor or ECM (Engine Control Module).
Load can be shared among parallel running generators through load sharing. Load sharing can be achieved by using droop speed control controlled by the frequency at the generator, while it constantly adjusts the engine fuel control to shift load to and from the remaining power sources. A diesel generator will take more load when the fuel supply to its combustion system is increased, while load is released if fuel supply is decreased.
[edit] Supporting main utility grids
In addition to their well known role as power supplies during power failures, diesel generator sets also routinely support main power grids worldwide in two distinct ways:
[edit] Peak lopping
Maximum demand tariffs in many areas encourage the use of diesels to come on at times of maximum demand. In Europe this is typically on winter weekdays early evening peak when cooking and lights are on as people come home—around 5:30–7:00 PM, whereas in the United States this is often in the summer to meet the air conditioning load.
[edit] Grid support
Emergency standby diesel generators, for example such as those used in hospitals, water plant, are, as a secondary function, widely used in the US and the UK (Short Term Operating Reserve) to support the respective national grids at times for a variety of reasons. In the UK for example, some 0.5 GWe of diesels are routinely used to support the National Grid, whose peak load is about 60 GW. These are sets in the size range 200 kW to 2 MW. This usually occurs during, for example, the sudden loss of a large conventional 660 MW plant, or a sudden unexpected rise in power demand eroding the normal spinning reserve available.[2]
This is extremely beneficial for both parties - the diesels have already been purchased for other reasons; but to be reliable need to be fully load tested. Grid paralleling is a convenient way of doing this. This method of operation is normally undertaken by a third party aggregator who manages the operation of the generators and the interaction with the system operator.
In this way the UK National Grid can call on about 2 GW of plant which is up and running in parallel as quickly as two minutes in some cases. This is far quicker than a base load power station which can take 12 hours from cold, and faster than a gas turbine, which can take several minutes. Whilst diesels are very expensive in fuel terms, they are only used a few hundred hours per year in this duty, and their availability can prevent the need for base load station running inefficiently at part load continuously. The diesel fuel used is fuel that would have been used in testing anyway. See Control of the National Grid, National Grid Reserve Service[3][4]
A similar system operates in France known as EJP, where at times of grid extrema special tariffs can mobilize at least 5 GW of diesel generating sets to become available.In this case, the diesels prime function is to feed power into the grid.[5]
During normal operation in synchronization with the electricity net powerplants are governed with a five percent droop speed control. This means the full load speed is 100% and the no load speed is 105%. This is required for the stable operation of the net without hunting and dropouts of power plants. Normally the changes in speed are minor. Adjustments in power output are made by slowly raising the droop curve by increasing the spring pressure on a centrifugal governor. Generally this is a basic system requirement for all powerplants because the older and newer plants have to be compatible in response to the instantaneous changes in frequency without depending on outside communication.[6]
[edit] Cost of generating electricity
See: Relative cost of electricity generated by different sources
[edit] Typical operating costs
Fuel consumption is the major portion of diesel plant owning and operating cost for power applications, whereas capital cost is the primary concern for backup generators. Specific consumption varies, but a modern diesel plant will consume between 0.28 and 0.4 litres[7][8] of fuel per kilowatt hour at the generator terminals.
However diesel engines can operate on a variety of different fuels, depending on configuration, though the eponymous diesel fuel derived from crude oil is most common. The engines can work with the full spectrum of crude oil distillates, from natural gas, alcohols, gasoline, wood gas to the fuel oils from diesel oil to residual fuels.[9] This is implemented by introducing gas with the intake air and using a small amount of diesel fuel for ignition. Conversion to 100% diesel fuel operation can be achieved instantaneously.[10]
* Fuel cost 11p - 16p/kWh (using red diesel at 40p/litre)
* lifetime engine maintenance about is 0.5p/kWh - 1.0p/kWh[4]
[edit] Typical costs of conversion to paralleling for grid operation
To be able to operate in parallel with the mains certain modifications are necessary which include the following:
* Approx. £3k to fit a PLC / Genest Controller to the set
* Paralleling and synchronising gear and G59 equipment including switchgear modifications (this allows grid connection) Approx £10k
* Tidying up set (noise, larger fuel tank) Approx another £5k
* So for a 1MW set…£13/kW
* 50 kW…maybe £260/kW
This capital cost of £13/kW - £260/kW is low compared to combined cycle gas turbines that cost £350/kW.[4]
[edit] Generator sizing and rating
[edit] Rating
Generators must be capable of delivering the power required for the hours per year anticipated by the designer to allow reliable operation and prevent damage. Typically a given set can deliver more power for fewer hours per year, or less power continuously. That is a standby set is only expected to give its peak output for a few hours per year, whereas a continuously running set, would be expected to give a somewhat lower output, but literally continuously, and both to have reasonable maintenance and reliability.
To meet the above criteria manufactures give each set a rating based on internationally agreed definitions.
These standard rating definitions are designed to allow correct machine selection and valid comparisons between manufacturers to prevent them from misstating the performance of their machines, and to guide designers.
Generator Rating Definitions[11]
Standby Rating based on Applicable for supplying emergency power for the duration of normal power interruption. No sustained overload capability is available for this rating. (Equivalent to Fuel Stop Power in accordance with ISO3046, AS2789, DIN6271 and BS5514). Nominally rated.
Typical application - emergency power plant in hospitals, offices, factories etc. Not connected to grid.
Prime (Unlimited Running Time) Rating: Should not be used for Construction Power applications. Output available with varying load for an unlimited time. Average power output is 70% of the prime rating. Typical peak demand 100% of prime-rated ekW with 10% of overload capability for emergency use for a maximum of 1 hour in 12. A 10% overload capability is available for limited time. (Equivalent to Prime Power in accordance with ISO8528 and Overload Power in accordance with ISO3046, AS2789, DIN6271, and BS5514). This rating is not applicable to all generator set models.
Typical application - where the generator is the sole source of power for say a remote mining or construction site, fairground, festival etc.
Base Load (Continuous) Rating based on: Applicable for supplying power continuously to a constant load up to the full output rating for unlimited hours. No sustained overload capability is available for this rating. Consult authorized distributor for rating. (Equivalent to Continuous Power in accordance with ISO8528, ISO3046, AS2789, DIN6271, and BS5514). This rating is not applicable to all generator set models
Typical application - a generator running a continuous unvarying load, or paralleled with the mains and continuously feeding power at the maximum permissible level 8760 hours per year. This also applies to sets used for peak shaving /grid support even though this may only occur for say 200 hour per year.
As an example if in a particular set the Standby Rating were 1000 kW, then a Prime Power rating might be 850 kW, and the Continuous Rating 800 kW. However these ratings vary according to manufacturer and should be taken from the manufacturer's data sheet.
Often a set might be given all three ratings stamped on the data plate, but sometimes it may have only a standby rating, or only a prime rating.
[edit] Sizing
Typically however it is the size of the maximum load that has to be connected and the acceptable maximum voltage drop which determines the set size, not the ratings themselves. If the set is required to start motors, then the set will have to be at least 3 times the largest motor, which is normally started first. This means it will be unlikely to operate at anywhere near the ratings of the chosen set.
Manufactures have sophisticated software that enables the correct choice of set for any given load combination. Sizing is based on what type of appliances, equipment, and devices that will be serviced by the generator.[12]
[edit] Correct Generator Installation
To ensure correct functioning, reliability and low maintenance costs generators must be installed correctly. To this end manufacturers provide detailed installation guidelines[13][14] covering such things as:
* Sizing and selection
* Electrical factors
* Cooling
Types of cooling
1. air cooling
2. water cooling
* Ventilation
* Fuel storage
* Noise
* Exhaust
* Starting systems
These are frequently ignored causing problems for users
[edit] Diesel engine damage due to misapplication or misuse of generating set
Diesel engines can suffer damage as a result of misapplication or misuse - namely internal glazing (occasionally referred to as bore glazing or piling) and carbon buildup. This is a common problem in generator sets caused by failure to follow application and operating guidelines. Ideally, diesel engines should be run at least 60-75% of their maximum rated load. Short periods of low load running are permissible providing the set is brought up to full load, or close to full load on a regular basis.
Internal glazing and carbon buildup is due to prolonged periods of running at low speeds and/or low loads. Such conditions may occur when an engine is left idling as a 'standby' generating unit, ready to run up when needed, (misuse); if the engine powering the set is over-powered (misapplication) for the load applied to it, causing the diesel unit to be under-loaded, or as is very often the case, when sets are started and run off load as a test (misuse).
Running an engine under low loads causes low cylinder pressures and consequent poor piston ring sealing since this relies on the gas pressure to force them against the oil film on the bores to form the seal. Low cylinder pressures causes poor combustion and resultant low combustion pressures and temperatures.
This poor combustion leads to soot formation and unburnt fuel residues which clogs and gums piston rings, which causes a further drop in sealing efficiency and exacerbates the initial low pressure. Glazing occurs when hot combustion gases blow past the now poorly-sealing piston rings, causing the lubricating oil on the cylinder walls to 'flash burn', creating an enamel-like glaze which smooths the bore and removes the effect of the intricate pattern of honing marks machined into the bore surface which are there to hold oil and return it to the crankcase via the scraper ring.
Hard carbon also forms from poor combustion and this is highly abrasive and scrapes the honing marks on the bores leading to bore polishing, which then leads to increased oil consumption (blue smoking) and yet further loss of pressure, since the oil film trapped in the honing marks is intended to maintain the piston seal and pressures.
Unburnt fuel then leaks past the piston rings and contaminates the lubricating oil. Poor combustion causes the injectors to become clogged with soot, causing further deterioration in combustion and black smoking.
The problem is increased further with the formation of acids in the engine oil caused by condensed water and combustion by-products which would normally boil off at higher temperatures. This acidic build-up in the lubricating oil causes slow but ultimately damaging wear to bearing surfaces.
This cycle of degradation means that the engine soon becomes irreversibly damaged and may not start at all and will no longer be able to reach full power when required.
Under-loaded running inevitably causes not only white smoke from unburnt fuel but over time will be joined by blue smoke of burnt lubricating oil leaking past the damaged piston rings, and black smoke caused by damaged injectors. This pollution is unacceptable to the authorities and neighbors.
Once glazing or carbon build up has occurred, it can only be cured by stripping down the engine and re-boring the cylinder bores, machining new honing marks and stripping, cleaning and de-cooking combustion chambers, fuel injector nozzles and valves. If detected in the early stages, running an engine at maximum load to raise the internal pressures and temperatures allows the piston rings to scrape glaze off the bores and allows carbon buildup to be burnt off. However, if glazing has progressed to the stage where the piston rings have seized into their grooves, this will not have any effect.
The situation can be prevented by carefully selecting the generator set in accordance with manufacturers printed guidelines.
For emergency only sets which are islanded, the emergency load is often only about 1/4 of the sets standby rating, this apparent over size being necessitated to be able to meet starting loads and minimizing starting voltage drop. Hence the available load is not usually enough for load testing and again engine damage will result if this us used as the weekly or monthly load test. This situation can be dealt with by hiring in a load bank for regular testing, or installing a permanent load bank. Both these options cost money in terms of engine wear and fuel use but are better than the alternative of under loading the engine. For remote locations a Salt water rheostat can be readily constructed.
Often the best solution in these cases will be to convert the set to parallel running and feed power into the grid, if available, once a month on load test, and or enrolling the set in utility Reserve Service type schemes, thereby gaining revenue from the fuel burnt.
Saturday, September 10, 2011
VIBRATION MONITORING AND ANALYSIS OF MECHANICAL SYSTEMS.
Vibration monitoring and analysis can be a useful part of a preventive or predictive maintenance program.There are a variety of vibration monitoring systems available.Some use permanently mounted sensors to continually monitor vibration levels,while other systems require readings to be taken periodically with handheld sensors.The type of system used depends on the equipment being monitored.The maintenance supervisor should compare the potential benefits of a vibration monitoring system,such as preventing damage and reducing outages,to the overall cost before deciding which system to use or whether to use any system at all.
PROXIMITY PROBE SYSTEMS.
A proximity probe is a non contacting type sensor which provides a direct current voltage directly proportional to shaft position relative to the probe.In a hydroelectic power plant or a large pumping plant,proximity probes are used to measure the main shaft runout on the turbine/generator or pump/motor
ACCELEROMETER SYSTEMS.
There is a number of accelerometer based vibration monitoring systems available,varying greatly in complexity and capability.Accelerometers are lightweight vibration sensors that,as the name implies,provide an electrical output proportional to the acceleration of the vibration of the machine being checked.
PROXIMITY PROBE SYSTEMS.
A proximity probe is a non contacting type sensor which provides a direct current voltage directly proportional to shaft position relative to the probe.In a hydroelectic power plant or a large pumping plant,proximity probes are used to measure the main shaft runout on the turbine/generator or pump/motor
ACCELEROMETER SYSTEMS.
There is a number of accelerometer based vibration monitoring systems available,varying greatly in complexity and capability.Accelerometers are lightweight vibration sensors that,as the name implies,provide an electrical output proportional to the acceleration of the vibration of the machine being checked.
Wednesday, September 7, 2011
express: OPERATION OF A WATER CHILLER
express: OPERATION OF A WATER CHILLER: The heated cooling agent steam is sucked out of the evaporator by the compressor and is compressed to the condensation pressure.The overheat...
OPERATION OF A WATER CHILLER
The heated cooling agent steam is sucked out of the evaporator by the compressor and is compressed to the condensation pressure.The overheated gas flows from the compressor into the aircooled condenser.In the condenser the cooling agent is cooled down by the air to such an extent,that it changes from gas to liquid. It flows on into the collector through the filter dryer and the inspection glass to the thermally controlled expansion valve.From here it flows as expanded cooling agent liquid to the non circulating water cooler.Here the cooling agent evaporates.The amount of heat required for this evaporation is taken from the circulating water and so the cycle can start a new.
In the suction pipe between evaporator and compressor there is a fluid absorber.At standstill of the plant,drops,which are not evaporated in the evaporator,seperate in the fluid absorber.
When starting the compressor,this fluid is sucked through the suction pipe.Thus a suction of too much cooling agent at starting the compressor,which could cause trouble,is prevented.
Tuesday, September 6, 2011
express: Daily checklist and maintenance on a diesel genera...
express: Daily checklist and maintenance on a diesel genera...: Drain water sediment from fuel tank/fuel filter Check the fuel level in the service tank Clean air filter Check the lube oil level Check the...
Daily checklist and maintenance on a diesel generator set
Drain water sediment from fuel tank/fuel filter
Check the fuel level in the service tank
Clean air filter
Check the lube oil level
Check the battery terminal
Check the water level
Check the tension of the belt/unusual noise
Check for leakages[oil,water,coolant]
Check exhaust gas
General physical inspection for work loose parts.
WITH THESE ABOVE DAILY CHECKLISTS,PROBLEMS,MAINTENANCE COSTS,WILL BE MINIMISED,AND THE SYSTEM RELIABILITY WILL INCREASE.
THANKS FOR READING.
Sunday, September 4, 2011
MAINTENANCE OF AIR COMPRESSORS
Air compressors are a common piece of equipment found in most pumping plants and maintenance shops.There are a number of different types of compressors available,but the two most common types which are the reciprocating and the rotary screw compressors.
RECIPROCATING COMPRESSOR.
A reciprocating compressor compresses air in a cylinder,against a cylinder head,by a reciprocating piston.
MAINTENANCE SCHEDULING
LUBRICATION
WEEKLY- Check that oil or grease cups are full and that crank case oil is at proper level.Replace or add the correct lubricant to bring to proper levels in crankcase or oil reservoir.
ANNUAL- Clean oil or grease cups and piping.Check condition of lubricant and change if required.
PACKING GLAND.
WEEKLY- Check for excessive leakage and scoring on piston rod.Adjust packing as necessary.
ANNUAL- Replace packing as necessary.
CYLINDER
Not scheduled- Check cylinder walls for wear and scoring.
PISTON
Not scheduled-Check piston for wear. Check clearance with micrometer.Examine rings for tightness and fits.
CONNECTING ROD
Not scheduled- Check for distortion or bending.Check bearing bolts and nuts for damage and replace as required.
Thursday, September 1, 2011
express: MAINTENANCE OF HYDRAULIC SYSTEMS
express: MAINTENANCE OF HYDRAULIC SYSTEMS: The right way to perform maintenance on a hydraulic system utilizing the Maintenance Best Practices
Most companies spend a lot of money t...
Most companies spend a lot of money t...
MAINTENANCE OF HYDRAULIC SYSTEMS
The right way to perform maintenance on a hydraulic system utilizing the Maintenance Best Practices
Most companies spend a lot of money training their maintenance personnel to troubleshoot a hydraulic system. If we focused on preventing system failure then we could spend less time and money on troubleshooting a hydraulic system. We normally accept hydraulic system failure rather than deciding not to accept hydraulic failure as the norm. Let’s spend the time and money to eliminate hydraulic failure rather than preparing for failure. I worked for Kendall Company in the 1980’s and we changed our focus from reactive to proactive maintenance on our hydraulic systems and thus eliminating unscheduled hydraulic failure. We will talk about the right way to perform maintenance on a hydraulic system utilizing the Maintenance Best Practices.
Lack of maintenance of hydraulic systems is the leading cause of component and system failure yet most maintenance personnel don’t understand proper maintenance techniques of a hydraulic system. The basic foundation to perform proper maintenance on a hydraulic system has two areas of concern. The first area is Preventive Maintenance which is key to the success of any maintenance program whether in hydraulics or any equipment which we need reliability. The second area is corrective maintenance, which in many cases can cause additional hydraulic component failure when it is not performed to standard.
Oil Pump
Preventive Maintenance
Preventive Maintenance of a hydraulic system is very basic and simple and if followed properly can eliminate most hydraulic component failure. Preventive Maintenance is a discipline and must be followed as such in order to obtain results. We must view a PM program as a performance oriented and not activity oriented. Many organizations have good PM procedures but do not require maintenance personnel to follow them or hold them accountable for the proper execution of these procedures. In order to develop a preventive maintenance program for your system you must follow these steps:
1st: Identify the system operating condition.
a. Does the system operate 24 hours a day, 7 days a week?
b. Does the system operate at maximum flow and pressure 70% or better during operation?
c. Is the system located in a dirty or hot environment?
2nd: What requirements does the Equipment Manufacturer state for Preventive Maintenance on the hydraulic system?
3rd: What requirements and operating parameters does the component manufacturer state concerning the hydraulic fluid ISO particulate?
4th: What requirements and operating parameters does the filter company state concerning their filters ability to meet this requirement?
5th: What equipment history is available to verify the above procedures for the hydraulic system?
As in all Preventive Maintenance Programs we must write procedures required for each PM Task. Steps or procedures must be written for each task and they must be accurate and understandable by all maintenance personnel from entry level to master.
Preventive Maintenance procedures must be a part of the PM Job Plan which includes:
* Tools or special equipment required performing the task.
* Parts or material required performing the procedure with store room number.
* Safety precautions for this procedure.
* Environmental concerns or potential hazards.
PM Procedures for Hydraulic Systems
A list of Preventive Maintenance Task for a Hydraulic System could be:
1. Change the (could be the return or pressure filter) hydraulic filter.
2. Obtain a hydraulic fluid sample.
3. Filter hydraulic fluid.
4. Check hydraulic actuators.
5. Clean the inside of a hydraulic reservoir.
6. Clean the outside of a hydraulic reservoir.
7. Check and record hydraulic pressures.
8. Check and record pump flow.
9. Check hydraulic hoses, tubing and fittings.
10. Check and record voltage reading to proportional or servo valves.
11. Check and record vacuum on the suction side of the pump.
12. Check and record amperage on the main pump motor.
13. Check machine cycle time and record.
Preventive Maintenance is the core support that a hydraulic system must have in order to maximize component and life and reduce system failure. Preventive Maintenance procedures that are properly written and followed properly will allow equipment to operate to its full potential and life cycle. Preventive Maintenance allows a maintenance department to control a hydraulic system rather than the system controlling the maintenance department. We must control a hydraulic system by telling it when we will perform maintenance on it and how much money we will spend on the maintenance for the system. Most companies allow the hydraulic system to control the maintenance on them, at a much higher cost.
In order to validate your preventive maintenance procedures you must have a good understanding and knowledge of “Best Maintenance Practices” for hydraulic systems. We will convey these practices to you.
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