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
Wednesday, September 9, 2009
Generator Rating Definitions
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 based on: Applicable for supplying power in lieu of commercially purchased power. Prime power is the maximum power available at a variable load for an unlimited number of hours. 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.
Typical application - emergency power plant in hospitals, offices, factories etc. Not connected to grid.
Prime (Unlimited Running Time) Rating based on: Applicable for supplying power in lieu of commercially purchased power. Prime power is the maximum power available at a variable load for an unlimited number of hours. 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.
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[5][6] 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.[7] 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 achieveved instantaneously.[8]
* Fuel cost 11p - 16p/kWh (using red diesel at 40p/litre)
* lifetime engine maintenance about is 0.5p/kWh - 1.0/kWh
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.[7] 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 achieveved instantaneously.[8]
* Fuel cost 11p - 16p/kWh (using red diesel at 40p/litre)
* lifetime engine maintenance about is 0.5p/kWh - 1.0/kWh
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 to the set
* Paralleling and synchronising gear and G59 equipment (this allows grid connection) Approx £5k
* 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
* Approx. £3k to fit a PLC to the set
* Paralleling and synchronising gear and G59 equipment (this allows grid connection) Approx £5k
* 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
Peak Shaving
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 around tea time (3 pm), whereas in the United States this is often in the summer to meet the air conditioning load.
Grid support
Emergency standby diesel generators such as those used in hospitals, water plant etc, are, as a secondary function, widely used in the US and the UK 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 say the sudden loss of a large conventional plant of say 660 MW, or a sudden unexpected rise in power demand eroding the normal spinning reserve available.
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.
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[2][3]
A similar system operates in France known as EJP, where at times of grid extremis 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
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.
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[2][3]
A similar system operates in France known as EJP, where at times of grid extremis 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
Power plants - electrical "Island" mode
One or more diesel generators operating without a connection to an electrical grid are operating in "island" mode. Several parallel generators provides the advantages of redundancy and better efficiency at part loads. An island power plant intended for primary power source of an isolated community 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 a live bus-bar. 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 ECU (Engine Control Module). Typical manufacturers are ComAp, GAC, Woodward and Heinzman who dominate this market
Load can be shared among parallel running generators through load sharing. Like auto-synchronization, load sharing can be automated by using a load sharing module. The load sharing module will measure the load and frequency at the generator, while it constantly adjusts the engine fuel control to shift load to and from the remaining power sources. As the prime mover of a diesel generator runs at constant speed, it will take more load when the fuel supply to its combustion system is increased, while load is released if fuel supply is decreased.
Generators can be electrically connected together through the process of synchronization. Synchronization involves matching voltage, frequency and phase before connecting the generator to a live bus-bar. 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 ECU (Engine Control Module). Typical manufacturers are ComAp, GAC, Woodward and Heinzman who dominate this market
Load can be shared among parallel running generators through load sharing. Like auto-synchronization, load sharing can be automated by using a load sharing module. The load sharing module will measure the load and frequency at the generator, while it constantly adjusts the engine fuel control to shift load to and from the remaining power sources. As the prime mover of a diesel generator runs at constant speed, it will take more load when the fuel supply to its combustion system is increased, while load is released if fuel supply is decreased.
Subscribe to:
Posts (Atom)
