How to calculate a Diesel Prime mover capacity when a driven Generator rated output power is known

I want to know as to how do someone calculate the Diesel Prime mover capacity when the Generator rated output power is known which is driven by it.
Are there some rules or thumb rules or an International standard. Please point it out to me so that I can use the same to check.
In general, if the Diesel engine and generator were packaged and supplied by one company the Diesel engine rating is less than that of the generator. Otherwise, the Diesel engine governor would have to limit the diesel engine’s power output in order to prevent the generator from being damaged (usually by overheating due to excessive current flowing in either or both the generator stator or rotor (field)).

There are exceptions to every general rule and some applications may require different equipment.

I’m unaware of any international or regional technical regulation or standard about the relationship of Diesel engine to generator ratings. It’s mostly about protecting the driven device (the generator in this case) from excessive power input (which would result in excessive power output, since generators convert torque to electrical power (specifically amperes).

Also it doesn’t generally make economic sense to use a diesel rated for higher output than the generator it is driving—and be forced to limit the power output to protect the generator from damage.

Hope this helps!
I want to know as to how do someone calculate the Diesel Prime mover capacity when the Generator rated output power is known which is driven by it.
Are there some rules or thumb rules or an International standard. Please point it out to me so that I can use the same to check.

Have a attentionned read on this article from the link below:

Thats a interesting approach for Diesel genset & plant designing and optimization

I am sure that can highlight some points that you are looking for!

Always glad to support !
Any time!

Diesel Engine

The diesel engine is the most important part of the genset. It is the prime mover that drives the generator (alternator) to produce electricity. All diesel engines are similar to each other in the concept but they differ in many aspects such as the number of cylinders, if the cylinders are line or V-type, how the fuel is delivered to the cylinders, governing system, cooling system, air charging system, air intake system, rotational speed and recently the engine tier for COx and NOx emissions. All these details affect the decision of which engine to use and which performance is expected. Engines are rated in KW or HP. Their performance is measured in their fuel consumption in liters or gallons per KWh produced, its thermal efficiency, noise level, lube oil consumption and exhaust gas emissions.

We do not know what kind of utility this genset is attended to be implemented....

You may better have to ask OEM/VENDOR office support for giving you best advices on thsi case..

We do not know about capability curves of teh generator ...Capacity /output of Generator...

Some diesel prime mover ( small size ) can react faster/quicker for KVAR fluctuation than those bigger (output capacity)

Many points here remains unclear post is incomplete

Provide more details so we can try to give better support from here

Here is some notes

  • iesel engine generator (DEG) system shall provide the source of standby power for critical electrical loads when normal electrical power is not available.
  • The generator set shall be supplied as a complete package comprising diesel engine, generator, controls, cooling system, starting system, and diesel day tank. The generator set package shall conform to NFPA 70 Article 702, NFPA 110.
  • The generator set shall be supplied in accordance with the electrical one line diagram which shall indicate the generator kW, output voltage, and the protective relays required for generator protection. ANSI relay designations shall be utilized.
  • Engine-generator unit and accessories shall be designed for a 20-year life expectancy, and shall be capable of operating at 105 percent of rated speed without overstressing any part of the engine, generator or accessories.
  • Engine-generator unit shall be capable of continuous operation at all loads up to and including rated load at the specified operating conditions and at 110 percent of rated load for two (2) hours out of every 24 hours.
  • Engine-generator shall start, reach full speed and be ready to pick up load in no more than 15 seconds. System load shall be picked up immediately after engine is stable.
  • Engine-generator shall be capable of unattended operation at rated full load or any partial load, while maintaining rated voltage and frequency for a period not exceeding two (2) days. Engine-generator shall be capable of being started and exercised under partial or full load for a period of at least two (2) hours per week.
  • DEG system shall be capable of accepting 85 percent of rated load or shedding 100 percent load without exceeding an 8 percent frequency and 10 percent voltage variation at the generator terminals, and shall be capable of starting the largest motor connected as essential load without exceeding a 2 percent frequency droop and 15 percent voltage drop. DEG shall be capable of accepting 50 percent of rated load without exceeding a 5 percent frequency droop.
  • Engine-generator set shall be able to start under black-start conditions, that is, without power for the auxiliary devices on the generator set, using only generator set battery, or the air contained in the starting air tanks and fuel supplied from the day tanks.
  • A constant speed governor shall be supplied for the generator set that has the capability for load sensing and will maintain isosynchronous speed of the engine at ± 0.25 percent of steady state speed.

You got teh NFPA article reference ...

So as I wrote before many points/criteria have to be taken in account for a correct designing of DieselGenset Plant §

Any time!

I am sure can help you !
Diesel Generator Enclosure
Self-contained enclosure shall be provided for the diesel generator set.The enclosure shall be manufactured such that all part are accessible for inspection and minor maintenance without removal of the enclosure or enclosure roof. It shall include the following features:

a. The enclosure and all other items shall be designed and built by the supplier as an integral part of the entire diesel generator set, and shall perform without overheating in the environment specified.

b. It shall be constructed of minimum 14-gauge sheet metal, suitably reinforced to reduce vibration in the operating mode.
c. A minimum of four doors are required. The doors shall be hinged so that they can be opened to provide complete access to the equipment inside the enclosure without removing the doors.
d. The side and rear panels shall be completely and simply removable to permit major service access.
e. Doors shall be lockable.
f. All exterior steel surfaces, including those in contact with the foundation, shall be epoxy-or epoxy-mastic-coated as a minimum. Interior surfaces shall have the vendor’s standard finish. All fasteners shall be corrosion resistant.
g. Batteries shall fit inside the enclosure and alongside the engine (batteries under the generator are not acceptable).
h. The unit shall have coolant and oil drains piped to the outside edge of the skid in an accessible location. Each drain line shall have a valve located near the fluid source.
i. Air Intake louvers shall be sized to provide sufficient airflow for engine combustion, engine cooling and generator cooling. The louvers shall open automatically when the engine receives the start signal and close when the engine stops. They shall also allow manual over-ride.
j. The air intake and exhaust outlet shall be configured such that exhaust gas recirculation to the air intake will not occur under any wind direction.
k. 120 VAC lights, light switch, 120 V receptacles, and an associated load panel shall provided. The 120 V source will be provided by others.
l. Diesel generator set shall not generate noise in access of 85dba at a distance of 1 meter. If the sound pressure level will exceed 85 dba, the vendor shall notify the purchaser and additional cost for modification to ensure the sound pressure does not exceed 90dba at 1 meter. dba.

Transport units heavier than 25 kg shall have eyebolts, lugs, or extension pieces clearly identifiable to be used for hoisting.

A separate junction box or boxes shall be provided on the generator enclosure for connections to space heaters, temperature detectors, therm
Power System IEC References
International Electrotechnical Commission (IEC)

60038 Standard Voltages
60059 Standard Current Ratings
60076 Power Transformers
60364 Low Voltage Electrical installations of Buildings
60909 Short circuit currents in three-phase a.c. Systems
60949 Calculation of thermally permissible short-circuit currents
60986 Short circuit ternperature limits of electric cables with rated voltages from 6 kV (Um-7,2 kV) up to 30 kV ) (Um=36 kV)
61800-2 Adjustable speed electrical power drive systems – Part 2: General requirements- Rating specifications for low voltage adjustable frequency a.c. power drive systems
61800-3 Adjustable speed electrical power drive systems – Part 3: EMC requirements and specific test methods.
Sequence of Electrical Work
  • Electrical system calculations for most projects are an iterative process. Sufficient data is not available at the beginning of a project to make final calculations. However, calculations must be made early in the project to properly specify the electrical equipment and to insure that use of large electrical drive motors is feasible.
  • A number of preliminary calculations must be performed using various assumptions to arrive at an over-all one line diagram. Once the over-all one line diagram has been selected these calculations must be further refined using updated load estimates to allow procurement of major long-lead-time electrical equipment.
  • As more information becomes available the calculations are updated and expanded to more detail levels to define the electrical equipment at the secondary level.
The data base is continuously updated until at the completion of the project it accurately represents the as built electrical system.

Electrical Load Summary
  • There are actually three different types of load summaries required: (1) Main (or utility) Load, (2) Essential or Stand-By Power and (3) UPS Power. Preparation of the main load summary and maintenance of an accurate data base is the major task. The other load summaries do not have as many loads or bus summaries.
  • The load summary can be produced using a custom data base or spread sheet developed specifically for the project or the load summary tools contained in the master calculation package such as ETAP, EDSA, or PTW can be used. The load summary shall be electronically linked to the calculation data base such that single entry of data is required. It is preferred that the load summary be electronically linked with the mechanical equipment list and the electrical one line diagrams to permit single point data entry and insure consistency between these documents.
  • The load summary shall contain the information and assumptions outlined below:
    a. Equipment Number
    b. Service
    c. Status (operating or spare)
    d. Mechanical Equipment Rated maximum kW and normal brake kW
    e. Motor rated voltage, kW, efficiency and power factor at full, 3/4 and 1/2 load
    f. Calculated motor load for mechanical equipment maximum and normal bake loads (kW, kVAR and kVA)
    g. Utility factor
    h. Heating load kW
    i. Lighting Load kW, kVAR and kVA
  • Preliminary load estimates shall use motor nameplate rating in kW and shall assume a power factor of 0.85. As actual driven equipment loads and motor data become available, the motor loads shall be calculated from this data.
  • Spare motors shall not be included in the overall total load. However, spare motors shall be included in the loads of buses, transformers, and feeders to which they contribute, in order to obtain the maximum operating load on individual equipment. When both the operating motor and its spare would contribute to the same load, if both were operating, only the operating motor shall be included in the load.
  • Lighting and receptacle transformer operating loads shall be included at 80% of the transformer kVA rating. Substation transformers and load bus shall be sized to accommodate future load growth thus it is appropriate to include these loads at the initial design value.
  • Intermittent short time loads such as motor operated valves shall not be included.
Load Flow Study
  • A load flow study shall be run immediately after completion of data entry as a first check on the electrical system and to de-bug data in case errors were made. Once the system model has been confirmed, system load flow cases can be run or other calculations such as short circuit analysis can be started.
  • The load flow study is used to confirm that voltages and loading on different elements of the system are within project parameters. For redundant systems the load flow shall be performed with one supply interrupted to insure that the system will operate satisfactorily in this condition.
  • The load flow study provides information on the power factor of the circuits and buses of the electrical system.

Can you give a quick reply on my latests posts ....

That would be great to hear from original poster how about our contributions in this forum

At least a Thanks for your support ...would be welcome

Ohh Sorry, I was busy in the last two days due to which I could not see the inputs from all of you. Good inputs by all of you. I will read them and revert. Thanks a lot.