How to calculate the generator you need
Selecting the right genset is a critical task that goes beyond simply estimating power. An incorrect calculation can result in oversized equipment, which implies unnecessary costs, or undersized equipment, compromising the operation of the entire installation.
Below, we show you how to correctly calculate the generator set you need, considering all the technical factors involved.
How to proceed with power calculation
Firstly, you need determine the required power, carrying out a load assessment. In order to do this correctly, it is also necessary to consider the start-up peaks caused by some types of loads such as electric motors.
Load assessment: The first step is to identify all the loads that the genset will have to feed. This includes machinery, electrical systems, safety equipment, and any other critical devices to be powered by the genset. It is essential to add up the constant powers of all these loads considering that all the loads might not be connected at the same time.
Consideration of start-up peaks: Some machinery has a peak electrical demand at start-up which can be between 2 and 5 times higher than their consumption in normal operation. Most commonly, these are the ones driven by electric motors, some examples and their classification are given below:
- Light starting: Turbines and fans (2 to 3 times of normal consumption).
- Medium start: Conveyor belts and compressors (3 to 4 times of normal consumption).
- Heavy start-up: Cranes and lifting equipment (4 to 5 times of normal consumption).
Calculation will also depend on the type of motor drive. If the electric motor is powered by a frequency inverter (or other advanced system) the starting peak may vary. E.g. Direct starts, the most unfavourable case.
It is also important to know the moment each load shall be started as it may be the case that all the loads do not start at the same time, this is called the load-step start.
F.i. In order for the diesel engine to be able to handle the high starting peaks, a genset of twice as much power as the highest starting peak is considered.
Total power calculation: Sum of the constant powers identified in the load assessment.
Table for calculating the power of a generating set
The above calculations can be expressed in a table like this one:
Equipment / Load | Constant Power (KW) | Simultaneity factor | Starting factor | Start-up Power (kW) | Load-Step Start | Total Power (kW) |
Machine A | 5 | 1 | 3 | 15 | 1 | |
Machine B | 8 | 1 | 2 | 16 | 1 | |
Lighting | 3 | 1 | 1 | 3 | 2 | |
Compressor | 10 | 1 | 4 | 40 | 2 | |
Fans | 4 | 1 | 2 | 8 | 1 | |
Total Constant Power | 30 kW | |||||
Load-Step 1 Start-up | 39 kW | |||||
Load-Step 2 Start-up | 43 kW | |||||
Needed Power | 86 kW (2 x 43kW) | |||||
Safety Margin (10%) | 94.6 kW | |||||
Power Factor (0.8) | 118.25 kVA |
How to use this table
- Equipment or load: List the equipment or loads to be connected to the genset.
- Constant power (kW): Enter the rated power of each piece of equipment in kilowatts (kW).
- Simultaneity factor: Indicate a figure to express how many loads are operating simultaneously.
- Start-up factor: Apply a start-up factor for each equipment according to its type (e.g., 2 for light start-up, 4 for heavy start-up).
- Starting power (kW): Multiply the power by the starting factor.
- Starting step: Indicate the different steps to express which loads start simultaneously.
- Total power (kW): Add the starting powers to obtain the total power required.
- Safety margin: Apply a safety margin (10% in this case).
- Power Factor: Divide the adjusted total power by the power factor (normally 0.8) to obtain the apparent power in kVA, which is used to select the genset.
Environmental conditions affecting genset power requirements
Extreme environmental conditions can have a significant impact on the performance and efficiency of a generator set. It is crucial to consider these variables when calculating the required power and selecting the right equipment.
Extreme temperatures
- Low temperatures: In cold climates, engine start may be slower and engine oil may thicken, reducing efficiency and increasing wear. It is essential to consider a genset with engine & fuel preheating systems, as well as oil suitable for low temperatures.
- High temperatures: Excessive heat can cause the engine to overheat and reduce the cooling capacity of the system. Generator sets in these environments should be equipped with enhanced cooling systems, such as larger capacity radiators or additional fans.
Altitude
At higher altitudes, air density decreases, which affects both combustion and cooling capacity. This results in a reduction of the power available from the genset. It is considered that for every 300 metres of altitude above sea level, engine power decreases by approximately 3-5%.
Adjustments required according to environmental conditions
- Power adjustment: Recalculate the required genset power to consider losses associated with altitude and temperature.
- Selection of suitable components: Ensure that the genset has specific components for operating in extreme environmental conditions, such as enhanced cooling systems or corrosion protection.
- Additional maintenance and testing: Implement a regular maintenance programme that includes FATs in the actual environmental conditions in which the equipment will operate to ensure optimal performance and prevent unexpected failures.
Taking these environmental factors into account is essential to ensure that the genset will operate reliably and efficiently, regardless of the conditions it is exposed to.
Genesal Energy Engineering Department takes all these critical factors into account when designing and selecting the most suitable generator set for each project. We ensure that each piece of equipment is perfectly adapted to the specific environmental conditions and energy needs of our customers, guaranteeing optimum performance, durability and efficiency, no matter where.