Easy Guide to Calculating Diesel Generator Size and Capacity

Table of Contents

1. Introduction
2. What is a DG or Diesel Generator Set?
3. Types of DG Backup
   • 3.1 Full Backup
     • 3.1.1 Example: Hospital
     • 3.1.2 Example: Research Lab or Office
   • 3.2 Partial Backup
     • 3.2.1 Example: Residential Complex
     • 3.2.2 Exception for High-End Residential Places
4. Determining DG Set Rating
   • 4.1 Calculation for a Residential Complex
     • 4.1.1 Lighting Loads
   • 4.2 Conversion from Kilowatt to KVA
   • 4.3 Considerations for DG Set Load Capacity
5. Additional Considerations
   • 5.1 Power Plant Example
   • 5.2 Determining Load Current Capability

Introduction

In this article, we will discuss how to determine the rating of a DG (Diesel Generator) set. Understanding the types of DG backup and the calculation process for different applications is important for efficient power backup planning. We will explore the concept of full backup and partial backup, as well as considerations for selecting the appropriate DG set rating.

What is a DG or Diesel Generator Set?

A DG or Diesel Generator set is a backup power source that runs on diesel fuel. It is used to produce electricity when the main power supply is unavailable. DG sets convert mechanical energy into electrical energy to provide power during emergencies.

Types of DG Backup

3.1 Full Backup

Full backup is required in sectors where uninterrupted power supply is crucial. Examples include hospitals, research labs, important offices such as banks and government institutions, and defense offices.

3.1.1 Example: Hospital

Hospitals require a 24-hour power supply for critical operations and sophisticated equipment. Hence, a full backup is necessary to ensure uninterrupted power in these facilities.

3.1.2 Example: Research Lab or Office

Research labs or important offices that rely on continuous power supply also fall under the category of full backup. These establishments require backup power for their essential operations.

3.2 Partial Backup

Partial backup is suitable for applications where only essential loads need to be supported during power outages. Residential complexes with a mix of essential and non-essential loads are a common example.

3.2.1 Example: Residential Complex

Residential complexes often have essential loads such as lighting and certain appliances that require backup power. However, non-essential loads like air conditioners can be excluded from the backup power supply.

3.2.2 Exception for High-End Residential Places

In cases where the residence belongs to a billionaire or a millionaire, the client may request a 24-hour power backup for all essential and non-essential loads. In such high-end residential places, the backup power supply needs to cater to the entire residential facility.

Determining DG Set Rating

4.1 Calculation for a Residential Complex

Let's consider the example of a residential complex with 50 floors, where each floor requires a backup load of 2 kilowatts. In this scenario, the lighting loads play a crucial role in determining the DG set rating.

4.1.1 Lighting Loads

To calculate the total load to be backed up by the DG set, we multiply the number of loads (50) by the load per floor (2 kilowatts). The total load comes out to be 100 kilowatts.

4.2 Conversion from Kilowatt to KVA

It's important to note that DG set ratings are specified in KVA (kilo volt ampere), not kilowatts. The conversion between the two is given by the formula: kilowatt = KVA x power factor (cos phi). In most cases, the power factor (cos phi) is considered as 0.8.

Dividing the total load (100 kilowatts) by the power factor (0.8), we get 125 KVA as the required DG set rating.

4.3 Considerations for DG Set Load Capacity

To ensure the reliable operation of the DG set, it should not be loaded beyond 80% of its full load capacity. Therefore, if we want to back up a 125 KVA load, we need to select a DG set with a rating that is 80% of that load.

Using the formula 80% of the desired load = DG set rating, we can calculate the DG set rating as follows: X x 0.8 = 125 KVA, where X denotes the desired DG set rating. Upon calculations, the DG set rating comes out to be 156.25 KVA. Selecting a DG set with a rating of 160 KVA would be appropriate to handle the 100 kilowatt load effectively.

Additional Considerations

5.1 Power Plant Example

In a power plant with multiple generating units, it's important to consider the load demand and the simultaneous operation of the units. Power plants typically run a maximum of three units simultaneously while keeping one unit for maintenance.

5.2 Determining Load Current Capability

If you need to determine the load current capability of a DG set, you can utilize the following formula: Load Current (Ampere) = DG Set KVA / (√3 x Voltage). For example, with a DG Set rating of 160 KVA and a three-phase voltage of 400 volts, the load current capability would be approximately 230.94 Amperes.

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