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What is a Three-Phase Diesel Generator?

A generator is an electromechanical device that converts rotational kinetic energy into electrical power in accordance with Faraday’s laws of electromagnetic induction. Three-phase diesel generators convert some of the chemical energy contained in the diesel fuel to mechanical energy through combustion.

Typically, an internal combustion engine powered with diesel or petrol is used to rotate an armature made up of copper coils wound around a metal core in a magnetic field produced by a series of magnets. Although generators are typically diesel powered, there is no reason why petrol, natural gas, or even steam could not be used to provide the rotational energy required.

A generator is often referred to as a genset because it consists of two primary components: the engine and an alternator or generator end. Three-phase diesel generators produce voltage in three sequential sine waves with an offset of 120° between them. The three waves produce AC voltage in each single revolution, producing continuous, stable voltage provided that the engine runs at constant revolutions per minute (RPM). Three-phase diesel generators usually produce a voltage output of 480 volts. Three-phase diesel generators are generally considered superior to their single-phase (1P) counterparts as they are more efficient, have better energy density, weigh less, and have a smaller footprint than an equivalent 1P unit. They are usually also less costly than 1P units of similar output power. The power density and efficiency characteristics of three-phase diesel generators are particularly important when high power is required at constant demand.

It is No Longer a Matter of Choice

With Eskom likely to continue struggling to provide power reliably in the short to medium term, most commercial and industrial businesses are virtually obliged to make the investment and procure a three-phase diesel generator. Note that 1P generators are only suitable for small loads and they are generally suited to residential and possibly office use. 1P gensets are not usually available in output capacities larger than 50 kVa. Although procuring a three-phase diesel generator is often considered a grudge purchase, the cost of procuring a genset should be compared to the costs to a business of power outages, interruptions of production, poor service to customers, and revenue losses.

The Flexibility of a Three-Phase Generator

A three-phase diesel generator is an incredibly versatile and flexible source of electrical power. They may be connected in two configurations, namely the Delta or the Y connection or the Star connection. In a Delta connection, the ends of the three windings join to form a closed loop which has the appearance of the Greek letter Delta. In a Y or Star connection, one end of each winding is joined together, leaving the other ends for connecting externally. This configuration looks like the letter Y or a star.

One of the phases of a three-phase diesel generator may be used to supply 1P loads, provided the power output rating of the individual phase is not exceeded. It is also possible to derate certain gensets (ones with the reconnectable-type ends) by converting them from 3P to 1P. This would reduce the power output of the unit by approximately 30%.

Multiple three-phase diesel devices may be connected in parallel to provide redundancy or to increase the system capacity. This is often the case where additional load is added and the initial device becomes inadequate. Two or more gensets are electrically joined to combine their power output. It is better and easier to parallel identical generators than units of different capacities.

Most large three-phase diesel devices will be able to output 50 or 60 hertz frequency. Running the engine at 1800 RPM will provide 60 Hz output and at 1500 RPM, 50 Hz. There are limitations to which gensets this can be done with, and specialist advice should be obtained before making any assumptions.

Sizing a Three-Phase Diesel Generator

A common misconception is that if a genset has more than adequate output, for example 100 kVa where the actual requirement is 50 kVa, this will be an acceptable unit for the site. Sizing a generator is far more nuanced than simply purchasing the biggest machine possible. Too large a three-phase diesel device is inefficient as it uses far more diesel than necessary, not to mention that it will be considerably more expensive than one half its size. What makes matters worse is that gensets should ideally be run at about 75% of capacity as running in the correct thermal range increases their life span and cuts down on maintenance.  Running diesel engines on less than 30% load for extended periods is generally very bad for them.

On the other hand, specifying a unit too small for the actual loads puts the unit under stresses that fall outside its design envelope. Depending on how stressed the unit becomes, output can deteriorate to a level where it causes damage to the equipment connected to it or the genset itself fails.

Buying New or Used

Buying a high-quality, new, three-phase diesel generator is the route that provides the most peace of mind with the least risk. There are, however, reputable companies that offer used three-phase diesel generators that have been properly serviced and/or refurbished that come with bankable support and a full service history. Some form of warrantee should be provided as well as an assurance that backup and spares are available for the product. Units fitted with well-known engine brands such as Perkins or Volvo are also usually a safer bet. A used unit will obviously be less costly than a new machine.

Making the Right Choices Requires Expertise

PacB is renowned in the industry as a manufacturer of superior-quality large three-phase diesel generators. Engaging with us will ensure the best outcome with regards to the cost, reliability, and durability of the solution. Our company has years of experience in the industry and will provide expert advice on anything to do with gensets and power generation in general. The bigger the installation, the more complex the engineering requirement becomes. The experience and expertise we have allow us to help customers make fully informed decisions on the type of device best suited to their specific environment. They will also understand the existing, on-site, electrical installation and make sure that you purchase a machine correctly sized and configured for your needs.

Leave questions like voltage and frequency, peak demand, harmonics, and total power required to the experts. Contact PacB today and be guaranteed to always have electrical power.