Cummins PT Pump with MVS Governor

how does a diesel generator governor work dieselo blog

In modern-day generators, Governor is used to regulating the fuel supply hence controlling the speed and output of the generator. Without this, the engine can overrun itself and breaks into 100 small pieces. So to avoid such things from happening, in this article, we will learn about the governor. Its function in diesel generator, and how to adjust on a Cummins generator.  

What is governor control in the generator? Why do we need it? 

A governor is a regulating or a controlling device used to control the flow of fuel to the engine. By controlling the amount of fuel passed to the engine, its running speed is controlled, hence the output is managed. 

Governors are used in all sorts of machines including generators, trucks, lawnmowers, etc.   

Why do we need a Governor? 

Diesel engine generators are common machines used to generate power for industrial purposes. By using an internal combustion engine, the generators produce power using diesel as fuel. 

The amount of power produced is dependent on the speed of the engine which again depends on the fuel supply. But to maintain a specified output, the engine must also rotate at a constant speed. However, the speed can vary depending on the increase and decrease of the load on the generator. 

So to always keep the output constant, despite increasing or decreasing load, a governor is used.  

How does a diesel generator governor work?

how does a diesel generator governor work dieselo blog
While governors today are of many types. Conventional Governors use centrifugal force along with the working action of spring to control the flow of fuel. These types of Governors are called mechanical governors and are the most basic type.

Generally, a governor is connected to the camshaft which is driven by the crankshaft using a gear. Sitting on the camshaft, a governor rotates at the same speed as the camshaft. On the governor, you have flyweights that are hinged on one side. These weights have one loose side, that moves outwards due to centrifugal force.  

This force is caused by the engine rotation, which also determines how much the flyweight moves. Depending on the type of governor the flyweight can be connected to a button or directly to a metering valve. Both of which are linked to the main fuel supply.

As the generator engine starts, the governor’s arm rotates along creating centrifugal force. The force pushes the flyweights outwards. In turn, the flyweight pushes the button/metering valve outwards opening the connection to the fuel supply. The fuel reaches the injectors supplied to the cylinders and power is produced. 

But in Diesel generators, the output must always be constant despite the varying loads. If the load is reduced less power production is needed. Hence the speed of the engine is reduced by limiting the fuel supply. Similarly, if the load increases fuel supply is increased increasing engine speed, to fulfill extra power requirements.  

It is the type of governor that decides how the fuel supply is controlled.  

Types of Governor in Generators: 

Mechanical Governor: 

mechanical governor dieselo blog
A mechanical governor is the most basic and cheapest type of governor found in the market. These types of governors are easy to fit and repair can easily be upgraded and only needs a screwdriver to adjust the speed.  What makes it different is that it doesn’t need any input from the engine. And rather uses springs action to limit fuel supply and maintain speed.  

 Electrical Governor:

electrical governor dieselo blogWhen a Mechanical Governor is connected with an engine speed sensor and operates based on its feedback it is called an Electrical governor. All mechanical govs have the option to be retro-fitted as electrical. This type of governor has more accurate fuel control with a wider level of flexibility and can also be programmed. 

Electric Control Unit: 

electric control unit dieselo blog

The most modern and advanced form of governor is ECU. These are electronic control units that use multiple sensors to calculate the ideal fuel requirement. An ECU controls the fuel supply along with the fuel injections and the air supply for the proper air-fuel mixture. 

Based on the input of sensors, ECU calculates the injection rates, quantity, and timing to get the optimal power needed. In generators particular, an ECU can easily adjust the engine output depending on the load without any manual interventions. 

How do you adjust the governor on a Cummins generator?

For a Cummins Generator with a panel mounted governor control adjusting the governor requires adjusting four potentiometers. These are located on the engine/generator control panel. Use the image below as a reference.  
how do you adjust the governor on a cummins generator dieselo blog

The Gain Control is a one-turn potentiometer used to control the sensitivity of the governor. To increase the sensitivity, it needs to be turned in a clockwise direction. This in response will shorten the governor’s reaction time towards load changes. Doing the opposite would increase the response time, making it slower.  

The Droop Control is also a one-turn potentiometer. To increase the speed droop, it needs to be rotated clockwise. And can be adjusted from 0% to 5% speed droop. Turning it fully counterclockwise would enable isochronous operations. Rotating to 40 gets 3% droop while 80 gets to 5% droop. 

A 20-turn potentiometer is given for controlling the Idle Speed. By rotating clockwise, the speed can be increased. Similarly, the Run Speed control which controls the governor speed at no load is also a 20-turn potentiometer and operates the same way. 

All these controls would help you adjust your governor to the required parameters. 

For Generators, at 60Hz load would have no load governor speed at: 

  • 60.0 Hz (1800RPM) for isochronous operation
  • 61.8 Hz (1854 RPM) for 3%  speed droop
  • 63.0 Hz (1890 RPM) for 5% speed droop

For Generators at 50Hz load would have no load governor speed at: 

  • 50.0 Hz (1500 RPM) for isochronous operation
  • 51.5 Hz (1545 RPM) for 3% speed droop
  • 52.5 Hz (1575 RPM) for 5% speed droop
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