A generator set is an autonomous device capable of producing electricity. A generator set is a machine that moves an electric generator through an internal combustion engine. They are commonly used when there is a deficit in the generation of electricity from somewhere, or when power cuts are frequent. Likewise, the legislation of the different countries may require the installation of a generator set in places where there are high densities of people, such as hospitals, data centres, shopping centres, restaurants, prisons, administrative buildings, etc.
Basics of the Common Engine Generator Set
One of the most common utilities is to generate electricity in those places where there is no electricity supply. They are generally remote areas with few infrastructures and very little inhabited. Another case would be in premises of public concurrence: hospitals, factories, etc places where the electrical energy of the network is insufficient and another source of alternative energy is necessary to be supplied.
They run from all fuels. The most frequent are gasoline, diesel, kerosene, natural gas, LPG, biofuels and the most powerful heavy fuel oil. The unit can be put into operation in different ways: manually, electrically or through compressed air, depending on the power.
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The efficiency of generator sets increases with their power but remains limited to the maximum allowed by the Carnot cycle, from which mechanical and electrical losses in the alternator and transmission must be subtracted. (The Carnot cycle is a theoretical ideal thermodynamic cycle) In particular, moderate power groups are characterized by poor efficiency and high consumption.
For example, for a commercial product that delivers 5,500 W, powered by a 9.55 kW gasoline engine that consumes about 2.5 L of fuel per hour when used at 2⁄3 of its rated power (i.e. 3,600 W): taking into account the inevitable heat losses in internal combustion engines, this results in an efficiency not exceeding 40% of the power fuel calorific.
Parts of a Engine Generator Set
A generator set consists of the following parts:
- Engine: The motor represents the mechanical energy source for the alternator to rotate and generate electricity. There are two types of engines: gasoline and diesel engines. Generally, diesel engines are the most used in generator sets for their mechanical, ecological and economic performance.
- Engine regulation: The motor regulator is a mechanical device designed to maintain a constant motor speed about load requirements. The speed of the motor is directly related to the output frequency of the alternator, so any variation of the motor speed will affect the frequency of the output power.
- Engine electrical system: The electrical system of the motor is 12 V or 24 V, negative to mass. The system includes an electric starter motor, one battery (s), and the sensors and alarm devices available to the motor. Typically, an engine has an oil pressure hand, a temperature thermocontact, and a contact on the engine’s charge alternator to detect a charge failure in the battery.
- Cooling system: The engine cooling system can be using water, oil or air. The air cooling system consists of a large capacity fan that passes cold air along the engine to cool it. The water/oil cooling system consists of a radiator, an indoor fan to cool its components.
- Alternator: The output electrical energy is produced using a shielded, splash-protected, self-excited, self-regulating and brushless alternator precisely coupled to the motor, although brush alternators can also be coupled for those groups whose operation will be limited and, under no circumstances, forced to higher regimes.
- Fuel tank and bench: The engine and alternator are coupled and mounted on a high-strength steel bench The bench includes a fuel tank with a minimum capacity of 8 hours of operation at full load.
- Vibration isolation: The generator set is equipped with anti-vibration plugs designed to reduce the vibrations transmitted by the motor-alternator group. These insulators are placed between the base of the motor, the alternator, the control panel and the bench.
- Muffler and exhaust system: The silencer is installed to the engine to reduce noise emission.
- Control system: One of the different types of panels and control systems can be installed to control the operation and output of the group and to protect it against possible malfunctions. The control system manual provides detailed information on the system that is installed in the generator set.
- Automatic output switch: To protect the alternator, a suitable automatic output switch is supplied for the model and output regime of the generator set with manual control. For generator sets with automatic control, the alternator is protected by contactors suitable for the appropriate model and output regime.
- Other accessories installable in a generator set: In addition to the above, other devices help us control and maintain, automatically, the correct functioning of it. For the automatic regulation of the motor speed, an electronic control card is used for the input signal “pick-up” and output of the “actuator”. The pick-up is a magnetic device that is installed right in the gear located in the motor, and this, in turn, is coupled to the gear of the starter motor. The pick-up detects the speed of the motor, produces a voltage output due to the movement of the gear moving through the magnetic field of the pick-up tip, therefore, there must be a correct distance between the pick-up tip and the motor gear. The actuator is used to control the speed of the motor under load conditions. When the load is very high the speed of the motor increases to provide the required power and, when the load is low, the speed decreases, that is, the foundation of the actuator is to automatically control the speed of the engine without sudden accelerations, generating the power of the engine continuously. Normally the actuator is coupled to the engine’s fuel oil input device.
When the group is in a place very far from the operator and operates 24 hours a day, it is necessary to install a mechanism to restore the spent fuel. It consists of the following elements:
Racking pump: It is a 220 VCA electric motor in which a pump is coupled that is responsible for supplying the fuel to the tank. A maximum and minimum level indicator buoy detects a very low level of fuel in the tank and activates the racking pump.
When the cold conditions in the environment are intense, a heating device called pre-heating resistance is available that helps the engine start. Air-cooled generator sets usually use an electric radiator, which is placed under the engine, in such a way that it keeps the oil at a certain temperature. In water-cooled motors the pre-heating resistor is coupled to the cooling circuit, this resistor is fed from 220 WL and heats the cooling water to heat the engine. This resistor has an adjustable thermostat; in it, we select the right temperature for the group to start in a few seconds.
