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A simple guide to the main components and maintenance of a generator – Part 1: The engine

A simple guide to the main components and maintenance of a generator – Part 1: The engine
The vast majority of companies could not operate without electrical power. Without it, their staff can’t use or service appliances, operate electrical technology or work on computers. It’s for this reason that generators are a major component in business security.
The vast majority of companies could not operate without electrical power. Without it, their staff can’t use or service appliances, operate electrical technology or work on computers. It’s for this reason that generators are a major component in business security, because generators provide a continuous electricity supply when there is a mains failure. Critical power specialist, Powertecnique, is one of the leading companies in the world of generators. 

Over the coming 4 weeks we’re going to be running a series of blog posts which will describe the key parts of a generator, and the maintenance that a unit requires to keep it functioning efficiently. These posts will cover:
  • The engine which converts fuel into mechanical, or kinetic, power

  • The alternator which converts mechanical power to alternating electrical power

  • The control panel which manages the operation of the engine and alternator

  • The daily, weekly, monthly and long-term maintenance checks carried out by operators and engineers.

This week we start with the engine.

Engine
“The engine of a generator will typically be gas oil (diesel) powered. There are two main exceptions; the very small portable generators (which are only a few kW), which are likely to be petrol, and combined heat power and base load applications, which may be gas. 

“Generator engines convert fuel energy into mechanical power to turn the alternator and heat. The heat is removed in the exhaust flue gas which can reach up to 500°C, transferred to the coolant and radiated from the engine. The residue of combustion, the flue gas, is toxic and so it is important that it is safely vented. 

“The right engine for a particular application must be sized not only to support the anticipated load, but also the period of operation, load profile and load type. There are four power categories: COP (Continuous Operating Power), PRP (Prime Power), LTP (Limited Time running Power), and ESP (Emergency Standby Power) defined in ISO 8528. The generator power will be defined using one of these categories along with its performance class, and a similar engine could have up to a 30% difference in power depending on the power category.

“There are four performance classes defined in order to cover the various requirements of the supplied electrical systems as follows: Class G1 General-purpose applications; Class G2 Lighting systems, pumps, fans and hoists; Class G3 Telecommunications and thyristor-controlled loads; and Class G4 Data-processing equipment or computer systems.

“The power category of the generating set will affect certain important performance characteristics, its economical and reliable operation, and the intervals between maintenance and repair. Long periods on low load are not good for an engine as combustion chamber temperatures drop so low that the fuel may not burn completely. This can cause carbon to clog the injector spray holes and piston rings, possibly resulting in stuck valves. If the engine coolant temperature becomes too low, raw fuel will wash the lubricating oil off cylinder walls and dilute crankcase oil so that all moving parts of the engine will suffer from poor lubrication.

“What constitutes a low load will be dependent on the engine but is typically less than 30%. If low loads cannot be avoided then a load bank should be used periodically to fully load the generator and clear the carbon deposits. The oil should be sampled to ensure it has not been diluted, and changed if necessary.
“The generator size is specified in kVA at 0.8 power factor (PF) meaning that the real power available for the generator will be 80% of the kVA rating.  If the load PF is greater than 0.8 then the generator needs to be rerated accordingly. 

“Power available from an engine will decrease with increasing ambient temperature. Although a generator may operate happily at 40°C or more, the power available from the engine may be reduced.”

Author: Petya Asgarova

22/06/2015 09:30:00
Listed in : Key parts of a generator  
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