Electric power generators can be classified in one of three ways depending on their mode of operation: continuous, prime, or standby. Continuous and prime power generators are very similar as they function as the main source of power and are designed to operate continuously or for extended periods of time. The major difference between the two is that continuous generator sets are designed to operate continually with a consistent load while prime generators are designed to operate for long durations at variable load. The other type of generator – standby/emergency – are to be run only when there is an outage to the utility grid or the main source of power in a backup situation.
Continuous and prime generators are primarily used in remote locations such as mining and oil and gas operations, construction, ships, etc., where there is no access to the grid to supply electric power. These are also used when there is a limitation on the amount of electric power that can be drawn from the grid. In rare cases, it may also be cheaper to generate power through a diesel generator than to buy electric power from the grid. On the other hand, the need for standby power arises when there is a temporary disruption in the primary supply of electrical power, such as when your main grid goes out from a storm.
Like any other machinery running continuously for long hours, continuous or prime generators also need to be rugged to handle the heavy loads supported by them. Additionally, these units have to be able to handle friction between moving parts for longer periods of time and also handle sustained heat generation. This leads to prime generators being more expensive than generators of similar capacities used for standby or backup support.
There are several features that need to be incorporated in continuous power diesel generators to make them function efficiently over long periods of time. Some of these are detailed below:
1. Cooling Systems
A. Continuous/Prime Generators
(i) For the engine:
Prime generators typically have a large cooling system. Continuous fuel combustion in the engine causes enormous amounts of heat to be generated. This heat has to be removed by artificial means in order to prevent inevitable buildup of temperature. Engines are often cooled by circulating cooling water in a jacket around the engine. The circulating water absorbs heat from the engine and is in turn cooled by a large-sized radiator fitted with a fan. A cooling system is also required to cool lubricating oil. In very large industrial generators (2250kW and above), a cooling tower or other elaborate system is often required.
(ii) For the alternator:
The alternator is also subject to temperature rise due to continuous flow of current through the windings of the alternator. Therefore, the alternator needs to have heavy-duty winding. The alternator operates continuously to provide uninterrupted power supply. Therefore, there is no specific cooling time that can be allotted for the alternator to cool down naturally. The cooling system usually restricts the temperature rise of an alternator to 105oC.