Table of Contents
Prime mover- Prime mover are Mechanical machines that convert primary energy of a fuel into Mechanical Energy
What is Prime mover
Electrical energy is produced by electric Generators from Mechanical energy. Prime movers Generate Mechanical energy. The primary energy of a fuel or fluid is Transformed into Mechanical energy by prime movers, which are Mechanical devices. Another name for them is “Turbines or engines.” Coal, gas, oil, and nuclear fuel are the common fossil fuels used in prime movers.
In essence, thermal energy is created when the fossil fuel is burned in a Combustor. A working fluid then absorbs thermal energy and Transforms it into Mechanical energy within the prime mover.
Steam is the working fluid for coal or nuclear fuel Turbines, but it is the gas or oil in combination with air, in gas turbines, diesel, or internal combustion engines.
On the other hand, water from an Upper-level Reservoir’s potential energy could be Transformed into kinetic energy that strikes a Hydraulic turbine’s runner, changes direction and Momentum, and Generates Mechanical work at the turbine shaft as it rotates against the electric generator’s “braking” torque when the load is electric.
Wave energy is similarly converted into mechanical work in special tidal Hydraulic turbines. Wind kinetic energy is converted into mechanical energy by wind turbines.
A complete Classification of prime movers is very difficult due to so many variations in construction, from topology to control. However, a simplified one is shown below
Basic prime mover generator system
In general, a prime mover or turbine drives an electric generator directly, or through a transmission. The prime mover is necessarily provided with a so-called speed governor (in fact, a speed control and protection system) that properly regulates the speed, according to electric generator frequency/power curves.
The reference speed (frequency)/power curve.
It should be noted that the turbine is equipped with a servomotor, which opens one or more control valves to regulate the flow of fuel (or other fluid) through the turbine, thereby regulating the mechanical power at the turbine shaft.
A fairly accurate Measurement of the turbine shaft speed is made, and it is compared to the reference speed. The Servomotor is then controlled by the speed controller to open or close control valves and change speed. The reference speed Fluctuates. When power is increased to the rated value in AC power systems with parallel generators, a speed droop of 2% to 3% is permitted.
The speed droop is required for two reasons as follows:
- With a few generators of different powers in parallel, fair (proportional) power load sharing is provided.
- When power increases too much, the speed Decreases accordingly signaling that the turbine has to be shut off.
The point A of intersection between generator power and turbine power is statically stable as any departure from it would provide the conditions (through motion equation) to return to it.
|Coal or nuclear fuel
|Up to 1500 MW/unit
|Electric power systems
|Gas or oil
|Gas (oil) + air
|From watts to hundreds of MW/unit
|Large and distributed power systems, automotive applications (vessels, trains and highway and off-highway vehicles), and autonomous power sources
|Gas turbines Diesel engines Internal combustion engines Stirling engines
|With rotary but also linear reciprocating motion
|Up to 1000 MW/unit
|Large and distributed electric power systems, autonomous power sources
|Medium- and low speed >75 rpm
|Up to 10 MW/unit
|Distributed power systems, autonomous power sources
|Wind or wave turbines
|Speed down to 10 rpm