How We Deliver Power to You

The steam generating units are the foundation units of our generating system, and are often referred to as the “base load” units. The process of electricity generation via the steam generating units is as follows:

Heavy-duty oil is taken from a bulk storage tank (typically 25,000 barrel capacity) and is supplied to a fuel pumping and heating set. At the pumping and heating set this fuel oil is heated to approximately 220°F in order to reduce its viscosity, and to enable it to burn easily. The heated fuel oil is pumped under pressure (approximately 250 psig) to the furnace of a steam generator (boiler) where it mixes with a large volume of air and is burnt. After combustion takes place a large volume of high temperature gas (approximately 2400°F) is released. The heat, which is now available, is transferred to very high purity de-mineralized water contained in hundreds of tubes, which form part of the construction of the boiler. The water is converted into high temperature and high-pressure steam through different stages of boiling and super heating within the confines of the boiler tubes. This high pressure, high temperature steam then passes through a main steam pipe to the turbine. (The turbine is a device used to convert the heat energy contained in the high pressure temperature steam into mechanical energy.) The turbine shaft is connected to the rotor of an electric generator and causes this rotor to rotate at high speeds. Coils of wire (field windings) are embedded into the rotor of the generator through which direct electrical current is allowed to flow. As this current flows, a strong magnetic field is formed. This rotating magnetic field is allowed to interact with another set of wires (stator coil), which are in this case stationary. It is this interaction of the magnetic field with the stationary wires that produces electricity.

Renewable energy is high on our agenda. We boast eight hydroelectric plants among a mix of generating units, which contribute approximately 23 megawatts to the grid. The hydro plants are: Upper White River, Lower White River and Roaring River in St. Ann, Rio Bueno A and Rio Bueno B in Trelawny, Maggotty in St. Elizabeth, and Rams Horn and Constant Spring in St. Andrew.Power is generated by harnessing the stream flow of a river and using its Potential Energy due to the difference in height between its level and the center of the turbine. A hydro-turbine converts the Potential Energy of the water to Mechanical Energy.Hydroelectric generation is an inexpensive and environmentally friendly way of producing electricity. Hydro power plants do not burn fuel to produce electricity; therefore, the associated costs are not subject to increases resulting from rising fuel prices. However, the effectiveness of hydro units depends largely on the availability of water and the quality of the stream flow.

We have a Power Purchase Agreement (PPA) with Wigton Wind Farm Limited, as part of our commitment to support the development of renewable energy. Electricity is purchased from the wind farm, which is located at Wigton, Manchester. The wind farm consists of twenty-three 900-kilowatt strategically placed wind turbines with an estimated capacity of 20.7 Megawatts (MW) of power.Power is generated as wind turn windmills that are advantageously placed on the Manchester hills. This too is an inexpensive and environmentally friendly way of producing electricity. However, the effectiveness of these units depends on the consistency of the wind flow.

We also produce additional energy through the use of gas turbine engines. These gas turbines, which utilize relatively expensive oil to produce electricity, are used primarily at those times in the day when energy demand is at its peak.

The newest addition to our generating fleet is the 120-megawatt combined cycle plant at the Bogue Power Station in Montego Bay.The Bogue plant consists of three individual units: two combustion turbine generating units with a total capacity of 80 megawatts and one 40-megawatt steam generating unit. The two combustion turbines operate on diesel fuel but are capable of converting to natural gas at any point in the future. Heat from the exhaust of both these combustion turbines is harnessed to produce steam by way of two heat recovery steam generators that are used to drive a steam turbine capable of producing an additional 40 megawatts.Combined cycle technology is recognized internationally as one of the most advanced and efficient means of generating electricity. This technology allows for greater efficiency of conversion, that is, it utilizes less fuel to generate each unit of electricity relative to the Company’s other generating units. The result: reduced fuel costs to JPS, and ultimately to you our valued customers.