IN AUGUST 2007 ENERGY POWER CONSULTING ENGINEERS UNDERTOOK AN ASSIGNMENT FOR BOOKER TATE TO INVESTIGATE THE TECHNICAL ASPECTS AND THE ASSOCIATED COSTS IN CONVERTING TOWER HILL SUGAR FACTORY FROM 3300 VOLTS, 50HZ TO 4150 VOLTS, 60HZ. The conversion was in preparation for the new the cogeneration plant that was being built adjacent to the Factory. As the one of the distribution voltage levels on the Belize grid operates at 13800, 60Hz the new plant would be designed and built to match these levels. Tower Hill Factory had previously operated as an islanded factory disconnected from the national grid.
It was recommended that the 50 to 60 Hz conversion at be undertaken over a phased period with initial capital expenditure for electrical power and control equipment to be spent during Phase 1 of the project. Phase 1 had to be completed by the start of the 2009/2010 grinding season
It was also recommended that the injection water pump station be upgraded during Phase 1 of the project to improve the reliability of injection water supply. Advantages were identified in upgrading the B-Station Centrifugals from pole-changing motor drives to Variable Voltage Variable Frequency (VVVF) drives which were namely:
Overall station capacity enhancement due to increase in number of cycles per hour.
Reduction in power consumption per machine cycle from 2.5 kWh/Tonne of massecuite for a pole-changing drive to1.2 kWh/Tonne of massecuite for VVVF drive.
Technological enhancement as a consequence of installing VVVF drives leading to improved electrical reliability
Similar advantages were not identified on the Plantation White (PW) and A Batch centrifuge machines. Because of their age, it was likely that these machines would be due for as this was when the cogeneration plant was coming online.
In order to establish the true initial capital expenditure, it was strongly recommended that equipment specifications be prepared and preliminary designs be undertaken immediately so as to obtain equipment pricing from potential suppliers and manufacturers.
With initial capital expenditure estimated to be significant, it was recommended that new power transformers connecting the factory and new cogeneration plant be supplied with dual secondary windings, one rated at 4150 volts and the other at 3560 volts. In so doing, some of the existing larger drives in the factory would remain until replaced or rewound but in the interim, would operate at a marginally higher voltage of 3560 volts, 60 Hz. At this voltage level and frequency, the volts/hz ratio of 59 closely aligned the original ratio of 66.
It was recommended that the existing main medium voltage switchboard in the factory powerhouse be divided into two sections with one dedicated to the new voltage level of 4150 volts, 60Hz while the other be used for the intermediate voltage of 3560 volts.
Potentially cheaper than replacing or modifying gearboxes of gantry cranes, it was recommended that variable speed drives be considered although any change-out would need to be checked with specialist crane engineering companies to ensure that serviceability and operation was not compromised.
Planned grinding mill modification from steam turbine to electro-hydraulic drives was considered significant. Discussions with potential suppliers should also include the intended mill control philosophy and the integration thereof into the overall factory automation control specifically for the cane preparation and Milling Train.
Similar advantages were not identified on the Plantation White (PW) and A Batch centrifuge machines. Because of
their age, it was likely that these machines would be due for replacement in the short-term to improve throughput and
therefore it was recommended that the PW be upgraded with new pole-changing motors and the A batch machine motor be rewound.
It was suggested that the phased transition from 50 to 60 Hz would not only bring about an overall improvement in electrical equipment standards but also improve the reliability of machinery and personnel safety.
It is recommended that any future equipment or design for the conversion to 60Hz should ensure that it is compatible with the longer - term strategy of the factory control system.
It was recommended that the new electrical shredder drive consider the effects of power swings due to its very nature of operation (Subsequent power studies undertaken by Energy Power Consulting Engineers modeled the effects of the shredder motor starting and accurately determined the peak power during start-up and the impact this would have on the new cogeneration plant).