The first American sea port was founded in 1606 when Samuel de Champlain sailed into the harbour at Gloucester, Massachusetts. Since that time, ports have become everything from simple docks, to break-bulk terminals, to massive and fully automated container terminals. Every one of these facilities requires electricity to operate. This paper discusses ideas and issues associated with providing electrical power to these facilities.
Types and sizes of electrical loads
In commercial electrical distribution there are two main components to consider, ‘Demand’ and ‘Usage’. Most people can relate to usage since that is what a typical residential electric bill represents. Usage; a measure of the energy consumed over time, is measured in kilowatt-hours (kWh). Demand is the measure of power, or energy per unit of time, and is measured in watts (W) or kilowatts (kW). For example, a typical light bulb is rated in watts. The demand for a 100 watt bulb is just that, 100 watts. If the bulb is energised for 10 hours the usage is 1000 watt-hours or 1 kWh. The distinction between usage and demand is important as utility companies must provide enough capacity in both power plants and infrastructure to meet the peak demand, otherwise brown-outs or black-outs can occur.
Figure 1 provides a comparison of typical entities and their electrical demand. These figures come from various sources and are presented for comparative purposes only.
Types of electrical service
Electrical service has three major classifications – Low Voltage (up to 600V), Medium Voltage (1kV to 35kV[1]), and High Voltage (69kV and higher). In addition to the voltage classification power is also either delivered as single-phase or three-phase. There are cost and reliability issues associated with each class of service. Each utility provider has unique requirements and offerings to handle the cost and reliability issues associated with each class of service.
Power is delivered overhead and/or underground. High-voltage is problematic underground especially over long distances and is typically cheaper to run overhead. Distribution voltages (medium or low) can be overhead or underground. Overhead typically has a lower first cost but has the added risk for wind damage and the poles being knocked down by trucks or other yard equipment. Overhead lines are not generally accepted in container yards due to the inherent safety risk of accidental contact by containers being lifted from below. Underground distribution is less affected by weather and vehicular impact but is initially more costly and requires additional up-front planning to avoid other underground utilities and to ensure adequate capacity and room for expansion. Locations of port facilities are often in rural or undeveloped areas with little or no electrical infrastructure in place. Initially the available single-phase power line is adequate to support the lights and guard shack. As a facility plans to expand, the available capacity of the utility provider must be considered (often augmented) to support the expected demand of the new facility. Frequently a Certificate of Convenience and Necessity (CCN) must be obtained along with an Environmental Impact Study (EIS) before a utility provider will extend or expand service. In most cases these are very long, 1-2 year, lead-time items. The cost of these items, also non-trivial, is typically borne by the requestor. The methods for calculating the cost of service is likely as varied as the number of service providers. The tariffs vary based on the amount of power purchased, the voltage at which it’s purchased, and the peak demand required for the facility. Generally speaking it is cheaper to buy power at higher voltages. Reasons for this include: the amount of equipment between the owner and the transmission network is reduced, the amount of power being purchased is large, and there is only one Point of Common Coupling (PCC) to be metered. However, in order to purchase power at medium or high voltage the facility must make an investment in a distribution system that accepts this level of service. Bundled into the equation for the cost of power are two additional factors for consideration: reliability of service and maintenance, including mean time to repair. Many port facilities that evolve based on need have many PCC’s (meters) as it is impractical to do anything other than have the utility provider set another meter to provide power to the required location.
Reliability of Service
The high voltage transmission network in the United States is very reliable. The catastrophic failures that make the news are based on human error and lack of generation capacity rather than the network. This network is the backbone of ‘the grid’ and is designed to be trouble-free. The towers are tall, broad, well supported structures located in large swaths of cleared area to remove any potential interference by the forces of nature or man. Compare this to the single line running down the road on wooden poles, stretching across driveways, just clearing the top of the trucks running underneath. Therefore the closer the PCC is to this backbone the more reliable the connection will be. The time to restore service, in the unlikely event of a failure, will also be as short as possible because restoring this line first is required in order to restore the downstream lines. Just as cost and reliability are more favorable at higher transmission voltages, distribution costs are also affected by the distribution voltage. Transmission typically refers to the utility-owned side of the PCC, while distribution refers to the client side. In a residence the PCC is the meter. The utility company is responsible for everything outside a building including the transformer to provide the proper voltage, and the owner is responsible for everything inside including the panel, breakers, lights, and outlets. The main reason for raising the distribution voltage is to reduce the size and cost of the cables running from one point to another. Power (watts) is the product of voltage (V) and current (I). For a constant load, as voltage increases, current decreases, and vice versa. Every cable connecting a piece of equipment to a panel has a loss associated with it. The loss takes the form of heat and is a function of the resistance of the cable. The resistance is a function of the length and the cross-sectional area of the cable. Losses are a function of the square of the current. Therefore, the best way to reduce these losses is to lower the current by increasing the voltage. There is a cost trade-off between the reduced size of the cable needed for higher voltage and the specialised insulation required for high voltage cables. Two common distribution voltages that are easily manageable in underground and overhead configurations are 12.47kV and 13.3kV. As electrical demand in container terminals increases, distribution systems utilizing 33kV or 35kV will become more prevalent.
Substation – Own or Lease
Depending upon the selected distribution voltage and the voltage being provided by the utility the substation requirements will vary. The Port of Houston’s Bayport terminal for example buys power at 138kV and has an extensive substation to manage distribution.
Owning and maintaining a high voltage substation can be a daunting task. Many factors should be considered when deciding how to proceed in this arena. Some utility providers identify a substation as ‘everything required to get from the transmission voltage to the distribution voltage’. Other providers make the distinction between a switchyard, which contains the transmission side switches and breakers, the transformers, and the substation which contains only the medium or low voltage distribution equipment. These distinctions come into play when the
division of cost and responsibility are discussed. A complete substation is expensive. A 25 MW substation could easily reach the USD 10M mark. Perhaps the more concerning issue is that of maintenance. If the utility owns the substation then they bear the burden of maintaining it. They keep the spares, equipment and manpower necessary for this task. They also control the tariff the port pays for electricity and in some cases if the substation is dedicated in whole or in part to the port a separate lease fee will be negotiated. Some utility providers will not allow customer owned equipment on the high voltage network and require full control of the switchyard. The customer may have full ownership of the transformers and distribution network. When making the lease vs. buy decision the port must consider the lead time of major components that may fail, however unlikely, and have a plan to mitigate the downtime due to the failure. Additionally the customer that owns the substation controls their own destiny in terms of response time to a failure as opposed to relying on the utility company. In both scenarios, capacity planning and growth must be planned well in advance. Regardless of who owns the substation, significant expansion will be a slow process. The exception to this is when the port has foreseen the growth and designed and implemented the system such that additional capacity can be added rather quickly.
Reliability & Redundancy
The cost of downtime for port operations will vary greatly with the type of port facility being studied. For a simple break-bulk operation losing power during the day may have absolutely no impact on the loading or unloading process. Conversely a container terminal that loses power to its dock cranes during the loading process is very aware of the costs being incurred during outage. As the port defines the electrical infrastructure required the cost of downtime must be a major factor. While the utility providers may provide redundancy in the grid there is no guarantee of service and it falls completely on the port to make sure operations are maintained to the necessary levels in the event of a failure. Figure 2 shows a topology for a port with dock cranes, refrigerated container support, buildings and lights. In this topology there is redundancy in every major electrical component. In the event of a failure power can simply be re-routed and operations will continue. This ‘loop’ topology allows the port to continue to operate while replacement s are ordered and installed. This scenario does not preclude the need for uninterruptable power supplies and standby generators to protect critical and sensitive computer equipment during the time required to reconfigure the switches. This scenario further assumes that the entire operation can be supported by a single utility feed and a single transformer. This configuration does not preclude the port from using the capacity of the second transformer but does limit the capacity that can be delivered in an emergency situation.
Summary
Some ports need little power, having but a few lights for security, while others surpass the power needs of Disneyworld™. The path from one extreme to the other can be complex with many items to be considered. Some of the key questions to be answered include:
How much power is required?
Where will the power come from?
How reliable is the power?
How much will it cost?
How much redundancy is required?
The port authority that recognises the complexities of electrical service installation and expansion and has the ability to plan for the current needs as well as future growth is in a much better position to successfully grow and prosper.