Gas Scheduling provides the link between customer demand and Gas Control’s operation of the system. It is the role of Gas Scheduling to receive nominations for gas onto the system and schedule them according to the pipeline’s various rules of operation. If nominations exceed system capacity, they are scheduled based on the priority rules set forth in the pipeline’s tariffs. Schedulers on interconnected pipelines and interconnected storage fields must also work together on a daily basis to determine how much gas can flow, and then to track ownership of the gas as it moves from one system to the next.
Scheduling gas on a pipeline is a complex task. In the past, when only a few parties held contracts to move gas, nominations were made with a paper nomination form and a fax machine. In today’s marketplace, with literally hundreds of entities owning space on a pipeline, nominations are made via internet access to a pipeline’s nomination system. Complexity in scheduling has also increased in recent years as pipelines now accept and process nominations throughout the gas day rather than once daily, which was the norm a few years back.
At various peak periods, a pipeline system cannot physically accept and deliver all the gas that customers have nominated. When this happens, the pipeline must schedule the available space according to predetermined priorities. Pipelines generally have two levels of priority: firm and interruptible. Firm customers are always scheduled first, followed by interruptible. If all firm nominations cannot be accommodated, they are generally reduced pro-rata (i.e. everyone’s nomination is reduced by the same percentage) to the capacity available on that day. Interruptible nominations are often scheduled based on price paid since interruptible service is frequently discounted. Priority rules for pipelines are spelled out in the pipeline’s tariffs.
Unlike pipeline schedulers who have a primary goal of fulfilling firm customers’ nominations and maximizing pipeline throughput, LDC schedulers are most concerned with ensuring all customers have adequate supply to fulfill their end-use demands. Thus, LDC schedulers generally schedule flows based on expected deliveries from upstream pipelines and/or local storage facilities and on forecasts of expected customer usage. It is the scheduler’s job to schedule the LDC system so that enough gas is available in the pipeline at a high enough pressure for all end-use customers to be able to use the amount of gas they desire (while, of course, maintaining the safety and integrity of the system). Like with pipelines, most LDCs offer both firm and interruptible services. In some regions this is called core (firm) and non-core (interruptible). On days when there is insufficient supply and/or pipe capacity to satisfy all needs, customers are curtailed in order of priority in the LDC tariffs.
If gas deliveries do not match forecast demand, schedulers may meet demands by drawing from line pack, withdrawing gas from storage or, as a last resort, imposing flow orders or curtailments. Like pipeline scheduling, LDC scheduling has become increasingly complex with the evolution of the gas industry. At one time, schedulers simply managed the gas utility’s own sources of supply and storage. Now schedulers must juggle deliveries from numerous marketers and independent storage fields as well as downstream fluctuations from huge power plants that are ramping up and down hourly based on electric market conditions.