Power Flow Control Solutions for a Modern Grid Using SMART Power Flow Controllers. Kalyan K. Sen
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СКАЧАТЬ in electrical engineering. A controller, also referred to as a compensator, is a general term to describe a regulator that regulates voltage, current, phase angle of a line voltage, resistance, reactance, impedance, and so on, directly or indirectly in an electric circuit. A controller can be designed to perform a task (e.g. voltage regulation) and/or multiple tasks with varying cost and complexity. In the simplest term, a SMART Controller is what one procures is based on what one needs. A SMART Controller is an evolving technology that uses the best technical features from all previous concepts to meet the present need by blending functional requirements with the most cost‐effective solution. A SMART Power Flow Controller (SPFC) enhances the power flow controllability in electric power transmission and distribution systems. It is recommended that utilities choose a solution that meets their need in terms of reliability, robustness, cost‐effectiveness, component non‐obsolescence, efficiency, ease of relocation, and interoperability.

      Electricity flows freely from a higher potential to a lower potential. If two or more lines with different impedances are connected in parallel, the current in each line is, in some form, inversely proportional to the respective line impedance. This free flow of electricity might take longer paths to reach its destination and cause unwanted power losses in the lines. Additionally, this free flow may cause some transmission lines to be overloaded or underloaded. If the impedance of a line is larger compared to that of the lines connected in parallel, the current and the resulting power flow through the higher‐impedance line is lower compared to that in the neighboring lines, and vice versa. Therefore, power flow in a line is, in some form, inversely proportional to the impedance of the line.

      Transmission Reliability Margin (TRM) – the amount of Transmission Transfer Capability (TTC) needed to ensure that the interconnected transmission network is secure under a reasonable range of uncertainties in system conditions. These uncertainties may result from the following:

      1 Simultaneous limitations with a parallel path.

      2 Reservations for unscheduled flow, i.e. loop flow.

      3 Reservations for unplanned transmission outages, i.e. for paths in which contingencies have not already been included in the calculation of TTC.

      TRM does not include reservations for planned outages and other known transmission conditions, which have been included in the calculation of TTC (Minimum of {Thermal Limit, Voltage Limit, and Stability Limit}).

      Capacity Benefit Margin (CBM) – the amount of TTC reserved by the load‐serving entities to ensure access to generation from interconnected systems to meet generation reliability requirements. These reservations may include the following:

      1 Transmission reserved by the Control Area Operator to accommodate operating reserves (spinning and supplemental). Such operating reserves may not exceed NERC and WECC applicable pool requirements or individual members’ reliability requirements.

      2 Transmission reserved for the import of ancillary services (such as spinning reserves) from another control area.

      3 Transmission reserved for generation patterns and generation contingencies. These patterns and contingencies must be based upon reasonable, publicly available assumptions subject to evaluation in applicable dispute resolution proceedings.

      According to “Available Transfer Capability Definitions and Determination,” North American Electric Reliability Council, June 1996, TTC is defined as

      (1‐1)

      Available Transfer Capability (ATC) is a measure of the transfer capability remaining in the physical transmission network for further commercial activity over and above already committed uses. Therefore,

      Inadequate management of reactive power and line voltage caused the blackout. Most of the recent power network blackouts have been related to line voltage collapses, which tend to occur from lack of reactive power supports in heavily stressed conditions, usually triggered by system faults. One of the ways to improve the reliability of the line when faced with similar occurrences would be to regulate the effective impedance of a line between its two ends with an Impedance Regulator (IR), which is also known as a Power Flow Controller (PFC).