M.SERV. SOCIALES ESTE REVISION DE SISTEMA POR

For most utilities, real-time monitoring systems provide up-to-date information on major substation equipment and some transmission line conditions. However, this is not true for most distribution facilities.

EPRI and the Tennessee Valley Authority have identified several requirements for advanced condition sensors, such as devices that determine the instantaneous condition of switches, cables, and other grid components.

They have found that first of all, costs must be low for the sensors, including their installation and maintenance. Second, inspections must be easily implemented, with special attention to hard-to-access locations, such as energized conductors on structures and inside cabinets. Third, the sensors must be small in size and secure from damage. Finally, they must not create problems related to electromagnetic compatibility (EMC).

Table 2 describes some advanced utility monitoring systems that are either commercially available or are currently under development.

Goverment Series: Smart Grid

Table 2: Advanced Utility Monitoring System

Advanced Utility Monitoring System

System Description

Wide-area monitoring system (WAMS) See Figure 5

x GPS-based phasor monitoring unit (PMU).

x Measures the instantaneous magnitude of voltage or current at a selected grid location.

x Provides a global and dynamic view of the power system, automatically checks if predefined operating limits are violated, and alerts operators.

x Provides a global view of disturbances, as shown in Figure 5.

x Compares generator operation points to allowable limits to keep generators in a safe state.

x Tracks inter-area, low-frequency power oscillations and presents results to system operators; also used to tune damping controllers.

x Combines phasor data with conventional SCADA (supervisory control and data acquisition) data for enhanced state estimation.

x The Consortium for Electric Reliability Technology Solutions is one of several groups striving to develop WAMS technology for North America.

x Of the many sensing and measurement technologies currently under development, WAMS may have the greatest potential for enabling grid reliability improvement.

Dynamic line rating technology See Figure 6for an example

x Measures the ampacity of a line in real time.

x The Power Systems Engineering Research Center has sponsored development of a computer program that calculates line sag and current-carrying capacity in real time using inputs from both direct and indirect measurements.

x One university, with support from the National Science Foundation and a local utility, plans to develop a wireless network for dynamic thermal rating of a line at a target cost of $200 per sensor; this would allow the determination of dynamic thermal line rating for all spans, eliminating the need to identify a critical span.

Conductor/

compression connector sensor

Image courtesy of EPRI.

x Measures conductor temperature to allow accurate dynamic rating of overhead lines and line sag, thus determining line rating.

x Measures temperature difference between conductors and conductor splices.

x Interrogation via helicopter, ground, BPL, or wireless.

x Battery-free.

x Unique serial number tied to asset GPS location.

Insulation

x Continually monitors leakage current and extracts key parameters.

x Critical to determining when an insulator flashover is imminent due to contamination.

x Clip-on, wireless, battery-free.

x Unique identification number.

x On-board storage of key parameters.

x On-board storage of solar power.

x Ability for interrogator to reset data.

Advanced Utility Monitoring System

System Description

Backscatter radio technology

Image courtesy of EPRI.

x Provides improved data and warning of transmission and distribution component failure.

x Communicates data back to a substation or other data collection point.

x Small, low cost, reliable.

x Battery-free, with minimal electronics and long service life.

x Radiation-free for reduced EMC concerns.

x Uses inexpensive, off-the-shelf components.

x Always “awake,” enabling fast inspection speeds.

Electronic instrument

transformer x Replaces precise electromagnetic devices (such as current transformers and potential transformers) that convert high voltages and currents to manageable, measurable levels.

x Fiber-optic-based current and potential sensors, available from several venders, accurately measure voltage and current to revenue standards over the entire range of the device.

Other monitoring

systems x Fiber-optic, temperature-monitoring system: Provides direct, real-time measurement of hot spots in small and medium transformers, thus addressing utility concerns about the safety and reliable operation of high-voltage equipment.

x Circuit breaker real-time monitoring system: Measures the number of operations since the last time maintenance was performed, as well as operation times, oil or gas insulation levels, breaker mechanism signatures, etc.

x Cable monitor: Determines changes in buried cable health by trending partial discharges or through periodic impulse testing of lines.

x Battery monitor: Minimizes battery failure by assessing cell health, specific gravity liquid level, cell voltage, and charge/discharge characteristics.

x Sophisticated monitoring tool: Combines several different temperature and current measurements to dynamically determine temperature hot spots; measure dissolved gases in oil; evaluate the high-frequency patterns and signatures associated with faulty components and report the health of transformers and load tap changers in real time.

x Many of these systems are commercially available.

Table 2: Advanced Utility Monitoring System

Goverment Series: Smart Grid

Figure 5: This sample image of a WAMS record-and-replay function display provides a global view of disturbances. Graphic under IEEE copyright.It appeared in the article, “WAMS Applications in Chinese Power Systems” in the IEEE Power & Energy Magazine, V4:1 (Jan/Feb 2006). Image courtesy of IEEE Power and Energy Magazine.

Figure 6: A real-time rating characteristic. Historically, line ratings have been based on assumed static conditions, but in-service conditions can differ substantially from those assumptions. This figure illustrates the dynamically increased power rating achievable with actual conditions provided by tower-mounted weather stations, line tension monitors, and/or visual cameras. Image courtesy of EPRI.

Advanced Protection Systems

In the past, more than 70 percent of major system disturbances have involved protective relaying systems, not necessarily as the initiating event but as a contributor to the cascading nature of the event. Today, products to reduce this problem are increasingly available. Compared to the electromechanical and analog relays of the past, new digital relays include many value-adding functions, such as fault location, high-impedance distribution fault detection, more sophisticated transformer and bus fault detection, self checking

diagnostics, adaptive relaying and greater use of networked digital communications. As these new digital devices continue to be deployed throughout the grid, reliability will be significantly enhanced.

Table 3 describes two advanced protection technologies.

Advanced Protection System

System Description

Fault-testing recloser x Applies a very fast, low-energy pulse to the line to determine if a fault is still present.

x Minimizes damage caused by reclosing into faulted lines.

x Significantly reduces damaging fault-current and voltage sags on the faulted line and adjacent feeders.

x Substation transformers experience fewer through-faults, thus extending service life.

x Cables, overhead conductors, splices, and terminations experience less thermal and mechanical stress from through-fault currents.

Special protection

system x Real-time monitoring of key generation assets or transmission lines and their associated power flows.

x Upon a change of status (like loss of generation and/or loss of transmission), a pre-programmed set of actions takes place (e.g., wide-area load shed, generator redispatch, separation of interties).

x Allows power transfers across the grid that would not comply with single or multiple contingencies under normal criteria.

x Allows operators to load transmission lines closer to thermal limits or beyond normal voltage or system stability limits.

Table 3: Advanced protection systems

R

R

D

Research and development will support the integration of the sensing and measurement capabilities discussed previously as they come to market. In addition to utilities, EPRI and various equipment vendors are actively engaged in important R&D efforts.

Table 4: Research and Development Related to Sensing and Measurement.

Research and Development Related to Sensing and Measurement

Name Description

The Consortium for Electric Reliability Technology Solutions (CERTS)

x Is working to accelerate meaningful opportunities for customers to participate voluntarily in competitive electricity markets.

x Studies focus on determining the effect of demand response on market efficiency and on demonstrating advanced demand-response technologies and strategies that will improve the reliability of the grid.

x Work on WAMS contributes to this key technology area.

Goverment Series: Smart Grid

Research and Development Related to Sensing and Measurement

Name Description

x Reliability-based vegetation management through intelligent system monitoring.

x Digital protection systems using optical instrument transformers and digital relays interconnected by an IEC 61850-9.2 digital process bus.

x Optimal placement of PMUs for state estimation.

The California Energy

Commission x Advanced metering design, costs, and benefits.

x Tariff design.

x The evaluation of dynamic rates and programs for small customers.

x The evaluation of DR programs for large customers.

Table 4: Research and Development Related to Sensing and Measurement

R

R

Customer metering has always fallen within the purview of state regulatory bodies. So, too, have the tariffs that determine how and what a customer will pay. Hence, a metering transformation cannot occur without the support and encouragement of these regulators.

The Energy Policy Act of 2005 (EPAct) is very clear in this regard. The following sums up the spirit of this new law:

It is the policy of the United States that time-based pricing and other forms of demand response, whereby electricity customers are provided with price signals and the ability to benefit by responding to them, shall be encouraged, and the deployment of such

technology and devices that enable electricity customers to participate in such pricing and demand response systems shall be facilitated, and

unnecessary barriers to demand response

participation in energy, capacity, and ancillary service markets shall be eliminated.

The law is also very proactive in requiring electric suppliers to employ advanced metering and communications technology. It will certainly motivate regulators to more seriously address the need for these technologies.