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Spotlight

Synchrophasors for Smart Systems

Wed, 02/19/2014 - 13:31

In the last two years SEL has implemented, together with CFE, several projects to prevent blackouts and improve management of the electrical power system all over Mexico. Mauricio Toache, Director General of SEL Mexico, explains the company has been promoting synchrophasors, which seek to understand a system’s parameters by measuring electrical variables on an electricity grid. CFE is using synchrophasors in different locations and making decisions based on their measurements as this makes it possible to design and implement a smart system that makes decisions, speeding up processes.

A synchrophasor characterises the electrical parameters on an electricity grid, using a common time source for synchronization. The basic synchrophasor system building blocks are formed by GPS satellite synchronized clocks, phasor measurement units (PMUs), a phasor data concentrator (PDC), and visualization software. Multiple PMUs provide synchronized phasor measurements from across an interconnection to a PDC which collects and aligns the data for analysis. Synchrophasors are used for real-time situational awareness, disturbance recording and analysis, wide-area monitoring and control, high-precision state estimation, system model verification, and island detection, among its many other applications. Satellite synchronized clocks allow time-stamped measurements that enable data to be aligned on reference time base, providing an accurate and comprehensive view of a power system. The advantage of synchrophasors is that they allow the dynamic measurement of the system’s state in real-time and enable a snapshot view of the power system as a whole.

PRACTICAL APPLICATION OF SYNCHROPHASORS

Mexico began exporting electricity to Guatemala in 2010, with the transmission of 120MVA. The power system in Guatemala is part of the long, interconnected network in Central America that runs from the south of Mexico to Panama. A 400kV line from the Tapachula substation in Mexico to the Los Brillantes substation in Guatemala interconnects the Mexican power grid with the two power systems. A power transformer takes the voltage level down to 230kV, which is the SIEPAC (Central American Electrical Interconnection System) transmission voltage level. The transmission system in Guatemala distributes the imported power to the local loads, but mostly wheels the power from Mexico to the SIEPAC system via the Ahuachapan substation in El Salvador. One of the challenges of operating the interconnected system is complying with the security requirements of interconnection with Mexico. In the past, the link with Mexico was not allowed to operate during certain periods of the day when the system was more prone to instability. These limitations to operation were not in the best interest of Guatemala’s AMM (Wholesale Market Administrator) as downtime in the link to Mexico threatened to compromise the security of the Guatemalan power system. Unstable active power oscillations between Guatemala and El Salvador on November 27, 2011, among other occurrences that ended in blackouts, prompted AMM to find the proper tools to guarantee the stable operation of the power system. AMM realized the potential that synchrophasors presented in providing information and as flexible tools to operate the power system in stable conditions.

AMM now monitors the operation of the Guatemalan power system using supervisory control and data acquisition (SCADA) systems and synchrophasors. A traditional SCADA system is in operation supplying pertinent data to the operators every 4 seconds. AMM operators also have access to visualized, real-time synchrophasor data, which are updated 30 times per second. The faster rate allows the operator to view and recognize transients never before seen in the SCADA system. Preexisting but invisible phenomena are now visible and actionable due to low latency and the simultaneous measurement of information (data coherence). This overcomes data collection limitations associated with typical SCADA client-server communication. One example is the recovery of the power system after a transmission line fault. Operators can now visualize the power oscillations, generation trips, and power flows in the interconnection lines

The coherent nature of the synchrophasor measurements allows the implementation of both simple and sophisticated algorithms. A simple algorithm, for example, is the sum of two active power quantities measured from different nodes on the network. With traditional SCADA measurements that are not synchronized, mathematic operations using less reliable measurements are questionable. One of the direct benefits of synchrophasors has therefore been to satisfy the Mexican power system requirements, helping Guatemala prevent interconnection limitations as stated above. They have ensured the secure operation of the Mexican power system and have prevented the unwanted oscillation associated with the Central American system. With this scheme in service, the interconnection between Mexico and Guatemala no longer has restrictions during certain moments of the day, providing Guatemala and the rest of the Central American countries with a more stable power system and additional energy resources.