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SOLUT IONS
— Load Shedding
The Tmax XT has many load shedding algorithms to avoid power unbalance in low voltage plants and to reduce stress for all the components.
Purpose The Tmax XT embeds patented functions based on load shedding which reduce the microgrid stress in all situations. Typically, it is the main protection trip unit of the low voltage microgrid located at the interface point with the medium voltage grid that is able to control the plant in all circumstances. A microgrid under islanding conditions After the Tmax XT circuit-breaker opens, due to the in- terface protection system intervention or external command, the microgrid should seemlessly pass from an on-grid to off-grid state. When it operates in a stand-alone capacity, the power absorption from the main grid ceases, so that the microgrid loads remain supplied by local generation, such as from a diesel GenSet or an energy storage system. This microgrid generation can be always active or started by Auto- matic Transfer Switching (ATS) logic after the discon- nection from the main grid, depending on the plant configuration. During the islanding transition, it is very important to avoid a frequency drop, otherwise the generation protections could trip and jeopardize the microgrid stability with a consequently long downtime. The Tmax XT employs current and voltage measurements, and integrates two different fast load shedding types of logic to reduce this blackout risk. This protects the microgrid during intentional or unin- tentional islanding operations: • The Basic Load Shedding algorithm is a simple form of logic able to recognize the microgrid disconnec- tion event and shed a group of not priority loads thus ensuring a fast time response and power bal- ance. • The Adaptive Load Shedding algorithm is an ad- vanced algorithm available with the Tmax XT as an enhancement of the basic version. The intelligent software embedded in the unit sheds the non-pri- ority loads very quickly according to the microgrid power consumption and frequency measurements. Moreover, the software has a dedicated configura- tion for backup generation related to Automatic Transfer Switching (ATS) and the software itself is even able to estimate the energy produced by a so- lar plant based on the plant geography settings.
Load Shedding is available on the Tmax XT platform sharing some information about the loads under control in the plant. Application examples • Grid-connected plants with running GenSets These contribute to self-consumption together with potential renewable sources and support the load power supply in emergency conditions. This is the case for hybrid photovoltaic diesel remote communities connected to weak distribution grids where there are a lot of daily faults, or facili- ties located in geographical areas where there are frequent environmental events, for example hurri- canes or earthquakes. • Grid-connected plants with back-up GenSets These are started up after main generator trans- fer switching logics and require high reliability. For example, hospitals, banks or data centers.
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