Remedial Action Schemes (RAS) are designed to monitor and protect electrical systems by automatically performing switching operations in response to adverse network conditions to ensure the integrity of the electrical system and avoid network collapse.
Typical automatic remedial actions include:
Generator tripping for reduction of energy input to the system
Tripping of load, insertion of braking resistors, series capacitors, opening of interconnecting lines and system islanding
Remedial Action Schemes (RAS) are often applied to large power systems for control of the system during severe abnormal conditions when traditional localized control is inadequate. Recent events such as 9/11, Hurricane Katrina, Tsunamis, and others have shown that now more than ever, complete backup RAS control centers are essential to disaster recovery.
RAS systems are typified by large numbers of diverse communication paths providing real time information from a wide geographic area. The communications paths are usually a mix of every media available from lease circuits, to audio circuits, to dark fiber, and recently, IP networks. These communication systems are all designed to transport data from substations and deliver it in real time to a single site for use by the RAS control computers. Traffic from the control centers to the substations allows control of the power network.
In planning a second control center, the issue of delivering the same information to two geographically separated sites at the same time becomes paramount. Today technology allows the users to meet the challenge to accomplish this with a minimum of impact on field equipment while using the existing communications paths. The use of modern IEDs can minimize the equipment needed to collect the field data and to transport the variety of processed or raw information needed for operation of RAS.
The amount of raw data available in a power system can easily overwhelm the bandwidth available to communicate it back to the control center. The GARD 8000® RAS module provide ways to reduce the amount of raw data by pre-processing it prior to transmission. It can prove to be very inefficient to transport all of the raw data only to combine the various values after the data arrives at the control center. If the mathematical combination and simplification can be done at remote sites, the required communication bandwidth is reduced.
Once mathematical capabilities are introduced at the measurement sites or substation level, data can be normalized so that all of the variability in collection methods and sensors is isolated from the control center. Localized changes only need to be normalized to the previously expected values, thereby eliminating any impact on the control center programming.
The RAS action is generally performed by a central controller. The controller needs data collected by field units; the GARD 8000® RAS Module. The field units are capable of measuring currents and voltages and/or transducer quantities (W, VAr) and deliver these to the central unit for evaluation and comparison with data from other points in the power system. The GARD 8000® also acts as a remote controller, such as performing breaker operations via programmable logic and inputs/outputs when a command is received from the central unit.