From Practical Power System Protection
9.8 The Future of Protection for Distribution Systems
With the second generation of microprocessor relays now available, the emphasis is on the broader use of the protection relays as data acquisition units and for the remote control of the primary switchgear. Protection relays continuously monitor the primary system parameters such as current, voltage, frequency, etc. as part of the protection function of detecting faults. Since faults seldom occur, protection relays are expected to fulfill the protection requirements for a very small portion of their lifetime.
By utilizing the protection relays for other duties during the periods when the power system is normal, it permits integration of the various systems such as protection, supervisory control and data acquisition and results in savings on other interface components such as measuring transducers for current and voltage, meters, circuit breaker control interface, etc.
Improvements in digital communications by means of optical fibers allow the information available at the relay to be transferred without interference to the substation control level for information or event recording.
The following information is typically available from the relay:
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Measurement data of current and voltage
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Information stored by the relay after a fault situation
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Relay setting values
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Status information on the circuit breakers and isolators
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Event information.
The communication link to the relay can also be used for control purposes:
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Circuit breaker open/close commands
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Remote reset of the relay or auto-reclose module
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Changes to the protective relay settings.
Figure 9.26 shows the components of an integrated protection and control system...
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