The signals may be initially input to several simultaneous sample-and–hold circuits before multiplexing, or the time relationship between successive samples must be known if the phase relationship between signals is important. Numeric relays take the input analog quantities and convert them to numeric values. These might include: The accuracy of the measured values can only be as good as the accuracy of the transducers used such as VTs CTs, and the A/D converter. [info]It then has the capability to act as a disturbance recorder for the circuit being monitored, so that by freezing the memory at the instant of fault detection or trip, a record of the disturbance is available for later download and analysis. With the experience gained with static and digital relays, most hardware failure mechanisms are now well understood and suitable precautions taken at the design stage. A digital protective relay may also be called a "numeric protective relay". Typical functions that may be found in a numerical relay other than protection functions are described in this section. button manually or via the system interface (SCADA or DCS). The digital protective relay is a protective relay that uses a microprocessor to analyze power system voltages, currents or other process quantities for the purpose of detection of faults in an electric power system or industrial process system. If suitable VTs are used, supervision of the VT/CT supplies can be made available. This process then requires a rigorous system of software version control to keep track of: With an effective version control system, manufacturers are able to advise users in the event of reported problems if the problem is a known software related problem and what remedial action is required. Numerical relays, on the other hand, operate on digitized secondary signals. As with earlier generations of relays and according to market segmentation, manufacturers offer different versions, each with a different set of functions. parts hence accurate operation. The content is copyrighted to EEP and may not be reproduced on other websites. The first numerical relays were released in 1985. The task of entering the data correctly into a numerical relay becomes a much more complex task than previously, which adds to the possibility of a mistake being made. Substation LAN is integrated with fiber optics to compete with the communication capacity. Finally, as well as tripping the CB as required under fault conditions, it can also be arranged for a digital output to be used for CB closure, so that separate CB close control circuits can be eliminated. To understand simply it is like a brain in our human Numerical relays All numerical relays utilize so-called sampling technique of the input current and voltage signals. used. The Unlatch The digital signal processor (DSP) in a numerical relay normally can handle both the relay protection function calculations and general management of the relay such as HMI and I/O. Numerical relays perform many more functions than earlier generations of relays so testing them is more complex. The distinction between digital and numerical relays is particular to Protection. Advantages of Numerical Relays: Numerical relay consists of many functions in one relay thus replace many traditional relays with one. change the entire settings of the relay by simply changing Group setting. Gives entire details of fault Frequent configuration is not needed. These protocols helps to communicate relays among Numerical relays are natural developments of digital relays due to advances in technology. The argument against putting many features into one piece of hardware centres on the issues of reliability and availability. trip command given Fault levels are significantly different on parts of the network that are energized under normal and emergency generation. No maintenance is needed like For more information on the different types of disturbance recording, read this technical article. The values that the relay must measure to perform its protection function have already been acquired and processed. Advantages of Numerical relays 1. relays is communication between relays and other equipment in the network is Analogue signals are converted to digital form using an A/D converter. It is also called numerical relay. As CTs and VTs for protection functions may have a different accuracy specification to those for metering functions, such data may not be sufficiently accurate for tariff purposes. Numeric relays are programmable relays. 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