Numerical relay
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In utility and industrial
Description and definition
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. A digital protective relay may also be called a "numeric protective relay".
Input processing
Low
quantities.Only the fundamental component is needed for most protection algorithms, unless a high speed algorithm is used that uses subcycle data to monitor for fast changing issues. The sampled data is then passed through a low pass filter that numerically removes the frequency content that is above the fundamental frequency of interest (i.e., nominal system frequency), and uses Fourier transform algorithms to extract the fundamental frequency magnitude and angle.
Logic processing
The relay analyzes the resultant A/D converter outputs to determine if action is required under its protection algorithm(s). Protection algorithms are a set of logic equations in part designed by the protection engineer, and in part designed by the relay manufacturer. The relay is capable of applying advanced logic. It is capable of analyzing whether the relay should trip or restrain from tripping based on parameters set by the user, compared against many functions of its analogue inputs, relay contact inputs, timing and order of event sequences.
If a fault condition is detected, output contacts operate to trip the associated circuit breaker(s).
Parameter setting
The logic is user-configurable and can vary from simply changing front panel switches or moving of
The relay may have an extensive collection of settings, beyond what can be entered via front panel knobs and dials, and these settings are transferred to the relay via an interface with a PC (personal computer), and this same PC interface may be used to collect event reports from the relay.
Event recording
In some relays, a short history of the entire sampled data is kept for oscillographic records. The event recording would include some means for the user to see the timing of key logic decisions, relay I/O (input/output) changes, and see, in an
Data display
Digital/numerical relays provide a front panel display, or display on a terminal through a communication interface. This is used to display relay settings and real-time current/voltage values, etc.
More complex digital relays will have metering and communication protocol ports, allowing the relay to become an element in a
Comparison with other types
By contrast, an electromechanical protective relay converts the voltages and currents to magnetic and electric forces and torques that press against spring tensions in the relay. The tension of the spring and taps on the electromagnetic coils in the relay are the main processes by which a user sets such a relay.
In a solid-state relay, the incoming voltage and current wave-forms are monitored by analog circuits, not recorded or digitized. The analog values are compared to settings made by the user via potentiometers in the relay, and in some case, taps on transformers.
In some solid-state relays, a simple
History
The digital/numeric relay was invented by George Rockefeller.[2] George conceived of it in his Master's Thesis in 1967–68 at Newark College of Engineering.[3] He published his seminal paper Fault Protection with a Digital Computer [4] in 1969. Westinghouse developed the first digital relay with the Prodar 70 [5] being developed between 1969 and 1971. It was commissioned in service on a 230kV transmission line at PG&E's Tesla substation in February 1971 and was in service for six years.[6] In 2017, George received the IEEE Halperin Electric Transmission and Distribution Award.[7] The award was for "pioneering development and practical demonstration of protective relaying of electric power systems with real-time digital computer techniques." George was chairman of the IEEE Power System Relaying and Control (PSRC) committee (1981-1982) as well as a member of the "Computer Relaying Subcommittee" which was created by the PSRC in 1971 and disbanded in 1978. He wrote the foreword for the PSRC tutorial on Computer Relaying produced in 1979.
In 1971 M. Ramamoorty was the first to describe [8] calculation of impedance for distance protection using discrete Fourier analysis.
The first practical commercially available microprocessor based digital/numeric relay was made by
Protective element types
Protective elements refer to the overall logic surrounding the electrical condition that is being monitored. For instance, a differential element refers to the logic required to monitor two (or more) currents, find their difference, and trip if the difference is beyond certain parameters. The term element and function are quite interchangeable in many instances.
For simplicity on one-line diagrams, the protection function is usually identified by an
A listing of device numbers is found at
- 11 – Multi-function Device
- 21 – Distance
- 24 – Volts/Hz
- 25 – Synchronizing
- 27 – Under Voltage
- 32 – Directional Power Element
- 46 – Negative Sequence Current
- 40 – Loss of Excitation
- 47 – Negative Sequence Voltage
- 50 – Instantaneous Overcurrent (N for neutral, G for ground current)
- 51 – Inverse Time Overcurrent (N for neutral, G from ground current)
- 59 – Over Voltage
- 62 – Timer
- 64 – Ground Fault (64F = Field Ground, 64G = Generator Ground)
- 67 – Directional Over Current (typically controls a 50/51 element)
- 79 – Reclosing Relay
- 81 – Under/Over Frequency
- 86 – Lockout Relay / Trip Circuit Supervision
- 87 – Current Differential (87L=transmission line diff; 87T=transformer diff; 87G=generator diff)
See also
References
- ^ "Schweitzer Programmable Automation Controller". Schweitzer Engineering Laboratories. Archived from the original on 9 September 2015. Retrieved 21 November 2012.
- ^ "George Dorwart Rockefeller - Engineering and Technology History Wiki". ethw.org. May 2018. Retrieved 2019-02-13.
- ^ Rockefeller, George D. (1968-05-31). Fault protection with a digital computer (MS thesis). Newark College of Engineering.
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- ^ "IEEE Herman Halperin Electric Transmission and Distribution Award". Institute of Electrical and Electronics Engineers (IEEE).
- .
External links
- "Understanding Microprocessor-Based Technology Applied to Relaying" Working Group Report, IEEE Power System Relaying Committee
- Abdelmoumene, Abdelkader; Bentarzi, Hamid (23 June 2017). "A review on protective relays' developments and trends". Journal of Energy in Southern Africa. 25 (2): 91–95. .
- http://www.scielo.org.za/pdf/jesa/v25n2/10.pdf A review on protective relays' developments and trends
- Video that explains overcurrent protection testing: https://www.youtube.com/watch?v=bQ6fZrrP0H4