Line Protection Operate Time: How Fast Shall It Be?

Abstract

An ultra-high-speed protective relay has been an important topic within the scientific community, and specifically within the power industry, for decades. The main drivers are the anticipated improvements in power system stability and power transfer capability which have become even more important with the increased penetration of renewable generation sources. The relay operate time is a relatively small part of the required improvement, since the circuit breaker interrupting time contributes the major part of the total fault clearing time. The first promising results in reducing the fault clearing time, from two or three cycles, down to one power system cycle, date back to 1976 when the relay operate time of 1.5 ms was achieved. Availability of sub-cycle breakers was anticipated in the early 1980-s. Nevertheless, almost forty years later, commercially viable ¾ cycle breakers are still not available and their impact on the total fault clearing time has been omitted from most of the literature. The numerical relays operate time improvement has become the only goal and results are wrongly equalized with improvements in the total fault clearing time and directly correlated with improvements in power system stability. In this paper the real benefits of ultra-high-speed relay operate time are analyzed, considering the characteristics of the state-of-the-art circuit breakers and their interrupting time of 1.5-2 power system cycles (older circuit breakers are slower). A more holistic view, including interactions between protective relays and circuit breakers, as well as final benefits to utilities, is given in the paper.

Numerical Investigation of the Use of Electrically Conductive Concrete-Encased Electrodes as Potential Replacement for Substation Grounding Systems

“…For the square ECON-EE section with a 266.7 mm side, the values obtained are 0.45 s and 0.83 s for body weights of 50 kg and 70 kg, respectively, and they increase to 0.66 s and 1.21 s for the ECON-EE square section with a 520.7 mm side. These values remain significantly higher than a typical fault clearing time of 40 to 90 ms, considering a breaker opening time of 2 to 5 cycles and a relay operating time of half a cycle, as mentioned in [33], and significantly higher than the duration of a lightning strike. Finally, for the step voltage (Figure 14), although the values of the step voltage obtained with the ECON-EE square sections are higher than the values obtained for the copper grid with vertical rods, the ECON-EE values remain lower than the values recommended by the IEEE Std 80 for a current fault duration of up to 3 s. In these figures, the touch and step voltages obtained for ECON-EE square sections with 266.7 mm and 520.7 mm sides and for the copper grid with vertical rods are also represented for comparison.…”

A Novel Passive Over-Current Trip Device for Seismic Resilience

“…However, due to the high dependence of power supply, there is a significant risk of failure of high-voltage circuit breakers when there is a disruption to the power supply. Such a risk would impose on modern microprocessor-based digital relays, solid-state relays and recently invented travelling-wave relays because they all rely on external power supplies to operate [5]. Solid state relay (SSR) is an electronic relay that controls semiconductor switches, allowing for either open or closed actions when external power supplies are applied to its control terminals [6].…”

“…Moreover, the duration of the fault clearing strongly affects power system stability. The decrease of fault clearing time reduces the synchronous generator rotor acceleration during the fault, consequently help to maintain power system stability [5]. With the increased penetration of renewable energy resources (RES), the need of a high-speed breaker is in urgent demand because the reduced inertia further increases the system acceleration during a fault.…”

Time-Domain-Based Distance Protection for Transmission Networks: Secure and Reliable Solution for Complex Networks

“…The recent literature highlights how the unusual fault characteristics of inverters result in incorrect tripping of phasor-based distance relays, characterized by missing in-zone faults and tripping for out-of-zone faults [13,14]. Moreover, the operating time of distance protection is between 0.75 to 1.5 cycles [15] which is high compared to ideal fault detection decision time of half cycle [19,20,39].…”

“…Moreover, these methods may not be reliable for fault occurring near voltage zero crossing point and faults near to busbars (close-in faults), since successive TW reflections can reach the IED location within a time less than the sampling interval adopted in TW filtering techniques [18]. In [19,20], it is further analyzed that the reduction in fault detection time can only result in a modest (~13%) improvement in the average fault clearing time. This improvement comes with the added risk of compromised protection security, due to chances of operating for momentary disturbances that never develop to real faults [20,39].…”