Influence of Converter-based Power Sources on the Distance Relay under System Asymmetrical Faults

Advanced Protection Schemes of Modern Transmission Grids with Large-Scale Power Electronics

“…Clearly, the relay tends to over-reach during resistive faults under this control mode. Meanwhile, the above over-or under-reaching issue becomes worse for a fault scenario with larger fault resistance [105]. The above trends are also true for the L-G fault AG studied in Figure 2-19.…”

“…This is because of the transmission angle for the real power transfer across the line, which in turn causes the angular difference of the two-sided currents. This issue becomes even severer for the distance relay installed at terminals of a power transmission grid connecting FCGs [105]. Because the real power output from FCGs is adjustable according to the active power transfer requirement during fault conditions in various Grid Codes.…”

“…Because the real power output from FCGs is adjustable according to the active power transfer requirement during fault conditions in various Grid Codes. The apparent impedance seen by the distance relay 𝑅 1 can be expressed as [105],…”

“…However, the 'virtual' reactance 𝑖𝑚𝑎𝑔𝑖𝑛𝑎𝑟𝑦 (1 + 𝐼 ̇𝑟 𝐼 ̇𝑠) 𝑅 𝑓 will produce the error in Xdirection due to the angular difference between 𝐼 ̇𝑟 and 𝐼 ̇𝑠 . In theory, the apparent impedance of the distance relay at FCG-based plant side can be either tilted up or down [105]. Because the Grid Codes from different countries follow different regulation requirements during grid faults [31,106].…”

“…In addition, one can see that the relay over-or underreach under the L-G fault is slighter than the L-L fault situation. This benefits from the evident zero-sequence current during a L-G fault [105]. On the other hand, the influence of the FCG penetration level on distance protection is tested.…”