Contemporary power systems comprise a huge share of investment. The systems of electric power involve distribution, transmission, generation of electric energy. The development of power systems has contributed to very advanced networks expanded across vast areas (Makwana & Bhalja, 2016). In this regard, the appropriate functioning of an up-to-date power system is highly relevant upon the effective running of the transmission lines. Modern ultra-high voltage (UHV) and extra high voltage (VHV) transmission lines are at risk of adverse weather conditions. Consequently, they are probably to be exposed to myriad of electrical faults (Jena & Pradhan, 2011). In case where the faults are not removed or detected faster, then they can be a source of power system instability, which leads to shut down of huge parts of the network or the entire network. Nonetheless, the outcome and causes of faults can be reduced by running the power systems in an appropriate manner and utilizing refined protective relays.
Digital distance relays are normally utilized for the safeguard of extended UHV and EHV transmission lines. Largely, a conservative digital distance relays determines the resident end currents and voltages of the transmission lines to measure the error impedance and moves the line in case the fault impedance is below the fixed impedance (Kasikci, 2018). However, for a huge resistance solitary line-to-ground error, the digital distance relay measure the fault impedance that is not comparative to the impendence of the problematic area of the transmission line due to the existence of fault resistance in that path. Digital distance relay is a non-unit network of safeguard providing large technical and economic advantages (Kumar & Jena, 2017). Contrary to neutral and phase overcurrent protection, the major benefits of this type of relay are that its fault handling of protected circuit is fundamentally self-regulating of source impedance differences (Izykowski, Rosolowski & Saha, 2015).
a) Types of distance Protection (Quad and Mho)
The distance relay aspects can be formulated to adhere to a series of diverse operating standards polygonal characteristics, mho, reactance, and plain impedance can be distributed. Currently, most manufactures provide a chance of either quadrilateral (quad) or circular (mho) characteristics (Makwana & Bhalja, 2016). Precisely, a mho relay is a top-speed relay and is commonly referred to as the admittance relay. Furthermore, using this relay, the function torque is acquired by the volt-amperes aspects and the managing component is established owing to the voltage portion. It suggests that a mho relay is a guiding relay, which is controlled by voltage. Kumar & Jena, (2017) argued that the mho element utilizes the voltage and current assessed at the relay to decide if the ostensible impendence schemes within the mho features. The assessment is completed by making comparison between different angels of the operating amount (IZ-V) and the polarizing amount (V, where V=IZf). In cases, the angle is equal to or below 900, then the impedance of fault Zf plots inside the characteristics, while the function would generate an output (Kumar & Jena, 2017). On the other hand, if the angle is more than 900 then Zf is outside the features and no output will be generated.
The mho relay’s operates in circular form and its diameter is virtually independent of V, and I with the exception of low magnitude of the current and voltage when the effect of the spring is considered which forces the diameter to reduce. The circle’s diameter is demonstrated by the equation as K1 / K2 = ZR (representing the ohmic relay setting) (Jun-ying, Yao-yu, Gang, Lang-feng & Yan-fei, 2011).
The relay functions in case the impedance observed by the relay inside the circle (Kasikci, 2018). The operating features indicate that circle moves via the origin that ensures that the relay is obviously directional. Since the relay is certainly directional, features demands only a pair of associates that forces it to become fast tripping to clear faults and minimize VA loads on a transformer for the current. The angle of impedance of the safeguarded line is usually 700 or 600 (Jena & Pradhan, 2011).
Quad features demand minimal processing power, especially in converted relays having overcurrent beginning. The comparator of phase angle utilizes current and voltage phases acquired through the Discrete Fourier Transform (DFT) technique. It consumes higher processing power although it offers operators with other advantages (Makwana & Bhalja, 2016). The perfect relay must have the capacity to offer characteristics shapes for every impedance loop which accomplish the best submission solution.
The only benefits of the quad characteristics as compared to the mho are that it can offer higher resistive handling. For phase-to-earth errors, the resistance of the fault in overhead lines is 1-200 ohms without earth wires. In this respect, mho cannot pr