Comparison Between Distance Element Method and High Speed Discriminating Method in Loss of Field Protection

If a synchronous generator loses its field, it will act as an induction generator and it absorbs reactive power from the power system, which might cause damages to the synchronous generator itself. Traditionally, distance relay with zone 1 and zone 2 mho circles are used mostly for synchronous generator loss of field protection. Zone 1 distance element has some delays and zone 2 distance element is instantaneous. The relay measures output current and terminal voltage at the synchronous generator terminal and calculates the internal impedance of the generator by looking into the synchronous generator at its terminal. The relay also stores the distance relay of the zone 1 distance element and zone 2 distance element mho circles and it continuously compares the calculated impedance with the mho circles. Once the calculated impedance falls within the zone 1 mho circle, the relay starts a timer and if the calculated impedance still falls into the zone 1 distance element mho circle after the timer times up, the relay will trip the generator. For the zone 2 distance element mho circle, a similar outcome will be obtained but with the only difference being if the impedance falls within the zone 2 distance element mho circle, the relay will trip the generator instantaneously. In 1979, a new method of synchronous generator loss of field protection was intriduced by D.C. Lee, P. Kundur and R.D. Brown in Ontario Hydro. It uses generator field voltage and terminal voltage as inputs. Once the field voltage reduces to a certain level, a timer starts and if the field voltage does not recover to its health level before the time relay ends, the loss of field protection trip condition 1 will be satisfied. Meanwhile, the generator terminal voltage is monitored as well. If the generator terminal voltage reduces to a certain level, the loss of field protection trip condition 2 will be satisfied. Once both of the two conditions are satisfied, the loss of field relay will trip. This thesis focuses on investigating the required tripping time of these two methods. As renewable energy generation is being called all over the world, this thesis also investigates to see the compatibility of such new high speed discriminating method with a wind farm renewable energy in parallel with the traditional synchronous generator. Following is the contributions of this thesis: Time difference between the traditional mho method and the high speed discriminating method on a single synchronous generator in loss of field protection. Time difference between the traditional mho method and the high speed discriminating method on a single synchronous generator in parallel with a wind farm in loss of field protection. Reactions of both methods when an out-of-step fault occurs in the system right at the joint bus of a synchronous generator and a wind farm. The power system is simulated in PSCAD v 5.0.1 (64-bit) environment. All data is handled and manipulated with Matlab 2022a (64-bit) version.

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