effects of the current transformer saturation? Results: The saturation of transformers occurs when the peak and bottom points is just about to become flat, as shown in Fig.1 and Fig.2. And the flux in the core of the transformer is shown in Fig.3. After the saturation, the voltage waveform becomes distorted and harmonics are located at the frequencies which are odd times fundamental one, i.e. three, five, seven and nine times. As the number grows up, the peak value drops from 0dB to -36dB, as shown in Table 1. Harmonics 1st 2nd 3rd 4th 5th Frequency 50 150 250 350 450 Peak 0 -19.2 -24 -34.4 -36 Table 1 Harmonics of CT
Figure 1 Before Saturation Figure 2 Under Deep Saturation Figure 3 Plot of flux in transformers 1.5.2 Short-circuit studies and fault estimation The second part of the lab session examines various faults across a radial transmission and distribution system. The cases of three-phase, single-phase and phase-to-phase faults are simulated in this experiment.
1.Three-phase faults on unloaded systems: Connect Line 2 (0.15pu) from the transmission line selection to the grid supply and to the distribution transformer DTX1 and configure a three-phase fault at point F3 (TP20) on the secondary side of the distribution transformer. Set the fault timer to 0.5 sec. In the beginning of this experiment, the recordings are shown in Table 2: MeterMLBV/V106.8209.9212.4I/mA109.7288.8339P/W6.8847.0657.77Q/var19.243.59110.88pf0.3380.4550.463lagginglagginglaggingTable 2 Recordings before the experiments •Apply the fault at TP20 by closing the fault CB. Measure and note the currents and voltages in the relay that tripped because of the fault. •Repeat the three-phase fault experiment for faults at F2 (TP17) and F1 (TP2). Record the respective measurements from the respective relays. D1B(TP20) D1A(TP17) TP2 fault duration/ms 280 300 CB op time/ms 26 35 Relay trip time/ms 249 260 Ia/A 27.45 26.15 81.02 Ib/A 30.58 28.82 82.3 Ic/A 30.79 25.28 80.65 Vab/V 3.032 1.63 Vbc/V 3.483 1.676 Vca/V 3.182 1.544 Table 3 Fault recoding at TP20, TP17 and TP2
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- Power System Relays