Lab Report 1.pdf

4 procedure basic operation of hvdc transmission

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4. PROCEDURE: Basic operation of HVDC Transmission system 1. Turned on the power supply and set the voltage control knob to 100% 2. In HVDC Transmission System Control window, the firing angle of bridge 1 (rectifier) was slowly decreased to 0° in order to increase the bridge 1 DC voltage to maximum value. In the metering window, It was observed that the dc line current I dc (I2) was approximately zero because of the conduction of the thyristor was not
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, delayed (i.e. firing angle is 0°). Thyristor will conduct only after certain turn on delay time (t on ) . The turn on delay time means the time interval between the application of gate signal and conduction of thyristor. During that interval, current was null. So that current will flow after the t on. 3. Set the firing angle of bridge1 to 15° to decrease the bridge1 dc voltage slightly below the maximum value, which was a typical setting because it allows the effect of ac voltage fluctuations on the system operating point. 4. Decrease the bridge2 dc voltage by slowly decreases the firing angel of bridge 2, which causes the dc line current I dc (I2) to increase. Increase the dc current till it reaches the maximum value, which was given in Table 1. Voltage (V) Frequency (Hz) DC line current I dc (A) 240 50 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Table 3. Values of the DC line current I dc When the DC line current Idc was high, the firing angle of bridge2 was 146° 5. Set the DC line current I dc to each of the value listed in Table1 by varying the firing angle of bridge2. For each DC line current, record the system parameters in Data table. The System parameters were firing angle of bridge 1 & 2, DC line current and voltage, active power, reactive power and DPF. DC current (A) (I2) DC voltage (V) (E2) Firing angle bridge1 Firing angle bridge 2 Active Power (W) Reactive Power (VAR) DPF bridge 1 DPF bridge 2 0.15 298.9 15 156 69 157.9 0.95 0.92 0.2 297 15 154 64 148 0.95 0.91 0.25 295.8 15 153 54 124.4 0.94 0.89 0.3 294.3 15 151 49.3 102.8 0.94 0.88 0.35 292.9 15 150 45.4 103.2 0.95 0.87 0.4 292 15 149 31.6 71.3 0.94 0.86 0.45 290 15 147 27.4 62 0.95 0.84 0.5 289 15 146 25.8 59.7 0.94 0.83 Data Table 1. Varying the firing angle of bridge2 at constant bridge1 firing angle 15°
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, 6. According to the recorded data, by decreasing the firing angle of bridge2, the dc current was increasing . So that dc current flowing through transmission system can be varied by firing angle of the bridge2 (inverter) and thus the amount of power transferred to be adjusted. To operate an HVDC transmission, system operating point was required. The point where the voltage-current relations of the rectifier and inverter bridges intersect was considered to be the operating point and it was done by varying the firing angles of thyristor bridges 1 and 2. 7. The firing angles of the converter station1 and converter station2 were adjusted to operate respective station as rectifier and inverter. The Polarity of voltage and power on both transmission line and the ac side of converter station1 were positive. The voltage at the bridge 2 was also positive polarity even if it operates as an inverter. It was because of the bridges in converter stations 1 and 2 were connected in opposite directions . Therefore,
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