Lab Report 1.pdf

# Exchanged between a thyristor bridge and the ac

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exchanged between a thyristor bridge and the AC source to which it was connected. Reversing the direction of power flow on the transmission line 35. Increase the ac side of the bridge2 voltage to nominal value and set the firing angle of bridge1 to 165° to turn thyristor bridge1 into inverter. The DC line current was null because both bridge1 and 2 now acted as an inverter. DC current (A) (I2) DC voltage (V) (E2) Firing angle bridge1 Firing angle bridge 2 Active Power (W) Reactive Power (VAR) 0.08 78.91 165 165 0.669 0.012 Data Table 7. Bridge1 acts as an inverter 36.Set the buck-boost to -15% and 0% on the regulating autotransformer of station1 and station2 respectively. 37. Decrease the firing angle of the bridge2 and observed the DC line current. DC current would start flow when bridge2 starts to acts as a rectifier. Decrease the firing angle of bridge2 to 25°, so that DC line current should be equal to 0.4 pu. From now on bridge1 would act as an inverter and bridge2 as a rectifier.

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, DC current (A) (I2) DC voltage (V) (E2) Firing angle bridge1 Firing angle bridge 2 Active Power (W) Reactive Power (VAR) 0.281 -267.9 165 25 -43.55 -74.82 Data Table 8. Bridge2 acts as a rectifier and operating DC current at 0.4 pu 38. The Dc voltage was negative polarity due to bridge2 was reverse connected with respect to bridge1 , which means cathode of bridge2 was connected to the common anode of bridge1. The DC power was negative polarity because the current flows from station2 to station1 , which indicates that power was flowing from station2 to station1 . 39. Set the firing angle of bridge2 (rectifier) to so that the DC line current was approximately 0.7 pu ( 0.35A) DC current (A) (I2) DC voltage (V) (E2) Firing angle bridge1 Firing angle bridge 2 Active Power (W) Reactive Power (VAR) DPF bridge1 DPF bridge2 0.35 -268.8 165 22 -75.12 -191.2 0.97 0.91 Data Table 9. Vary the firing angle of bridge2 to make 0.7pu DC current The power transferred was -75.12W 40. The firing angle of bridge2 (inverter) was 22° and the DPF of bridge1 and bridge2 were 0.97 and 0.91 . Both DPF of bridge1 and bridge2 were acceptable . DPF values of 0.9 and above were generally acceptable. Higher the DPF , the lower the amount of reactive power exchanged between a thyristor bridge and the AC source to which it was connected. 41. The same amount (approx) of power transferred from bridge1 to bridge2 compared to the power flow from bridge2 to bridge1. 42. From the observation, the direction of power flow in an HVDC transmission can be reversed by selecting the proper transformer tap and adjusting the firing angle of the bridge in each station while maintaining a good DPF at both bridges.
, Effect of AC line voltage fluctuations at the rectifier bridge on the system operating point 43. Lowered the ac voltage in bridge2 (rectifier), which makes the DC current decrease rapidly. Set the firing angle of bridge2 (rectifier) to 25.3° so that DC line current was at 0.5 pu, which was 0.25.

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