Transmission lab manual pages, Lab Reports of Electrical Engineering

Download Transmission lab manual pages and more Lab Reports Electrical Engineering in PDF only on Docsity! Department of Electrical Engineering, FEST, Indus University, Karachi Electrical Power Transmission (Lab Manual) Page 15 LAB NO 02 Manipulation of the Performance of an overhead Transmission Line in Matched-Load Operation OBJECTIVES Upon successful completion of this experiment, the students will be able to:  Measurement of current and voltage relationships of an overhead line in matched-load operation.  Interpretation of the terms characteristic wave impedance, lagging and leading operation, efficiency and transmission losses. THEORY: This operating case is present when the transmission line is terminated (i.e. matched) by an ohmic consumer resistance equivalent to the characteristic impedance. The power transmitted in this case is called natural load. The line current is just large enough for the reactive power consumption of the line inductor and capacitance to cancel; the transmission line thus does not require any external reactive power for operation. As, in this case, the active power losses in transmission are minimal in real transmission lines (i.e. low-loss), this is to be viewed as the optimum case. However, the load on a system changes constantly according to the performance of the consumers. Operation with natural load thus seldom occurs. When the current in the transmission line changes, the reactive power balance is disturbed. If the current is lower, the line acts capacitive. If the current increases, the line has an inductive performance. In both cases, the active power losses increase in real transmission lines. If the voltage at the beginning of the line is kept constant, an increase in the voltage may be noted at the line end lagging operation (cf. no- load as limiting case).The voltage at the line end drops in leading operation (cf. short- circuit as limiting case). In order to guarantee the consumer a constant voltage, the voltage must be regulated at the supplying transformer in the case of changing system loads. The load capability of overhead transmission lines (i.e. the thermal limit rating) is significantly higher than the natural load. In practical operation, the overhead transmission lines are most often loaded in Leading mode. Department of Electrical Engineering, FEST, Indus University, Karachi Electrical Power Transmission (Lab Manual) Page 16 In matched-load operation, the transmission line is terminated with an ohmic resistance having the value of the characteristic impedance. The consumer current I2 is in-phase with the voltage U2. EQUIPMENTS: 1 IT 6017 Three-phase power supply unit 1 IT 6019 Power circuit breaker 1 IT 6003 Three-phase transformer 1 IT 6002 Overhead line model 1 IT 6004 Resistive load 2 IT 6035 Moving-iron ammeter (2, 5 A) 2 IT 6037 Moving-iron voltmeter (600 V) 1 IT 6048 Power meter CONNECTIONS: Fig. 2.1 Block Diagram of Transmission Line Department of Electrical Engineering, FEST, Indus University, Karachi Electrical Power Transmission (Lab Manual) Page 19  Leaving the resistive load unchanged to the approx value of the characteristic wave impedance (R5 = 213 ohm)) measure voltage and current at both ends of the line for all possible supply voltage, which can be set on the secondary side of the three-phase transformer. OBSERVATION TABLE: 2.2 In case of matched load only the active power is transmitted so, in accordance with the equation: Calculate the total active power P1 at the start end and the total active power P2 at the end of the line. Calculate the line transmission losses: And the line transmission efficiency: Department of Electrical Engineering, FEST, Indus University, Karachi Electrical Power Transmission (Lab Manual) Page 20 CALCULATION: Department of Electrical Engineering, FEST, Indus University, Karachi Electrical Power Transmission (Lab Manual) Page 21 Since the line and the load form a series circuit the ratio of the transmission power converted in the two elements and thus the efficiency are independent on the magnitude of the supply voltage. However, if a constant power is supposed to be transmitted, then a higher supply voltage would be more favorable, because the line losses drop as current decreases. Note: In real overhead lines corona losses also arise, which have a slight negative effect on the efficiency. Furthermore, the value determined above only applies for the exceptional case of matched load. Department of Electrical Engineering, FEST, Indus University, Karachi Electrical Power Transmission (Lab Manual) Page 24 LAB NO 3 To Mend and Measure the Performance of an overhead Transmission Line in ohmic-inductive load OBJECTIVES Upon successful completion of this experiment, the students will be able to:  Measuring and interpreting the current and voltage ratios of a transmission line with mixed ohmic-inductive and pure inductive loads.  Interpreting the current and voltage ratios of a transmission line with mixed ohmic-inductive and pure inductive loads. THEORY: Transmission line possesses resistance R, inductance L, leakage conductance G and capacitance. All low voltages overhead lines having length up to 80 km are categorize as short line. In a short line, the shunt capacitance C and shunt conductance G are neglected. The series resistance R and series inductance for the total length of the line is considered. A single phase supply line is short in length and operates at low voltage. It has two conductors. Each conductor has resistance R1 and inductance L1. The inductance is affected equivalent to the inductive reactance X1=2pifL1. A balance three phase circuit consisting of three separate identical single phase circuit therefore the calculation for balance three phase line are carried out in similar manner as singe phase line, the difference being that per phase base is adopted. In this line all the given voltages are line to line values that all the current are line current. However, the load on a system changes constantly according to the performance of the consumers. When the current in the transmission line changes, the reactive power balance is disturbed. If the current is lower, the line acts capacitive. If the current increases, the line has an inductive performance. In both cases, the active power losses increase in real transmission lines. If the voltage at the beginning of the line is kept constant, an increase in the voltage may be noted at the line end lagging operation (cf. no- load as limiting case).The voltage at the line end drops in leading operation (cf. short- circuit as limiting case). In order to guarantee the consumer a constant voltage, the voltage must be regulated at the supplying transformer in the case of changing system loads. Department of Electrical Engineering, FEST, Indus University, Karachi Electrical Power Transmission (Lab Manual) Page 25 Loads that power electrical motors are inductive loads. These are found in a variety of household items and devices with moving parts, including fans, vacuum cleaners, dishwashers, washing machines and the compressors in refrigerators and air conditioners. In contrast to resistive loads, in a purely inductive load, current follows a sinusoidal pattern that peaks after the voltage sine wave peaks, so the maximum, minimum and zero points are out of phase. EQUIPMENTS: 1 IT 6017 Three-phase power supply unit 1 IT 6019 Power circuit breaker 1 IT 6003 Three-phase transformer 1 IT 6002 Overhead line model 1 IT 6004 Resistive load 1 IT 6005 Inductive load 1 IT 6048 Power meter 1 IT 6049 Power factor meter 2 IT 6035 Moving-iron ammeter (2,5 A) 2 IT 6037 Moving-iron voltmeter (600 V) EXPERIMENT PROCEDURE: Step 1: Assemble the circuit in accordance with the foregoing topographic diagram, Set primary-side of the three-phase transformer in delta connection 380 V and using bridging plugs set the secondary-side to star UN + 5%. Step 2: Insert all bridging plugs connecting the capacitance to overhead line model. Step 3: To end terminals of line connect a three-phase balanced ohmic-inductive load: Step 4: Set the load resistance value to R1 and begin with the value L4 = 1.27 H of the inductive load. Step 5: Starting at R1 value reduce the resistance value in steps to R3, R4 and R5 in that order. Step: 6 For each step measure the following quantities: voltage U1, current I1, active power P1 and reactive power Q1 at the beginning of the line, and voltage U2, current I2 and cos_2 at the line end. Department of Electrical Engineering, FEST, Indus University, Karachi Electrical Power Transmission (Lab Manual) Page 26 Fig. 3.1 Circuit Diagram of ohmic-inductive load Department of Electrical Engineering, FEST, Indus University, Karachi Electrical Power Transmission (Lab Manual) Page 29 At Inductive load: L5 = 0.9 H. Table: 3.5 observations At Inductive load: L6 = 0.64 H. Table: 3.6 observations Note: The inductive load also consumes an active power due to ohmic resistance and iron losses of the inductor Department of Electrical Engineering, FEST, Indus University, Karachi Electrical Power Transmission (Lab Manual) Page 30 Task: A current-voltage vector diagram for the case of a mixed ohmic inductive load with power factor of 0.8. Note: (The operating capacitance of the line is disregarded here).) Department of Electrical Engineering, FEST, Indus University, Karachi Electrical Power Transmission (Lab Manual) Page 31 Review Questions:- Q1: What is the Effect of increase in capacitive and inductive load on Apparent Power. ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ Q2: What is the effect of change in inductive and capacitive load on VR ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ Q3: What is the change in Voltage drop when inductive and capacitive loads are varied ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ Q4: Write down the change in Power factor and angle in all cases ? ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ Q5: How overhead transmission line are classified? ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ Q6: What is the effect of load power factor on regulation and efficiency of a transmission line? ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________