AC electrical power is generated in power stations, usually far from end users. This power is then transported over long distances using high voltage and low loss transmission lines. High voltage is achieved by using step up transformers and is fed to the transmission lines. Similarly, at user end, step down transformers are used to provide power to the users. This is possible only by using transformers. Transformers are used for stepping up the voltage of the generator to values which are suitable for high voltage systems, for power exchanging between networks, for stepping down the voltages to the medium voltage level and then for feeding the power into the low voltage network. In this laboratory a three-phase transformer is investigated. It consists of three individual poles with different connection possibilities on the primary side and variable secondary voltage. Power transmission lines are used to transmit electrical energy from the power stations to the consumers. Advantage of three-phase systems is that it provides the consumers with two different levels of voltage, so that they can use their equipment in the best possible way. A three-phase model of an overhead power transmission line (with a simulated length of 360 km long, a simulated voltage of 380 kV and a simulated current of 1000 A) is used, with a scale factor of 1:1000. Transmission line characteristics are investigated under various load conditions. Circuit configurations are then connected for the demonstration of various neutral point connections in three-phase mains systems. Different voltage levels are used for transmitting power; the levels are determined by the amount of power and the distance; the higher the transmission voltages, the lower the currents as well as the transmission losses. However the network investment cost increases with the voltage. Asymmetrical short-circuits are also simulated. Other topics covered by this laboratory are reactive power compensation, the basic circuits of power engineering, series and parallel connections of operating equipment (lines, transformers), circuit involving the conversion of delta connections to star connections, circuit involving the conversion of star connections to delta connections, busbars, disconnectors, power circuit breakers, voltage and current transformers.
Experiments:
Three-Phase Transformer Experiments
- Determination of the vector group of the three-phase transformer.
- Determination of the voltage transformation ratio of the transformer operating at no-load.
- Determination of the current transformation ratio of the transformer operating with short-circuit.
- Determination of the equivalent circuit quantities based on the consumed active and reactive power.
- Measurement of the effect of the load type and magnitude on the performance of the secondary voltage.
- Determination of the efficiency of the transformer.
- Investigation of the zero-impedance of the three-phase transformer with various connection modes.
- Examination of the load capacity of the secondary side using a single-phase load with different connection modes on the primary side.
- Determination of the influence of a delta stabilizing winding.
- Demonstration of the possibility of utilizing a three-phase transformer in economy connection (auto-transformer).
Overhead Line Model Experiments
- Measurement of the voltage in no-load operation.
- Concept of operating capacitance.
- Line model with increased operating capacitance.
- Measurement of current and voltage relationship of an overhead line in matched-load operation, interpretation of the terms: characteristic wave impedance, lagging and leading operation, efficiency and transmission losses.
- Measurement and interpretation of the current and voltage ratios of a transmission line during a three-phase short-circuit.
- Measurement and interpretation of the current and voltage ratios of a transmission line with mixed ohmic-inductive and pure inductive loads.
- Measurement and interpretation of the current and voltage ratios of a transmission line with mixed ohmic-capacitive and pure capacitive loads.
- Investigation on the performance of a transmission line with isolated neutral point connection in the case of a fault to earth.
- Measurement of the earth-fault current and the voltage rise of the fault phases.
- Determination of the inductance of an earth-fault neutralizer for the overhead line model.
- Investigation on the performance of a transmission line with a fault and comparison of the current values with those determined during earth-fault with isolated neutral point system.
- Measurement of the fault currents of the results with those for a three-phase fault.
- Investigation on the effect of parallel compensation on the voltage stability at the load and the transmission losses of the line.
- Investigation on the effect of series compensation on the voltage stability at the load.
- Use of measurement techniques to determine the zero-phase sequence impedance of the overhead line model and comparison of this value with the theoretical one.
Alternator and Parallel Operation Experiments
- Measurement of the voltage distribution in the series connection of two lines without operating capacitance.
- Measurement of the voltage distribution in the series connection of two lines with operating capacitances.
- Measurement of the voltage distribution in the parallel connection of two lines without operating capacitances.
- Measurement of the voltage distribution in the parallel connection of two lines with operating capacitance.
