Calculate the transformer losses when the resistor connected for all six cases (10V, 20V, 30V, 40V, 50V, and 60V). Explain any discrepancies between input power and output power. List the sources of losses in the transformer circuit.
EEE307 ELECTRIC ENERGY CONVERSION LAB 2 THE SINGLE PHASE TRANSFORMER 1.1.1 OBJECTIVE To study the voltage and current ratios of a transformer. 1.1.2 DISCUSSION All transformers exhibit the same basic properties. When mutual induction is permitted between two coils or windings, a change in current flowing through one coil induces a voltage upon the other coil. All transformers have a primary winding and one or more secondary windings. The electromagnetic coupling between the primary and secondary windings allows electrical energy to be transferred from the primary winding to the secondary winding. Electrical current entering the primary winding appears as an electromotive force (emf) at the secondary. Connecting the secondary winding to a load allows the energy to be transferred to the load. Since there is no electrical connection between primary and secondary windings (only a magnetic connection), the source and load can be electrically isolated from each other by means of a transformer. When a transformer is energized and loaded, AC current flowing in its windings creates an alternating magnetic field in its iron core. A small portion of the current, called the magnetizing current, is dedicated to the magnetic circuit in the creation of the magnetic field. Losses associated with the magnetizing current are reactive power (VARS). In addition, there are real power osses (Watts) the transformer, associated with the inherent resistance in the windings (copper losses) and with eddy currents and hysteresis in the core (iron losses). For these reasons, the total power delivered to the primary side of the transformer is always larger than the total power available at the secondary side. Even so, it is still reasonable to say that energy is conserved in the transformer and that the real, reactive and apparent power applied to the primary of almost any transformer equals the real, reactive and apparent power available at the secondary. When the voltage applied to the primary winding is raised above rated value, the iron core begins to saturate, which leads to a rapid increase in the magnitude of the magnetizing current. Saturation of the core also distorts the sinusoidal voltage and current waveforms. The resulting harmonics can lead to mechanical resonances which, in large transformers, can be damaging. Transformers are also very susceptible to damage from short circuit currents. 1.1.3 INSTRUMENTS AND COMPONENTS Power Supply Module (Both DC and AC), Transformer Module, Metering Module and Resistance Box. 1.1.4 PROCEDURE CAUTION! - DO NOT make any connections with the power supply ON. Get in the habit of turning OFF the power supply after every measurement. 1) Examine the construction of the Transformer Module paying particular attention to the laminated steel core and the windings. 2) Apply AC input of 10 volts to the primary and measure the voltage on the secondary for all three possible turns ratios. 3) Repeat part 2 with AC input of 10 volt increments for up to 60 Volts, Record all your readings. Make sure to also record the primary current. EEE307 ELECTRIC ENERGY CONVERSION LAB 2 THE SINGLE PHASE TRANSFORMER 1.1.1 OBJECTIVE To study the voltage and current ratios of a transformer. 1.1.2 DISCUSSION All transformers exhibit the same basic properties. When mutual induction is permitted between two coils or windings, a change in current flowing through one coil induces a voltage upon the other coil. All transformers have a primary winding and one or more secondary windings. The electromagnetic coupling between the primary and secondary windings allows electrical energy to be transferred from the primary winding to the secondary winding. Electrical current entering the primary winding appears as an electromotive force (emf) at the secondary. Connecting the secondary winding to a load allows the energy to be transferred to the load. Since there is no electrical connection between primary and secondary windings (only a magnetic connection), the source and load can be electrically isolated from each other by means of a transformer. When a transformer is energized and loaded, AC current flowing in its windings creates an alternating magnetic field in its iron core. A small portion of the current, called the magnetizing current, is dedicated to the magnetic circuit in the creation of the magnetic field. Losses associated with the magnetizing current are reactive power (VARS). In addition, there are real power osses (Watts) the transformer, associated with the inherent resistance in the windings (copper losses) and with eddy currents and hysteresis in the core (iron losses). For these reasons, the total power delivered to the primary side of the transformer is always larger than the total power available at the secondary side. Even so, it is still reasonable to say that energy is conserved in the transformer and that the real, reactive and apparent power applied to the primary of almost any transformer equals the real, reactive and apparent power available at the secondary. When the voltage applied to the primary winding is raised above rated value, the iron core begins to saturate, which leads to a rapid increase in the magnitude of the magnetizing current. Saturation of the core also distorts the sinusoidal voltage and current waveforms. The resulting harmonics can lead to mechanical resonances which, in large transformers, can be damaging. Transformers are also very susceptible to damage from short circuit currents. 1.1.3 INSTRUMENTS AND COMPONENTS Power Supply Module (Both DC and AC), Transformer Module, Metering Module and Resistance Box. 1.1.4 PROCEDURE CAUTION! - DO NOT make any connections with the power supply ON. Get in the habit of turning OFF the power supply after every measurement. 1) Examine the construction of the Transformer Module paying particular attention to the laminated steel core and the windings. 2) Apply AC input of 10 volts to the primary and measure the voltage on the secondary for all three possible turns ratios. 3) Repeat part 2 with AC input of 10 volt increments for up to 60 Volts, Record all your readings. Make sure to also record the primary current
