Department of Electrical and Electronics Engineering. BASIC ELECTRICAL
LABORATORY EXPERIMENTS (ENGG 103). EXPERIMENT 5:-
TRANSFORMERS.
Kathmandu University Department of Electrical and Electronics Engineering BASIC ELECTRICAL LABORATORY EXPERIMENTS (ENGG 103) EXPERIMENT 5:- TRANSFORMERS Objectives:
1. to understand the basic principle of operation of transformer
Materials and Equipments Required: 1. Transformer 2. Wattmeter 3. Resistive Loads 4. Ammeter 5. Variable AC power Supply Theory: Transformer is a static electromagnetic device which is used to transfer electric power from one circuit to another circuit with same frequency. It works on the principle of electromagnetic induction where the two electric circuits are linked by a common magnetic flux (mutual induction). It is used to step-up or step-down the voltage corresponding decrease or increase in current. The electrical energy is always transferred without a change in frequency, but may involve changes in magnitudes of voltage and current. It consists of two inductive coils which are electrically separated but magnetically linked through a path of low reluctance. Low reluctance path is achieved by the use of core with ferromagnetic material (reason for using Iron Core). One coil is connected to source of an AC voltage. The coil which is connected to the source is called primary winding and the other coil is called secondary winding. For transformer:
=
Primary power = Secondary power + Core loss (for practical transformer). For ideal transformer there is no core loss. Circuit Diagram:
Procedure: i) Connect the circuit as shown if figure 1 ii) Measure the primary and secondary resistance using multimeter For no load test i) Open circuit the secondary terminal. ii) Measure the primary voltage and secondary voltage. iii) Connect the wattmeter at primary side and measure the power consumption at primary side and primary current. For Load test (Resistive only) i) Make primary voltage at 220 V and connect load at secondary side. ii) Connect the wattmeter at primary and secondary side and measure the power consumption and current at primary and secondary side. iii) Repeat experiment for different load.
Observations:
No Load test: S.N.
Primary voltage
1
150
2
170
3
190
4
210
5
220
Primary Resistance
Secondary voltage
Secondary resistance
Turn ratio
Core loss
Load test: Primary voltage = 220 V S.N.
1 2 3 4 5
Primary power
Secondary power
Primary current (calculate)
Secondary Current
Core loss
Conclusions and Inference:
Discussion i) Write short notes on the principle of operation of transformer. ii) Why at no load there exists flow of primary current? iii) Why at low value of loads the primary current is less than secondary current for practical transformer?
