engineering maths

1. Transformer Open and Short Circuit Test (Pg 1
and 2)
Open Circuit Test

2. Theory(Open Circuit)
The transformer primary is connected to A.C. supply through ammeter,
wattmeter and variac. The secondary of transformer is kept open.
Usually low voltage side used as primary and high voltage side as
secondary to conduct open circuit test. The primary is excited by rated
voltage, which is adjusted precisely with the help of a variac. The
wattmeter measures input power. The ammeter measures input current.
The voltmeter gives the value of rated primary voltage applied at rated
frequency. A voltmeter is connected across secondary to measure
secondary voltage when primary is supplied with rated voltage. As
voltmeter resistance is very high, though voltmeter is connected,
secondary is treated to be open circuit as voltmeter current is always
negligibly small. When the primary voltage is adjusted to its rated value
with the help of variac, readings of ammeter and wattmeter are to be
recorded. The core-loss or iron-loss i.e. the no-load loss in a transformer
is determined by performing the open circuit test at normal sine wave
impressed voltage. To determine the shunt branch parameter of the
equivalent circuit, the LV (low voltage) side is connected to a normal
supply voltage and HV (high voltage) side left open. The wattmeter
connected in the LV side will then read the total hysteresis and eddy
current loss (W0) in the single phase transformer. Since the no-load
current is small, the copper losses due to it can be neglected.

3. Short Circuit Test
Theory(Short Circuit)
In this test, HV side is connected to A.C. supply through variac,
ammeter and voltmeter. The LV is short circuited with the help of thick
copper wire or an ammeter. As ammeter resistance is very low, though
ammeter is connected to LV side treated to be short circuited. This test is
done on a single phase transformer to find the series parameters of the
equivalent circuit. For this test, short circuits of terminals are done in the
low voltage side of the transformer and voltage is adjusted so that full-
load current flows. The loss during the short circuit will be full load
copper losses in both the primary and secondary windings, the core loss
being very small, it can be neglected.

4. Transformer (HV and LV sides)
Theory
Here the transformer is energized at rated voltage and the no-
load voltage measured. The secondary of the transformer is
connected to the load. Now, the load is to be varied from no-
load to full-load in steps and various readings of the current and
voltages are taken. All the time, keep primary voltage constant
at its rated value with the help of variac. The load is increased
up to the full-load current and the efficiency and the voltage
regulation are found.

5. Measurement of power in a three phase unbalanced circuit by
two wattmeter method.
Determination of steady state response of R-L, R-C and R-L-C
circuit and calculation of impedance and power factor.
Calibration of ammeter and wattmeter