3. INTRODUTION OF TAP CHANGERS
• A tap changer is a mechanism in
transformers which allows for variable turn
ratios to be selected in distinct steps. This is
done by connecting to a number of access
points known as taps along either the
primary or secondary winding.
• A tap changer is usually installed on a high
voltage section of a two-winding
transformer, due to the low current in that
area. The changers are also provided on
high voltage windings of an electrical
transformer if there is sufficient control of
voltage.
4. WHY TAP CHANGER ARE USED
• Voltage variation in power systems
is a normal phenomenon owing to
the rapid growth of industries and
distribution network. System
voltage control is therefore essential
for many purposes as listed above.
• While power distribution ther will
be voltage fluctuations in a
transformer due to the change in the
loads conected.
• To regulate the out put voltage this
tap changers are used .
5. OFF-LOAD TAP CHANGERS
• As the name indicates, in this
method tap changing is done after
disconnecting the load from the
transformer. Off load tap changing
is normally provided in low power,
low voltage transformers. It is the
cheapest method of tap changing.
The tap changing is done manually
though hand wheel provided in the
cover. In some transformers
arrangements to change the taps by
simply operating the mechanical
switches are also provided.
6. ON-LOAD TAP CHANGER
• On load tap changers are used to change the turns ratio
without disconnecting the load from it. Tap changing can
be done even when the transformer is delivering load. On
load tap changers considerable increases the efficiency of
the system.
• On-load tap changing is more convenient to consumers
and suppliers alike and the procedure lends itself to
automatic operation so that line voltages can be regulated
without manual intervention.
• On-load tap changing is illustrated in Figure
• During the operation of on load tap changers the main
circuit remains unaffected.
• Dangerous sparking is prevented.The taps on the
windings are brought to a separate oil filled compartment
in which the on load tap changer switch is housed.
8. OFF-LOAD TAP CHANGERS
• The winding is tapped at various
points. Since the taps are provided
at various points in the winding
single tap must be connected at a
time otherwise it will lead to short
circuit. Hence the selector switch is
operated after disconnecting the
load.
• To prevent unauthorized operation
of an off load tap changer,
mechanical lock is provided
