In this article we will discuss about the connection of
open-delta transformer. By this article we will discuss what is open delta
transformer .
Open delta transformer
In power transformation, three-phase transformation of
energy can be possible only by using two similar transformers in open-delta
configuration as shown in figger. This connection arrangement is also called
the V connection. The open-delta connection is often used in an emergency when
one of the three transformers in a delta-delta bank becomes defective or in
maintenance work.
When it is in good service, a consumer’s three-phase power
supply can be restored as soon as possible. The defective transformer can be
cut out of service.
The transformer which connection in open delta connection
are called open delta transformer.
Example of open delta transformer
It is show the connection
of open delta transformer. The open-delta connection can be used in an
emergency. Three 50-KVA transformers each rated at 2.4KV on the high-voltage
(HV) winding ad 240 volts on the low-voltage (LV) winding are connected in a
delta-delta from figger. This closed-delta bank is used to step down a 2.4KV
three-phase input to a 240 volt, three phase output to supply an industrial
consumer. If the three-phase power service is interrupted due to lightning strikes,
or other natural or man-made accidents and damages one of the transformer, then
service must be restored instantly. This situation shown in diagram.
The transformer 3 is the defective transformer. If all of
the leads of the damaged transformer are disconnected, and then closed-delta
bank automatically becomes an open-delta transformer bank.
NOTE; for open delta transformer
One transformer is removed; the triangular coil
arrangement is open on one side.
Because the schematic diagram resembles the letter V, this
arrangement is also called the V connection.
While the total KVA of the open-delta bank should be two-thirds
that of a closed-delta bank,the actual KVA rating of an open-delta bank is only
57.7% of the capacity of closed delta bank. Because, the currents of the two
transformers in the open delta connection are out of phase, resulting in the
total available capacity of the open-delta bank being only 57.7% instead of
66.7%.
In this open-delta example, three 50-KVA transformers connected
in a delta-delta bank.
For the closed-delta bank the total KVA capacity is
50+50+50=150 KVA.
When one transformer is disconnected, the transformer bank
changes to an open delta connection configuration and the total KVA capacity
now is only 57.7 percent of the original closed delta capacity,
150 x.577 = 87 KVA.
Application of open delta transformer
Hence it is the open delta connection configuration from
above example we can understand open delta connection. Now we will know that
application of open-delta connection.
It is the example of open delta transformer
Application of open-delta connection
The open-delta connection has a number of features that are
advantageous
1. The circuit can be employed in an emergency situation when
one transformer in a complete delt-delta configuration must be removed for
repair and continuity of service is required.
2. Upon failure of the primary or secondary of one
transformer of a complete delta-delta circuit, the system can be operated as
open delta circuit and can deliver three phase power to a three phase load.
3. A circuit is sometimes installed as open delta circuit
with the understanding that its capacity may be increased by adding one more
transformer to form complete delta –delta circuit.
Three phase to six phase conversion method
Four different are used for three-phase to six-phase
conversion:
1. Double-star connection
2. Double-delta connection
3. six-phase star connection
4. Diametrical connection
Hence it is the theory of open delta transformer if you will
find any incorrect above please comment below.
For knowing more about open delta transformer you must this video.