Conditions transformer can also be analyzed on the basis of the analysis of the acoustic vibrations emitted parts transformer parts. This method can be carried out, on line. Basis. off line transformer condition can be checked by measuring the resulting current when a voltage of 10 volts injected the altered frequency (a few kilo Hertz)
a. Transformer relationship deltas
3 phase transformer P, Q and R, as shown in Figure II.83 change input voltage transmission lines A, B, C be the output voltage transmission lines 1, 2 and 3. Channel source and input connected to the output channels connected to the load. The transformer is connected delta-delta. H1 for each transformer terminal connected to the H2 to the next transformer.
Likewise, the same as the terminals X1 and X2 to the next transformer connected together, as shown in Figure II.83. A schematic diagram is shown in Figure II.84.
The schematic diagram illustrated by showing not only the input connections, but also the phase relationship between the primary and secondary voltages. Each of the secondary windings in parallel and relationships described primary winding is coupled manner. Further sources of G generates a voltage EAB, EBC, ECA, as shown in the phase diagram. The primary winding is faced in the same direction, phase by phase, for example, primary transformer between channels A and B are faced horizontally, in the same direction as the phase EAB.
In relation delta-delta, the voltage between each input and output transmission line is in one phase. If the load is connected to channel 1-2-3 draw, then the result is the same amount of output current. This results in a current draw line in the input channel ABC.
As in some of the delta relations, that the current line is v3 times larger than the current one-mas ing IP and IS flowing in the primary and secondary windings, shown in Figure II.84. Power rating for the transformer bank rating is 3 times the single transformer.
Although the transformer bank is a 3-phase arrangement, each transformer is considered individually. As in the single-phase circuit, then the current H1ke IPmengalir of H2 in the primary winding is connected to the current IS flowing from X1 to X2 in the secondary winding.
b. relationship delta-star transformer
If the delta-star connected transformer, the primary winding is connected in the same way, as shown in Figure II.83. For the secondary winding is connected to all connected terminals X2 simultaneously connected to a common neutral (N), as shown in Figure II.85. In the delta-star relationship, the voltage through each primary winding is equal to the input line voltage. Channel output voltage is equal to v3 times the secondary voltage through each transformer.
Relatively large currents in the windings of transformers and transmission line are shown in Figure II.86. Flow line in phase A, B and C are v3 times the current in the secondary winding. Flow line in phase 1, 2 and 3 is equal to the current in the secondary winding.
Delta-star relationship produces 30 o phase difference between the voltage input channels and the output transmission line. Therefore, the output line voltage E12 is 30 o
precedes the input line voltage EAB, as can be seen from the phasor diagram. If the group enters the channel output isolated load, depending phasanya no problem. But if the channel is connected parallel to the channel input with other sources, 30 o phase difference may be going to make parallel parallel relationship is not possible, even if the line voltage is otherwise identical.
An important advantage of the relationship is that the star will produce a lot of isolation / insulation generated inside the transformer. Windings HV (High Voltage / High voltage) have been isolated / separated only 1/v3 or 58% of line voltage.
c. Transformer relationship of the stars
When the transformer is connected in the stars, to be considered is to prevent deviations from the line to neutral voltage (phase to zero). How to prevent menyimpangan is connect the neutral (zero) for the primary to the neutral (zero) source which is usually by means of ground (earth), as shown in Figure II.88. Another way is to provide each transformer with a third winding, winding called “tertiary”.
For three transformer tertiary windings are connected in delta as shown in Figure II.89, which often provide the branch where the voltage through the transformer installed. There is no phase difference between the input voltage and output transmission line transformer is connected to the stars.
d. transformers, open-delta relations
The open-delta relations to change voltage 3 phase system by using only two transformers connected in open-delta. Open-delta circuit is identical to the series of deltas, except that no one transformer (Figure II.90). However, relationships are rarely used because the delta capacitive load to the transformer bank is only 86.6% of the installed transformer capacity.
For example, if two 50 kVA transformers connected in open-delta transformer bank installed capacity is obviously 2×50 = 100 kVA. But, strangely enough never encountered this problem, that the transformer can only transmit 86.6 kVA transformer before it starts to become overheated (overheating).
Relation of open-delta is primarily used in emergency situations. Thus, if three transformers are connected in delta-delta and one of them is damaged and must be repaired / moved, then it is possible to insert loads in temporeri (emergency) with 2 remaining transformer.
