in delta, as shown in figure 3-35. A topographic vector

the indication should be approximately zero. Then, the

diagram of the three-phase secondary voltages is shown

delta is completed by connecting the X2 lead to A and

in figure 3-35, view A. the vector sum of these three

the X1 lead to B.

voltages is zero. This may be seen by combining any

If the three secondaries of an energized transformer

two vectors, for example, EA and EB, and noting that

bank are properly connected in delta and are supplying

their sum is equal and opposite to the third vector, Ec.

a balanced three-phase load the line current will be

When the windings are connected properly, a voltmeter

equal to 1.73 times the phase current. If the rated current

inserted within the delta will indicate zero voltage, as

of a phase (winding) is 100 amperes, the rated line

shown in figure 3-35, view B.

current will be 173 amperes. If the rated voltage of a

Assuming all three transformers have the same

phase is 120 volts, the voltage between any two line

polarity, the delta connection consists of connecting the

wires will be 120 volts.

X2 lead of winding A to the X1 lead of B, the X2 lead

The three secondaries of the transformer bank may

of B to X1 of C, and the X2 lead of C to X1 of A. If any

be reconnected in wye to increase the output voltage.

one of the three windings is reversed with respect to the

The voltage vectors are shown in figure 3-35, view C.

other two windings, the total voltage within the delta

If the phase voltage is 120 volts, the line voltage will be

will equal twice the value of one phase; and if the delta

1.73 x 120 = 208 volts. The line voltages are

is closed on itself, the resulting current will be of

represented by vectors, E1,2, E2,3, and E3,1. A

short-circuit magnitude, resulting in damage to the

voltmeter test for the line voltage is represented in figure

transformer windings and cores. The delta should never

3-35, view D. If the three transformers have the same

be closed until a test is first made to determine that the

polarity, the proper connections for a wye-connected

voltage within the delta is zero or nearly zero. This may

secondary bank are indicated in the figure. The X1 leads

be accomplished by using a voltmeter, fuse wire, or test

are connected to forma common or neutral connection,

lamp. In figure 3-35, view B, when the voltmeter is

and the X2 leads of the three secondaries are brought

inserted between the X2 lead of A and the X1 lead of B,

out to the line leads. If the connections of any one

the delta circuit is completed through the voltmeter, and

Integrated Publishing, Inc.
6230 Stone Rd, Unit Q
Port Richey, FL 34668
Phone For Parts Inquiries: (727) 493-0744 Google + |