IEEE C57.105-2019 pdf download

IEEE C57.105-2019 pdf download.IEEE Guide for Application of Transformer Connections in Three-Phase Electrical Systems.
The zigzag winding is also combined with either wye or delta connections in two-winding transformers to provide a desired phase relation and also a grounded neutral.
In this guide, the symbol ZZ indicates the zigzag connection, and the symbol ZZG indicates that the neutral is grounded. Table I shows application characteristics of transformer banks with zigzag-grounded secondaries.
4.4 T-T connections
Some three-phase distribution transformers consist of two single-phase transformers in a common tank with the interconnection of the two primaries and two secondaries in the manner shown in Figure 3(a) and Figure 3(b), the end of one winding connecting to the midpoint of the other to form a configuration similar to the letter T. This connection is also known as a Scott connection. The crossbar of the T is called the main winding, and the stem is called the teaser winding. Voltages of the main and teaser coils are such that balanced three-phase voltages are obtained. The neutral point of the secondary winding could be at one-third of the teaser coil from the main to simulate a grounded Y, four-wire connection as shown in Figure 3(b) or it could be at the midpoint of the main winding to simulate a delta with a grounded mid-tap, four-wire connection as shown in Figure 3(b). Although not actually a symmetrical connection, the three-phase T-connected transformer simulates the symmetrical Y and delta connections.
The possible application characteristics of T-connected transformers are shown in Table 1 and simulate standard delta-Y, Y-delta, delta-delta, and Y-Y connections. T-connected transformers may be paralleled with delta and Y combinations provided the usual requirements for paralleling are met (see 4.5.3).
The T-connection has three very interesting properties. First, if the neutral is grounded, a T-connected winding presents a low-impedance to zero-sequence current and permits the flow of such currents independently of the other winding. The implication of this fact is that the primary should not be grounded since the transformer will then act as a grounding transformer (see 4.6). T-connected windings are capable of providing a four-wire grounded service, even with an ungrounded primary, such as four-wire three-phase 120/208 V or 277/480 V service as shown in Figure 3(a), or four-wire three-phase 120/240 V service as shown in Figure 3(b) and may do so regardless of relative orientation of the windings. The symbol TG will be used in this guide to represent a T-connected winding with neutral grounded.
Second. the flow of triple-harmonic excitation currents in the windings and in the lines is not suppressed regardless of whether the primary or secondary is grounded or not, and these harmonics may flow on the phase conductors only. Harmonic voltages and currents and their effects are discussed in Clause 6.
Third. a T-connected transformer can be utilized to convert from a three-phase system voltage to a two- phase system voltage or three-phase primary voltage to a two-phase secondary voltage. Figure 3(c) shows an example of a three-phase system voltage to a two-phase system voltage conversion. Figure 3(d) shows an example of three-phase primary voltage to a two-phase secondary voltage using the secondary coil of a T-connected transformer with an auto-transformer.
4.5 Terminal markings, phase relations, and paralleling
Table I summarizes the application characteristics of each connection:
In general, however, the terminals of two-winding transformers and auto-transformers without tertiaries are designated by the alphabetic symbols H and X for the high voltage and low voltage, respectively, with numerical subscripts to distinguish the winding ends and taps. Neutral terminals of three-phase transformers are designated by the subscript 0; that is, HO, X0, and, for the case of a common neutral, H0X0. The three leads that connect to either full phase winding of a three-phase transformer are designated H1, H2, H3 or X1,X2, X3.