Three Phase Transformer

Three Phase Transformer
Three Phase Transformer

The purpose of a three-phase transformer is to facilitate the transmission of electrical energy between three-phase systems. It is an essential component in industrial and commercial applications, in addition to electrical power transmission and distribution networks. This transformer transfers current and voltage between three-phase windings by electromagnetic induction. The three-phase transformer is essential for balanced, efficient three-phase electrical systems.

Three-phase transformers transport electricity between three-phase systems. Each winding represents a three-phase power system phase. The primary winding receives power from the source, while the secondary winding sends transformed power to the load. In a three-phase transformer, electromagnetic induction converts current to voltage. It’s crucial to power transmission and distribution.

The significance of triphasing transformers

Three-phase transformers play a crucial role in numerous facets of electrical power systems. To commence with, they facilitate the effective conveyance and dissemination of electrical energy. Through the process of regulating voltage levels, these transformers enable the efficient and loss-free transmission of electricity over extended distances. Furthermore, they guarantee the equitable allocation of electrical energy in three-phase systems, thereby averting congestion and supplying dependable power to residential and industrial sectors. In conclusion, three-phase transformers facilitate the uninterrupted functioning of electrical devices and equipment, thereby enhancing the overall dependability and stability of the electrical infrastructure.

Three Phase Transformer Applications

Transformers operating in three phases have a vast array of applications across numerous industries and sectors. They are widely employed in power generation facilities to increase voltage levels in order to facilitate long-distance transmission with greater efficiency. Additionally, electrical substations utilize these transformers to regulate voltage and guarantee the secure distribution of power to a variety of consumers. Furthermore, to ensure the dependability of electrical systems and supply power to industrial machinery, heavy equipment, and large-scale commercial structures, three-phase transformers are utilized. Their utility is not limited to renewable energy systems; in fact, they are indispensable in the conversion and distribution of electrical energy in systems such as wind and solar power.

Three-phase transformers offer greater cost-effectiveness when it comes to power distribution and the provision of power to substantial loads. Although single phase transformers are utilized to connect the majority of utilization equipment, they are not favored for large-scale power distribution due to their economic disadvantages.

Three-phase power is utilized in nearly every sector of the electrical power system, including generation, transmission, and distribution. Furthermore, three-phase systems are utilized to supply or connect all industrial sectors. As a result, three phase transformers are utilized to step-up (or increase) or step-down (or decrease) the voltages in three phase systems. In contrast to single phase transformers, three phase transformers offer a multitude of benefits, including reduced size and weight while maintaining equivalent power handling capacity, enhanced operational characteristics, and more.

Three Phase Transformer

Three-phase transformers step-up or step-down high voltages in power transmission systems. Various producing stations produce 13.2KV to 22KV three-phase electricity. Power is transmitted at 400KV or 132KV to reduce distribution end power loss. To transmit power at high voltages, a three-phase step-up transformer is used. In the final stages of transmission or distribution, these excessive voltages are lowered to 6600, 400, 230, etc. A three-phase step-down transformer is used.

A single three-phase transformer or a battery of three single-phase transformers can be used to build a three-phase transformer.Three single-phase transformers with equal ratings and operational characteristics are connected properly to make the former. If a transformer fails, two open delta transformers will keep the system running at a reduced capacity. This connection ensures continuous supply. Mines use these because single-phase transformers are heavier to transport.

Three 1

One three-phase transformer with six windings on a multi-legged core can replace three single-phase transformers in a three-phase bank. Compared to three units of the same rating, this single unit saves weight, cost, iron in the core, and insulation materials. Single-unit installation takes less space than three-unit bank. The only downside of a single-unit three-phase transformer is that if one phase fails, the whole unit must be pulled from service.

Three-Phase Transformer Construction

A three-phase transformer uses a common magnetic core for primary and secondary windings. As with single-phase transformers, construction can be core or shell. Combining three shell-type single-phase transformers yields a bank of three-phase transformers. In a shell transformer, EI laminated core surrounds coils, while in a core transformer, coil surrounds core.

Construction Core Type

Core type three-phase transformers have three legs and two yokes. These yokes and limbs form a magnetic route. Primary and secondary windings are concentrically wounded on each limb. This transformer has round cylindrical coil windings. The primary and secondary windings of one phase are damaged on one leg. Balanced legs have zero magnetic flux in each phase. Normal conditions do not require a return leg. Unbalanced loads cause high circulating current flows, hence three single-phase transformers may be preferable.

Shell Type Construction

In shell type, three phases are more independent because each phase has independent magnetic circuit compared with core type transformer. The construction is similar to the single phase shell type transformer built on top of another. The magnetic circuits of this type of transformer are in parallel.

Working of Three Phase Transformers

Three-phase transformer operation

Figure below shows transformer main star-connected to cores. For simplicity, the image shows only the three-phase AC supply’s primary winding. Three 120-degree cores. Each core’s empty legs form middle legs.Three-phase supply excites primary, causing phase windings to carry IR, IY, and IB. These currents generate magnetic fluxes ΦR, ΦY, and ΦB at their centers. The middle leg carries all three fluxes because all cores share it. Total current vector sum in three-phase systems is always zero. Instantaneous flow entire same. No flux ever passes through central leg. Removing the middle leg does not affect transformer conditions.

Three-phase transformer connections

A single three-phase transformer or three single-phase transformers can transform three phases. Three-phase transformers and three single-phase transformers use the same windings for three-phase transformation. Coupled delta, star, or both primary and secondary windings. Three-phase transformer voltage and current depend on connection. A popular link is

  • Star-delta
  • Delta-star
  • Delta-delta
  • Star-star

Star – Delta Connection

Star delta

Utility companies lower distribution system voltage with this link.

  • This connects the transformer’s primary and secondary windings in star and delta fashion.
    Grounding the primary or high voltage neutral point is usually best.
  • The secondary-to-primary line voltage ratio is 1/3 times the transformer transformation ratio.
  • Phase difference between primary and secondary line voltages is 30 degrees.
  • HV windings with this winding require less insulation because the primary coil voltage is 58% of the primary line voltage.
  • Even with neutral wire-induced unbalanced currents at the main or HV side, this connection produces balanced three-phase voltage at the secondary or LV side. Lightning surge prevention is provided by neutral wire grounding.


Delta delta

  • Delta supply sources use this connection for single-voltage, high-current secondary loads. Motors use three-phase power.
  • Unbalanced loading is possible because three-phase voltages stay constant.
  • There is no phase difference between primary and secondary voltages.
  • This connects primary and secondary windings delta-style.
    Load voltage equals secondary voltage and primary winding voltage equals source voltage. The load current will be 1.732 times the secondary current, and the feeder current will equal the primary winding current.

Star – Star Connection

Star star

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