Three Phase Transformer When more power is needed

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Three Phase Transformer When more power is needed, three transformers can be tied together.

Three Phase Transformer When more power is needed, three transformers can be tied together. This is called three-phase.

How much is it stronger? It is stronger by 173. 2 % = 1.

How much is it stronger? It is stronger by 173. 2 % = 1. 732 = √ 3

Two types of 3Ø transformer construction st 1 type NP 1 NS 1 NP

Two types of 3Ø transformer construction st 1 type NP 1 NS 1 NP 3 NP 2 NS 3 Three-phase transformer bank composed of 3 single phase independent transformers

nd 2 type Three phase transformer wound on a single three legged core NP

nd 2 type Three phase transformer wound on a single three legged core NP 1 NS 1 NP 2 NS 2 NP 3 NS 3

Advantages of single 3Ø transformer over bank of 3 1Ø transformer • Occupies less

Advantages of single 3Ø transformer over bank of 3 1Ø transformer • Occupies less floor space for equal rating • Less weight • Cheaper to maintain and connected

Generating three- phase Three phase (3Ø) power is delivered from generator with 3 separate

Generating three- phase Three phase (3Ø) power is delivered from generator with 3 separate windings. These windings are equally spaced, with 120º apart.

Three-phase voltages • Because three source voltages are timed at 3 different intervals, they

Three-phase voltages • Because three source voltages are timed at 3 different intervals, they can be transmitted over just 3 conductors. • If three-phase transformer bank we need 6 conductors to transmit 3 separate single-phase loads.

Multiply √ 3 We calculate the total voltage of all 3 line of a

Multiply √ 3 We calculate the total voltage of all 3 line of a 3 phase transformer by multiplying the voltage of each single winding (phase) by √ 3. Why?

The reason is the angles of each phase are always 120º apart. By using

The reason is the angles of each phase are always 120º apart. By using trigonometric formula

How to tie 3 transformer together? Wye connection We call each single phase transformer

How to tie 3 transformer together? Wye connection We call each single phase transformer windings “Phases”. • In parallel • (+) to (+) and (-) to (-) The combination we call “Line”.

Simplified Wye connection L 1 -L 2 120 V Advantage? 120 V Single-phase, 120

Simplified Wye connection L 1 -L 2 120 V Advantage? 120 V Single-phase, 120 V fluorescent light Three-phase, 208 V heavy machine ? = Phase × √ 3 = 208 V , 1Ø L 2 –L 3 = Phase × √ 3 = 208 V, 1Ø L 3 –L 1 = Phase × √ 3 = 208 V, 1Ø L 1 - N L 2 - N L 3 - N Single -phase, 208 V oven = 120 V, 1Ø

How to tie 3 transformer together? Delta connection • In series • (+) to

How to tie 3 transformer together? Delta connection • In series • (+) to (-) They form a loop

Simplified Delta connection

Simplified Delta connection

Center tap

Center tap

Types of Three- Phase Transformers 1. 2. 3. 4. Wye / Wye (Y-Y) Wye

Types of Three- Phase Transformers 1. 2. 3. 4. Wye / Wye (Y-Y) Wye /Delta (Y-Δ) Delta -Wye (Δ-Y) Delta-Delta (Δ-Δ)

Wye-Wye Connection a a’ NP 1 b c NS 1 + VLP Vфp Vфs

Wye-Wye Connection a a’ NP 1 b c NS 1 + VLP Vфp Vфs NS 2 - NP 3 Line Voltage b’ + NP 2 The overall voltage ratio is VLS c’ NS 3 n n a b + VLp Vфp Np 2 Np 3 c where a is the voltage ratio of each phase Vфs Np 1 Ns 2 Ns 1 Ns 3 a’ b’ + V Ls c’

Wye-Delta Connection a a’ NP 1 b + Vфp VLP c The overall voltage

Wye-Delta Connection a a’ NP 1 b + Vфp VLP c The overall voltage ratio is NS 1 b’ + NS 2 Vфs NP 2 - VLS NP 3 c’ NS 3 n a b + where a is the voltage ratio of each phase c’ Vфp Np 2 Ns 2 Np 1 + Ns 3 VLp b’ Np 3 Ns 1 c Vфs VLs a’

Delta-Wye Connection a VLP b + - + Vфp N - P 1 NS

Delta-Wye Connection a VLP b + - + Vфp N - P 1 NS 1 a’ + + Vфs - c’ NP 2 VLS NS 2 c NP 3 The overall voltage ratio is b’ NS 3 n c + VLP + Vф. P NP 2 - NS 1 NP 3 b NP 1 a Vфs - + NS 2 a’ + VLS NS 3 b’ c’

Delta-Delta Connection a VLP b + Vфp - a’ NS 1 Vфs NP 1

Delta-Delta Connection a VLP b + Vфp - a’ NS 1 Vфs NP 1 VLs The overall voltage ratio is b’ NP 2 NS 2 c’ c NP 3 NS 3 a Ns 2 b c - Vфp V Lp NP 1 - +a’ + + - NP 2 NP 3 Ns 1 Ns 3 + Vфs V Ls - b’ c’