How 3 Phase Transformers Work- why we need them

‌What is a three-phase distribution?

Three phase power can be defined as the common method of alternating current power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by electric grids worldwide to transfer power.

 

Is a distribution transformer single-phase or three-phase?

A three-phase transformer is used to hold electrical energy from the main distribution circuit to the auxiliary distribution circuit. It transmits current to the secondary distribution circuit and at the same time reduces the voltage of the primary distribution circuit.

 

Understanding the Basics‌

A transformer is a static device that transfers electrical energy from one circuit to another through electromagnetic induction. It can step up (increase) or step down (decrease) voltage levels without any moving parts or direct electrical connection between the primary and secondary windings.

‌Single-Phase vs. Three-Phase Transformers‌

‌Single-phase transformers‌ are common in residential areas because homes typically don't need the high power capacity of three-phase systems. They connect to one phase and neutral from the grid, providing 120V and 240V for household use.

‌Three-phase transformers‌ are used in commercial and industrial settings where heavy machinery, large lighting systems, and high-power equipment are present. They provide a more stable and efficient power supply.

‌Delta (Δ) Primary and Wye (Y) Secondary Configuration‌

‌Delta (Δ) Primary‌: The primary winding is connected in a triangular (delta) configuration. This is often used in high-voltage transmission because it can handle unbalanced loads well.

 

‌Wye (Y) Secondary‌: The secondary winding is connected in a star (wye) configuration, which provides a neutral point. This is useful for distributing power at different voltage levels (e.g., 120V, 208V, 240V, 480V).

 

‌How a 200 kVA Three-Phase Transformer Works‌

A ‌200 kVA‌ transformer is rated to handle 200,000 volt-amperes of power (a measure of apparent power).

The ‌Delta primary‌ connects to the high-voltage grid (e.g., 4,160V or 13.8kV).

The ‌Wye secondary‌ provides multiple voltage outputs (e.g., 208Y/120V or 480Y/277V), which is common in commercial buildings.

The ‌three-phase power‌ from the grid is split into three separate but synchronized sine waves, each 120 degrees apart, ensuring a smooth and constant power delivery.

 

‌Why Three-Phase Power is Used‌

‌Efficiency‌: Three-phase power provides a more constant and balanced power output compared to single-phase.

‌Higher Power Capacity‌: It can handle much larger loads, making it ideal for industrial and commercial applications.

‌Better Motor Performance‌: Three-phase motors run more smoothly and efficiently than single-phase motors.

 

‌Power Distribution Journey‌

‌Generation‌: Power plants generate three-phase AC electricity.

‌Step-Up Transmission‌: Transformers increase the voltage to reduce energy loss over long distances (e.g., 345kV or 500kV).

‌Step-Down to Distribution‌: Substations reduce the voltage for local distribution (e.g., 4.16kV or 13.8kV).

‌Final Step-Down‌: Distribution transformers (like the 200 kVA unit) reduce voltage to usable levels for businesses (e.g., 208V or 480V).

 

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Technical Specification

1.S13-35kV Technical parameters of non-excitation voltage regulating transformer

Rated Capacity (kVA)	High voltage (kV)	Tapping range	Low voltage (kV)	Vector Group	Impedance Voltage (%)	No-load Loss (W)	Load Loss (W)	No-Ioad current (%)
50	35 38.5	±2x2.5% ±5%	0.4	Dyn11 Yyn0	6.5	160	1200/1140	1.3
100						230	2010/1910	1.1
125						270	2370/2260	1.1
160						280	2820/2680	1.0
200						310	3320/3160	1.0
250						400	3950/3760	0.95
315						480	4750/4530	0.95
400						580	5740/5470	0.85
500						680	6910/6580	0.85
630						830	7860	0.65
800						980	9400	0.65
1000						1150	11500	0.65
1250						1400	13900	0.6
1600						1690	16600	0.6
2000						1990	19700	0.55
2500						2360	23200	0.55

 

2.S13-35kV Technical parameters of non-excitation voltage regulating transformer

 

Rated Capacity (kVA)	High voltage (kV)	Tapping range	Low voltage (kV)	Vector Group	Impedance Voltage (%)	No-load Loss (W)	Load Loss (W)	No-Ioad current (%)
630	35	±2×2.5% ±5%	3.15 6.3 10.5	Yd11	6.5	830	7860	0.65
800						980	9400	0.65
1000						1150	11500	0.65
1250						1400	13900	0.55
1600						1690	16600	0.45
2000						2170	18300	0.45
2500						2560	19600	0.45
3150	35~38.5	±2×2.5% ±5%	3.15 6.3 10.5		7.0	3040	23000	0.45
4000						3610	27300	0.45
5000						4320	31300	0.45
6300					8.0	5240	35000	0.45
8000	35~38.5	±2×2.5%	3.15 3.3 6.3 6.6 10.5	YNd11		7200	38100	0.35
10000						8700	45300	0.35
12500						10000	53800	0.3
16000						12100	65800	0.3
20000						14400	79500	0.3
25000					10.0	17000	94000	0.25
31500						20200	112000	0.25

 

3.S13-35kV Technical parameters of on load tap changer

 

Rated Capacity (kVA)	High voltage (kV)	Tapping range	Low voltage (kV)	Vector Group	Impedance Voltage (%)	No-load Loss (W)	Load Loss (W)	No-Ioad current (%)
2000	35	±3×2.5%	6.3 10.5	Yd11	6.5	2300	19200	0.5
2500						2720	20600	0.5
3150	35~38.5		6.3 10.5		7.0	3230	24700	0.5
4000						3870	29100	0.5
5000						4640	34200	0.5
6300					8.0	5630	36700	0.5
8000	35~38.5		6.3 6.6 10.5	YNd11		7870	40600	0.4
10000						9280	48000	0.4
12500						1090	56800	0.35
16000						1310	70300	0.35
20000						1550	82100	0.35
25000					10.0	1830	97800	0.3
31500						2180	116000	0.3