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How to identify transformer wiring

Three phase or Delta?
WYE transformer

Quick way to identify WYE or DELTA

Three wires drop down from overhead power lines.
Applies to 3-transformer installation.
If one of the drop wires connects to only one transformer then that connection is WYE
If the drop wire connects to 2 different transformers, then that connection is DELTA

Delta WYE/ same as above

1 supply wire connects to TWO transformers
Each hot wire from the power pole connects to two transformers


1 supply wire connects to ONE transformer
Each hot wire from the power pole connects to one transformer
Transformer wiring
Larger image
Original image

Delta WYE

Transformer wiring/ how to identify transformer wiring

Image shows Delta Primary and 4-wire WYE Secondary
Primary is Delta: How do we know? Each hot wire connects to two transformers.... so they are wired in series
Secondary is WYE. One wire connects to all three transformers, and to Neutral. One wire from each transformer is Hot... so they are wired in parallel
System neutral connects to Neutral and ground
There are many different transformer configurations

This is 'most common type of wiring' because Delta has lower amps/ meaning less heat, so insulation on primary coil is less expensive.

Transformers can be wired different ways depending on the incoming electric supply and end user need.
Two key factors for the grid are economic performance and reliability.
Reliability is necessary because electricity must run clean without big-voltage spikes and low-voltage brownouts. Otherwise motors and HVAC equipment will have shorter lifespan.

Transformer configurations
Transformer manuals
What is 3-phase electricity/ power plant to end user

Delta WYE/ same as above

wye delta
Larger image


distribution transformers at substation handle high voltage

Primary WYE 69,000 volts
Secondary Delta 4,400 volts

Generally 4,400 volts is lowest voltage for distribution without heat loss from high amperage
The lower the voltage, the higher the amperage.

High amperage causes heat loss.
The transmission of electric power requires high voltage and low amperage.
When amperage is high, the distribution distance is reduced.

However high voltage switchgear is expensive
It is impractical for end user to install high voltage appliances and motors because of the expense

As a result, the end user must receive low volts with higher amperage
To meet demands on the grid, transformers are used to raise and lower volts and amps in inverse proportion
When volts are reduced, amps are increased.

What is 3-phase electricity/ power plant to end user
Transformer wiring

Why does transformer wiring differ.

1) Electricity is mathematical
For example: Cosine of phase angle is known as power factor
P is power factor
Power factor is cosine of phase difference between v and I

Research star-delta for more information
And read below

Power generation by Singh
3-phase power generation book at Amazon
Electric Power generation books at Amazon
3-phase wiring books at Amazon

2) Cost
Delta configuration reduces amperage for the same amount of voltage

3) How does WYE DELTA affect cost
3-phase is more efficient because it runs at higher average power vrs single phase.
It's like having a 3 legged bicycle rider on a 3 pedal bike, with each pedal spaced evenly apart vrs a two legged bike rider on an ordinary bicycle.

4) Cost for 3-phase motors and commercial equipment:
"During start-up, motors develop high currents of up to eight times the rated current, and they have high starting torque linked to this.
The high starting currents often lead to unwelcome voltage drops in the supply network which can affect reliability of other equipment, and cause surges that shorten life of expensive equipment.
And the high starting torque puts strain on mechanical parts, which wears out motors.
Electric companies determine limiting values for motor starting so the power surges and heavy-amp draws do not affect other users. Such as requiring 2-stage motors or star-delta or auto-transformer motor starters etc.
A 2-stage motor means the motor starts out in low gear, and when it gets to higher speed, it shifts to higher gear. This saves energy and wear and tear.
Motors have start winding for getting the motor started. And then the run winding for motor at full speed.
STAR or WYE configuration is used for the start winding. And then Delta is used for full speed.
For example: voltage applied to the STAR or WYE start windings. The voltage is reduced by a factor of 1√3 = 0.58 this connection amounts to approximately 30% of the delta values. The starting current is reduced to one third of the direct starting current. When motor reaches speed, the run winding (wired in Delta) takes over and motor receives full amperage and voltage.

Transformers and motor starting
Connect transformer to wire

Connect transformer to wire

Hot clamp

Hot clamp

Fuse (lightning arrestor)


Read about ohm's law/ electricity/ and what transformer does
Transmission and distribution lines
Larger image

Transmission and distribution lines

Generally transmission lines are higher off the ground
And carry higher voltage than distribution lines
For example transmission lines might be 69,000 V
While distribution lines can be a lower voltage

Transmission lines run between substations
Distribution lines run from the substation to the end-user location

Image shows transmission lines that run from the Rosenberg substation out into the country to another substation

The distribution lines also leave from the Rosenberg substation and distribute power in the town
Distribution lines can be identified because transformers connect to the distribution lines

Transmission and distribution wires are bare
They have no insulation covering the wire
This helps keep the wire cool and increases transmission distance
Wires are kept away from the poles using purified glass insulators
Other types of materials are also use for insulators
Birds sitting on the bare wire are not electrocuted as long as they do not touch two wires or any part of the pole
Electricity on the wire is a potential
The voltage potential is only reach if two wires come together or one wire comes together with a ground

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