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Joined: Mar 2004
Posts: 7
Junior Member
Can somebody explain how a corner grounded delta transformer works? Or does anyone know of any sites that give schematics??/

Joined: Oct 2000
Posts: 2,722
Broom Pusher and


Can somebody explain how a corner grounded delta transformer works?

The Corner Grounded Delta system is a 3Ø 3 Wire configuration, of which has one of the Secondary output Lines (AKA "Phases") intentionally connected to "Ground" via the Grounding Electrode System.
Similar to the methods used to Ground all other Solidly Grounded AC Power Systems, the "Corner Grounded" Delta has Ungrounded and Grounded Conductors, plus Equipment Grounding / Bonding Conductors.

Think of the method "Normally" done to Ground the Secondary side of any Transformer (when planning to have a Solidly Grounded AC System from the Secondary).
If the Transformer is a Single Phase 3 Wire output, the Center Tapped "Neutral" Terminal (X0) is "Grounded", and this Conductor becomes the Grounded Conductor.
If the Transformer has a Three Phase 4 Wire Wye connected Secondary, the Common Star Point - also "X0", is "Grounded" and the Conductor Terminated to it is the System's Grounded Conductor.

With the Corner Grounded Delta, everything is quite the same as shown in the examples above. Only on this system, the differences are:

[*] One of the "Normally" Ungrounded "Phases" will be Grounded - and thus become the System's Grounded Conductor,

[*] This is a "Single Voltage System" in simpler terms - only one Voltage is found between Phase Lines or Line and Ground,

[*] There is no "X0" Terminal,

[*] There is no "Neutral" Conductor,

[*] Single Phase 2 Wire or 3 Phase 3 Wire Circuits are available for use - but all are the same Voltage,

[*] Two of the "Phase Lines" will have full rated system Voltage to Ground, and one "Phase Line" will be Zero Volts to Ground.

Choose one - and only one Line to become the Grounded Conductor, and perform Grounding Techniques as commonly done on other Grounded systems (GES, Bonding, etc.).

An example:

3Ø Delta / Delta Isolated Transformer.
Primary = 4160 VAC 3Ø Delta,
Secondary = 240 VAC 3Ø 3 Wire Delta.
Secondary Terminal "X1" = ØA,
Secondary Terminal "X2" = ØB,
Secondary Terminal "X3" = ØC.

GES and Equipment Bonding is connected to Terminal "X3" - or ØC.
This makes ØC the System's Grounded Conductor. Color Code for this Conductor = White.

Voltages are as follows:
A-B: 240 VAC,
A-C: 240 VAC,
B-C: 240 VAC,
A-G: 240 VAC,
B-G: 240 VAC,
C-G: 0 VAC.
("G" = Ground / Equipment Grounding Conductor / Grounded Conductor).

Now to the 2nd question:


Or does anyone know of any sites that give schematics??

I know a very familiar site with "A Few Schematics", and luckily there are a few Schematics of the Corner Grounded Delta.
The site is closer than you think! - in fact... you are at the site! Just missed the Schematics area by one forum down!

Click on a link below, which will open a new Window with Schematics for viewing and printing:
(Be sure to click on the underlined colored text to open the link)

Corner Grounded 3Ø 3 Wire Delta

3 Phase Delta Transformer Schematics

Menu for Technical Reference Section

The last link opens the Technical Reference area's "Menu" - from which you may use to search topics of the area in one page.

Good luck!
Let us know the outcome!!!


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Mar 2004
Posts: 7
Junior Member

thanks for the valuable detailed info on this delta system. I have never had this situation in front of me and in a couple of weeks i have to hook up this type of xfmr. I will study your info and I already have follow up questions. I will post back later.


Joined: Apr 2002
Posts: 2,527

Is the corner-grounded transformer in a new or existing application?

There are some cautions on overcurrent-device application.

Joined: Mar 2004
Posts: 7
Junior Member
this xfmr is being added in an existing bldg. I don't have all the spec's yet but will shortly. I will post back with more info.

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