ECN Forum Forums Technical Discussion Electrical Theory and Applications transformer issue and hello

I think you "Hit The Target" on this issue, as it _appears_ to be a Tapped Secondary Winding... however..., the following statement has me Corn-Fused :



shaunkad;

I have some Questions regarding the readings you have posted.

1: Is this Transformer a Typical Single Phase Isolation Transformer - with:

1a: a Single Winding Primary Coil (H1 & H2); and Split-Coil Secondary Windings - both Secondary Coils are connected in Series (X1''''''X2--X3''''''X4); (120V/240V 1 Phase 3 Wire)

OR...

1b: Does the Primary Side have a "Jumper" from One Terminal - H1 for example, to a Terminal on the Secondary Side - X4 for example;

OR...

1c: Is the Secondary Side comprised of (3) Separate Windings, such as:

X1''''''X2 (120V), X3''''''X4 (240V), X5''''''X6 (120V)

2: Is the Secondary Side's "Neutral" Conductor Physically Bonded to the same Earth Reference as the Primary Circuit is? Is the Secondary Neutral Grounded at all? Is the only Equipment Grounding / Bonding Conductor the one from the Primary Circuit?

3a: If this Transformer is a "Center Tapped 3 Wire Secondary", are you measuring 115V between X1 and X2/X3, along with measuring 115V between X2/X3 and X4?

3b: Are you measuring 230V between X1 and X4, then measuring 200V between X1 and "Ground", along with measuring 60V between X4 and "Ground"?

4: Are you using a High Input Impedance (HI Z) Voltmeter, set on the 0-250VAC Selection?

5: Is there any Load on the Transformer when these Tests are performed?

6: Are there any issues with Load(s) connected to the Secondary, of which prompted you to perform voltage Tests?

7: Do you know who/m Setup this Transformer?

First thoughts would be you have an Auto Transformer - maybe unintentionally (i.e.: incorrectly hooked up).

Other reasons for the odd measurements would be from the Secondary "Neutral" is not Ground Bonded, the Split-Coils are connected improperly, using a High Z Voltmeter across an "Open Neutral" connection point, or the Transformer's Secondary Coil has an additional Tap - a "25%/75%" Tap, along with the "50%" Center Tap (Common Neutral Point).

If there are no connected Loads on the 240V output (L-L), connect a 240V Load which draws at least 1 Amp.
Leave any 120V (L-N) loads off for now.
Measure the L-L, L-N and L-G Voltage with either a Low Z Voltmeter, or Shunt the Leads of the HI Z Voltmeter with an appropriately sized Resistor.

After performing the above Test, connect (2) 120V 60W Incandescent A19 Lamps on "Both" L-N Connections. Now measure Voltage.
If anything changes, make note of the variations (Voltage and Light output).

Lastly, record the Nameplate Information on this Transformer, and post it with your next reply.

If the Nameplate also includes a Schematic, does it look like any of the following?:


FIG. 1: 480V x 120/240V 1 Phase 3 Wire Isolated Transformer
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FIG. 2: 480V x 240V 1 Phase 2 Wire Isolated Transformer
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FIG. 3: 1 Phase Isolated Transformer; Two 2-Wire Secondaries
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FIG. 4: 1 Phase Isolated Transformer; Multiple 2-Wire Secondaries
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FIG. 5: 1 Phase Isolated Transformer; Multiple Tapped Secondary Windings.
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-- Scott