ECN Forum Forums Technical Discussion Technical Reference Area New: 3 Phase 3 Wire Ungrounded Delta Drawings

Subject = New: 3 Phase 3 Wire ungrounded Delta Drawings


These are new drawings as of 05/03/2008. Feel free to comment.

The following drawings describe a 3 Phase 3 Wire Ungrounded Delta
Transformer connection, and the nominal Voltages at various points.

Drawings included are for 240V, 480V and 600V 3 Wire Deltas.

***NOTE: These systems are not "Physically" Grounded***
meaning a Low Impedance Circuit between any Line to Ground will draw very little Current - and the Voltage across that load will be very small - like 10 Volts across an Impedance of 100 Ohms.

HOWEVER!!! If measured across a High Impedance (Line to Ground), the Voltage to ground may at times exceed the Phase to Phase Voltage, by as much as 3 times the L-L Voltage - and possibly more!

What I am referring to here is measuring Voltage from Line to ground using a "Digital Volt Meter" - which typically have a very high input Impedance ( > 500K Ohm, possibly even 10Meg Ohm), will read a Voltage of 300 Volts and up.
Using a low Impedance meter - like an old "Wiggy" (Solenoid type Voltmeter), will display almost zero Volts when connected Line to Ground.

The same applies when fixed loads of low or high Impedance are connected L-G

Please take note of this issue (issue is due to "Capacitive Coupling Effect).

Now On To The Drawings!!!




Figure 1a: Schematic drawing of the 240VAC
3 Phase 3 Wire Ungrounded Delta.







Figure 1b: Layout drawing of the 240VAC
3 Phase 3 Wire Ungrounded Delta.


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Figure 2a: Schematic drawing of the 480VAC
3 Phase 3 Wire Ungrounded Delta.






Figure 2b: Layout drawing of the 480VAC
3 Phase 3 Wire Ungrounded Delta.


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Figure 3a: Schematic drawing of the 600VAC
3 Phase 3 Wire Ungrounded Delta.





Figure 3b: Layout drawing of the 600VAC
3 Phase 3 Wire Ungrounded Delta.


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