voltage transformers being earthed 3

[powercam]

hi ppl 2 questions

1.why is the white phase of a voltage transformer normally earthed?
2.I have a delta system. W-phase grounded, when I measure between phases I get 110V. What u are actually measuring is the voltage across a voltage coil. If I measure between the A-B = 110V, B-C = 110Vand A-C=110V. My question to you is how come if you measure between A-C you get 110V, you are actually measuring across 2 coils?
many thanks

cams

 

[scottf]

Keep in mind that each VT winding is on a different phase and while you're measuring "across two windings" for the A-C voltage, the voltage measured is the vectorial sum of the 2 windings amd not just adding the 2 magnitudes.

 

[RalphChristie]

See also thread238-81957


Regards

Ralph

 

[busbar]

 
Whether the VTs are open-delta—open-delta or wye—wye configured, there is normally an equilateral voltage ‘triangle’ at the secondary, reflecting a similar equilateral voltage ‘triangle’ at the primary.

One secondary terminal is customarily grounded to prevent electrostatically induced overvoltage coupled from the primary. Without that jumper, “600V”-rated wiring and components are subject to transient or resonant overvoltage.