If a 208v WYE connected ungrounded system gets a ground at phase A. What is the line voltage at phase B? Before the system gets grounded the voltage is 208V. After the system gets the ground, I think it still is 208V. The solution says 360V. What do others think?
208V WYE Connected Ungrounded System (Camara's # 18)
- Thread starter EEVA PE
- Start date
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I think I found the answer. It appears 360V is correct, because this is a WYE. One should multiple by sqrt 3. If this were a Delta, then it would be 208V.
Flyer_PE
Jr. PE / Sr. Company Pilot
Here's how I read this:
If I'm told I have an ungrounded-WYE 208v system I think I'm being told the line voltage is 208 (phase voltage is 120). With no ground present and balanced phase currents, the normal voltage reading from any phase to ground will be 120 Vac. If any phase is grounded, the voltage from either of the other phases to ground will be 208 Vac.
If I'm told I have an ungrounded-WYE 208v system I think I'm being told the line voltage is 208 (phase voltage is 120). With no ground present and balanced phase currents, the normal voltage reading from any phase to ground will be 120 Vac. If any phase is grounded, the voltage from either of the other phases to ground will be 208 Vac.
ElecPwrPEOct11
Well-known member
I think you're right Flyer_PE, the LINE voltage wouldn't change at all. Only the phase voltage would change (and by sqrt 3 to 208V).
There's a good phasor illustration in the Power Reference Manual p40-2. If the A phase is brought to ground, the phase voltages change (and their insulation must account for this). But I don't see how the LINE voltages would change at all.
Flyer_PE
Jr. PE / Sr. Company Pilot
It depends on what you think of as "phase voltage" in this system. I'm sticking with the idea that they are describing a 120/208 system. Since the system is ungrounded, if the phase voltage is defined as Line-neutral, that voltage will remain the same (120 Vac). A fault on one phase will cause the voltage between neutral and ground to be 120 Vac.
