Trouble Shooting open delta
Trouble Shooting open delta
(OP)
Can somebody tell me how to trouble shoot a machine that uses a three phase open delta power configuration since you can't reference each phase ground or neutral?
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Trouble Shooting open delta
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RE: Trouble Shooting open delta
or
If the system is floating, refer your voltage measurements to one phase.
or
Consider grounding one phase (corner grounding).
or
Ground the the center tap of one transformer if one is available.
Bill
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RE: Trouble Shooting open delta
Rafiq Bulsara
http://www.srengineersct.com
RE: Trouble Shooting open delta
RE: Trouble Shooting open delta
I do not see anything to troubleshoot here. If you measure correct phase to phase voltages between each pair, you should be fine in normal conditions.
Rafiq Bulsara
http://www.srengineersct.com
RE: Trouble Shooting open delta
RE: Trouble Shooting open delta
An aside—voltage measurements on an open-delta system should be no different than those on a (full) delta system.
RE: Trouble Shooting open delta
Regarding troubleshooting machine that utilizes open delta, you probaly want to monitor the incoming line voltage to establish a baseline (i.e. monitor for voltage sags, swells, transients that cause problem), and check equipment-system grounding to bad or lose connection; and to ensure compliance with NEC Article 250. Last but not least, on open wye-open delta configuration with one dummy phase or man made phase, the sensitive electronics are susseptible to voltage fluctuations, and any system fault on utility lines will cause voltage surge inside the facility. If this is the case, installing 3-phase xfmr bank would be one solution, and this modification will have other consequences or wiring changes as well. Not knowing exactly what type of problems or issues your machine is experiencing its difficult to help with solutions.
RE: Trouble Shooting open delta
Theoretically, and in practice, the phase-ground voltage on a symmetrical ungrounded delta (open or closed) should balance and should be the same as the phase-neutral voltage on a wye. This is because the capacitance and insulation resistance of the legs, if equal, cause the voltages to float at an equal level above ground.
As an example, the phase-ground voltages of a symmetrical 480V delta should be 277V each. In the case of an unintentional direct ground, the phase-ground voltages would read 480-480-0 with the zero leg being grounded. For a high impedance ground, it will be somewhere in between.
When dealing with the special case of an open delta, this still applies for a symmetrical winding, meaning the two legs are identical. For cases where the windings are not symmetrical, the phase-ground voltages will not be balanced, but it will be unbalanced in a predicatable way. Interpreting the phase-ground voltages in this case is a matter of understanding the transformer configuration.
I will add that for the type of work that I do, open delta transformers are very rare. I am speaking mostly from theory and instinct. If I am wrong someone here will (I hope) educate me.
RE: Trouble Shooting open delta
But if you read ZERO volts phase-to-ground it means you have a short to ground somewhere inside of the facility. First short will not shut you down on straight delta connection, but the following or second short in the system will cause voltage surge, damage equipment, and OSHA will get involved i.e. if there's personnel safety issue involved.
With respect to open-delta, on utility transformers, they are all over (anywhere you see 2 bucket transformer stations on utility poles serving 3-phase connections or facility incoming switchear-panel). When it comes to control power, we normally design for metering and protective relaying the supply voltage from open-delta, to save one transformer-basically for economics saving $$$$.
RE: Trouble Shooting open delta
Alan
RE: Trouble Shooting open delta
It may be worth noting that, for an open-delta secondary configuration, utilities will use an open-delta primary connection with three phases/cutouts, or possibly an open-wye primary with two phases/cutouts and a neutral connection.
RE: Trouble Shooting open delta
Only proper way to read-measure RMS voltage on open delta is to take phase-to-phase voltage readings (AB-BC-CA). No other way my friend.
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