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I'm not really having heart burn. The transformers are owned by the customer - they bought 480V delta-delta 330kVA, when they should have gotten 480V delta-wye. Now they want to convert the delta-delta to wye-wye and derate them to 150kVA. I know wye-wye is not common in facilities but also is...

Thanks - The source is a B-phase corner grounded delta, which is feeding these wye-wye transformers. The wye primary H0 is not grounded. The wye secondary X0 is grounded. This means I will now have a direct connection via the equipment grounding conductors and GEC conductors between the B-phase...

After a little more thought, I don't think it would work. If the source delta is B-phase corner grounded. Then the phase angle of A & C phases would be referenced to B and to ground. Now grounding the secondary Xo would create a phase shift primary to secondary. Wouldn't this create some pretty...

I have a customer that wants to feed several 330kVA 480V wye-wye isolation transformers from a 480V corner grounded delta source. No neutral available and no ground connected to the primary neutral point. The primary and secondary neutrals are not connected together and the wye secondary Xo is...

Hi - I see two issues. 1. Is use of the term "low impedance", I assume you actually mean high impedance, i.e., where the fault current is limited to a maximum value via either an resistor or inductor inserted in the place of the bonding jumper.. 2. However, it really doesn't matter, I would...

Ok- Here's the setup from someone who has been in the UPS industry for +26 years -> Your UPS is "not" separately derived. Meaning it use's the input supply neutral as an earthing reference for the output. When you unplug the supply, the output now is floating. Because of the stray distributed...

I'd recommend starting with NFPA 70-2005 Article 408.4, i.e., National Electrical Code. Here's what it says: "408.4 Circuit Directory or Circuit Identification Every circuit and circuit modification shall be legibly identified as to its clear, evident, and specific purpose or use. The...

Hi- You are faced with one of either two problems or issues. Neutral to ground voltage has traditionally been used as a figure of merit to judge available power quality. This has largely been promoted promoted by those who make isolation transformers/power quality equipment. However, the reality...

Hope - you locate the fault, before second fault appears. This illustrates the benefit of using ground fault detection and tapped grounding resistor with pulsing contactor to locate the fault without taking down the entire system. You can make your own pulsing circuit w/500V/10A contactor +...