Mike Dolt Enterprises
Mike Dolt Enterprises
User: halloranjrrf, Location: Fl
Asked on: Monday, March 28, 2011 at 11:05 am EDT
Answered on: Tuesday, May 14, 2024 at 3:22 am EDT
Question: I have a 3 phase 240 volt 3-wire delta system with no neutral or ungrounded conductor going to a 100AMP MB Square D QO panel at a pumping station that feeds two 10HP submersable pumps on VFD's. I need a neutral for 120 volts to feed PLC's, lights, outlets and instruments like ultra sonic level, mag meters and floats. Are my only options to come off of 3 phase panel to a transformer then to a lighting panel or am I not looking at the big picture.
You have a few options for providing a neutral for your 120V loads in this 3-phase delta system
Option 1: Transformer with Isolated Neutral
Install a 3-phase isolation transformer rated for 240V delta primary and 240/120V wye secondary. Connect the transformer's delta windings to the 3-phase power supply. The secondary windings of the transformer will provide 120V neutral-to-line.
Option 2: Zigzag Transformer Install a 3-phase zigzag transformer rated for 240V delta primary and 120/240V center-tapped secondary. Connect the transformer's delta windings to the 3-phase power supply. The center tap of the secondary winding will serve as the neutral.
Option 3: Scott-T Connection Create a neutral by using two single-phase transformers connected in a specific configuration called a Scott-T connection. One transformer is rated for 240V primary and 120V secondary (T1). The other transformer is rated for 240V primary and 120V secondary, with its windings connected in reverse (T2). Connect T1 and T2 to the 3-phase power supply in a specific way to create the neutral.
Option 4: VFD with Neutral Function If the VFDs driving the pumps have a built-in neutral function, you can connect their output to the neutral and ground of a new 120V panel. This option eliminates the need for additional transformers. However, you must ensure that the VFDs provide a reliable and stable neutral voltage.Each option has its own advantages and disadvantages. The best choice depends on the specific requirements and constraints of your system. It is advisable to consult with a qualified electrician to determine the most suitable solution for your application. Flag for review