MTW
Senior Member
- Location
- SE Michigan
Single phase four winding transformers can be very versatile, when you learn how to apply them in banks.
My shop has a 240/120V 4W 3Φ open delta service. I test and service customer equipment and motors of varying voltages. Instead of connecting a separate transformer for each test voltage, for each piece under test, I use a autotransformer bank. In open delta, to obtain four different output voltages, all at 3Φ. 120V, 200V, 240V, and 480V all from the same open delta bank. A selector switch to change voltages, and a start stop station to turn it on and off. The voltage can even be changed on the fly, under load.
Trying to start up a larger motor, loose on the floor, with 480V applied, can be a dangerous situation. That puppy can roll itself away, along with your connection leads, from the startup torque. Starting it gently with a 120V 3Φ, and then ramping it up in stages, to the nameplate voltage, makes it easier and safer. For a piece of equipment, you just dial in your voltage, and hit the start button.
Its built from two 480/240-240/120 1Φ units, in a open delta configuration. Has several contactors to switch the winding connections. And a bank of control relays to ensure proper interlocked contactor switching, so that when switched under load, there is no contactor arcing, if one contactor switches slower that the others.
It's not a manufacturer approved setup for the transformers, but it works excellent, and is only used under my control. The idea came from a motor test stand built in the 50's that I serviced for my local motor shop. They had a 480V Y service, and stepped things down. I reconfigured the design for a 240V input, and to go up and down from the middle voltage.
It has different capacities at each voltage, so I built it large enough to do do all of my normal testing. I even have had customers bring larger equipment on trailers. We string the leads out to the lot and fire them up, right on the trailers, to run them for troubleshooting.
It's a very handy thing to have, and makes quick work of a test setup. But there was some time spent to do the engineering, to make it function correctly.
MTW Ω
My shop has a 240/120V 4W 3Φ open delta service. I test and service customer equipment and motors of varying voltages. Instead of connecting a separate transformer for each test voltage, for each piece under test, I use a autotransformer bank. In open delta, to obtain four different output voltages, all at 3Φ. 120V, 200V, 240V, and 480V all from the same open delta bank. A selector switch to change voltages, and a start stop station to turn it on and off. The voltage can even be changed on the fly, under load.
Trying to start up a larger motor, loose on the floor, with 480V applied, can be a dangerous situation. That puppy can roll itself away, along with your connection leads, from the startup torque. Starting it gently with a 120V 3Φ, and then ramping it up in stages, to the nameplate voltage, makes it easier and safer. For a piece of equipment, you just dial in your voltage, and hit the start button.
Its built from two 480/240-240/120 1Φ units, in a open delta configuration. Has several contactors to switch the winding connections. And a bank of control relays to ensure proper interlocked contactor switching, so that when switched under load, there is no contactor arcing, if one contactor switches slower that the others.
It's not a manufacturer approved setup for the transformers, but it works excellent, and is only used under my control. The idea came from a motor test stand built in the 50's that I serviced for my local motor shop. They had a 480V Y service, and stepped things down. I reconfigured the design for a 240V input, and to go up and down from the middle voltage.
It has different capacities at each voltage, so I built it large enough to do do all of my normal testing. I even have had customers bring larger equipment on trailers. We string the leads out to the lot and fire them up, right on the trailers, to run them for troubleshooting.
It's a very handy thing to have, and makes quick work of a test setup. But there was some time spent to do the engineering, to make it function correctly.
MTW Ω
