hbendillo
Senior Member
- Location
- South carolina
Please see the attached photograph. I was called out by one of my clients to trouble shoot a problem they were having with some pump motors. Brief summary of installation:
Transformer in the picture is being use to step up voltage from 208 to 480 volts (Three-Phase) to provide a feeder to a set of well and irrigation pumps on a large residential property. The transformer rating is a 240-600 volt, three-phase with 7 taps on the 600 volt side to vary the output from 540 to 630 amps. The transformer was fed with a 208 volt circuit and the taps changed on the high side to produce the 480 volt output. Measurements confirmed the output to be roughly 485 volts.
The length of the feeder is about 800 to 100 feet. At the pump site another transformer, 480-240 volt dry-type , is used to step voltage down to feed two 240 volt, three-phase pumps. The owner was having trouble with the starter for the pumps kicking out and/or cycling until at some point one of the existing starters feeding a 30 HP pump failed completely and had to be replaced. The Owner and his Contractor thought is was a voltage problem because of the transformer configuration.
So we began our investigation by removing the cover of the transformer in question so we could look at the connections and measure voltages and found the damage to the connection shown. Apparently at some point the wiring connection to the lug in the picture worked loose through heating and expansion and began arcing. As you can see by the picture part of the lug on the transformer is completely burned off and the wire and lug connected to it barely making contact. It also shows a lot of damage to a portion of feeder the wire. So apparently this is their problem. The arcing connection playing havoc with the voltage supplying the pumps, possibly intermittent single phasing.
The owner wants to look into repairing the connection but I am wondering, what other damage may have been done to the transformer as a result of this condition besides the visible physical damage. How can you repair something like this? The entire transformer lug needs to be replaced but that won't be easy because wires from the transformer connected to the lug are welded to it. We may be able to figure something out but my instinct is to replace the transformer. Are there any other issues I need to consider besides the damaged lug?
Transformer in the picture is being use to step up voltage from 208 to 480 volts (Three-Phase) to provide a feeder to a set of well and irrigation pumps on a large residential property. The transformer rating is a 240-600 volt, three-phase with 7 taps on the 600 volt side to vary the output from 540 to 630 amps. The transformer was fed with a 208 volt circuit and the taps changed on the high side to produce the 480 volt output. Measurements confirmed the output to be roughly 485 volts.
The length of the feeder is about 800 to 100 feet. At the pump site another transformer, 480-240 volt dry-type , is used to step voltage down to feed two 240 volt, three-phase pumps. The owner was having trouble with the starter for the pumps kicking out and/or cycling until at some point one of the existing starters feeding a 30 HP pump failed completely and had to be replaced. The Owner and his Contractor thought is was a voltage problem because of the transformer configuration.
So we began our investigation by removing the cover of the transformer in question so we could look at the connections and measure voltages and found the damage to the connection shown. Apparently at some point the wiring connection to the lug in the picture worked loose through heating and expansion and began arcing. As you can see by the picture part of the lug on the transformer is completely burned off and the wire and lug connected to it barely making contact. It also shows a lot of damage to a portion of feeder the wire. So apparently this is their problem. The arcing connection playing havoc with the voltage supplying the pumps, possibly intermittent single phasing.
The owner wants to look into repairing the connection but I am wondering, what other damage may have been done to the transformer as a result of this condition besides the visible physical damage. How can you repair something like this? The entire transformer lug needs to be replaced but that won't be easy because wires from the transformer connected to the lug are welded to it. We may be able to figure something out but my instinct is to replace the transformer. Are there any other issues I need to consider besides the damaged lug?