wirenut1980
Senior Member
- Location
- Plainfield, IN
I have a customer with a milling machine that takes 480 V 3 phase supply from a 480Y/277 V solidly grounded service. The machine has an internal transformer that steps 480 V down to 200 V 3 phase for the motors and 100 V single phase for the controls (the machine is Japanese or something). They have fried 2 control boards in the past several months in this machine. The board operates at 24 V DC, and is fed by a power supply which is fed from the 100 V single phase. I measured incoming phase to phase voltages to the machine at 498 V, 495 V, 495 V. At the most, that is less than 4% above nominal. At the transformer secondary, I get about 219 V on the 3 phase voltages and 111 V on the single phase. So I have 4% high on the 480 V primary, and 11% high on the 100 V secondary. We opened up the compartment to look at the transformer and it does have taps on the primary (see attached pictures). The transformer appears to be tapped correctly for 480 V incoming voltage. It did not come out well in the picture I took, but for 480 V input tap, the connections are 1-4, 5-8, and 10-11.
I checked continuity between the incoming equipment grounding conductor and the machine ground bar and it checked good. They were not connected directly together by a wire, but rather through the machine enclosure. The resistance measured 0.2 ohms.
Any ideas on what I could do other than try to work with the machine manufacturer? The manufacturer is telling the customer that the incoming 480 V is too high. I did set a monitor at the incoming 480 V, just to make sure voltage was not getting much higher.
I think I have convinced the customer that there is something wrong with the transformer, but they do not know what to do now. The manufacturer states that they control devices can't handle more than 10% over the nominal 100 V rating.
Thanks in advance.
I checked continuity between the incoming equipment grounding conductor and the machine ground bar and it checked good. They were not connected directly together by a wire, but rather through the machine enclosure. The resistance measured 0.2 ohms.
Any ideas on what I could do other than try to work with the machine manufacturer? The manufacturer is telling the customer that the incoming 480 V is too high. I did set a monitor at the incoming 480 V, just to make sure voltage was not getting much higher.
I think I have convinced the customer that there is something wrong with the transformer, but they do not know what to do now. The manufacturer states that they control devices can't handle more than 10% over the nominal 100 V rating.
Thanks in advance.