Mike Dolt Enterprises
Mike Dolt Enterprises
User: rpetrovski, Location: Ohio
Asked on: Monday, April 4, 2011 at 6:25 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:45 am EDT
Question: I have a corner tapped Delta feeding a 480 to 240/120v single phase control transformer. On the Delta it is 480 to ground on all phases but the center tapped phase which is 0. Can this cause problems with the the control xmfr? I keep blowing fuses on the line side of the xmfr. The voltage and aps look ok when I replace the fuses. It only happens when the power to the xmfr is cycled. Could this be caused by inrush to the xmfr?
Possible Causes
Inrush Current
Yes, inrush current can be a potential cause. When the control transformer is first energized, a large surge of current can flow into the transformer's windings. This surge can cause fuses to blow if they are not rated appropriately for the inrush current.
Capacitor Failure
The control transformer may have a capacitor that is damaged or failing. This capacitor can help mitigate inrush current, and its failure can lead to excessive current draw and blown fuses.
Voltage Imbalance
Since the voltage to ground on the center-tapped phase is 0, it is possible that there is a voltage imbalance between the other two phases. This imbalance can put additional stress on the control transformer and lead to fuse failures.
Troubleshooting Steps
1.
Check Inrush Current
Measure the inrush current of the transformer using a clamp-on ammeter. If it exceeds the fuse rating, upgrade the fuses or install a current-limiting device.2.
Inspect Capacitor
Disconnect the transformer from power and use a multimeter to check the capacitor. Replace the capacitor if it is damaged or shows signs of failure.3.
Verify Voltage Balance
Use a voltmeter to measure the voltage between each phase of the Delta supply and neutral. Ensure that the voltage difference between any two phases is within acceptable limits.4.
Examine Control Transformer
Inspect the control transformer for any visible signs of damage, loose connections, or overheating. If any issues are found, replace the transformer.
Additional Considerations
Fuse Amperage
Ensure that the fuses on the line side of the control transformer are rated for the maximum inrush current and steady-state current draw of the transformer.
Cycling Time
If the blown fuses occur only when the power is cycled, it may indicate that the transformer is not given sufficient time to de-energize before it is re-energized. Allow a few minutes between power cycles to allow the transformer to fully discharge.
Surge Protection: Consider installing a surge protector on the line side of the control transformer to mitigate voltage spikes that could cause fuse failures. Flag for review