JoeStillman
Senior Member
- Location
- West Chester, PA
Please tell us that this gear is NOT fed from the same ungrounded delta transformers!
Industrial Facility Power Quality Issues
- Thread starter aelectricalman
- Start date
- Status
Please tell us that this gear is NOT fed from the same ungrounded delta transformers!
aelectricalman
Senior Member
- Location
- KY
Its a completely separate substation circuit. Its not fed from the same delta XFMR!
aelectricalman:
The burning up of drives, control wiring etc could have been prevented, had proper surge protection measures such as individual surge protection for drives etc were taken in your facility. It is not known from your posts so far that this protective measure was taken in your facility. It is also not clear whether the POCO's primary side supply system was also ungrounded in which case it is likely that the damaging transient over voltages originated there.
The burning up of drives, control wiring etc could have been prevented, had proper surge protection measures such as individual surge protection for drives etc were taken in your facility. It is not known from your posts so far that this protective measure was taken in your facility. It is also not clear whether the POCO's primary side supply system was also ungrounded in which case it is likely that the damaging transient over voltages originated there.
aelectricalman
Senior Member
- Location
- KY
I do know that on XFMR 1, that feeds two parallel equally sized 3000amp gear, one of the two services has the grounding protection but is turned off. The other was not installed. Had the 1st service been turned on, it would have only protected its service. Why one had it and the other did not is beyond me.
Also, the second XFMR did not have any protection.
This is the likely culprit. I do know exactly what the power company supplied to the facility. That is 480V ungrounded Delta. The reference to the A and/or C phase (depending on the service), is caused by the customer. Confirmed.
ATSman
ATSman
- Location
- San Francisco Bay Area
- Occupation
- Electrical Engineer/ Electrical Testing & Controls
STRIKING GROUND PHENOMENON ON UNGROUNDED SYSTEMS
STRIKING GROUND PHENOMENON ON UNGROUNDED SYSTEMS
? "Striking Ground Phenomenon
When one phase of an ungrounded system is grounded, as in the case of the PFCCB on the 12KV line, the other two phases are above ground by the phase voltage. When the ground is removed, the capacitance on the other two phases, acting like a single capacitor on each phase, holds a charge and maintains a voltage to ground as a DC offset voltage. If the phase is re-grounded, an additional voltage can be added to the capacitance of the other two phases, depending on the point of the AC voltage wave at which the conductor is grounded and ungrounded. If the ground is intermittent, such as a sputtering or arcing fault, the voltage can continue to build up until some insulation fails. This voltage to ground can easily reach six to eight times the phase voltage.
Note that this overvoltage is from the two (2) ungrounded phases to ground and that the phase to phase voltage of 12KV is not affected. These elevated voltages can and will pass through step-down transformers and cause multiple failures at widely separated points in the LV (480V, 208V) systems. SFE has witnessed several instances where this type of damage has occurred.
? Surge Protection Devices (SPD, formally known as TVSS)
An inspection of the buildings electrical distribution system revealed that no SPD devices were found installed at the building main breaker panel or the HSP fed from the main breaker. Even if an SPD had been installed in either of these panels it?s questionable whether or not this would have prevented the wide-spread damage caused by this event. SPD are only effective when they are sized properly and installed no further than 1? to 3 feet from the equipment they are protecting.
SFE recommends that SPDs be installed on the main bus of each bay of the Lucent Technology Rectifier Cabinets on the three 48VDC plants and both Main Breaker Panel and HSP panels."
This was taken from a report I wrote after investigating an incident that occurred in a phone co. central office here where (37) rectifier modules (200A each) failed after a power factor correction capacitor bank faulted on the 12KV Poco line feeding the buildings 12KV-480/277V transformer.
We were able to call the surrounding CO's to bring spare replacement modules to make the repairs before the (3) 48VDC battery plants were drained down. Due to the great team effort of internal techs and outside vendors, no calls were lost!
STRIKING GROUND PHENOMENON ON UNGROUNDED SYSTEMS
? "Striking Ground Phenomenon
When one phase of an ungrounded system is grounded, as in the case of the PFCCB on the 12KV line, the other two phases are above ground by the phase voltage. When the ground is removed, the capacitance on the other two phases, acting like a single capacitor on each phase, holds a charge and maintains a voltage to ground as a DC offset voltage. If the phase is re-grounded, an additional voltage can be added to the capacitance of the other two phases, depending on the point of the AC voltage wave at which the conductor is grounded and ungrounded. If the ground is intermittent, such as a sputtering or arcing fault, the voltage can continue to build up until some insulation fails. This voltage to ground can easily reach six to eight times the phase voltage.
Note that this overvoltage is from the two (2) ungrounded phases to ground and that the phase to phase voltage of 12KV is not affected. These elevated voltages can and will pass through step-down transformers and cause multiple failures at widely separated points in the LV (480V, 208V) systems. SFE has witnessed several instances where this type of damage has occurred.
? Surge Protection Devices (SPD, formally known as TVSS)
An inspection of the buildings electrical distribution system revealed that no SPD devices were found installed at the building main breaker panel or the HSP fed from the main breaker. Even if an SPD had been installed in either of these panels it?s questionable whether or not this would have prevented the wide-spread damage caused by this event. SPD are only effective when they are sized properly and installed no further than 1? to 3 feet from the equipment they are protecting.
SFE recommends that SPDs be installed on the main bus of each bay of the Lucent Technology Rectifier Cabinets on the three 48VDC plants and both Main Breaker Panel and HSP panels."
This was taken from a report I wrote after investigating an incident that occurred in a phone co. central office here where (37) rectifier modules (200A each) failed after a power factor correction capacitor bank faulted on the 12KV Poco line feeding the buildings 12KV-480/277V transformer.
We were able to call the surrounding CO's to bring spare replacement modules to make the repairs before the (3) 48VDC battery plants were drained down. Due to the great team effort of internal techs and outside vendors, no calls were lost!
ATSman
ATSman
- Location
- San Francisco Bay Area
- Occupation
- Electrical Engineer/ Electrical Testing & Controls
PFCCB Failure Case Study
PFCCB Failure Case Study
Case study on the subject. Mild cases cause software problems such as describe here. Extreme cases causes equipment damage.
http://dranetz.com/case-studies/utility-power-factor-capacitor-bank-switch-problem
PFCCB Failure Case Study
Case study on the subject. Mild cases cause software problems such as describe here. Extreme cases causes equipment damage.
http://dranetz.com/case-studies/utility-power-factor-capacitor-bank-switch-problem
- Status