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Tapping off an ungrounded 1000VDC Bus
- Thread starter LMAO
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rcwilson
Senior Member
- Location
- Redmond, WA
I'll answer your question with an example I ran into last week.
The 125VDC was ungrounded and fed a distribution panel that had all single pole breakers on the + bus. Negative wires to the loads were directly connected to the negative bus. The electrician locked out the pump circuit by opening the breaker and tagged it.
While he was working in the pump panel, an accidental ground was applied to 125VDC positive bus. That forced the negative bus to -125VDC to ground. All the "de-energized" wires inthe panel now became hot with 125VDC. A few sparks occurred and some wires melted, but fortunately no injuries. We changed to 2-pole breakers.
At 1,000 VDC, there may be some injuries if you only fuse one leg and that leg gets grounded. Either ground the negative bus, or use two-pole brekaers or two fuses. No unprotected wires.
The 125VDC was ungrounded and fed a distribution panel that had all single pole breakers on the + bus. Negative wires to the loads were directly connected to the negative bus. The electrician locked out the pump circuit by opening the breaker and tagged it.
While he was working in the pump panel, an accidental ground was applied to 125VDC positive bus. That forced the negative bus to -125VDC to ground. All the "de-energized" wires inthe panel now became hot with 125VDC. A few sparks occurred and some wires melted, but fortunately no injuries. We changed to 2-pole breakers.
At 1,000 VDC, there may be some injuries if you only fuse one leg and that leg gets grounded. Either ground the negative bus, or use two-pole brekaers or two fuses. No unprotected wires.
I'll answer your question with an example I ran into last week.
The 125VDC was ungrounded and fed a distribution panel that had all single pole breakers on the + bus. Negative wires to the loads were directly connected to the negative bus. The electrician locked out the pump circuit by opening the breaker and tagged it.
While he was working in the pump panel, an accidental ground was applied to 125VDC positive bus. That forced the negative bus to -125VDC to ground. All the "de-energized" wires inthe panel now became hot with 125VDC. A few sparks occurred and some wires melted, but fortunately no injuries. We changed to 2-pole breakers.
At 1,000 VDC, there may be some injuries if you only fuse one leg and that leg gets grounded. Either ground the negative bus, or use two-pole brekaers or two fuses. No unprotected wires.
You are correct and your answer was what I had in mind.
this is a DC link (recfier output) feeding a bunch of inverters. Also, it actually IS grounded. we tap off DC link with a couple of 1k or 10k resistors and connect the resistors other end and ground them. It is a wierd setup.
rcwilson
Senior Member
- Location
- Redmond, WA
DC Link bus on a multi-VFD drive would normally be ungrounded, but not floating. Resistors, like the 10K you mentioned, are connected from each bus to ground. If there is no ground fault, each bus is at 500V to ground. Ground detector circuits monitor the bus-ground voltage and alarm if a fault occurs.
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