Ground Current... Caused by motors?

[brian john]

Re: Ground Current... Caused by motors?

Walt there ARE; as previously mentioned, a number of steps one can take to minimize outage time IN LOCATING NEUTRAL GROUNDS.

If you do go the outage route i WOULD start at the main service isloate the neutrals one at a time then work the panels, THEN THE BRANCH CIRCUITS.. A megger at 100 volts dc is what we use.

Ust a thought.

 

[hurk27]

Re: Ground Current... Caused by motors?

Don
As I was reading the manual I can across this.

8.3.3 High Efficiency Mode
A High Efficiency Mode is available that allows the UPS to operate in an offline
bypass mode. In this mode, the UPS is operating on bypass, with the power
processing unit in standby, ready to automatically transfer to normal mode if a
commercial electrical power brownout, blackout, overvoltage, undervoltage, or
out-of-tolerance frequency condition occurs.

This is why I was thinking that it was set in this mode is that there would be no transfer in this unit if it is in normal mode as the load is always on the inverter, and this was one of the problems he mention in a prevous post.

would not consistently transfer to battery upon power outage

If this is a dual conversion UPS it would always be on unless it was in High Efficiency Mode.

I havent worked on many of these but I have ran into simular problems with standby systems. and when I read that this UPS does have that feature. It clicked.

I still think there is a ground bond on the neutral But now I don't think it could be the cause of the problem as in the wiring diagrams the input/bypass neutral is directly connected to the output neutral and the SDS neutral and does not go through the bypass switch like I thought. so it is always connected. The only thing that the bond will do is place parallel current on the grounding.

[ December 29, 2003, 09:26 PM: Message edited by: hurk27 ]

 

[waltppiva]

Re: Ground Current... Caused by motors?

Hurk: That's definately something that I will verify, whether or not the unit is running in high efficiency mode. Thanks.

Brian: Good advice regarding going about tracing bonds. That's what I had in mind. Thanks.

 

[don_resqcapt19]

Re: Ground Current... Caused by motors?

Wayne,
I looked at the drawing again and see that there is both a manual and a static bypass switch. I didn't think about the static bypass switch when I made my earlier post.
Don

 

[don_resqcapt19]

Re: Ground Current... Caused by motors?

Walt,
You have stated a couple of times that the normal source grounded conductor is connected directly to the UPS output grounded condcutor. I don't see how that is the correct connection for this UPS unit.
Don

 

[hurk27]

Re: Ground Current... Caused by motors?

Don
The reasone for this supply side neutral is because of the maintenance bypass switch. without it the neutral would float. the only way acording to the diagrams is if there is a isolating transformer installed (which he stated there wasn't) then there would be a derived neutral off this transformer.
But as the print shows this neutral is routed through the UPS to the output neutral E-12 terminal It even has the same terminal ident. E-12

[ December 29, 2003, 09:52 PM: Message edited by: hurk27 ]

 

[hurk27]

Re: Ground Current... Caused by motors?

Don I should add that since this UPS has two input's (main rectifier/bypass) when only one power source is used there is jumpers between the two. The rectifer input (inverter) does not need the neutral and there is no terminal for it but at the bypass terminals there is a input neutral terminal in the diagram for the one without any isolation transformers there is not suppose to be a bond to ground and this neutral just connects the to the output neutral along with the neutral from the Boost converter output. but not in any way should this neutral ever be bonded to ground.

Here is a quote from page 7-5 in the manual:

"The DC boost converter derives power from the unregulated DC rectifier and produces an elevated and stable DC voltage and current source for the inverter.
The boost converter also establishes the systems output neutral for supporting
single phase AC loads from any phase of the inverter output.
The output neutral of the system is connected with the required neutral supplied at the utility bypass input (E-12) and should never be bonded to ground at the modules output. The inverter produces a three phase AC output to a customers load without the use of a transformer.
The inverter derives power from the boost converters regulated DC and utilizes IGBT devices and pulse---width modulation (PWM) to produce a regulated and filtered AC output. The AC output of the inverter is delivered to the system output through the output contactor (K3)."

[ December 30, 2003, 02:04 AM: Message edited by: hurk27 ]

 

[don_resqcapt19]

Re: Ground Current... Caused by motors?

Wayne,

The boost converter also establishes the systems output neutral for supporting single phase AC loads from any phase of the inverter output.

That makes the output of the UPS a separately derived system.

The output neutral of the system is connected with the required neutral supplied at the utility bypass input (E-12) and should never be bonded to ground at the modules output.

The code requires a grounding electrode connection to the SDS. This manual requires an installation that is a code violation. It appears to me that they are using the utility source grounded conductor to provide the grounding electrode system for the output of the UPS.
Don

 

[hurk27]

Re: Ground Current... Caused by motors?

I agree It is a design flaw as when this unit is in bypass mode It is a non-sds but when it is in normal mode it is a sds the problem is installing a bond to the neutral for normal mode only. because the neutral (E-12) runs through the UPS and connects both input and output neutrals together it would require that the bypass switch to disconnect the bond or the neutral to the utility feed depending on the mode.

I'm just wondering if because of the neutral feeding through the UPS if this could be classified as a non-SDS system even though the inverter does isolate the output circuit?
If we look at article 100 definition of a Separately Derived System it say's for it to be a Separately Derived System there will be no solidly connected grounded circuit conductor, to supply conductors originating in another system. But this UPS does have this? so would it be treated like a non-SDS? If so then there should be no bond.
Or is this just a loop hole to allow the manufacture to get away without switching the neutral?

Separately Derived System. A premises wiring system whose power is derived from a battery, from a solar photovoltaic system, or from a generator, transformer, or converter windings, and that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.

The only problem I can see with this is the fact that any ground fault on the output side of the UPS will flow through the main service bonding jumper and this could be located at too far a distance to allow for a fast fault clearing. of course a GFP would solve this.

[ December 30, 2003, 07:16 PM: Message edited by: hurk27 ]

 

[hurk27]

Re: Ground Current... Caused by motors?

Don The code requires a grounding electrode connection to the SDS.

It is not the electrode that the code requires that is the main problem. yes the code does require an electrode but it is the main bonding jumper that is most inportant as without it there would be no fault return path. because a SDS supply neutral no longer has a connection to the grounding conductor. I look at it this way when we have a SDS supply system it is like we just started a new service from that point so a neutral/ground bond has to be made and a new connection to the electrode system has to be made. we can use the main service electrode if it is close enough. but 250.30 does say it has to be the closer one of the available electrode connections.
Or we can use the exception to (1) (2) (3) in 250.30 (A) (4) that allows use to use the same electrode that the service feeding the SDS is useing. Or I'm I getting mixed up?

By the way just got my IAEI card and package. So I still have much to learn LOL

 

[don_resqcapt19]

Re: Ground Current... Caused by motors?

Wayne,
You are correct that the bonding jumper between the output grounded conductor and the equipment grounding conductors for the circuits that are supplied by the UPS is more important than the grounding electrode system.
Even with the direct connection to the utility grounded conductor, I still see the UPS as an SDS. The utility grounded conductor is not a "circuit conductor" for the output of the UPS. The utility grounded conductor is being used as the GEC for the UPS output. This is really the same as a transformer where the grounding conductors of both the primary and secondary systems are tied together.
Don

 

[waltppiva]

Re: Ground Current... Caused by motors?

Originally posted by hurk27:
Here is a quote from page 7-5 in the manual:

... "The boost converter also establishes the systems output neutral for supporting
single phase AC loads from any phase of the inverter output..."

Page 7-5 in my manual is totally different. Are you sure you have the right unit (Powerware 9330-20). I did find a section in the Service manual that refers to a Neutral Regulator on page 7-10/section 7-4. "The name Neutral Regulator indicates that this circuit may have something to do with the control or creation of the system AC neutral like what is typically seen at the output of a wye type transformer, in fact, it does not. The unit uses the neutral provided to its input from the utility feed like many loads which require a neutral. In this particular case, the term refers to maintaining a balance from the positive DC link and negative DC link to the systems neutral input.

Without the neutral regulator, various single phase non-linear loads can create an imbalance in the boost output voltage as referenced to the systems neutral. Under severe conditions, the inverter may not be able to maintain its own output and may be forced to transfer the applied load to utility bypass until the condition clears itself. With the Neutral Regulator, DC link balance is able to be maintained allowing these types of loads to be supported."

Also, in the Owner's Manual there is a drawing that shows the wiring schematic for the unit in question. It is on page A-31, titled UPS System Options Cabinet Configurations Powerware 9330 (10-20kVA) Page 2 of 8.
This drawing shows the input neutral (terminated at the Bypass connection) jumpered directly to the output neutral. The maint bypass switch used in the options cabinet does not switch the neutral, only the phases.

Hope this clears things up.

 

[hurk27]

Re: Ground Current... Caused by motors?

Walt
I'm sure the online manual has been updated and may differ from your manual. but the same terms were described in this manual too. I don't have it on this computer I'm at right now but yes the one I'm using is for the PowerWare 9330-10/20 I think the 10/20 is because they combined the two manual's But what you described in the diagram is exactly what Don and Me is referring to is the violation of the nec. This UPS is a dual system. In the bypass or high efficiency mode it is configured as a non-SDS system, but when it is in normal mode the boost converter provides a separately derived neutral which must be bonded to the neutral for fault current. This is done but in a very unorthodox way as now the fault current depends on the bond back at the main service to open the OCPD and if this UPS system is located far from this main service the resistance loss in the circuit conductors and ground wire can be enough to cause the opening of the breaker to take to long causing any thing from wire failure to as much as a fire. now if the ground wire is up sized for this loss then I can't see a problem.
But I still think the problem you originally stated "sluggish transferring" would mean that the system is in high efficancy mode as it should not be transferring at all in normal mode. but there is a check list that say's this unit will switch on it's own if there is any problem in the output of the UPS. so there may be other problems too and when you get your shutdown window things like inverter output voltage, frequencies, sink with POCO frequency, all would cause this unit to transfer to standby. Should be checked. The manufacture as a e-mail address maybe you could Invite them in here to answer some of these question's and get a better answer?

 

[hurk27]

Re: Ground Current... Caused by motors?

Don This is really the same as a transformer where the grounding conductors of both the primary and secondary systems are tied together.
Don

So is this a violation of the NEC?
If not I think it just removes this system from being a SDS system wouldn't it? Making it a NON-SDS inwhich would not require the Bond? or the electrode.

 

[don_resqcapt19]

Re: Ground Current... Caused by motors?

I think that it is an SDS and the installation per the manual is in violation of the NEC rules.
Don

 

[waltppiva]

Re: Ground Current... Caused by motors?

Wayne, sounds like we're getting conflicting information from their documentation. I have sent an e-mail to Powerware and invited them into this discussion for clerification on this issue. We'll see what happens.

HOPE EVERYONE HAS A HAPPY & SAFE NEW YEAR!!!

 

[hurk27]

Re: Ground Current... Caused by motors?

Walt that would be good.

Don Think of this. A generator is a SDS until the neutral is wired to the supply and load. so why wouldn't this apply to a UPS?

[ January 01, 2004, 07:55 PM: Message edited by: hurk27 ]

 

[don_resqcapt19]

Re: Ground Current... Caused by motors?

Wayne,
You have a point with the generator comparision, but I don't like the idea of the remote main bonding jumper for the output of the UPS. I just read an article yesterday that pointed out how limited the output of an UPS is under short circuit and ground fault conditions. The output current under those conditions is often too low to cause the OCPD to open quickly. The remote main bonding jumper that results for a common neutral would reduce this fault current even more.
I guess part of my problem with this is the fact that the UPS system that I have worked with the most requires the grounding electrode connection to the UPS. Powerware FERRUPS UPS.
Don

 

[hurk27]

Re: Ground Current... Caused by motors?

That's why I said before that it is a very poor design. Unless the manufacture requires this UPS to be installed close to the main service? Or requires that the neutral to be over sized?

When I get a little more time I'll go through the manual to see if these requirements are in there. Now the UPS that has the isolation transformer does bond the output neutral to the grounding conductor and has a factory jumper right there for this. But there is no neutral connection between the input neutral to the output neutral. So it is a true SDS. And even has the requirement for the grounding electrode just as if this was a service but there is no connection to the main service from ether the neutral or the EGC,or GEC. As it is totally isolated.

 

[hurk27]

Re: Ground Current... Caused by motors?

Walt I hope you will let us know what you find out.
Thank's