120V 3 Phase supply on 120V single phase designed system - Earth Fault

DJDUNKY · Mar 26, 2012

Hi Guys,

We have a system installed in a marine enviroment. The system has 2 power supplies coming in to it. One is 3 phase 440VAC 60Hz and is used only to power a pump motor. The other is a 120VAC 60Hz supply for the control circuit etc. The panel consists of a PLC, 24VDC power supply, some relays, contactors and an E/Stop relay.

The system was designed to take a single phase 120VAC supply but we have found out that it is in fact being supplied by 2 phases of a 120VAC 3 phase supply.

The customer is reporting an earth fault on their detection system when the system is powered up and it disappears when powered down.

I initially thought it may be the incoming EMC filters but I have bypassed these and there is no change.

I have disconnected earth loops as well as disconnecting components but i cannot seem to track this down.

We have supplied 6 of these systems but they are reporting this problem on 4 of them.

Can anyone see an obvious way to test this or is it a needle in a haystack thing?!

Thanks

DJ

malcolmsanford · Mar 26, 2012

I'm assuming the system is incorporating a residual current monitor (RCM) have you set up the correct parameters?

DJDUNKY · Mar 26, 2012

Hi Malcolm, Unfortunately I do not know what type of RCM they are using on board until I attend again on Wednesday. I just wanted to try and understand where this may be coming from or being derived from.

Engineer54 · Mar 26, 2012

Can you post up the manufacturers schematic drawing for this system?? Makes things so much easier to see what were talking about analyse!!

DJDUNKY · Mar 26, 2012

Unfortunately I cannot as it's ITAR and as the system is for MOD we are not allowed to divulge such information.

It really is a simple system with a PLC, an HMI on the door etc with some relays, contactors and a 24VDC power supply. I am thinking that maybe one of the 120VAC components does not like being fed from 2 phases of a 120VAC 3 phase supply?

malcolmsanford · Mar 26, 2012

It does seem strange that out of the 6 systems you have installed 4 are causing a problem and 2 are functioning fine. To me unless you have had a bad batch of components and installed these into 4 of your systems, the other 2 have others, then the common factor is the RCM.

It would seem you do have some sort of conflict and I'm wondering if the 4 offending systems have a set up problem. My first look would be the RCM, and see what the tolerances are on the monitoring.

Really they are just basically a transformer where the load side LIVE conductors are monitored and should have a zero current and no induced voltage. Once you get a fault then voltage and current is diverted onto the CPC and then the transformer detects the in balance and alarms ....................very similar to the RCD.

Often there are settings or tolerances that can be set up on these.

Knobhead · Mar 26, 2012

It begs the question why has a different transformer been used? Is the stat point of this supply earthed?

plugsandsparks · Mar 26, 2012

I would use my brand new earth leakage clamp meter and go hunting. Would be useful to know, e.g. what size of current causes the alarm etc before you start and of course a good drawing to work out potential leakage areas, at least with a meter you can get a reading and start to pick away at components to see what effect they have on the reading.

DJDUNKY · Mar 27, 2012

plugsandsparks said:
I would use my brand new earth leakage clamp meter and go hunting. Would be useful to know, e.g. what size of current causes the alarm etc before you start and of course a good drawing to work out potential leakage areas, at least with a meter you can get a reading and start to pick away at components to see what effect they have on the reading.

What make an model clamp meter are you using?

Engineer54 · Mar 27, 2012

Why haven't you contacted the manufacturers of these units?? Got to be better than a bunch of guys guessing the contents and the possible problems of this equipment!!!

DJDUNKY · Mar 27, 2012

Engineer54 said:
Why haven't you contacted the manufacturers of these units?? Got to be better than a bunch of guys guessing the contents and the possible problems of this equipment!!!

I am the manufacturer!!! There is no reason for the earth fault but I cannot get to check this personally until the ship is nearby. They have had their own electricians looking for the fault but they have had no luck either.

Engineer54 · Mar 27, 2012

DJDUNKY said:
Hi Guys,

We have a system installed in a marine enviroment. The system has 2 power supplies coming in to it. One is 3 phase 440VAC 60Hz and is used only to power a pump motor. The other is a 120VAC 60Hz supply for the control circuit etc. The panel consists of a PLC, 24VDC power supply, some relays, contactors and an E/Stop relay.

The system was designed to take a single phase 120VAC supply but we have found out that it is in fact being supplied by 2 phases of a 120VAC 3 phase supply.

If your the manufacturer, Why are you surprised that 2 phases are being used for your 120V?? You have been asked what the earthing arrangement is for this isolating transformer, but no response so far?? Malcolm has asked about RCM or insulation monitors and settings, again no conformation of an RCM or insulation monitor being incorporated, or on the settings!!!

Surely if you built these units, you should know what components you have used in there construction!!

DJDUNKY · Mar 27, 2012

Engineer54 said:
If your the manufacturer, Why are you surprised that 2 phases are being used for your 120V?? You have been asked what the earthing arrangement is for this isolating transformer, but no response so far?? Malcolm has asked about RCM or insulation monitors and settings, again no conformation of an RCM or insulation monitor being incorporated, or on the settings!!!

Surely if you built these units, you should know what components you have used in there construction!!

Did you get out of the wrong side of bed this morning?

We have provided a unit specifically for a specified application. The user has now decided to change the supply from what was originally going to be 120V Live with a neutral to a 2 phase supply from a marine generator. We have no details or information and are not privvy to the type or setup of the detection system they are using which will be for all systems on board.

Knobhead · Mar 27, 2012

Without information nobody can progress. If the end user won’t give the information and changes their requirement then your looking for this place
View attachment 11462

Engineer54 · Mar 28, 2012

DJDUNKY said:
Did you get out of the wrong side of bed this morning?

We have provided a unit specifically for a specified application. The user has now decided to change the supply from what was originally going to be 120V Live with a neutral to a 2 phase supply from a marine generator. We have no details or information and are not privvy to the type or setup of the detection system they are using which will be for all systems on board.

No, it just seemed strange that your the manufacturer, of this unit but don't know what the specified application is for how or what is being used!! Oh, and Marine supplies are basically an IT derived system... which is why i added the Insulation monitor in my last post!

vaughant · Mar 28, 2012

Only seen something similar to this once before and it was the power supply not being tied to earth.it was giving me strange readings all over the place but the giveaway was dim lights and 9v between neutral and earth.turned out the boys had changed a psu but shoved it in the panel at the bottom rather than bolting it up to the metal frame.
Just thinking you maybe getting some odd readings cos of the 2 phases?