Elevator Boost Transformer

[Coachmike]

Two elevator cars running in a self storage facility. Car #1 is on it's 2nd transformer and has same issue as original transformer.
Transformer info below. According to the elevator co. they have replaced the VVVF drive- an AC Regeneration Unit.
Car#2 has no issues with similar equipment.

 

[jim dungar]

Make sure there is NO primary side neutral conductor from the 208V source.

 

[Coachmike]

No primary neutral conductor.
Transformer neutral connection is bonded to ground.
There is no secondary neutral.

 

[LarryFine]

Transformer neutral connection is bonded to ground.

Just as bad. The primary neutral on a wye-delta transformer should be left floating, as if it was a delta primary.

Wait, you have a wye-wye transformer, but the secondary neutral is floating? That sounds wrong by itself..

 

[tortuga]

Two elevator cars running in a self storage facility. Car #1 is on it's 2nd transformer and has same issue as original transformer.
Transformer info below. According to the elevator co. they have replaced the VVVF drive- an AC Regeneration Unit.
Car#2 has no issues with similar equipment.

Whats the nameplate amps of the drive?

 

[jim dungar]

Just as bad. The primary neutral on a wye-delta transformer should be left floating, as if it was a delta primary.

Wait, you have a wye-wye transformer, but the secondary neutral is floating? That sounds wrong by itself..

Now I see, the transformer is actually a wye autotransformer not a wye-wye isolation style. You do not have a separately derived system.

By bonding the 'secondary' neutral to ground, you have effectively created a neutral to ground point different than the one at your 208V service. I believe you should run a neutral conductor from your source to the autotransformer and end it there, do not rebound it at the transformer. Bond the transformer core and enclosure to your EGC.

 

[LarryFine]

Now I see, the transformer is actually a wye autotransformer not a wye-wye isolation style. You do not have a separately derived system.

You're right. I didn't look at the image. A neutral is needed.

By bonding the 'secondary' neutral to ground, you have effectively created a neutral to ground point different than the one at your 208V service. I believe you should run a neutral conductor from your source to the autotransformer and end it there, do not rebound it at the transformer. Bond the transformer core and enclosure to your EGC.

Agreed. You do need a source neutral run to the transformer.

 

[Coachmike]

Thank you gentlemen,
Engineers drawings show 3 phases and a ground. No neutral.
For clarity, a neutral should be run from source panel to N.
And the transformer case should be grounded via EGC.
Both Car's transformers are wired the same and car #2 has no issues.

 

[tortuga]

Still need the nameplate info of the drive.

 

[Coachmike]

Still need the nameplate info of the drive.

efforting

 

[LarryFine]

Engineers drawings show 3 phases and a ground. No neutral.
For clarity, a neutral should be run from source panel to N.

I would contact them to be sure, but I believe the neutral is required for the secondary voltages to be steady.

And the transformer case should be grounded via EGC.
Both Car's transformers are wired the same and car #2 has no issues.

Yes, grounding always. If #2 works wired the same, you need to find out what is different between them.

 

[jim dungar]

You could also try just lifting all connections to the N terminal, if your load is three wire. Just run the source side EGC to the transformer case and coil then to the load.

Part of the problem is your transformer output is not a separately derived system, but it got wired as one.

If the initial wiring was the same, maybe the question should be why hasn't transformer #2 failed?

 

[Coachmike]

UPDATE- the elevator contractor repaired something on the load side and blew a 60a fuse while doing so.
They then asked us back to test and everything worked.
Of course the elevator contractor would not admit they fixed anything.
As then all our time would be billable to them.
Thank you all for your input.

 

[Scozadd]

Two elevator cars running in a self storage facility. Car #1 is on it's 2nd transformer and has same issue as original transformer.
Transformer info below. According to the elevator co. they have replaced the VVVF drive- an AC Regeneration Unit.
Car#2 has no issues with similar equipment.

View attachment 2561584

I know old thread, but Schindler is providing same transformer to us and it's blowing the primary fuses with no load attached. Any suggestions?

 

[Coachmike]

Are you using dual element/ slo blo fuses? You have to account for inrush current.

 

[Scozadd]

low-peak, dual element time delay. This is from their submittals. Sent the transformer out with 20a fuses on the primary and 50a fuses on the secondary.

 

[Coachmike]

What size are the conductors?
Primary OCP should be higher amperage than secondary OCP on a boost transformer.

 

[Coachmike]

We had 60 amp OCP on primary 208v
and 40 amp OCP on secondary 480v
On our 20 KVA transformer feeding the Schindler MRL elevator.

 

[jim dungar]

low-peak, dual element time delay. This is from their submittals. Sent the transformer out with 20a fuses on the primary and 50a fuses on the secondary.
View attachment 2563632

I would think 100A primary (low voltage) side might even be too small given the spec says input FLA is 88.8A. But you need to select your fuse based on the time current information provided for the inrush current.

 

[Scozadd]

We had 60 amp OCP on primary 208v
and 40 amp OCP on secondary 480v
On our 20 KVA transformer feeding the Schindler MRL elevator.

We have 60a ocp on primary 208v feeding Schindler transformer. Guessing that even the 50a primary fuse is too small.