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Old 12-28-2018, 11:12 AM   #1
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Default Burning up cores/transformers

A bit of a unique situation and I'm reaching out to those with more knowledge than myself. Most everyone on this forum...
As some know, I'm an airport guy. Our airfield lighting is a series cct, constant current(6.6A), variable voltage. The field ccts are powered by a constant current regulator, CCR. Our airfield is about 95% LED. Every light has an isolation transformer.


Now to the problem, we have almost 50% of our cores( the transformer in the regulators) that now have a burn in them and I'm not able to operate at 6.6A. The tech thinks it may have been a lighting strike but we are talking 24 out of 54 regs with the same problem in the same spot on the core. We are sending one back to the factory for bench testing.


My PF in the building is 0.26, yes that is a correct.
Do you think that such a low PF may be overloading my cores and causing the burns that we have found?


We have tested the regs with a resistive load bank but that is so much different than the field load.


Tim.
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Old 12-28-2018, 03:22 PM   #2
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How are your ground readings? How often do you maintain the ccrs?
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Old 12-28-2018, 03:24 PM   #3
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Quote:
Originally Posted by canbug View Post
Our airfield lighting is a series cct, constant current(6.6A), variable voltage. The field ccts are powered by a constant current regulator, CCR. Our airfield is about 95% LED. Every light has an isolation transformer.


My PF in the building is 0.26, yes that is a correct.
Do you think that such a low PF may be overloading my cores and causing the burns that we have found?
I'd do the math and see how that compares to the regulators rating.

W/I x pf = V
The voltage is certainly going to be much higher at such a low power factor
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Old 12-28-2018, 03:37 PM   #4
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Originally Posted by canbug View Post
A bit of a unique situation and I'm reaching out to those with more knowledge than myself. Most everyone on this forum...
As some know, I'm an airport guy. Our airfield lighting is a series cct, constant current(6.6A), variable voltage. The field ccts are powered by a constant current regulator, CCR. Our airfield is about 95% LED. Every light has an isolation transformer.


Now to the problem, we have almost 50% of our cores( the transformer in the regulators) that now have a burn in them and I'm not able to operate at 6.6A. The tech thinks it may have been a lighting strike but we are talking 24 out of 54 regs with the same problem in the same spot on the core. We are sending one back to the factory for bench testing.


My PF in the building is 0.26, yes that is a correct.
Do you think that such a low PF may be overloading my cores and causing the burns that we have found?


We have tested the regs with a resistive load bank but that is so much different than the field load.


Tim.
Is this and LED retrofit installation or were these installed new as LED.
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Old 12-28-2018, 04:10 PM   #5
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Why is the power factor so low?
What is the max KW of the regulators?
What is the input voltage and output voltage, when properly operating?
Any issues with the isolation transformers?
Was there a know lightning strike in the area, prior to the failures or have you had regular lightning strikes?
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Old 12-28-2018, 04:47 PM   #6
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To answer a few questions;


How are your ground readings? How often do you maintain the ccrs?
Meggered monthly and all above 2 gig. Factory rep here every 6 months for PMs.


The Regs are not even close to the rating. We have 7, 15 ad 20KW


Is this and LED retrofit installation or were these installed new as LED.
New install, fixtures and regulators all from the same manufacturer in 2013.


I don't know why the PF is low other than the LEDs. Lights on, PF 0.27. Lights off and some basic building loads, PF 0.91

We have had lighting in the area but to affect 24 CCRs in the same physical location of the core just doesn't sound right.

Input voltage is 600 but because it is a constant current output, the output voltage varies. We have ccts that run at 700v all the way up to 1800v. The current is a steady 6.6A

We are sending one back to the manufacturer next week for more in depth bench testing.


Tim


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Old 12-28-2018, 06:02 PM   #7
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Quote:
Originally Posted by canbug View Post
To answer a few questions;


How are your ground readings? How often do you maintain the ccrs?
Meggered monthly and all above 2 gig. Factory rep here every 6 months for PMs.


The Regs are not even close to the rating. We have 7, 15 ad 20KW


Is this and LED retrofit installation or were these installed new as LED.
New install, fixtures and regulators all from the same manufacturer in 2013.


I don't know why the PF is low other than the LEDs. Lights on, PF 0.27. Lights off and some basic building loads, PF 0.91

We have had lighting in the area but to affect 24 CCRs in the same physical location of the core just doesn't sound right.

Input voltage is 600 but because it is a constant current output, the output voltage varies. We have ccts that run at 700v all the way up to 1800v. The current is a steady 6.6A

We are sending one back to the manufacturer next week for more in depth bench testing.


Tim

Did you say .27 PF ??? that is way too low that what can cause to overheat the transfomers.

what wattage the LED are you running on the airport system ( taxiway and main runway ) ??

I am suspecting with that low a PF you have sound like you do have serious issue with the circuit seems to tell me that something is " shorting " something out.

Did you try just turn the taxiway led light on and read the PF ? ditto with runway alone ( is this runway do have multi light level or just single brightness ? )

what type of series voltage regulator you are running ?
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Old 12-28-2018, 07:39 PM   #8
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Originally Posted by canbug View Post
To answer a few questions;


I don't know why the PF is low other than the LEDs. Lights on, PF 0.27. Lights off and some basic building loads, PF 0.91

We are sending one back to the manufacturer next week for more in depth bench testing.


Ti
You need to find the source of this low pf. Trying isolating one regulator at a time.
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Old 12-28-2018, 07:57 PM   #9
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Only thing that burns out transformers is toouch current,
So either the transformers are NOT fit for the job ?
Or
Other issue's are involved increasing current flow,
If you PF is really that low ?
Then start there
Possibly a pf correction capacitor may help !

But check for faults first
Having that many electronic power supplies one circuit
is bound to be a tricky load to start with,

because they are highly reactive.


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Old 12-28-2018, 08:16 PM   #10
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2 gig? That's great readings.

We have had multiple regulators go on fire feeding poor circuits. If you had bad ground readings I would have suggested that being the cause or as you mentioned a lightning strike. You mentioned it is a new system, the leds and regulators are both new? Were they installed by a decent contractor? We have found metal shavings, tools, rags etc found in regulators from both contractors and in house guys. If conduits enter through the top of the gear maybe check for metal shavings?

We have a very poor power factor at our switch houses as well, not sure if it is as poor as yours, will check sometime next week.
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Old 12-28-2018, 08:43 PM   #11
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2 gig? That's great readings.

We have had multiple regulators go on fire feeding poor circuits. If you had bad ground readings I would have suggested that being the cause or as you mentioned a lightning strike. You mentioned it is a new system, the leds and regulators are both new? Were they installed by a decent contractor? We have found metal shavings, tools, rags etc found in regulators from both contractors and in house guys. If conduits enter through the top of the gear maybe check for metal shavings?

We have a very poor power factor at our switch houses as well, not sure if it is as poor as yours, will check sometime next week.
Explain what you mean by ground readings. Are you saying the windings to ground?
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Old 12-28-2018, 08:44 PM   #12
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Quote:
We have tested the regs with a resistive load bank but that is so much different than the field load.
What was the line side pf when utilizing a resistive load bank.
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Old 12-28-2018, 11:16 PM   #13
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Are these the older 'sliding core' type or SCR type?

A PF of .27 doesn't sound all that far off to me considering what the load is. If the regulators were loaded more heavily, the PF would go up.

Is there any chance that more than one regulator is connected to the same secondary circuit? If so, they'll fight with each other until one of them burns up.

With normal incandescent lamps, there are no harmonics but with LEDs, they are present. It's possible that the harmonics are amplified in the field CTs and cause spikes in the regulator coil. Sort of like a flyback circuit in older CRT type TV.
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Old 12-29-2018, 12:03 AM   #14
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@brianjohn what I mean by ground readings is removing the regulator from service, looping the field circuit out and meggering the circuit to ground to test its insulation resistance.

As the insulation breaks down the regulators pump out more voltage to keep the current the same. Which if the readings were bad, can lead to the regulators failing.
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Last edited by Apelectric; 12-29-2018 at 12:05 AM.
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Old 12-29-2018, 01:28 PM   #15
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@brianjohn what I mean by ground readings is removing the regulator from service, looping the field circuit out and meggering the circuit to ground to test its insulation resistance.

As the insulation breaks down the regulators pump out more voltage to keep the current the same. Which if the readings were bad, can lead to the regulators failing.
I understand insulation resistance testing (Meggering) your terminology of test the ground threw me off.
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Old 12-29-2018, 01:39 PM   #16
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These regs have been in service since late 2013 without any big issues. We have burned up 2 cores along the way that were under warranty. Good install that I was involved with. We still use the contractor regularly. All feeds are underground and tested by the manufacturer every 6 months. The PF does go up with loading, the 0.27 was at brightness 2. Full load, brightness 5, PF 0.71.
Thanks for all the comments so far. We are sending back a reg to the manufacturer for testing next week.
I'll update as I get results.
For those in the field. It's all ADB Safegate regs and lights.

Tim.
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Old 12-29-2018, 05:47 PM   #17
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@brianjohn my fault, sorry about that.
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Old 12-29-2018, 09:14 PM   #18
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@brianjohn my fault, sorry about that.
No biggy different areas use different terminology.
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Old 01-16-2019, 08:38 AM   #19
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Any response from the manufacturer?
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Old 01-16-2019, 10:27 AM   #20
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Yes, they received the core and of course it passed all bench testing. Had a conference call and they mentioned that we should be checking our incoming feeder. They offered to send down 2 of their engineers with test equipment. Nice jester.


We have two utility feeds and a back up gen in this building. Our preferred feeder is from a new 25Kv sub and the airport is the only customer on this feed , both the new terminal and the FEC(Field Electric Center). That said, we cranked up the gen and took readings, all good. We tried on the alternate feed, all good. So it appears to be an issue with the "New" 25Kv feeder. It has happened in the last 6 months so we are asking the utility what has been added to the sub?


We are going to have Sheinder and the utility come and do a complete condition report and try to figure this thing out.


I guess the good news is that we don't have to replace all the cores.


I'll keep you updated.


Tim.
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