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Author Topic: Low Voltage Concern  (Read 1138 times)

Mark Hannah

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Low Voltage Concern
« on: June 04, 2018, 08:58:56 am »

I found a few posts about low voltage but they do not completely cover the information I'm looking for.  Posts such as opinions on what is too low and too high and what the utility company is legally obligated to provide at the closest and furthest point.

This is almost more of a request on how to go about addressing the issue.  I have been voicing the concern with the "venue" for a few years so...  Your responses will help me decide if the chain of emails I already have is good enough to cover me if we were to have show stoppage.

I'm uncertain how much detail to provide so I'll start out with a few bullets and answer any of your questions.

  • Without a load, the voltage is between 112 to 114 (G-H and N-H) and 198 (H-H).
  • With a load, I have seen the voltage drop to 100-104.
  • Incoming power from provider is 460v measured by facilities' electrical contractor.
  • Amp meter on distro isn't very accurate (doesn't show anything below 5A).  Educated guess = constant 30-35A when using lights.  Audio is probably 5-10 of that.
  • 100amp service.  Panel not labelled so I don't know what else might be on it.
  • UPSes will drop to battery.  Typically for only short durations
  • Self powered mains/monitors (Meyer).  No complete loss of audio.
  • Keyboard with less forgiving PSU has shutdown once in the past.
  • Reference PDF (link below) for RMS Voltage and Current from utility provider.

Thank you in advance.

https://drive.google.com/file/d/1TKRe0qEkQmk6nYvn4iJ9b5pn4xEP9ZGL/view?usp=sharing
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TJ (Tom) Cornish

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Re: Low Voltage Concern
« Reply #1 on: June 04, 2018, 12:07:01 pm »

I found a few posts about low voltage but they do not completely cover the information I'm looking for.  Posts such as opinions on what is too low and too high and what the utility company is legally obligated to provide at the closest and furthest point.

This is almost more of a request on how to go about addressing the issue.  I have been voicing the concern with the "venue" for a few years so...  Your responses will help me decide if the chain of emails I already have is good enough to cover me if we were to have show stoppage.

I'm uncertain how much detail to provide so I'll start out with a few bullets and answer any of your questions.

  • Without a load, the voltage is between 112 to 114 (G-H and N-H) and 198 (H-H).
  • With a load, I have seen the voltage drop to 100-104.
  • Incoming power from provider is 460v measured by facilities' electrical contractor.
  • Amp meter on distro isn't very accurate (doesn't show anything below 5A).  Educated guess = constant 30-35A when using lights.  Audio is probably 5-10 of that.
  • 100amp service.  Panel not labelled so I don't know what else might be on it.
  • UPSes will drop to battery.  Typically for only short durations
  • Self powered mains/monitors (Meyer).  No complete loss of audio.
  • Keyboard with less forgiving PSU has shutdown once in the past.
  • Reference PDF (link below) for RMS Voltage and Current from utility provider.

Thank you in advance.

https://drive.google.com/file/d/1TKRe0qEkQmk6nYvn4iJ9b5pn4xEP9ZGL/view?usp=sharing
Voltage dropping below 105-108v is too low. 110+ is better.

Practically speaking, the shortest path is probably bringing a boost transformer and billing your client for it.  You can let them know that this is necessary because the venue power is inadequate, and their choice is to fix the power issue - whether it's theirs or the POCO's - or continue paying you to work around the low voltage.  Your datalogger chart should be very helpful in making your case to venue management.


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Stephen Swaffer

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Re: Low Voltage Concern
« Reply #2 on: June 04, 2018, 12:37:19 pm »

There are 2 separate issues here-and 2 separate correct solutions-though TJ's solution might be the only one you can use.

First-and potentially the easiest to fix is the low voltage.  Line to neutral voltage on 460 volts (as opposed to 480-though often used interchangeably) is 265 v nominal.  In that case your readings, as recorded, look fine.  However, there will be a customer owned transformer somewhere on premises-probably close to the 120/208 panel.  If that is a 480 to 208/120 transformer, that would explain the low voltage.  There are most likely taps on that transformer that are intended to adjust the voltage.  They should have been adjusted by the installer to provide 120 volts nominal at the 120 volt panel-though it is conceivable (but not at all likely) that they are set where they are on purpose.  It should take a good commercial or industrial electrician less than an hour to correct this and get the voltage where it should be.

The second issue is the voltage drop from loaded to unloaded.  If this is consistent across all three phases, then it indicates something is undersized-maybe the transformer, more likely wire somewhere in the circuit.  The wire is probably large enough "by the tables" ampacity wise-but the designer (be they electrician or engineer) did not allow for voltage drop over the length of the wire.  This is obviously much more difficult and expensive to correct.  The "hack" work around in this case would be to set the taps on the transformer a little high-maybe 122-123 volts-so that the voltage still stays high enough to avoid drop out under load.
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Steve Swaffer

Mark Hannah

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Re: Low Voltage Concern
« Reply #3 on: June 04, 2018, 12:55:11 pm »

Tom & Stephen,

Thank you for your responses.

Tom,

The datalogger is actually from the Utility company sent to me via the venue.

I work for the federal govt.  It is their gear and the venue is free. The federal govt would most likely need to cover the cost of renting or purchasing a transformer.

Stephen,

I did suggest the facility re-tap the transformer.  Your verbiage is much better than mine so I hope you do not mind if I cut and paste some of it.

I thought I might add the utility company's response that came along with the log.

Regards,
Mark
 
Quote
Good Afternoon.  Per our discussion, the standard voltage class that we provide at the level specified below is 265/460V.  We are allowed nominal voltage ranges between 238/414V and 278/483V by COMAR.  However, we make sure to maintain voltages close to the voltage class that we commit to our customers.

I reviewed the readings taken from the facility and don't see any issues related to abnormal voltage drops.  Please see attached file.  In this case, Pepco typically refers it back to the customer to make amends on their end.

High temperatures typically lead to higher use of air conditioning which can increase the demand on the system.  This may affect the voltage level.  However, this is included during our planning process, and we compensate to ensure that our voltage levels are still maintained through high stress situations.
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TJ (Tom) Cornish

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Re: Low Voltage Concern
« Reply #4 on: June 04, 2018, 01:31:44 pm »

Tom & Stephen,

Thank you for your responses.

Tom,

The datalogger is actually from the Utility company sent to me via the venue.

I work for the federal govt.  It is their gear and the venue is free. The federal govt would most likely need to cover the cost of renting or purchasing a transformer.

Stephen,

I did suggest the facility re-tap the transformer.  Your verbiage is much better than mine so I hope you do not mind if I cut and paste some of it.

I thought I might add the utility company's response that came along with the log.

Regards,
Mark
This suggests distribution difficulties in the venue as Steve called out if the voltage is considered acceptable at the service entrance.  Sounds like you're on the right track working with the venue.

The POCO's minimum of 238/414 corresponds to about 104v after step-down, so while the measured is a lot better than that, it sounds like if the POCO wanted to be difficult, they have a lot of latitude in their policies to point to to avoid fixing the problem if it ever did measure that low.
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Nathan Riddle

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Re: Low Voltage Concern
« Reply #5 on: June 04, 2018, 01:45:18 pm »

The POCO's minimum of 238/414 corresponds to about 104v after step-down

Can you elaborate on that point? Asking for a friend  ;D
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TJ (Tom) Cornish

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Re: Low Voltage Concern
« Reply #6 on: June 04, 2018, 02:16:27 pm »

Can you elaborate on that point? Asking for a friend  ;D
The 480/277 voltage standard that many commercial facilities use for HVAC/machinery and distribution transforms down to the 208/120v voltage standard for common power.  277/120 = a stepdown ratio of 2.3:1.  238/2.3 = 104 and 278/2.3 = 121, so the POCO considers their nominal delivery range to be 104-121v.
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Nathan Riddle

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Re: Low Voltage Concern
« Reply #7 on: June 04, 2018, 02:20:07 pm »

The 480/277 voltage standard that many commercial facilities use for HVAC/machinery and distribution transforms down to the 208/120v voltage standard for common power.  277/120 = a stepdown ratio of 2.3:1.  238/2.3 = 104 and 278/2.3 = 121, so the POCO considers their nominal delivery range to be 104-121v.

Ahh, thanks! I was doing single/split phase calculations instead of 3p. Threw the numbers off in me head.
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Tim McCulloch

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Re: Low Voltage Concern
« Reply #8 on: June 04, 2018, 06:09:40 pm »

This is illuminating (no pun intended) as I'd never heard of nominal 460v service from a utility company.  Yes on 480 but not 460.

I'm with Swaffer - either there is undersized service wiring, the transformer isn't tapped in the right spot to deliver nominal 120/208v or 120/240v to the secondary, or both.

Other that getting a queasy feeling as voltage drops are you experiencing any failures or other issues?  I get shit from some touring personnel at one of our venues, particuarly in the summer when the grid is powering a whole bunch of air conditioning and the voltage drops.  They seem to think there is something we can do to make the PoCo flog the little rodents that turn the generators and raise the voltage but the reality is that on site, day of show, we can't do anything.

Presuming the venue can't be bothered to call an electrician a boost transformer, as suggested by TJ, is probably your best option.
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Stephen Swaffer

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Re: Low Voltage Concern
« Reply #9 on: June 04, 2018, 06:43:33 pm »

My guess is that this is an older venue.  460 used to be common-used to even see motors rated at 440 VAC (not in my day-but in motors made back when stuff was made to last decades not years-so I've seen a few-a lot of old prints show nominal 440 or 460 supplies).  The POCO has no incentive to swap out the transformer-just an added expense for something that is already working. That's why I think the voltage issue is a mismatch with a 480-208/120 transformer being fed with 460 nominal.

There is not enough info to tell where the voltage drop is coming from.  A loaded/unloaded measurement on both the incoming service and the 120 v supply would be needed to diagnose that.
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Steve Swaffer
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