OLTC requirement for the transformers

[mehdi1351]

Hello,
How we could able to get assurances from POCO to see whether the incoming power to our transformers are within healthy limits? I mean how should I know whether I have to consider OLTC for my transformer without having any info from the POCO on the grid voltage fluctuation?

 

[petersonra]

Normally here this is a problem for the utility not the customer. The tariffs require they provide voltage of a certain range.

 

[mehdi1351]

I know but at the end of the day they will not take the responsibilities on equipment malfunction due to voltage fluctuation that I am receiving.
Based on the engineering practice, OLTC is required if you have voltage fluctuation more than +/- %5

 

[petersonra]

I know but at the end of the day they will not take the responsibilities on equipment malfunction due to voltage fluctuation that I am receiving.
Based on the engineering practice, OLTC is required if you have voltage fluctuation more than +/- %5

This is a US based site that mostly deals with the national electrical code.

In the US getting the correct voltage to the customer is the utility's responsibility so is not covered by the US national electrical code.

 

[don_resqcapt19]

In the US the rules are typically set by the state utility commission. In Illinois that would be the Illinois Commerce Commission. This is what it required in Illinois.

Section 410.300 Voltage Regulation
a) Standard voltage. Each entity supplying electrical energy for general use shall adopt a standard service voltage of 120 volts (when measured phase to neutral) and shall maintain the service voltage within the allowable variations from that value at all times.

b) Allowable voltage variations. For service rendered at the standard service voltage, voltage variations as measured at any customer's point of delivery shall not exceed a maximum of 127 volts nor fall below a minimum of 113 volts for periods longer than two minutes in each instance. For service rendered at voltages other than the standard voltage value, voltage variations as measured at any customer's point of delivery shall not exceed 10% above or below the service voltage for a longer period than two minutes in each instance.

c) Variations of voltage in excess of those specified above shall not be considered a violation of this Section if caused:
1) by operations of a retail customer in violation of an agreement with or the rules of the entity;
2) by the operation of apparatus on a retail customer's premises that results in large inrush currents;
3) by infrequent and unavoidable fluctuations of short duration due to system operation; or
4) by acts of nature or other situations beyond the entity's control.

 

[mehdi1351]

In the US the rules are typically set by the state utility commission. In Illinois that would be the Illinois Commerce Commission. This is what it required in Illinois.

Yes you are right, but specifically in Texas, there are many energy harvesters that run the AI data centers and mining Crypto with green energy (Solar/Wind) and obviously they will inject power into the grid and if the POCO cannot regulate the voltage/frequencies on certain season/time, then we will definitely experiencing power fluctuations at the secondary of the transformers. That's the reason why I want to know whether I should consider the OLTC on my transformer, or not.
I guess the POCO shall advise us for such requirement?

 

[jim dungar]

Yes you are right, but specifically in Texas, there are many energy harvesters that run the AI data centers and mining Crypto with green energy (Solar/Wind) and obviously they will inject power into the grid and if the POCO cannot regulate the voltage/frequencies on certain season/time, then we will definitely experiencing power fluctuations at the secondary of the transformers. That's the reason why I want to know whether I should consider the OLTC on my transformer, or not.
I guess the POCO shall advise us for such requirement?

What is your service voltage?

 

[mehdi1351]

What is your service voltage?

Not too sure on the primary, but on secondary should be 460 to 480Vac 3phase

 

[jim dungar]

Not too sure on the primary, but on secondary should be 460 to 480Vac 3phase

Are you buying power at 480V or at the utility primary voltage.
Is the transformer yours or the utilities?

My non-Texas experience is at 480V you get what the utilities gives you, subject to their regulations. If you want to specify some conditions, like a OLTC, you need to be under a primary voltage contract.

 

[mehdi1351]

The POCO at Texas (i.e Swecpco) is the utility company and they told me that the transformer size and selection is their responsibilities, hence I only gave them the load list and based on the load list they will order the transformers ( which is 2x 3MVA). So I am buying power at 480Vac , not at utility primary.
It was agreed that transformer owned by Swepco and this would be between the site land lord and the Swepco. My company renting the site
I know that Swepco take the responsibility of the size and selection of the transformer but my main concern is, what if I get voltage fluctuations due to lots of power injections into the grid? Is there any chance for me to claim against POCO through the insurance company? or?

 

[jim dungar]

The POCO at Texas (i.e Swecpco) is the utility company and they told me that the transformer size and selection is their responsibilities, hence I only gave them the load list and based on the load list they will order the transformers ( which is 2x 3MVA). So I am buying power at 480Vac , not at utility primary.
It was agreed that transformer owned by Swepco and this would be between the site land lord and the Swepco. My company renting the site
I know that Swepco take the responsibility of the size and selection of the transformer but my main concern is, what if I get voltage fluctuations due to lots of power injections into the grid? Is there any chance for me to claim against POCO through the insurance company? or?

The utility is usually charged with making replacement equipment available during emergencies. They will not want to stock a spare 480V unit with an OLTC for a single customer. If you want better voltage regulation you will have to supply it yourself.

 

[mehdi1351]

The utility is usually charged with making replacement equipment available during emergencies. They will not want to stock a spare 480V unit with an OLTC for a single customer. If you want better voltage regulation you will have to supply it yourself.

Thank you very much Jim for the respond. That's make sense

 

[zbang]

Hmm....
We're not lawyers and aren't giving legal advice .
The NEC is not a design code, it's a fire safety code; there are building codes that address things like voltage drop.
The customer equipment should be capable of working on the nominal voltage +- 10%, if it can't then the customer needs to provide the appropriate conditioning, be it a OLTC, UPS, or what.
If the grid frequency is off by more than a couple tenths of a Hz, something is massively wrong out there. If that's a problem for the customer equipment.... see above.

It's all a matter of degree, 25kva of sensitive loads vs 500kva; the conditioning for those may be different.

 

[JoeStillman]

Here in PA, voltage tolerances are regulated by the state public utility commission and it's defined in the tariff. Different classes of service have different tolerances, with wider tolerances at higher voltages. I'm not familiar with the Republic of Texas, but most other states are similar. Check your tariffs.