Applying large loads to the grid? 1

[TugboatEng]

I'm going to ask this very generally but has anybody experienced rules from their grid operators with regards to large loads? For instance I may need to apply a 5-10 MW load to the grid multiple times per day. Is the grid going to tolerate this or will I need to schedule the loading? This is an inverter load so it won't see inrush like a motor load.

 

[jghrist]

This would have to be answered by the utility (grid operator). There could be limitations from capacity, voltage drop, or flicker (frequent voltage changes up or down) affecting other customers.

 

[crshears]

And the reason for these being factors are: [1] the total generating capacity on the grid at any given time, i.e. my former employer's grid has routinely peaked at 20 GW post-COVID, and due to that grid's load diversity the sudden application of ~100 MW of load from an arc furnace didn't even register as a blip [although that customer had local flicker-killing apparatus that had to be fully in service as a condition of the operation of said furnace].

[2] The capacities of the high-voltage circuits, step-down transformers, low-voltage feeders etc. vis-à-vis the real and reactive power step loads being applied and/or removed.

[3] The response times and operating condition of any associated static voltage compensation schemes.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[LittleInch]

If you just did it I don't think they would be very amused, especially if your local grid wasn't very strong.

That's not a massive load in an industrial area though so although it would need to be modelled by them to see the impact on others it should be acceptable.

Don't know what your connection agreement says - maybe time to dig it out.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TugboatEng]

I'm playing customer on this project. I was just curious if there would be any coordination required to apply a large load such as this. From the responses it doesn't seem like there is going to be any trouble provided we have the proper connection agreement.

 

[crshears]

Location can mean everything; the arc furnaces I referenced were all in Central / South-Western Ontario, where the grid is quite robust.

There is/was, in contrast, a large paper mill connected to the north-east portion of that same grid but with "baling wire" conductor - not really bailing wire, but quite current limiting, and every time that customer wanted to start a 40 MW thermo-mechanical pulping mill they would call the Integrated System Operating Centre to confirm the prevailing connectivity, generation patterns and power flows were satisfactory. Both the ISOC and the customer cared, the ISOC because this could cause issues for other customers, and the customer itself since failed start-ups were hard on their equipment.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[cranky108]

What you believe is large, may not be that big to the utility.
It may be big to the distribution system, and that location, but not to the utility as a whole.
Then again, we have companies come in and ask for 100MW capacity, and rarely do they exceed 10MW of load.
I think we should bill by requested capacity, and that might slow some of them down.

 

[stevenal]

There are a number of IEEE and ANSI standards dealing with this. If your load causes flicker, sag, or harmonics outside the limits and customers complain; you may have a problem with the serving utility.

 

[waross]

I think we should bill by requested capacity, and that might slow some of them down.

That is how farms, ranches and residential acreages are billed in this area.
My single family acreage on 40 acres is billed (partly) on a 5 KVA demand.
5 KVA is the minimum.
My previous single family residence on 1.5 acres was billed on a minimum 5 KVA demand.
The utility installs a sealed 35 Amp breaker. (Actual demand available = 8.4 KVA.
We have access to the breaker handle to reset and to turn the power off, but the enclosure is sealed.
If you want a bigger breaker you pay a higher demand rate.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[FacEngrPE]

NASA’s National Transonic Facility (NTF) in Hampton, Virginia. The ABB equipment supplies and
controls a giant fan that generates wind velocities in excess of Mach 1. 101 MW variable speed drive for a 135,000 horsepower synchronous motor.
During an open house lecture some years ago the report was that Dominion Power requires a call to dispatch when operating these large wind tunnels.

https://www.nasa.gov/directorates/armd/armd-aetc/national-transonic-facility-ntf-quick-facts/

https://www.nasa.gov/directorates/armd/aetc/national-transonic-facility-ntf/

 

[TugboatEng]

ABB is likely going to be the supplier for our equipment. My company is funny. They keep me in the dark because they know I'll ask for change orders. They also know I can fix the problems later for less.

 

[LittleInch]

Many moons ago I was involved with adding new pumps to a pump station in a rural location. The pump station had been there since the 1940's.

In discussions with the local electrical supplier as we wanted to install bigger drives, they asked what was on the system at the moment. It wasn't a big machine (350-400kW), but was a HUGE iron thing which had a start current of about 6-8 times FLC. Starting times would vary , but the grid guys then passed knowing looks at each other and said -Ah, we were wondering why our grid nearly browns out randomly. As they said all they ever supplied was a connection - they never knew what was on the other end, especially very old connections.

One of our other booster pump stations was banned from starting between certain hours as it browned out the network and all the local farmers complained as their milking machines all dropped off the cows being milked, or so the story went.

So the devil is definitely in the detail of the grid supply and their modelling of a start / stop event.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[cranky108]

My old company had a good number of rural customers, and there limit was 200 amps (the size of the meter. I know this because one of the meter shops had a meter that was melted, glass and all.
That is not to say they may have had a small user rate, for things like cable TV power boosters, but most residences were 200 amps. And that is the same here, but not very rural.
That said, our company has been replacing pad mounted transformers in recent years from 25 kVA to 50 kVA, because of increasing AC and hot tubs. But as now the trend has been grow houses, so the 50 KVA installations has been increasing.

That said, our small substation transformers are sized at about 20 to 25 MVA, so there is a loading issue for the distribution, but not the transmission.

 

[bacon4life]

3 time ranges of concern:
transient-The inverter should prevent any inrush/flicker issues.

seconds to minutes-If the load is connected to a medium voltage circuit there could be voltage regulation devices like LTCs or switched capacitors address steady-state voltage changes caused by the load. Typically these can had a few changes per day but would get worn out if the had to switch many times per day. For a load connected to a transmission source, a 10 MW load will have a negligible impact on voltage.

minutes to hours-Some large loads must provide scheduling information so that appropriate amounts of generation capacity can be procured. In my area 5-10 MW is lower than the required threshold, but it is nice to have the info if it is available from customers. For customers that have consistent consumption patterns, the load forecasting algorithms can adequately handle a 10 MW load. It would be helpful to have notice about changes to operating patterns (e.g. the load will be offline for 2 weeks of maintenance or changing from 5x8 operation to 4x10 operation).

As example of a voltage control challenge, I have a distribution circuit with a 3 MW manufacturing plant. The plant has low power factor so there is a nearby switched capacitor to control steady state voltage. During coffee and meal breaks most of the machines get turned off, which causes a high voltage situation. The capacitor switches off after 5 minutes to control the high voltage. At the end of the coffee break all the motors are restarted. Since the capacitor is still offline, the plant has both steady state low voltage and a motor starting transient voltage dip. After about 5 minutes the capacitor bank switches bank on, restoring good steady state voltage.