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Checklists

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Today I’m starting a new-ish feature where I’m publishing a different thought as a twitter audio at least, and maybe a video depending on where I’m located.

This first thought is on checklists, and their importance in every electrical safety program. This came to me, again, when I was meeting with a client and they were getting started developing their electrical safety program. I was there to help them with an arc flash analysis update, and we started talking about the minimum viable electrical safety program.

Some background

To get there, I had to fly and I noticed something that I see every time I fly, but I haven’t thought about in a while, the pilots were doing their checklist. This was a short flight, and these pilots must do the same routine pretty much every day. They know it in and out, but the checklist helps them consiously go through all the steps every time. Its like if you drive the same part of raod often and then one day completely forget drviing it as you go though. You don’t want to space out on routine tasks.

This is where the checklist comes in, with a very routine task you may skip over steps, but with a checklist you make the check as you go through, mentally remembering to do that thing. I recommend that checklists be used for all tasks that are high risk starting out, and then add in non-routine medium risk tasks as the electrical safety program matures. An example of a medium risk task may be changing a 347V ballast at height.

Minimum Viable Checklists

The two checklists that ever electrical safety program should have are:

  • Energized Electrical Work Permit
  • Lock-Out-Tag-Out

These checklists allow the worker and manager to manage the hazards associated by those tasks, which are always medium-high risk, to make sure that everyone stays safe.

Let me know what you think about this first Daily Musings. If you want to see or hear it live follow me on Twitter and Linkedin. For now I will at least do a live audio to Twitter and maybe a video on Linkedin in the future.


Battery Economics and Grid Stabilization

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I read an article last week about how using electric cars for grid stabilization will shorten the life of the batteries. In fact the article uses the trigger word detrimental!

But if you understand how the electrical utility industry works, and some basic understanding of battery chemistry, that’s a no brainer. The real question is how detrimental is it? How much shorter is the total life of the battery? Is that increase in depreciation more than the utility will pay for another energy source on a second by second basis?
This is not a hindrance to the technical implementation of electric cars, household batteries like the Tesla Powerwall and other distributed sources as a grid stabilization means. Its an economics and business challenge.
Can you provide enough revenue to the car owner (asset owner) to cover the increased depreciation of the asset and a reasonable profit? Is this expense from the grid operator more or less than it would pay to a different party in the market for a similar service?
See its not that the idea to use car batteries is bad, its that in today’s market there is no feasible way to provide the generation services the utility needs in a way that they can use. To give an everyday analogy, you don’t buy gas for your car by the milliliter from your neighbor, you go to a service station and buy it by the liter. utilities do the same thing; however electricity isn’t gasoline, its tied to a network and if you can aggregate a lot of different sources in a local geographic area; and offer it to a utility in a way they can integrate to their system, now it can start to make sense.

However, today that isn’t possible, but not for technical reasons for practical ones. There aren’t enough cars (or other assets) connected to the grid and the cost of generation isn’t high enough to cover the added depreciation to the asset. This is changing and we are spending a lot of time researching ways to make this happen, sooner. It won’t be long before you will be asked to sign up to be part of an aggregated pool to sell energy to the utility and then get a small cheque based on how much the aggregator sold both locally and internationally.
Over the next couple of months I will be deep diving in on this topic and others in our newsletter. It is at most once a week and at least once a month, all depending on what we have to say at the time. You can join below!

Generator Motoring: What It Is and How to Protect Against It.

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Generator motoring is exactly what it sounds like: the generator acts like a motor. In a typical generator, a prime mover (such as a steam turbine) supplies mechanical power to the generator, which is converted to electrical power and delivered to the electrical system.

Generator Motoring can seriously damage your wind turbines
Generator Motoring can seriously damage your wind turbines

What Causes Generator Motoring?

Generator motoring is a condition that happens when the prime mover can not supply enough power to the AC generator to account for the load demand on the generator. The electrical system needs to make up for this loss in prime mover input power. When this happens, the generator begins to act like a motor, by absorbing real power from the electrical system. This is to make up for the supplied power deficiency by speeding up the prime mover.

Consequences of Generator Motoring

Protection against generator motoring is designed to protect the prime mover as opposed to the generator. Motoring does not necessarily harm your generator, but it will cause the prime mover to overheat. Field excitation should remain the same as before generator motoring occurs, so the same reactive power will be flowing from the generator.
So with generator motoring, real power flows in to the generator and reactive power flows in to and out of the generator.

Motoring can destroy prime movers, such as wind, steam, and hydro turbines.
Motoring could cause your prime mover to overheat, ruining your turbine.

Generator Motoring is Hard to Detect

Any relay designed to detect generator motoring has to be extremely sensitive to respond to the first increment of reverse power (power flowing in to the generator from the electrical system as opposed to power flowing out of the generator into the electrical system).

Reverse Power Required During Generator Motoring is Different for Different Prime Movers

When the prime mover spins at synchronous speed with no power input, the approximate reverse power required to cause generator motoring is different for different types of prime movers.
As a % of nameplate rating in kW, the approximate reverse power required to cause a generator to motor is:

  • Condensing steam turbine – 3%
  • Non-Condensing steam turbine – 3% or greater
  • Diesel Engine – 25%
  • Gas turbine – 50%
  • Hydraulic Turbine – 0.2 to 2%

To elaborate on this information and demonstrate how truly difficult it is to detect generator motoring, here’s a short example. Let’s look at a steam turbine. This steam turbine is able to supply 99% of any system losses at no load. The other 1% must be supplied by the generator, so the generator beings to motor. If the losses are 3% of regular power, the motor supplies 1% of 3%, which is 0.03% of nameplate rated power. This is very hard to detect.

Different types of prime movers have different motoring characteristics. These hydro turbines are different than the wind turbines pictured above.
Different types of prime movers have different motoring characteristics. These hydro turbines are different than gas turbines or diesel engines.

How to Protect Against Generator Motoring

Generator motoring protection can be provided by limit switches or exhaust hood temperature detectors. If you need a large number of these devices, add a reverse power relay. Reverse power relays are common in diesel generators, where unburned fuel is both an explosion hazard and a fire hazard.
 
Hopefully now you know a little bit more about generator motoring. If you have any other questions, about motoring or anything else, feel free to e-mail me at cole@jmkengineering.com. Also, make sure to sign up for our weekly newsletter below: we cover a wide variety of topics, possibly including answers to questions you have after reading this article!
As always, thanks for reading!

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