Ok, do you know what a generator transient is? Do you know how your genset will respond to transients large and small? Today Bryan Snyder walks us through it all.
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Ok, do you know what a generator transient is? Do you know how your genset will respond to transients large and small? Today Bryan Snyder walks us through it all.
Email us: powerbytes@cat.com
LinkedIn: https://www.linkedin.com/showcase/cat-electric-power/
Facebook: https://www.facebook.com/Caterpillar.Electric.Power/
Lou: Good Day and welcome everyone to Power Bytes! I am your host Lou Signorelli and Power Bytes is your destination Podcast for power generation conversation. As always please know how much we appreciate you, our listeners. We hope you find our topics helpful and interesting. There are several ways for you to get in touch with the show. You can send us an email at powerbytes@cat.com, visit us at Cat Electric Power on Facebook or LinkedIn. If you enjoy your time with us today, please remember to subscribe to our podcast.
Lou: Ok, do you know what a generator transient is?
Do you know how your genset will respond to transients large and small?
Well joining me today via the Cat Electric Power Hotline is one of our resident application experts Mr. Bryan Snyder. For our returning listeners you will recognize Bryan from his work on the Overcurrent Protection and a few other Podcasts. For our new listeners Bryan has 20 years of experience with Caterpillar and a career of focusing on integrated systems and gensets. Welcome Bryan and thanks for joining us today.
Bryan: Thank you Lou, it's great to be back.
Lou: Bryan, can you help us define what is a transient on a genset?
Bryan: Whenever there is a sudden change in the load supported by the genset the frequency or voltage of the generator is likely to be impacted for a temporary period. This change from steady-state operation is considered a transient. If the load on a generator increases, the speed of the generator slows down this can impact the frequency and the voltage of the generator causing them to dip. If the load decreases suddenly the speed of the generator is likely to increase. This will cause the generator to overshoot. The measure of how large the dip or overshoot and the time it takes for the generator to return to steady-state operation is called the transient response of the generator.
Lou: So, what causes the load on the generator to change suddenly?
Bryan: There are several reasons for a sudden change with loads, large motors or other loads often cause sudden changes when they are turned on. If there are several Automatic Transfer Switches in a system, they cause transients when they switch to add or remove loads. There are also large sudden demands when things like transformers are connected to the generator by a switch or other method. The size of the load and the nature of the load will determine how large of a transient response is on the generator.
Lou: Can you explain what is happening in the engine when a transient occurs?
Bryan: Sure, this is often better with visuals, but if you can image an engine is operating with a specific amount of fuel and air being supplied to the cylinders to produce the necessary power to support the steady-state load. This is what is called the break mean effective pressure or BMEP. When a large load is added the power being produced under the steady-state operation can no longer support the demand from the load and the speed begins to slow. To increase the BMEP the engine applies more fuel as the fuel increases the Engine BMEP will rise. During this time most modern engines will also use turbo chargers to increase the air into the engine as well. When the engine BMEP has met the requirement of the load the speed stops dropping and starts to rise. The engine will continue to increase fuel and air until it reaches a maximum fuel setting. During this period the speed will return back to the steady-state setting and the fuel is reduced back to a steady state operation with the new BMEP and power level.
Lou: I understand there are some industry standards to define how transient response should be measured. I did a little leg work and found ISO 8528. What can you tell us about the standard and its application?
Bryan: Yes, ISO 8528-5 is the most common standard for transient response. The standard has two primary concepts that are critical to evaluation of a generators transient performance. The first is that the load steps applied to a generator should be based on the BMEP of the generator. As the standard states, a higher BMEP usually makes loading in several steps necessary. What this means is that you may have two generators with the exact same output rating for power, but because one has a higher BMEP rating it might take more steps per the standard to get to the full power. This is often overlooked or misunderstood in specification when customers request a generator meet a specific performance category.
The performance categories are the second part of the standard. There are 4 basic categories. G1 which is typically acceptable for general purpose loads like lighting. G2 which is more common for loads like pumps or motors. G3 which is most common for things like telecommunications equipment and is most often referenced in standards. Finally, there is G4 which is most common for highly sensitive application like Data Centers. For G1-G3 there are specific values allowable for everything from steady-state operation to the allowable dip and recovery times. For the G4 it is an agreement between the manufacturer and customer on what the performance should be.
It should be noted that if you are using any of these rating categories, the load steps should be based on the load steps we previously referenced. We will often see specs that require the product to meet a G3 requirement but then the customer may question why the product isn't meeting the performance at a 0-50% load step. It is the intention of the standard to create a level field for evaluating performance of different generators. If the customer is looking for specific performance to meet their applications load steps it would be recommended to specify exactly the performance, they need rather than simply referencing the standard.
Lou: That's interesting, does Caterpillar have any tools to help users calculate or predict a transient response?
Guest: Absolutely, if a customer has specific loads, we recommend they use our Spec Sizer software. I know you have spoken about this with other in other Podcasts, but if they go to specsizer.cat.com they can add the loads and specify the level of acceptable transient. This can help the customer to select the right generator set for the application. Some customers may only have 500kW of load, but because of the transient response they need, the system may recommend a 750kW generator set. Spec Sizer is very helpful at making sure you get what you need to support the application rather than getting a product to site and finding you have an issue.
Lou: Thanks Bryan, there are definitely more Podcasts our customers can listen to for more details on Spec Sizer. Are there other tools we have for customers if they are still having difficulty?
Bryan: Yes, I would recommend if a customer has a complex application that they work closely with their local dealer. The dealers and Caterpillar have resources that can help with making adjustments and evaluating a SpecSizer file and there are also other internal tools and transient analysis software that can help evaluate more complex applications. We may even be able to help by looking at other technologies like energy storage systems, available from Caterpillar, to provide improved transient response and other valuable benefits.
Lou: This has all been great information. Are there any last recommendations you can provide for customers that are evaluating their transient response?
Bryan: Yes, in general there are some items that we would recommend for application with a particular focus on transient response capability. First would be to look for an externally sourced excitation system. This would be either a permanent magnet or an internally excited generator. Having the external source for excitation energy allows the generator voltage to recover faster during a transient. Also, we would recommend a lower sub-transient reactance. This also will allow the generator to respond faster to loads like motors or transformer inrush. Finally, if you already have a generator onsite that you need to improve the transient response, there are changes that can be made to the voltage regulator that may improve the response. We can't get into a lot of the details here, but adjusting the volt/hz settings, loop gains and if you have a Caterpillar generator, I recommend looking at the Transient Load Relief function as part of the EMCP controls. You can get more details on all these items from your local dealer.
Lou: There you have it folks. I'd like to thank Bryan Snyder for sharing his expertise with us and Thank you, our listeners.
If you'd like a more detailed and perhaps site-specific discussion, please contact your local dealer to set that up.
If you'd like to experience Cat's industry leading tools such as specsizer, please go to specsizer.cat.com or consult your local Cat dealer.
If you’d like to suggest other topics for the program or have some feedback to share, please write us here at powerbytes@cat.com or visit Cat Electric Power on Facebook or LinkedIn. Please remember to subscribe to our Podcast wherever you listen to your favorite podcasts. Till next time, thanks for listening to Power Bytes and have a great day!