Voltage Regulation: What is it and Why it's Important

Today we speak to Sr. Controls Expert Ryan Byrd about the importance of voltage regulation.  As much of the 'why' as the 'how' in this discussion. Send Feedback to Powerbytes@cat.com

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Transcript

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 conversations.  As always please know how much we appreciate you, our listeners.  We hope you find our topics both helpful and interesting.  We would appreciate your feedback and suggestions for new topics. 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 leave us a 5-star rating wherever you listen to your favorite podcast; It really does help.

Lou: Today's topic is Voltage Regulation.  What is it and why is it important?  Clearly most of us understand that our electrical devices of all sized rely on a properly regulated voltage.  We've come to take it for granted.  Today, I'd like to delve into the subject just a bit deeper to highlight it's not just the what but perhaps something of the how it's regulated by a standby genset.

Joining me today is Ryan Byrd (Electrical Engineer – Undergraduate and Graduate school at Southern Illinois University, former residential electrician, former Navy Nuclear Electrician, currently working on genset control systems for almost 16 years with Cat).  Welcome Ryan and thank you for being with us today.

Ryan:  Thank you, Lou.  Glad to be here.

Lou: Ryan, first help us understand voltage regulation from a practical perspective.  What is voltage regulation? 

Ryan: The voltage output of a generator set is managed by the excitation system.  As load varies from no-load to full load on a generator set, the voltage will change.  Voltage regulation speaks to the ability to maintain a consistent voltage as the load changes.  If you consider a product like a portable generator, they typically have fixed excitation systems.  In these systems as load is added the voltage drops due to its internal impedance and the power factor of the load.  With a generator set that is used in a standby application you  want to maintain a more consistent voltage.  With those products, an automatic voltage regulator is used to adjust the excitation within the rotor to maintain a consistent voltage across all load ranges.

Lou: Why is it so important to maintain a consistent voltage? 

Ryan:  The reasons for voltage regulation actually depend on the application. In an application with a single generator set, the entire facility is based on the established voltage from the generator set.  Much deviation away from the designed voltage may risk some of your equipment not working, or worse yet, damaging equipment or causing injury to people.  In applications that require a generator set to operate in parallel, voltage regulation is extremely critical.   Tight voltage regulation assists with several functions in a paralleled system, from the paralleling itself, to managing the kVAR contribution from each source, and limiting the circulating currents between sources.  Circulating currents create heat which could limit the power output of the generator and shorten its life.  Without the ability to regulate voltage it would be nearly impossible to operate generator sets in parallel.

Lou: Can you talk a bit more about how the Automatic Voltage Regulator (or AVR) works? 

Ryan: Certainly.  The AVR draws power from an external source, either the output of the generator, a permanent magnet or an auxiliary winding, which is converted to DC power to generate a magnetic field in the Exciter.  When this magnetic field passes by the armature (usually by the spinning of the rotor), a voltage is generated on the output of the generator.  The voltage regulation system also senses the output voltage from the generator and will compare the sensed voltage to a reference voltage.  If the generator output is lower than the reference voltage, the regulation system will boost the magnetic field on the exciter to increase output voltage.  If the generator output is higher than the reference voltage, the regulation system will lower the magnetic field on the exciter to decrease output voltage.

Lou:  Does Caterpillar use just one type of AVR and what are some of the features? 


Ryan: Caterpillar uses a variety of voltage regulators, with the most common on our medium and larger generator sets being the IVR, or Internal Voltage Regulator, and the CDVR (or Cat Digital Voltage Regulator).  The IVR is available exclusively on our generator sets using the EMCP 4 line of controllers.

The CDVR was introduced in 2004.  It has its own software, but can be programmed using the Caterpillar Electronics Technician software as well.  It has been widely accepted in the market due to its reliability and ease of use.  It utilizes its own sensing for voltage and current and has its own protections that are programmable by the end user.  The CDVR also allows for a variety of programming for specific site requirements that include loading profiles and gain tuning.  It can also operate in AVR, VAR, or PF mode.  It can be given a requested regulation value via communications, or an external bias signal.  The CDVR can also work in Droop mode, Line drop, or Cross Current Compensation.

The IVR was introduced around 2014.  It has the same features as the CDVR (minus the ability for Cross Current Compensation due to not having a dedicated current transformer), but simplifies the system.  The IVR includes the EMCP and an Excitation Module.  The voltage and current sensing from the CDVR are removed since the ECMP already has those connections.  Other terminals are also removed for the same reason.  With the IVR system, the EMCP takes over all the processing and programmable functions contained in the CDVR.  The excitation module simply provides the excitation voltage to the generator.  It receives a simple signal from the ECMP telling it how much voltage to generate.  By placing the processing tasks in the EMCP, wiring is simplified and programming is centralized as well.  

Lou: Sounds like a win for customers in that we have eliminated some components which increases reliability.    Because the IVR intelligence is located in Cat's genset controller, does that allow the user to customize the voltage regulation and hence the genset performance?

Ryan:  With both the CDVR and IVR, there are multiple set points that can be leveraged to fine tune how the voltage regulator responds.  However, with the IVR, we have the capacity for enhanced voltage regulation techniques due to having the calculations done directly inside the EMCP.  The EMCP offers something with IVR called Transient Load Relief (or TLR), which is an optional group of set points that allow the customer to define the voltage regulator response based on dynamic changes to load, not just a pre-programmed slope.  This optimizes the genset load acceptance performance.

Lou: Can you explain the Transient Load Relief a bit further? 

Ryan: Typically when you have a large load added to a generator the speed will drop as the engine responds to the additional load, and the voltage will drop proportional to the speed.  The speed reduction, voltage drop and recovery of the generator will depend on the amount of load added and the programming of the voltage regulator.  A large load step could cause a low voltage for an extended period of time.  The TLR set points allow the customer to reduce the voltage to a customer programmed value as soon as the large load is applied.  By dropping the voltage in this way, the generator can recover much faster by working to match the engine torque capability.

Lou:  Clearly voltage regulation is very important to keep facilities up and online.  The tightness of that regulation is the key.  If the generator set is allowed to wander off with respect to voltage, critical equipment could go offline and be very costly for the user.  It seems to me from our discussion today that Cat spends a lot of time focusing on this as part of our advanced controls strategy, would you agree?

Ryan:  Yes.  The better the generator can tightly control the output voltage, or respond in a customized way, then the better Caterpillar can meet the customer needs.

Lou:  There you have it.  Thanks For joining us today Ryan and Thank you our listeners  for joining us here on Power Bytes.  For more information on this and other topics please contact your local Cat dealer or write us here at powerbytes@cat.com, visit Cat Electric Power on Facebook or on LinkedIn.  Till next time; thanks for joining us on Power Bytes.