Your questions answered: Designing system-level controls in a power system

Electrical engineers specifying paralleling power systems must understand the difference between generator set paralleling and system-level control. Read more for questions left unanswered during the live webcast

By Hassan Obeid September 9, 2020

On Aug. 25, 2020, the webcast Designing system-level controls in a power system left some questions unanswered. They’re addressed here by Hassan Obeid, Global Technical Advisor for Systems and Controls – Critical Protection, Cummins Power Generation.

How do you size the E.G.?

You will need to use a sizing tool for that. Most manufacturers have a sizing tool. You can use the sizing tool from the Cummins website.

Does Cummins paralleling control have protection built in?

Yes. The spec sheet lists all the elements that are built in.

Can we synchronize two generators from different manufactures?

Yes, you want to make sure we evaluate the winding pitch and then make sure the units allow for speed and voltage bias. We can add the Cummins paralleling control on top of the third-party unit.

Can paralleling be done on a lead-lag basis to allow maximum fuel efficiency and ensure engines can pull a higher load if in parallel configuration in case one unit shuts down?

Yes, you can go into leading PF, but you can only go for a certain amount otherwise the electromagnetic field gets weaker and can cause pole slip. We need to understand the application and the region you intend to operate the generator set.

System level control of Cummins had the possibility of export and import information and commands for an external SCADA?

Yes, you can export all the data to a SCADA.

Should you have a sequence of operation for failure?

Yes, there should be. You can start out with templates which your local Cummins rep will be more than happy to provide

You showed a specification. Is it available to consultants?

Yes, there are templates. Please reach out to your local Cummins rep in your area and they will be more than happy to provide you with templates.

Is there an example or template sequence of operations available from Cummins?

Yes, there are templates. Please reach out to your local Cummins rep in your area and they will be more than happy to provide you with templates.

Can the Cummins generator control manually paralleled?

Yes, the Cummins paralleling control does manual paralleling safely without the need for additional components.

Is it possible to synchronize third party controllers with PCC?

Yes, it is. We can add the Cummins paralleling control on top of the third-party unit. All we need is the speed and voltage bias in the third-party control.

Can the system control mentioned be tailored to different applications?

Yes, it can be used in and tailored to different applications.

Can this controller be added to an existing system that may include non-Cummins equipment?

Yes, it can be added. More information of the system is needed though.

Does Cummins design and integrate the components of a power system you mentioned?

Yes, Cummins designs, builds, tests and integrates all the components of power systems. From generator set paralleling and transfer switches to system level controls, switchgear and digital solutions.

Are the system level controls shaker table tested to obtain seismic certification?

Yes, they are and they have seismic certifications.

Does your system permit individual generators to connect to multiple buses, but only one bus at a time? For example, GenA is connected to BusA, Gen B is connected to BusB, and GenC can be connected to either BusA or BusB?

Yes, it can do that.

Can you address microgrid control, e.g., solar and or wind with the reciprocating machines?

We have done many systems that involves solar, storage, etc. with a reciprocating machine. This can get lengthy, please reach out to a local Cummins rep to discuss this further. The most important aspect is to manage power production and load consumption. Synchronizing these assets is simple

For the simple two-generator paralleling, do we need to have two parallel controller or just one parallel controller like the single utility/generator (grocery store example)?

To parallel two units, all you need is the Cummins onboard paralleling control. That same control is also capable of paralleling one generator with one utility without any additional hardware

Are the CT’s and PT’s generally wired directly to the system level controller?

There is no need to bring the CT’s/PT’s into the system level control.

Can your system level controller be integrated with open MQTT based cloud (multisite) solutions?

The system can be placed on a network and the entire system can be accessed from anywhere as long as you have access to it. It can be inside the firewall and you will be able to pull up the screes through an IP address.

How do you synchronize two generators? What are factors to be concerned about?

The onboard paralleling control handles that. The things to consider:

  • Winding pitch
  • First start
  • Speed and voltage bias (which allows for synchronizing phase, voltage and frequency).

Protection philosophy suggestions for generators motoring action while on initial loading, correct?

The generator is self-protecting for a lot of elements. So, you will not be able to motorize it. But you need to size the generator set appropriately so will be able to handle the initial torque otherwise the generator set will shut down. But it will not be damaged since it has protective elements built in.

How do you engage manual operation mode? Is that a switch at each breaker? A switch at the system level controller?

Simply from the HMI of the system level control. Which is an option on the HMI. If the HMI fails, then you can place the system in manual from a hardware switch in the gear.

Are there are many sizes of the control systems depends on the load or the generators power?

One control that fits all sizes. We have placed the same controller on 25 kW generator sets and it is the same control that controls and parallel the 3.5 MW generator set that Cummins makes.

Does the sequence of operations need to follow the standard construction discipline numbering systems?

No, it doesn’t.

Any issues with load shedding via SCADA (i.e., requesting SCADA to shed prioritized loads as opposed to opening circuit breakers)?

It is not recommended to shed through another system unless that system is monitoring the overload signal from the generator sets. The system level control monitors the overload signal from the generators and then issues the commands to shed loads.

On the two utility and multiple generator application, how is the load sharing handled when both utility sources are present? Are they the same source (just two feeders)?

In that example I showed, the two utilities were not sharing the loads. Every utility was feeding on load bus. You cannot parallel two utilities for more than 100 msed.

Is this system level control considered as a cloud computing or edge computing? Or hybrid? How to compare it with traditional SCADA system?

I would consider it more of Edge. So, a SCADA is more of graphical view and control of the entire system, from chillers to heat exchangers and other parts. The system level control and also be used to be a SCADA or pass information to a SCADA. The system level control handles the backup power block of the system and usually the SCADA designer stays away from that.

In your experience, who writes the sequence of operations, the specifying engineer or the system-level controller provider?

Both can be involved in writing the sequence of operations. The consulting and specifying engineer can have a basic sequence of operations and the provider can help support it and provide more insight if needed.

Can we parallel generators that are different kilowatts? I was told that they all need to be the same capacity.

Yes, you can. Cummins generator set paralleling controls are intelligent enough to account for different size units.

How do we go about parallel generators from different manufacturers? What information do we need to obtain on the existing generator to do so?

You need to know the winding pitch and if the existing generator set allows speed and voltage bias. We can easily add the Cummins paralleling controls to another non-Cummins set

Where can you locate the system controller, is it integrated with the generator or can be remote?

System level control is a stand-alone unit that can be mounted next to a distribution board in the electrical room, for example.

What will happen if the paralleling gear main bus is overloaded?

Then load shedding schemes engages to shed the noncritical loads.

Author Bio: Hassan Obeid is a global technical advisor for systems and controls — critical protection at Cummins Power Generation, focusing on technical vision, business strategy and solving a wide range of complex problems.