AmpSentry™: The ultimate protection

by Cummins Europe,
Cummins Power Generation

Hospitals, data centers, water/wastewater, and a wide range of other critical infrastructure and institutional facilities that require continuous or near continuous uptime, typically utilize a generator set for a reliable backup power when the normal power source is unavailable.

For over one hundred years Cummins Power Generation has been at the leading edge of generator set design and innovation, helping the world push forward to meet customer, market, and environmental demands.

AMPSentryIt is the spirit of constant innovation that keeps Cummins Power Generation at the pinnacle of the power, and in that spirit comes AmpSentry™, which is the Cummins trade-marked name for the protection functions within the generator set control; the PowerCommand® Control. AmpSentry™ as a utility grade protective relay which gives the designer the assurance of reliable protection when it comes to protecting the generator set and loads.

AmpSentry™ Protective Relay Functions

Cummins Power Generation generator sets with AmpSentry™ protective relay provide the alternator protection that is required by codes and standards and by facility owners desiring good alternator protection. Because AmpSentry™ protective relay is specifically designed for alternator protection, it can provide necessary protection without the compromises and limitations that are necessary with other approaches. Some of AmpSentry™ protection elements and advantages are:

  1. Ampsentry™ has been designed to identify and regulate fault currents within the thermal damage curve of the alternator, protecting the alternator and permitting the downstream fault to clear.

  2. To minimize severity of short-circuit faults, AmpSentry™ adjusts the shutdown time to protect downstream equipment. The shutdown time from high severity to low are listed below:
    Short Circuit Failure: Shutdown Time:
    LINE-NEUTRAL (L-N) 2 Sec
    LINE-LINE (L-L) 5 Sec
    3-PHASE SHORT 10 Sec

  3. AmpSentry™ “remembers” the heating effects of a fault and accelerates tripping when a subsequent fault occurs before the alternator has a chance to properly cooldown. Consequently, an inexperienced operator would not be able to cause an alternator failure by repeatedly starting and short circuiting a generator set.

  4. Overcurrent protection which is the most critical protection function in an alternator protection scheme, because most modern alternators (those with excitation support systems such as permanent magnet generator driven voltage regulators) have the inherent ability to drive the alternator to destruction on a short circuit or ground fault condition. Thus, the overcurrent protection function must be matched to the thermal damage curve of the alternator. AmpSentry™ perfectly matches the alternator thermal damage curve.

An additional feature of AmpSentry™ is Maintenance Mode – which is an important safety feature that provides protection to personnel from the threat of arc flash energy. When maintenance mode is enabled AmpSentry shuts down the generator set (by shutting off fuel and excitation) as soon as it recognizes that current on any phase has exceeded 300% of the generator set rating. Tests have demonstrated that excitation is shut off within 50ms of the occurrence of the fault; thereby, greatly reducing the energy available to support an arc flash.

How AmpSentry™ works

Overload regulation:

When the PowerCommand® Control measures current in any phase as exceeding 110% of the generator set standby rating a current summing integral will be activated so that the generator will shut down based on the AmpSentry™ time-current curve. This allows AmpSentry™ to protect the alternator and the feeder cables connected to the alternator.

Fault current regulation:

When the PowerCommand® Control measures current in any phase as exceeding 300% of the generator set standby rating the control recognizes that this is a fault condition and begins to regulate current in the phase with the highest level of current to 300% of rated current. The purpose of this is to allow a downstream overcurrent protection device (OCPD) to clear the fault, maintaining a coordinated system. AmpSentry™ overcurrent protection function is in effect during a fault and will shut down the generator set based on the time current curve if the fault is still active.

In summary

Protecting the generator set with an effective and reliable means while still maintaining a coordinated system is essential in all power system designs. The PowerCommand® generator sets incorporate, as standard, a highly reliable protective functions that are designed to protect the generator set and provide a nominal level of protection to the load without making a significant impact on reliability. These protective functions are all under the name of AmpSentry™.

Cummins Power Generation generator sets with AmpSentry™ protective relay provide the alternator protection that is required by codes and standards and by facility owners desiring good alternator protection. Because AmpSentry™ protective relay is specifically designed for alternator protection, it can provide necessary protection without the compromises and limitations that are necessary with other approaches.

A special thank you to Ahmed Jaffer (Senior Global Product Manager), Hassan Obeid (Global Technical Advisor) and Andrew Frazer (Consultant Development Leader).

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Cummins Power Generation awarded the highest recognition from the China data center industry


Cummins Power Generation (CPG) has been honored for its first PowerBlocTM project. The China Engineering Construction Standardization Association, China’s most prominent organization defining data center-related industrial standards, awarded CPG as part of the Data Center Scientific and Technological Achievement Awards. The winner’s list was officially announced during the 9th Data Center Standards Summit. 

Launched in May 2021, PowerBloc was designed by the CPG China team and is manufactured in the CPG China plant in Wuhan, a city in central China. PowerBloc integrates diesel units (power systems), water tanks (cooling systems), fuel tanks (fuel systems), silencers (noise reduction systems), electrical switch cabinets (control systems), and fire protection systems in a highly integrated 40-foot standard container. The first of three PowerBloc gensets was installed at customer sites in September. The standard Installation Quality Assurance (IQA) test, 12-hour continuous load and one-hour overload tests were completed with the customer. The results not only validated 10 square meters of space saving compared to the traditional containerized unit, but demonstrated extra stable operation, low noise, low emission, and excellent performance of this innovative solution.

The PowerBloc project and its remarkable technical innovation has set a new benchmark for standby power in the data center field, especially the containerized area. The award represents the highest of its kind in the China data center industry.

“The concept, design, development and application of PowerBloc is just another vivid example of how our people live Cummins’ vision of innovating for our customers to power their success,” said Wang Lei, General Manager of CPG China. “The driver for this solution was to erase the pain point for our customers in the data center industry. The applause from the customers and the recognition from the industry gives us more confidence to further innovate value-added solutions for this industry.”

During the Summit, the China Data Center Committee also released a Data Center Containerized Diesel Generator Set Technical White Paper, which was co-authored with CPG. Cummins interpreted in detail the design elements, the problems existing in the application and the future development direction for containerized gensets serving as standby power systems.

CPG also utilized this opportunity to showcase its unique capabilities in providing power systems for data centers. The CPG booth attracted many participants from the design institutions that provide power system planning and design. The event was webcast and drew great attention from the public.

CPG has kept the leading position as the diesel genset provider in the China data center industry and continued its reputation as a lifecycle solution provider. Key customers include China Telecom, China Mobile, China Unicom, Alibaba, Tencent and ByteDance.

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Cummins Inc.

Cummins is a global power leader that designs, manufactures, sells and services diesel and alternative fuel engines from 2.8 to 95 liters, diesel and alternative-fueled electrical generator sets from 2.5 to 3,500 kW, as well as related components and technology. Cummins serves its customers through its network of 600 company-owned and independent distributor facilities and more than 7,200 dealer locations in over 190 countries and territories.

Components of Microgrids

Microgrids are technology marvels. Check out the different components that come together under a microgrid.

Utility grids and microgrids have a lot in common. Both serve the same function—to provide electrical power to consumers. Both are subject to the same constraints—ensuring that electrical generation and electric load are equal at all times. Their components, however, are different. 

Microgrids are at a much smaller scale than utility grids and as a result include components that are accordingly scaled down. 

Here are the main components of a microgrid:

Electricity generation resources within microgrids

The beating heart of a microgrid consists of a set of electricity generation resources. Typical generation resources found in microgrids include diesel and/or natural gas generators, solar arrays and wind turbines.

The most basic microgrids are usually built around one or more diesel generators. When natural gas is available, gas generators are also among the options available. Older island microgrids, for example, are based on a small power plant consisting of a few diesel engines coupled to alternators. Generators are the default choice to power a microgrid because they can cover a wide range of loads and because they can be used as backup power. They start quickly, are responsive to changes in load, and can operate on a variety of fuels. 

Fuel cell technology is emerging as a valid option to provide on-demand power on microgrids. Fuel cells can run on natural gas, hydrogen and other less common fuels. Although their cost remains too high to be widely used, hydrogen fuel cells are seen as a potential source of small-scale CO2-free electricity.

Typical components of an island microgrid
Click the image to take a closer look at microgrid components

Intermittent energy resources within microgrids

The cost of solar panels has become so low that, in some regions, their installation on homes and businesses is a no-brainer. University campuses, industrial facilities and others equipped with a microgrid can install solar arrays in large numbers, thus achieving significant savings on their energy bills. In fact, many build a microgrid specifically to be able to better integrate and take advantage of their solar resources. 

Energy storage within microgrids

Many homeowners sometimes choose to supplement their home photovoltaic installation with a battery pack. Likewise, many microgrid owners incorporate battery energy storage in their system. With the price of lithium-ion batteries at an all-time low, the benefits of adding an energy storage resource often justify the additional cost. 

For one, battery energy storage systems provide a service known as “time-shifting”. Time-shifting batteries collect extra electricity from an oversized solar system during the day, and then discharge the battery after the sun has set to meet overnight load demands. Similarly, batteries can be discharged at times when the solar array output does not match the load requirements such as short periods of peak demand. This allows the owner to maximize the use of intermittent resources.

Another benefit of battery systems is their ability to instantly respond to changes in electricity demand on the microgrid. Having a battery serve as standby capacity is often much more cost-effective than idling an extra generator 24/7 in case demand increases unexpectedly. Think of energy storage as the fat on the microgrid where energy is stored.

Load management within microgrids

Some microgrid owners have the option to actively manage electricity demand in the same way that they manage electricity generation. 

By default, when a large electric machine starts up somewhere on the microgrid, the generators supplying the microgrid need to quickly ramp up to meet the additional demand. Microgrids that actively manage demand have another option. They can decrease demand somewhere else on the microgrid, for example by switching off a building’s AC temporarily. The result is that demand and generation are again balanced out without increasing generation.

Control and communications within microgrids

Microgrids need a brain and a nervous system to operate safely and effectively, thus needing to possess sophisticated microgrid control systems

Wide-area utility grids serve millions of consumers and have a considerable amount of inertia, limiting the potential for fast, uncontrolled changes. Microgrids, in contrast, include fewer loads and resources and are more sensitive to variations in load and generation. Starting up several large electrical machines without the assurance that an equivalent amount of generation is available is a sure way to crash the microgrid. 

A microgrid’s control system typically includes multiple controllers and sensors distributed over its territory. A Supervisory Control and Data Acquisition (SCADA) system is also required to collect data and distribute instructions. 

If the SCADA system is the nervous system of the microgrid, then the energy management software is the brain; that software can be highly sophisticated. Artificial Intelligence (AI) and machine-learning features allow modern energy management software to learn to better anticipate load from the consumers on the microgrid and generation from renewable assets, to optimize the system to run in the most cost-effective way. Maximizing the use of renewable resources, minimizing fossil fuel costs and maintaining the reliability of the equipment and the microgrid, all while dispatching the load, is all taken care of by the energy management software, within the parameters specified by the owner of the microgrid.

Switchgears, inverters and other equipment

Finally, microgrids include other critical components such as electrical cables, circuit breakers, transformers and more. These components are the bones, muscles and blood vessels of a microgrid. They connect generation resources to consumers, and allow the microgrid’s control system to effect changes to the state of the microgrid.

Automatic transfer switches, for instance, isolate different generation assets to ensure that, for example, the AC inverter associated with a solar array does not feed electricity to a diesel generator. Inverters convert the DC power supplied by batteries or by solar panels to AC power that is adequately synchronized to other AC resources on the microgrid. 

Interested in more on microgrids? You might also like: 

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