By Mark Siira

Paralleling switchgear technology and capability has dramatically improved to allow increased flexibility, lower cost and higher reliability. System integration by generator set manufacturers during the last 10 years has enabled step function improvement in the simplicity and reliability of paralleling controls with the use of digital technology. Kohler Power Systems embarked on that path in the late 1990s and has introduced sophisticated and lower cost solutions to paralleling of multiple generators or connecting to the electric utility grid.

Paralleling switchgear systems typically control whether power is provided from the electric utility to the customer load, or from a customer-owned power source (generator systems) to the load by controlling the opening and closing of circuit breakers to establish or break connections between the utility, load, and generator.

Historically, the suppliers of paralleling switchgear wrote specifications around their “standard” product. Before the digital technology prevalence in the late 1990s, this practice was an effective way for manufacturers to prevent competitors from applying new technology solutions. The transition to digital paralleling has resulted in all companies using technology to provide various functional performance specifications with a single, relatively modular hardware offering. Additionally, this technology has inherent reliability, design for manufacturability and easy commissioning along with a significant cost reduction achieved through reduced wiring complexity, reduced component count, and physical reduction in the number of metal sections required to perform generator paralleling. Other benefits to this approach, such as reduced lead times, reduced application engineering, and reduced design time allow for enhancement to the customer experience in the purchase of the equipment.

Shift to Digital Paralleling

This trend began in the late 1990s as many companies looked to electric utility deregulation and Y2K as reasons to invest in distributed generation technology. General design objectives for the shift to digital paralleling were:

• Increased functionality of the generator control and engine control modules;
• Software-based controls rather than discrete-control components;
• Multi-function user interface;
• Flexibility of systems to meet project requirements; and
• Reduced lead time, footprint, and cost.

 

Software Based Controls and Advanced Generator Controls

Kohler’s design concepts shifted all control logic into PLCs. This was a massive product development effort, but used the 20 years experience in building these systems as great leverage. Software modules were developed for most major functions, including Load Sharing (real and reactive) and synchronization. In conjunction, a concurrent development of Kohler’s DEC-550 generator controller provided significant metering, voltage regulation and system status data links to the switchgear. Generator protective relay functions were integrated into the generator controller to provide an extra layer of integration to the controls.

Multiple Programming of Operating Modes

System architecture changes results in a flexible, configurable switchgear system that can operate in a variety of modes, perform multiple transfer types and other switching operations while operating in response to – and independently of – commands or information from outside sources. Maximum flexibility of the switchgear system was achieved through implementing software that includes the necessary programming and related information for switchgear system operation. Operating modes can be specified from the factory or changed at different stages of the implementation of the system at the user site. An example of some operating modes would be: Isolated Operation, Base Load, Import / Export mode.

Why Digital is Better

Because the architecture requires less sheet metal, fewer components and less wiring, it results in reduced cost. Companies who make generators have integrated much of the functionality of the system into the digital generator controllers which further reduces the number of components and labor. Additional benefits demonstrated include a smaller footprint for the system, shorter lead times, and increased performance and reliability.

Why PLC Based?

Kohler and other companies have chosen to run the software controls on PLC hardware, which is the most effective way to implement paralleling switchgear control. PLCs have proven to be reliable platforms for industrial controls and are available worldwide if replacement parts are needed. This approach also provides efficient use of available processors in the system. Traditional systems also use PLCs for basic engine start and input/output functions. We have eliminated the multiple and sometimes conflicting processors resident in the discrete components.

The use of PLCs allows the system to be controlled by a high speed Modbus Plus network, with communication to the generators and other system components through Modbus network. This “fly-by-wire” architecture results in the least amount of hardware and wiring, while providing significant redundancy for system protection.

An additional benefit of this architecture is its ease of modification to meet requirements of the project – even after the hardware has been manufactured. The software based controls even allow tweaking of the sequence of operation and display of information at startup.

User Interface

Development of the digital switchgear included replacing discrete meters and switches with a multi-function, graphic-user interface. This ensures that the switchgear system operates in the proper mode and performs the proper transfers or other switching operations for any operational situation. Of course, analog meters are still available if the customer requires this feature.

This multi-function user interface provides a better solution for stationary power systems:

• It has proven easier to operate and requires less operator training to manage and monitor the system.
• The HMI provides more information on the systems state and history.
• All of the setup commands and confirmations are performed in one place on the system.
• It provides a complete system control summary with the actions and results displayed on the same screen.
• With a built in web server, it allows for remote access to the system information.
• Digital switchgear has proven to have faster setup and commissioning.

Conclusion:

The PD300 digital switchgear system parallels three generators with the utility to provide the customer with soft-load, closed-transition emergency operation, as well as maintain parallel operation for peak shaving. A traditional arrangement would have required an additional eight feet of space, making the location of this equipment impractical.

Configurable paralleling systems in the past five years have made great progress in both technology and acceptance to the power-generation industry. Continued investments by major generator system manufacturers will continue to improve flexibility, functionality and reduce cost, while delivering the customer a more reliable system with a single source of responsibility.

Mark Siira is the director of switching systems for the Kohler Power Systems-Americas Division. In this role, Siira has P&L responsibility for the switchgear and systems business and is responsible for sales, marketing, engineering and manufacturing. Additionally, Mr. Siira has led the development of distributed generation strategies and manages business development activities. He has a Bachelor of Mechanical Engineering Degree from GMI Engineering and Management Institute (now Kettering University), Flint, Mich., and a Master of Business Administration Degree from Harvard University, Cambridge, Mass.