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  • GE Energy Digital Energy

    Zenith Energy Commander Paralleling Switchgear Application Guide

  • • Flexibility

    • Increased Reliability

    • Uninterruptible Maintenance

    • Cost Savings

    • Scalability

    • Proven Experience

    • World-Class Global Service

    Information contained in this application guide is based on established industry standards and practices. It is published in the interest of assisting in the preparation of plans and specifications for medium and low voltage paralleling switchgear. Neither the General Electric Company nor any person acting on its behalf assumes any liability with respect to the use of, or for damages or injury resulting from the use of any information contained in this application guide. This guide should be considered a supplement and should be used in conjunction with the GE Switchgear medium and low voltage application guides.


    Paralleling is an operation in which multiple power sources, usually two or more generator sets, are connected and synchronized to a common bus (same parameters in regards to frequency, phase angle, etc.).

    Why Zenith Energy Commander?

    Zenith Energy Commanderprovides customer facilities with reliable power switching systems. Since the inception of paralleling switchgear (PSG), many successful Energy Commander installations have been supplied with a focus on providing reliability.

    Zenith Energy Commander has evolved and adapted to the changing technologies in engine generator design, switchgear controls and monitoring systems. It reflects GE’s continuing commitment to reliable solutions for critical power applications.

    Why Parallel?

    There are several advantages to employing PSG in an electrical design, such as flexibility, increased reliability, ease of uninterruptible maintenance and application/operation cost savings. It is because of these advantages that PSG has become one of the best choices for meeting today’s power requirements.


    Paralleling power sources allows for a wide variety of choices in the generation, distribu- tion and utilization of the system’s power.

    Increased Reliability

    Systems in which part of the load is very critical may be best served by paralleling one or more generator sets. Under parallel operation all the generator sets are started at once. The first set to reach the proper parameters will assume the most critical portion of the load, with the remaining sets picking up lower priority loads. In addition, by using a load shedding application, the failure of one generator set will not interrupt power to the critical loads, as less critical loads can be shed.

    Uninterruptible Maintenance

    When one engine - generator set is out of service for maintenance or repair, having others synchronized on the same bus can provide the needed back-up power, should an outage occur.

    Cost Savings and Scalability

    Savings can be realized on the application when a number of smaller sets would be less expensive than one large set or when the load makes it impractical to divide into several sections, each with it’s own generator. Also, when it is anticipated that the load will grow significantly in the future, the capital investment can be reduced by starting with small sets and paralleling additional units as load increases dictate.

    GE Energy – Digital Energy

    Zenith Energy Commander Paralleling Switchgear

  • Emergency or Standby Power

    > Features The emergency system is used to supply power to building loads during a power failure.

    Paralleling switchgear controls the system transfer to generators and return back to normal sequences of operations.

    Paralleling switchgear controls the addition of load on/off generators (load add/shed).

    Transfers between utilities and generators occur in open transition or passive momentary closed transition (no active synchronization of sources).

    > Components System typically consists of paralleling switchgear product and automatic transfer switch or auto throw-over products

    > Sequence of Operation 1. Utility fails.

    2. ATS’s (or ATO’s) send start signal to PSG

    3. Generators start and parallel to bus.

    4. PSG Controls the ATS’s transfer to paralleled generators. (load add)

    5. PSG controls optimization of generators. (shutting off and starting generators as needed)

    6. PSG controls load shed operation. (shutting off loads and/or ATS/ATO devices non-critical if generators become overloaded)

    7. Utility returns.

    8. ATS transfers back to utility (open transition... lights blink, or momentary closed transition... lights stay on, depending how ATS is configured)

    9. Generators shut down.

    10. Peak shave often used to send non-emergency start to system to transfer ATS or ATO devices onto generators to “shave” load off the utility.

    Generator Generator





    Figure 1 Multiple Gen Sets, No Utility Transfer Control with ATS’s

    > Configuration Example

    Page 1 • TB-2103

    Zenith Energy Commander Paralleling Switchgear System Applications

  • > Configuration Example

    Prime Power

    > Features On-site prime power systems are most often used where there is no utility source available.

    The required electricity is generated entirely on-site, typically at facilities such as island resorts, mines, mills or other remote locations.

    Since utility is not available in prime power systems, ATS’s/ATO’s and utility/tie breakers are not required.

    > Components Generators are the only source of power. The system typically consists of PSG product with no ATS/ATO products.

    > Sequence of Operation 1. System enable signal causes generators

    to start and parallel to bus.

    2. PSG controls optimization of generators. (shutting off and starting generators as needed)

    3. PSG controls load shed operation. (shutting off loads non-critical if generators become overloaded)

    4. PSG controls frequency of generators for clock/time correction.

    5. Removing system enable signal will shutdown the generators.

    Figure 2 Multiple Gen Sets, No Utility Transfer Control

    Generator Generator

    Load Load

    Parallel with Utility

    > Features Parallel with utility systems are utilized whenever generators are to be actively synchronized and paralleled with utility sources for short or long durations.

    These systems are often also used for standby use.

    PSG controls the generators transfer operations with the utility source(s) as well as the power management (loading controls) to direct power the appropriate direction.

    Transfers may occur in short duration (momentary closed transition), a somewhat longer duration (softload/unload closed transition), or a sustained duration (maintained parallel with utility).

    Power management in maintained parallel situations includes controlling import levels from utility, export levels to utility, or base load levels where generators are loaded to set amount disregarding the import and export contribution from utility.

    “Co-generation” is often used for maximizing generator efficiency with heat recovery systems.

    > Components System combines generators with utility sources. It typically consists of PSG product which controls the ATS/ATO operations.

    10 2 4 6 88 12 Noon

    11 3 5 79 1

    ON OFF

    Utility Purchased Power

    Generator Non-Purchased Power

    kW Demand Threshold



    > Peak Shave Example

    Zenith Energy Commander Paralleling Switchgear System Applications

    TB-2103 • Page 2

  • Utility

    Generator Generator

    Load Load


    Generator Generator

    Load Load


    Load Load

    Utility Utility

    Generator Generator

    Load Load Load Load


    Generator Generator

    Load Load

    Sequence of Operation 1. When used for standby, the PSG

    operates in the same manner as the emergency standby sequence. If not used for standby, the generators remain offline when utility is not present.

    2. Non-emergency start signal is sent to PSG for peak shave or exporting power to utility applications.

    3. Generators start and parallel to bus and with utility.

    4. PSG controls the transfer of loads off the utility onto the generators in momentary closed transition (if emergency standby is also utilized) or softload closed transition.

    5. In maintained parallel with utility applications, the PSG controls the amount of import power from utility, export power to utility, or base loads the generators to a fixed amount non-dependent upon the utility- supplied power. With emergency standby applications not maintaining paralleling with utility, the PSG in this case controls the synchronizing of generators with utility and momentary closed transition transfer onto the generator bus.

    6. PSG controls optimization of gen- erators (shutting off and starting generators as needed).

    7. PSG controls load shed operation if emergency standby is also utilized.

    8. Non-emergency start signal is removed.

    9. PSG controls the soft unload of generators off the utility or momen- tary closed transition from utility if emergency standby is utilized.

    10. Generators shut down.

    Figure 3 Multiple Gen Sets, Utility and Generator Main-Tie Transfer Control

    > Configuration

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