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Paralleling Industrial Generators

Industrial Generator Paralleling and Load Sharing Basics

Paralleled Generators on Roof
Facilities that use multiple generators often operate them in a parallel configuration. This is especially true for mission critcal facilities like large data centers and government faclities. Synchronization is the term used when generators are operating in parallel. The frequency, phase, and voltage of each generator must match. This can be illustrated with a sine wave on an oscilloscope. The first step of understanding paralleling, is to understand the basic generator control functions. Go to Parallel Operation of Generator Sets for benefits and details on of operating generators in parallel.

For two or more generators to operate in parallel, the following conditions usually must be met and maintained:
  • Waveform - Must produce adequate sine wave
  • Phase Sequence - Order which voltage peaks are reached on the sine wave form must match
  • Frequency - Time it takes for one positive and one negative peak on sine wave form must match 
  • Phase Angle Difference - Difference in phase angle between two sine waves must not exceed established value in a three-phase system
  • Voltage Amplitude Difference - Sine wave voltage peaks must match
When generators are operated in parallel many configurations can be utilized.  The most common way is to distribute and share the load evenly throughout the generators on-line. When the load increases, all generators equally increase fuel to accept the load. When operating generators in parallel the capability is additive (2 kW parallel with 2 kW = 4 kW capability).

Redundancy can be gained with parallel units. Redundancy can be thought of as a backup. If a facility requires two generators to supply backup power, a third generator of the same size can be the back-up. The redundant generator can be placed in the line-up while the main generator has maintenance or repair tasks completed. Additionally, the redundant generator can be used when primary generators have reached their capability and additional power is required.

Paralleling Generator Considerations

Generators that serve larger power demands are the most commonly used in parallel applications. Often acquiring generator(s) to satisfy immediate demands can offer an extra level of difficulty. When upgrading an existing system or designing a new system, the following points can be added into the equation:
  1. Use generators of the same load rating, ideally ones with the same alteranotr pitch
  2. Avoid mixing generators that are equipped with paralleling controls with those that are not equipped
  3. For generators with paralleling controls, avoid mixing manufacturers
The above considerations are used when determining what type of generators can operate together in a parallel configuration. However, there are acceptations to any rule thumb. When circumstances demand, extra equipment and systems can be used to satisfy most any generator demands. To see an example of one of our power generation technicians load testing four 500 kW generators for a customer, watch the video.

Paralleling Generators without Advanced Controls

Older generators that were developed without paralleling hardware and software can still be introduced into the paralleling arena. These generators can provide the needed power but need hardware with software to establish communications with one another. 

Manually paralleling generators through a switchboard configuration was the first method developed. This requires an operator to perform the paralleling task whenever a generator is brought online or removed from operation. If a generator fails, the operator must place the redundant generator online. To accomplish this, the main control panel must be manned during all parallel operations. When the oncoming generator meets all of the parameters it is switched online as the working generator is switched offline. The operator must engage and disengage the switches at the same time or oncoming generator will drop offline.

Generators without the advanced paralleling controls are largely considered to be analog units. Technology advancements in paralleling switchgear controls allow automatic generator paralleling functions during utility power failures. Each generator has an independent controller that reports to a master controller. The master controller completes the parallel tasks for the system. Analog technology interfaces with digital controls to obtain the best automated controls possible. Go to Kinsley for more information on these style panels.

Generators with Paralleling CapabilitiesCummins Generators with Paralleling Controls

Today generators are manufactured with hardware and software installed for paralleling capabilities. Each generator manufacturer offers a different paralleling hardware and software package. Available in both sound-attenuated and skid only styles for indoor and outdoor applications. Manufacturers design paralleling systems to work with like systems. To avoid difficulties, when using manufacturer supplied paralleling systems, it advised to stay with the same generator throughout the lineup.

Cummins PowerCommand Control (PCC) system employs the Engine Control Module (ECM) to control engine functions and monitoring. The generator set controller is responsible for paralleling, genset protection, voltage regulation, load sharing, and generator monitoring. The Human Interface Panel (HMI) allows user interface, input of configurations and setting, alarm monitoring, generator start/stop functions and manual paralleling operations. Generator set controller, ECM, and HMI are all connected and communicate via a data link network.

These generators can be connected with or without a digital master control unit. Facilities that parallel a minimal number of generators may not use the master unit concept. Generators without a digital master control can:
  • Parallel with one another
  • Perform load demand functions
  • Single generator can synchronize with the grid for base load and peak shave operations
  • Single load shedding
Large facilities the employ many generators often turn to a master control panel configuration. The master control panel communicates with each generator via connection to the HMI portion of the parallel controller. This configuration is required when:
  • Synchronizing multiple generator sets with the utility or multiple utility feeds
  • Load and capacity management operations
  • System monitoring and control
  • Complex systems operation
The backup power needed for the facility or complex determines the type of generators and the style of system used. All of the major generator manufacturers offer their control systems. With the large selection of paralleling switchgear, we can upgrade existing analog or digitally controlled paralleling systems. As always, we recommend only working with experienced technicians or commercial electrical contractors when electricity is involved.

Diesel Service & Supply has been helping companies design, test, install, service, de-install, and produce large reliable power systems for over 37 years.  We have worked on projects paralleling gennerator sets for big power requirements commonly in the multiple-megawatt range and often up to and above 20 MW for customers.  If you have any questions on paralleling gensets call us anytime at 800-853-2073 or contact us online for more information.

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