Bulletin #19

Basic questions for design of a paralleling application for generator sets

Paralleling of generators involves the arrangement of two or more generators to provide a combined output to the load.   Paralleling may also involve tying one generator to the utility or primary energy source to provide additional capacity or to protect against potential utility failures.

The practice of paralleling generators has long been in use on standby power systems requiring total capacity over 2MW.  On these applications, it is common to see two or more generators of equal capacity paralleled to achieve greater output capacity.

The main advantages of paralleling applications are:

1. Redundancy/Reliability - The availability of more than one generator allows for some of the load to remain under power, in the event one machine should fail.

2. Fuel economy - In periods of low demand, one generator may be taken offline.  A single machine under load provides with lower fuel consumption than that obseved on a larger generator operating at very low load levels.  By design, diesel engines are most efficient when operated near their full load ratings.

3. Ease of maintenance - Multiple generators allow for scheduled maintenance to be performed on one unit while still retaining the availability of standby power from the remaining units.

4. Lower cost - In many cases, it is more economical to install two or more machines than to install a single machine with equal total rating.  This is especially the case on gas fueled engines and medium sized generators.

Paralleling of generators requires equipment dedicated to monitor and control three main factors: frequency (prime mover speed), generator voltage and phase.  A qualified paralleling switchgear manufacturer can design and assemble components to conduct these tasks.  In order for the switchgear manufacturer to present a proposal, certain questions will need to be answered:

• What is the number of units to parallel?

• What are the generator and engine model numbers?  What is the engine fuel type?

• Is there an electronic governor on the engine?  What type and model?

• Will the parallel operation be initiated manually or automatically?

• Is there a requirement for the standby source to operate in synchronism to the utility?

• Are there specific requirements for industrial grade or utility grade protection (i.e.: reverse power relay, etc.)?

• Is there any requirement for remote access/comunication to control functions?

These are some basic questions that will provide an overall view of your requirements.  For more details on a specific application, please contact us.  Davidson Sales Company represents Thomson Technology, Inc., manufacturer of generator controls, transfer switches and paralleling equipment.  For more information on TTI's paralleling equipment, please see GCS2000 Brochure.

Mailing Address: P.O. Box 9086, Daytona Beach, Florida 32120-9086 USA

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