Application Engineering

Please read the Warranty Statement carefully before proceeding with any design or ordering materials or labor.

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Applying transfer equipment in electrical systems affects many design considerations. The chapter discusses the basic function of a transfer switch – to enhance availability of power to critical electrical loads and to provide a means to switch the load between two or more available sources of power.

Manual or automatically operated transfer switches are illustrated, together with the location of the transfer switches within the electrical system. Account should be taken of any device that may operate to disconnect power to the load (disconnects, breakers, fuses).

Requirements and Recommendations:

• The transfer switch should be installed as close to the load as possible.
• For critical applications, such as in some healthcare situations, more than one transfer switch may be required – each transfer switch may be used to start a common generator.
• Certain types of transfer switch require upstream circuit breakers or fuses in order to limit fault level at the switch. Check the switch rating and the fault level capability of the supply.
• To ensure reliable operation of the electrical system, the coordination between circuit breaker settings is vital and must be checked at the commissioning stage and whenever a change is made to the electrical system.
• The use of instantaneous tripping will provide additional fault energy limitation but may compromise device coordination.
• Critical loads may require segregation in order to comply with code requirements.
• Transfer of load to the generator will involve a degree of step-loading. Check that the generator is capable of accepting the load step while maintaining a satisfactory quality of supply.
• Check that the setting of the voltage and frequency failure detection is within the capability of the load equipment. Some solid-state and process control equipment is particularly sensitive to voltage and frequency fluctuations and may demand closer tolerance settings.
• Use of transfer equipment may be optional – installed by the user to facilitate process continuity, etc., or may be code mandated or legally required.
• An extensive range of transfer equipment is available to suit various applications, codes and standards.
• Non-automatic transfer switches are available for use in permanently-staffed situations, where power outage does not pose an immediately life-threatening situation or where a mobile generator can be connected. Non-automatic switches may have manual or electrical actuators.
• Closed transition transfer switches avoid the load experiencing a second interruption for re-transfer after utility outage.
• A changeover pair of interlocked air circuit breakers can be used if there is a need to interrupt fault current.
• Solid state transfer switches have lower fault current carrying capacity than electromechanical switches and require supplies to be synchronized before transition.

For information regarding your application contact your nearest distributor.

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