Transfer Switches

“Emergency Power” Quality & Reliability

Electrical power has become so essential to modern life that its uninterrupted availability is presumed. During emergencies it may mean the difference between life and death, between the preservation of industrial operations and shut-down, or between a steady flow of information and a paralyzing silence. Storms, accidents and disasters, unpredictable as they are, cannot be discounted where electrical energy is concerned. The Electrical engineers at IPSI , therefore, anticipate the unpredictable and provide emergency power sources for broadcasting facilities, military installations, firehouses and police stations, government offices, hospitals, livestock/poultry confinement, and a host of other applications.


But the switch from a normal source to an emergency generator is a complex transition. If constant service is to be maintained, the function must be performed automatically, safely, dependably, by a rugged, reliable automatic transfer switch. ATS is designed to transfer electrical loads from a normal (preferred) source to an emergency source when normal source voltage falls below prescribed levels. The transfer switch automatically re-transfers the load back to the normal source when power is restored to operating levels.

ATS Series Operation

When the normal line fails or the voltage drops to a predetermined point (usually 70 percent of nominal), the phase relay(s) are de-energized. The main control relay drops out, closing the circuit to the emergency drive solenoid and, if applicable, closing a circuit to start the engine generator set. When the emergency source reaches 90 percent of rated voltage and 95% of rated frequency, he emergency drive solenoid is energized through the emergency coil-control relay, causing the main contacts to disconnect the load from the normal source and connect it to the emergency source. After the drive solenoid has completed its electrical stroke and is seated, the emergency coil control relay opens to disconnect it. The transfer switch is now mechanically locked in the emergency position.

When normal voltage is restored to a predetermined point, (usually 90 percent of nominal), the voltage-sensing phase relay(s) energize. The main control relay closes, and the normal drive solenoid is energized through the normal coil control relay. After the drive solenoid has completed its electrical stroke and is seated, the normal coil control relay opens to disconnect it. The transfer switch is now mechanically locked in the normal position.

Optional Neutral Switches

All current levels are available in four pole designs for multi-source power systems with ground fault protection that may require switching the neutral. The neutral switching contact is on the same shaft as the associated main contacts. This insures proper operation, and avoids any possibility that the neutral contact will fail to open or close as is possible with other transfer switch designs, where the neutral pole is an add-on accessory. The neutral contact is identical to the main contacts, having the same current carrying and the same high withstand and closing ratings.

Overlapped neutral contacts that “break last and make first” are provided for system safety.


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