Cornelius I Series Wartungshandbuch PDF herunterladen (Seite 13)

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COMPRESSOR START RELAY

This is a current type relay and contains a N.O. contact which is connected in series with the start winding of the

compressor. The relay coil is electrically in series with the run winding. When power is applied, the compressor

draws high current which sets up a magnetic field in the magnet coil which causes the relay to operate, closing

the relay contact. As the compressor approaches operating speed, the current flowing through the coil de-

creases, permitting the relay contact to open, thereby opening the starting circuit.

POTENTIAL RELAYS

The potential relay is used as a compressor starting relay, The contact in the potential relay is N.C.. The mag-

net coil is connected across (parallel) the start winding and is affected by induced voltage, generated by the start

winding. As the compressor comes up to design speed, the voltage across the relay coil increases and at run-

ning speed is sometimes as much as 2 1/2 times the supply voltage. This voltage sets up a magnetic field

which causes the relay to operate. The starting relay is calibrated to remove the start capacitor (open the start-

ing circuit) at approximately 85% of the motor design speed.

NOTE: BOTH TYPES OF RELAYS ARE DESIGNED TO OPERATE WITHIN VERY NARROW LIMITS OF

VOLTAGE AND CURRENT DICTATED BY MOTOR DESIGN, THEREFORE, WHEN MAKING A REPLACE-

MENT OF A RELAY ALWAYS PROVIDE AN EXACT REPLACEMENT, RECOMMENDED BY THE COMPRES-

SOR MANUFACTURER.

CAPACITORS – GENERAL

An electrical capacitor is a device which stores up electrical energy. Capacitors are used with single phase mo-

tors to provide starting torque and improve running characteristics; by feeding this energy to the start winding in

step with the run winding.

Any capacitor has three (3) essential parts, two (2) of which are usually foil plates separated and insulated by

the third part called the dielectric.

Two general types of capacitors are used with electric motors. The electrolytic starting capacitor usually uses a

very thin film of oxide on the metallic plate as the dielectric. The running capacitor usually is of the liquid filled

type.

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Cornelius I Series Wartungshandbuch Seite 13