Contactors and motor starters

Burhanuddin YamaniOktavian Lintin

Nur Endah Lizarifin

Magnetic Contactors

Magnetic contactors as a magnetically actuated device for repeatedly establishing or interrupting an electrical power circuit

Application

To switch power on and off to a pumpTo switch power on and off to a distribution panelUsed with pilot device to control temperature and liquid level of a tank

Advantages• Matter a build a magnetic contactor that will handle large currents of high

voltage, and the manual apparatus must control only the coil of contactor• Allow multiple operation• Automatically initiate the proper sequence of events• Automatically controlled by very sensitive pilot device• Increasing the safety of an installation• The control equipment may be mounted at a remote point• Possible with equipment such as PLC

Type of operating electromagnets

• Clapper• Bell-crank• Horizontal-action• Vertical-action

DC Contactor vs AC Contactor

DC Contactor• Large number of turn• High ohmic resistance• Limited by resistance

AC Contactor• Small number of turns• Low ohmic reistance• Limited by impedance

Shading Coils

• Shading Coils is a single turn of conducting material munted on the face of the magnetic assembly

• It use to reduce the noise on the contactor

Main contact of a contactor

• Act as switch• Must carry their rated current without overheating, make

current without bouncing or welding, and interrupt current without undue arcing

Auxiliary Contacts

• Have a much lower current rating and are used like a relay to interlock or hold circuit

Raw material of contacts

• Copper• Silver

Arc suppression

• Arc suppression is required to keep the contacts in the device from burning up

Arc Chutes• Often called blowout coil• Help to extinguish an electric

arc at contacts opening under ac and dc loads

• Connected in series with the load, provide a magnetic field that blows out the arc

Contactor Sizes and Ratings

• Magnetic contactors are rated by NEMA (National Electrical Manufacturers Association) according to the contactors ability to carry rated current for 8 hours without overheating according to size and type of load to be controlled.

• Magnetic contactors are also rated for the type of load to be utilized or actual applications. Load utilization categories include :

Nonlinear load Resistive loads Inductive loads Capacitive loads

• Enclosed magnetic contactors must be housed in an approved enclosure based on the environment in which they must operate to provide mechanical and electrical protection. More severe environments require more substantial enclosures. Sever environment factors to be considered include:

o Exposure to damaging fumeso Operation in damp placeo Exposure to excessive dusto Subject to vibration, shocks, and tiltingo Subject to high ambient air temperature.

• There are two general types of enclosures:1. nonhazardous-location, are further subdivided into the

following categories: General-purpose Watertight Oiltight Dusttight2. hazardous-location, are classified into two categories: Gaseous vapors Combustible dusts

Solid-state Contactor

• A solid-state contactor is a power-switching device designed to replace magnetic contactors for application involving both resistive and inductive loads.

• Solid-state three-phase contactors are especially suited to high-cycling applications owing to the absence of arc-producing air gap contacts.

• Silicon-controlled rectifiers (SCRs) is the most common high-power switching semiconductor that enable reliable control of electric power from 1 kW to 1000 kW for most types of resistance heaters, motors, and other inductive loads.

• Two SCRs connected in inverse-parallel are necessary to switch ac power

• Zero-fired control refers to turning on the SCRs at the zero voltage crossing for full cycles, applying full power or no power with the proportion of full cycles, or determining the resulting power to the load. This is some times called integral cycle mode or burst firing