SECTION I
SECTION II
Normal connections for4 Direct-on-line (DOL) starters
SECTION III
Normal connections for19 Star-delta starters
SECTION IV
Normal connections for70 reversing Starters
Normal connections for75 pole changing Starters
SECTION V
Applications79
SECTION VI
Chart of relay ranges90 & back up fuses
SECTION VII
Information for Installation &107 Preventive Maintenance
SECTION VIII
Trouble shooting chart111 for starters
SECTION IX
Capacitor ratings for115 power factor improvement
SECTION X
Switchgear Standard Products Range118 Switchgear Training Centers *
Section IV
contains wiring diagrams of the starters which are not manufactured by L&T at present. Wiring diagram of such starters are given for reference purpose. General
SECTION I
General Relay setting
Tripping of starters
Back up fuses
Coil Voltage
essential to keep the following points in mind :
1) Relay setting The overload relay unit is the protection center of the motor starter. Relays come in a number of ranges. Selection of a relay for a starter depends upon motor hp and duty. A selection table indicating the proper range for different ratings is given in section VI. For all direct-on-line starters, relays should be set to the actual load current of the motor. This value should be equal to or lower than the full load current indicated on the motor name plate. Here is a simple procedure for setting the relay to the actual load current: Set the relay to about 80% of full load current. If it trips, increase the setting to 85% or more. The relay should never be set at more than the actual current drawn by the motor (The actual current drawn by a motor will be less than the full load current in most of the cases, as motors may not be loaded to capacity.) The relay operates on the phase currents in Star-Delta starters. It should, therefore, be set at 0.6 times actual load current. A procedure similar to the one described for setting relays in DOL starters can be followed for Star-Delta starters.
2) Tripping of starters A starter may trip due to the following conditions; a) Low voltage or failure of power supply b) Persistent overload on the motor In the first instance, the tripping occurs through the coil which opens the contacts when voltage falls below a certain level. The starter can be restarted as soon as supply is back to normal. The relay trips the starter when there is an overload. It can be restarted only after the relay is reset. However, the cause of overload must be investigated before restarting, or else the starter will trip again. Persistent overloading can reduce the life of the motor. 23 L&T offers manual reset type thermal overload relays. These relays clearly discriminate between tripping caused by an overload and tripping due to failure of supply voltage. MN relays also give protection against single phasing and overload. MN relays are provided with Auto/Manual reset facility.When a starter trips because of an overload, it cannot be restarted by pressing the start button. The stop button has to be pressed first to manually reset the relay before restarted. The relays can be reset only after the bimetals have cooled sufficiently.
Resetting must therefore be carried out after one or two minutes. This will also permit the motor to cool down. Back-up fuses Motor starters must never be used without back-up fuses. The sensitive thermal relay mechanism is designed and calibrated to provide effective protection against overload fuses preferably the HRC cartridge type, are essential for protecting the installation as well as the thermal overload relay of motor starter against short circuits. A reference table indicating fuse ratings for different ratings is given in Section VI. It is recommended that the use of semi-enclosed, rewirable tinned copper fuses may be avoided. Coil voltage Selection of coils depends on the actual supply voltage available. A wide variety of coil voltages like 24V, 42V, 110V, 220V, 230 / 250V, 360V, 400 / 440V ac are available as standard for L&T contactors and starters.
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