Bch Electric Limited

Brand	BCH
Condition	New
Available Power	Upto 800HP
Standard Tappings	50% , 65% and 80%
Auto Transformers Type	Air Cooled /Oil cooled

When a squirrel cage motor is started on full voltage Direct On Line, the electrical system experiences a current surge. The peak starting current can be as high as 6-8 times the rated current & this can cause a voltage dip in supply system. Also, the motor & driven equipment experiences a torque surge, which can cause serious mechanical problems,. In most cases, it is desirable to reduce these surges to safe levels, particularly for higher rating motors (>10HP)
The normal approach is to start the motor on reduced voltage & open-transition Star-Delta starting is most common. For this, the motor must have all leads (6 or 12) brought out to facilitate star/delta connection. Supply is applied to motor with stator winding star-connected. This gives the effect of reduced voltage (58%) on  the windings & the peak starting current is limited to 1.7-2.5 time rated. The peak starting torque is also limited to 0.25-0.4 times rated torque. When the motor speed is close to torque-equilibrium, the Star contactor is opened & Delta contactor is energised to connect the stator windings in Delta.
S-D starting can be used in applications where low starting torque is permissible. However, main problem comes during transition from star to delta. A high transient current is generated during transition, & care must be taken to prevent nuisance tripping of SCPD. In certain applications, equipment may be subjected to mechanical jerk also, leading to high wear & tear.An effective reduced voltage starting method is Auto Transformer Starter, which provides solution to transient problems & has other advantages over star-delta starting.

Features:
Range

• 10 tank Processed bolted construction enclosure
• Superior gasket,

Protection

• Short Circuit (with MCCB or SDFU)
• Overload and Single Phasing (with Overload relay)
• Under voltage/Over Voltage /Single Phasing/Phase Reversal
• Other protections available on request

Metering and Indication

• Voltmeter with selector switch
• Ammeter with selector switch
• R,Y, B phase indication
• Motor ON, OFF and Trip indication

Advantages of Auto-transformer Starter

• Flexibility: Different voltage taps of auto-transformer allows adjustments for a range of starting current and  torque requirements. In applications like mixing, extruding or conveyor, such flexibility to alter starting parameters can be a definite advantage, because the besttapping can be selected during commissioning as per required starting torque. The standard taps are 50%, 65% and 80% of the full line voltage. Accordingly, the starting torque is 25%, 42% and 64%. Voltage applied to the motor may be increased in multiple steps also to achieve very smooth acceleration.
• Smoothness: BCH ATS are closed transition type, an arrangement that maintains a continuous power supply to the motor during the transition from reduced to full voltage. This avoids the high transient switching current characteristic of open-transition type starters, & there in no danger of nuisance tripping of SCPD in case of ATS. Also, the transition is smooth & no mechanical jerk is forced on the equipment. This feature is particularlyuseful in applications like pumps, fans & compressors, where it helps to reduce wear & tear of equipment.
• Performance: An ATS provides highest starting torque per ampere of line current drawn. So, it is best used where high torque is required to overcome the inertia of the load, & at the same time starting current must be limited to minimum.