• Samrakshana Electricals Limited

Circuit Breakers For Transformers

Samrakshana Circuit Breakers provide short circuit and thermal protection for both pad mounted and overhead distribution transformers. These are applied immersed in the transformer oil on the low voltage side to protect the transformer against secondary faults and excessive overloads.
 
Features & Advantages:
Magnetic Trip: Type CQR breaker, as a standard feature, is furnished with an instantaneous magnetic trip element in addition to the standard bimetallic thermal trip element, which increases the opening speed of the breaker under high fault current conditions. This increased opening speed permits the circuit breaker to interrupt higher values of fault current than would be normally possible without greatly increasing the size of the breaker.
 
Low Losses: designed to minimise electrical losses incurred in the breaker. For any given load current, a distribution transformer breaker's losses are a cumulative result of three resistances: bimetal element resistance, contact resistance, and lead resistance. Samrakshana breaker has been designed to minimise these resistances.
 
Rugged Construction: All mechanical load carrying members are made of metal, thus providing a physically rugged breaker. In addition, each breaker has a metal wrapper above the trip mechanism to provide further protection against damage in handling and installation.
 
Flexibility In Mounting: the circuit breaker can be mounted in either the vertical position with the back slightly elevated, or the horizontal position, making it directly interchangeable with that of other manufacturers. Although both mountings are available, the preferred mounting is in the horizontal position. This mounting allows several additional benefits: the bimetal element is mounted as close as possible to the top oil level, which is the hottest oil, thus permitting maximum thermal protection; the contacts are as far as possible below oil, so should there be a leak in transformer tank, the danger of breaking an arc above oil is minimum; and finally, the length of lead is minimised because the breaker bridges part of the distance between the low voltage winding and the low voltage outlet bushing.
 
Short circuit capacity: Samrakshana breaker has a short circuit capacity of 10,000 symmetrical amperes at a maximum of 350 V per pole, provides sufficient interruption rating for a worst case fault. In other words, a bolted fault between the low voltage breaker lead and the neutral bushing (ground). Furthermore, the breaker's own internal impedance (mostly resistance) plus the extra impedance of the arc being drawn apart substantially limits the fault current through the breaker, thus providing additional protection to the transformer from short circuits.
 
Reliability: These circuit breakers are subjected to a battery of tests including interruption capability test, insulation and di-electric test, electrical resistance test, calibration repeatability test, thermal and mechanical stability test.
 
Samrakshana breakers have passed all the above mentioned tests. As part of production testing, all circuit breakers are also resistance tested and calibration tested (thermal and magnetic) to ensure strict quality control. This combination of design and production tests ensures reliable performance of the breaker throughout distribution transformer’s life cycle.