ELECTRICALE4U

The Current Transformer Current Transformers produce an output in proportion to the current flowing through the primary winding as a result of a constant potential on the primary     The  Current Transformer  (  C.T.  ), is a type of “instrument transformer” that is designed to produce an alternating current in its secondary winding which is proportional to the current being measured in its primary.  Current transformers  reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the actual electrical current flowing in an AC transmission line using a standard ammeter. The principal of operation of a basic current transformer is slightly different from that of an ordinary voltage transformer. Typical Current Transformer Unlike the voltage or power transformer looked at previously, the current transformer consists of only one or very few turns as its primary winding. This primary winding can be of either a single

Auto transformer Starter An  Auto transformer Starter  is suitable for both star and delta connected motors. In this method, the starting current is limited by using a three-phase auto transformer to reduce the initial stator applied voltage. The figure below shows the motor with the  Auto transformer starter. It is provided with a number of tappings. The starter is connected to one particular tapping to obtain the most suitable starting voltage. A double throw switch S is used to connect the auto transformer in the circuit for starting. When the  handle H  of the switch S in the START  position. The primary of the auto transformer is connected to the supply line, and the motor is connected to the secondary of the auto transformer. When the motor picks up the speed of about 80 percent of its rated value, the handle H is quickly moved to the  RUN  position. Thus, the auto transformer is disconnected from the circuit, and the motor is directly connected to the line and achieve

Starting Methods Of A DC Motor By  Kiran Daware   DC Machines Basic operational voltage equation of a  DC motor  is given as E = E b  + I a R a    and hence,     I a  = (E - E b ) / R a Now, when the motor is at rest, obviously, the back emf E b  = 0. Hence, armature current at the moment of starting can be given as I a  = E / R a . In practical  DC machines , armature resistance is basically very low, generally about 0.5 Ω. Therefore, a large current flows through the armature during starting. This current is large enough to damage the armature circuit. Due to this excessive starting current - the fuses may blow out and the  armature winding  and/or commutator brush arrangement may get damaged. very high starting torque will be produced (as torque is directly proportional to the armature current), and this high starting torque may cause huge centrifugal force which may throw off the armature winding. other loads connected to the same source may experience a dip in the