Machine Parts

1. Determine primary voltage and frequency.  2. Determine secondary voltage required.  3. Determine the capacity required in volt-amperes. This is done by multiplying the load current (amperes) by the load voltage (volts) for single phase. For example: if the load is 40 amperes, such as a motor, and the secondary voltage is 240 volts, then 240 x 40 equals 9600 VA A 10 KVA (10,000 volt-amperes) transformer is required. ALWAYS SELECT THE TRANSFORMER LARGER THAN THE AC TUAL LOAD. This is done for safety purposes and allows for expansion, in case more load is added at a later date. For 3 phase KVA, multiply rated volts x load amps x 1.73 (square root of 3) then divide by 1000.  4. Determine whether taps are required. Taps are usually specified on larger transformers.  5. Use the selection charts in the Acme catalog. 

In some cases, transformers can be operated at voltages below the nameplate rated voltage. In NO case should a transformer be operated at a voltage in excess of its nameplate rating unless taps are provided for this purpose. When operating below the rated voltage the KVA capacity is reduced correspondingly. For example, if a 480 volt primary transformer with a 240 volt secondary is operated at 240 volts, the secondary voltage is reduced to 120 volts. If the transformer was originally rated 10 KVA, the reduced rating would be 5 KVA, or in direct proportion to the applied voltage. http://newmachineparts.blogspot.com/

If the counter emf   becomes equal to the applied voltage, then current through the armature conductor will be zero and for this armature of motor will not rotate. Thus again the counter emf of the motor will be zero. So the counter emf can never be equal or greater than terminal voltage of a motor. Explain the universality of the statement that motor action is always accompanied by generator action or vice versa:  When armature of motor rotates in magnetic field, then the conductors cut flux and for this reason a voltage is induced across the armature. This is the motor action accompanied by the generator action. In the case of a generator, current flows through the conductors of the armature. When a current flowing conductor is placed in a magnetic field, it rotates. Thus it is the generator action accompanied by motor action. What are the detrimental effects of armature reaction on the performance of a dc machine?    Mecha...

  The use of shunt generator is somewhat restricted. It is used to supply power to equipment located within the immediate vicinity of the generator. Its use is not satisfactory for supplying power to remotely located points because not only does the terminal voltage of the generator drop as load increases, but there is also a voltage drop in the line. The greater the load the greater the greater the voltage drop in line. The combined effect of the reduction in generator voltage plus the line drop makes the shunt generator unsatisfactory for the transmission of power over long distances. Diverter resistor: A resistance shunting the series field of a compound generator to adjust the degree of compounding to produce a desired voltage regulation is called diverter resistor. Why a self excited shunt generator will not build up voltage?     How can the voltage, current and power ratings of a generator be adjusted?     ...

Reasons for not building up voltage of a self excited shunt generator: ·          No residual magnetism: The start of the build up process requires some residual magnetism in the magnetic circuit of a generator. If there is little or no residual magnetism, because of inactivity or jarring in shipment, no voltage will be generated that can produce field current. ·          Field connection reversed: The voltage generated due to residual magnetism is applied to the field and current flows in such a direction as to produce lines of flux in the same direction as the residual flux. If the field connections are reversed, the lines of flux produced by the current flow will oppose the residual flux so that the generated voltage will decrease rather than increase. ·          Field circuit resistance too high: If the field circuit resistance is greate...