History and Discovery of Electricity Electricity is one of our most useful sources of energy today. It is hard to imagine how a modem industrial society could exist without electricity. But until the mid-1800s, no one knew much about electricity or how to use it. Until then, electricity was nothing more than a scientific curiosity. …
Operating a DC Shunt Motor on AC Power What will happen if you connect a dc motor to an ac source? When the ac source changes polarity, the current in the motor will reverse. But the reversal will occur in both the armature winding and the field winding. Therefore, the torque on the armature will …
Universal Motors The universal motor is a special kind of ac series motor that performs almost as well as a dc motor. It delivers a high starting torque, its speed can be adjusted, it is small in size, and it is inexpensive. There are two main differences between dc series motors and universal motors. The …
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Transformer Cooling Methods A transformer in operation develops heat as a result of the copper and core losses during operation. Heat is not produced rapidly in small transformers, but the rate is much higher in large transformers. The rate of heat production determines how high the operating temperature rises above the ambient temperature. There are many …
Autotransformer Introduction The prefix auto means self. An autotransformer is a self-induced transformer. It has the primary and secondary windings electrically connected. When the transformer is used as a step-down transformer, the entire winding serves as the primary winding. The section XY is common to both the primary and secondary windings. As with the two-winding …
Instrument Transformers Current transformer and voltage transformer measuring instrument transformers are designed to operate at low current and low voltage. Safety is also a reason for not connecting test instruments to sources operating at high voltage. An instrument transformer reduces high voltages and currents to safe values. Instrument transformers performs two functions. It serves as …
Basic Transformer Construction A transformer consists of two coils mounted in fixed positions relative to each other. One coil is supplied by an alternating current. As the current alternates, the magnetic field it produces also alternates. This alternating field induces an alternating current in the second coil, which supplies a load. A simple transformer construction consists …
Transformers have high efficiencies, especially the larger sizes operating at 50 to 100% of full load. However, they are not perfect. Some losses occur in all transformers. Transformer losses are divided into two types Copper losses Core losses Copper loss Copper loss is the loss of power caused by the resistance of the copper windings. …
Dry Cell The potential difference between the terminals of a dry cell is about 1.5 volts (abbreviated V), regardless of the size of the cell. The potential difference depends only on the chemicals used in making the cell. The size affects only the length of time required for discharge. Dry Cell Size The larger the …
Measuring Current measuring current on certain troubleshooting jobsis required. You will need to know how much value of current is flowing in part of a circuit. Measuring the current establishes part of the basis for analyzing the circuit which can lead you to the cause of the problem. To measure the current, you use an …
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