Electrical Machines

Grounding transformer or Earthing transformer

Grounding transformers are used to obtain a neutral when an existing delta-connected or ungrounded systems are to be grounded. These transformers provide a path for the flow of fault currents during unbalanced ground faults. They can be found in transformer substations where neutral might not be available as the transformer windings are delta connected. Types … Read more

Torque-speed calculator & speed-torque calculator

Here is a calculator that can be used to calculate torque from speed and speed from torque. Torque-speed calculator Enter motor torque N.mlb.inlb.ft Enter motor power hpkW Calculate Result Motor speed rpm Speed-torque calculator Enter the motor speed RPM Enter the motor power hpkW Calculate Result Torque in N.m N.m Torque in lb.in lb.in Torque … Read more

Rogowski Coils

A Rogowski coil is an electrical transducer, that functions similar to a current transformer and is used in a variety of applications to measure alternating current (AC). It is named in honor of German physicist Walter Rogowski for his contributions to the field of electronics. Construction-wise they are a bit different from the normal current … Read more

Star-Delta starter wiring diagram – Control and power wiring diagrams

The power and control circuits of a star-delta starter are discussed in this article with the help of an actual star-delta starter wiring diagram. You can find the instructions to calculate the ratings of contactors for a star-delta starter circuit here: Star-Delta starter design tool. Further operation in detail can be found here: Star-delta starter … Read more

Transformer cooling methods

Transformers are the most efficient electric machine. A typical transformer is over 99% efficient. The small inefficiency is due to copper losses, core losses-hysteresis and eddy currents losses, stray and eddy current losses occurring in the transformer. These losses result in temperature rise. Various transformer cooling methods are adopted in order to maintain sufficient operating … Read more

Types of Transformer windings

Transformer windings constitute the electrical circuit of a transformer. They are made up of current-carrying conductors wound around the core. The primary windings form the input to the transformer and the secondary windings form the output. The construction of the transformer windings should be stable enough to ensure safe operation. It should also be mechanically … Read more

Insulation materials used in transformers

Insulation materials are one of the most important elements in a transformer. They are used to electrically separate the conducting parts of a transformer from each other and from other components. Internal insulation failures are the major cause of transformer failures. This article intends to give you an overview of insulation materials used in transformers. … Read more

Transformer core

A transformer core serves the following three important purposes: Provides mechanical support to the windings. Provides a low reluctance closed ferromagnetic path to the magnetic flux. Reduces the losses due to flux leakage. The primary and secondary windings of a transformer are wound over the core but physically separated from each other. The transformer core … Read more

Hysteresis loss and Eddy current loss and their difference

In electric machines, a varying magnetic field causes eddy currents in all metallic parts and hysteresis in ferromagnetic core. The losses caused due to eddy currents are known as eddy current loss and that caused due to hysteresis is known as hysteresis loss. In the following sections, we will learn, eddy currents, the phenomenon of … Read more