## Three-Phase AC Power: Star & Delta Connection

The most economical way to mass produce AC power is by steam turbines that drive large three-phase AC generators (alternators — Figure 1). Figure 1. Steam turbines drive large 3-phase AC generators This is why most electrical-utility power generating plants are located on a river that has been dammed to …

## Single-Phase AC Power

In a single-phase (or 3-phase for that matter) AC electrical power distribution system, both the load current (as electrical utilization loads are connected) and the applied voltage that causes it to flow are transmitted along the length of the circuit conductors varying in amplitude with time and periodically reverse between …

## Power Transformer Differential Protection

A power transformer’s main task is to transform an electrical power from one voltage level to the other voltage level. A power transformer is the most important part of the electrical system as well as well the most expensive part. The function of all other electrical equipment (e.g. circuit breakers, …

## High-Voltage DC Power Transmission

Advantages and disadvantages of a High-Voltage DC power transmission system should be analyzed in detail. Only then can we raise the question: Is AC energy transmission the most efficient option for the 21st century? AC energy transmission is the most common mode of energy transmission in the world. DC transmission …

## Electrical Formulas Excel Sheet

This particular Electrical Formulas Excel Sheet will assist you to get a quick answer to the quantities related to the following topics: 1 – Basic Concepts of Electricity 2 – Electrical Quantities and Components 3 – OHM’s Law 4 – Series Circuits 5 – Parallel Circuits 6 – Series-Parallel Circuits …

## DC Motor Starters and Their Circuit Diagram

This article covers various types of starters for the DC motors including: Manual Starters Automatic Starters Definite Time Starters Counter EMF Starter Current-Limit Starter Each type of starter along with its circuit diagram is described in detail in this section. Manual Starters Recalling the equivalent circuit of a DC motor, …

## Reduced Voltage Motor Starters

Induction motors draw very large currents when started at full voltage. Thus, it is desirable, especially for large motors, to start them at reduced voltage to keep the starting current low. Reduced voltage motor starting methods include resistance starting, reactance starting, autotransformer starting, wye-delta starting, part-winding starting, and electronic soft …

## Speed Control Methods of DC Motor

The major advantage of DC motors has been the ability to control the speed-torque characteristic over a fairly wide range of speeds for a given torque. Variable-speed AC drives now make it possible to use induction motors to perform tasks that previously could only be done by DC motors. However, …

## Types of DC Motors and Their Characteristics

DC Motor Speed Characteristics When a load torque is applied to a motor, the motor will slow down due to the load opposing the machine’s rotation. Eventually, the machine’s electromagnetic torque will equal the load torque and a new steady-state speed will be reached. How the speed changes depends on …

## Losses and Efficiency of DC Machine

The losses in a DC machine affect its cost, rating, and performance. The efficiency of a rotating machine is frequently determined by measuring the losses, using techniques that are precisely defined by ANSI, IEEE, and NEMA measurement standards. The efficiency is defined the same way as it is for transformers …

## Self-Excited DC Generator Working

The magnetization curve produced when the machine is separately excited still applies in the case of self-excited DC generator. That is, a given value of field current will produce a specific value of the generated voltage at a given speed, regardless of how the field winding is connected. However, there …

## DC Generator Characteristics

As shown by equation 1, the terminal voltage of the separately excited DC generator would be expected to decrease in a linear manner due to the voltage drop across the armature circuit resistance. $\begin{matrix} {{V}_{t}}={{E}_{a}}-{{I}_{a}}{{R}_{a}} & {} & \left( 1 \right) \\\end{matrix}$ Figure 1 shows the linear decrease that would …

## DC Generator Operation

When operated as a generator, the armature of the DC machine is driven by a prime mover. As the armature coils move through the flux created by the stator field, a voltage is induced in them. To understand the operation of the DC generator we need a specific relationship for …