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# DC Machines

## 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, …

## 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 …

## Voltage Source Inverters (VSI) Operation | VSI Working Principle

The voltage source inverter is a somewhat older design and less expensive to implement. Various implementations of the VSI are also known as six-step, twelve-step, or even eighteen-step inverters. Voltage Source Inverters Operation  In the VSI, the switches are turned on and off at regular intervals to deliver rectangular pulses …

## Variable-Frequency Drive Working Principle | Variable-Speed Induction Motor Drive

The induction motor is basically a constant-speed motor, as it operates within 3% of the synchronous speed, which is determined by the frequency and number of poles in the machine: $\begin{matrix} {{n}_{s}}=\frac{120\times f}{P} & {} & \left( 1 \right) \\\end{matrix}$ Although torque at a given slip is proportional to the …

## Pulse Width Modulated Inverter | PWM Inverter

The Pulse Width Modulated (PWM) inverter offers the ability to change both the magnitude of the voltage and the frequency using a fixed DC voltage as the input. This means a diode rectifier can be used as the front end of the drive, which appears as a constant power factor load …

## Current Source Inverter Operation

Both the VVI and PWM are voltage-source inverters; i.e., they provide a voltage to the motor similar to what it would normally receive from the power system, except at variable frequency. Current Source Inverter Working A current- source inverter, on the other hand, acts as a constant current source to …