ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Speed Control In DC Machine

Updated on January 2, 2014

Speed Control

One of the most important advantages of the dc machines which out ruled the ac machines in industry is the ability of the speed control of dc machine is much superior and easy compared to ac machines.

Speed of the dc machine can be controlled by:

  1. By applying the voltage to the terminals of the dc machine
  2. By introducing external resistance in the armature of the machine
  3. By varying the flux per pole (φ) of the machine

The first two methods involve the adjustments to be done on the armature side of the dc machine whereas the third method requires adjustment in the field side of the dc machine. Therefore speed control of the dc machine are classified as armature control method and field control method. In armature control method the speed of the dc machine decreases as the applying voltage will be reduced on the other hand in field control method weakens the flux per pole of the dc machine and speeds above the rated speeds are attained

Armature Control method of Speed Control:

In armature control method voltage applied to the armature terminals is varied with out changing the field current.

Speed of the dc shunt motor by armature control can be obtained by:

  • By connecting an variable external resistance in series to the armature circuit so that voltage applied to the dc machine can be varied
  • By connecting an variable resistance in shunt to the armature circuit and other variable resistance in series to the armature shunt circuit.
  • By providing the varying voltage to the armature terminals. The voltage provided should be separate from the voltage that provide to the field circuit

i) Armature Resistance Control Method:

In armature resistance control method a variable resistance is connected in series to the armature circuit. When the resistance of the rheostat is increased, current flowing through the circuit reduces and the voltage drop at the armature is less compared to line voltage. Thus speed of the machine reduces in proportional to the applied voltage.

This method is employed only in applications where speed variation is required for shorter duration and not continuous. This is because of the larger resistance required and high power loss during the operation at the rheostat. Ex: printing machines, cranes, hoists

ii) Shunt Resistance Control Method:

Armature resistance method is simple and easy but have disadvantages as the speed not only depends on the resistance value but also on the load current (variation in the load during the drive operation results in the variation in the speed of the machine). Therefore a divertor (shunt resistance) is employed along with the series resistance.

In this method the change in the armature current (because of the load torque) does not affect the change in the voltage across the terminals hence the speed.

iii). Armature Voltage Control:

In this method of speed control a variable source of voltage is provided to supply the power to the armature circuit. Voltage to the field circuit should be different from the variable voltage source provided to the armature.

By this method disadvantages such as poor voltage regulation and low efficiency in case of voltage resistance method is avoided, however this method is costlier compared to the other. The adjustable voltage source can be from a adjustable voltage generator or from a adjustable rectifier

Field Control Method of speed control:

In DC machines weakening of the field of the dc machine increases the speed of the dc machine and strengthening of the field will cause to reduction in the speed of the machine. Hence by weakening the field of the machine speed above the rated speed can be attained.

Speeds above the rated speed can be attained by:

  • Providing a variable resistance in series to the field circuit so that variation in the resistance value results in increase or decrease in the field of the machine resulting in the speed control.
  • By variation in the reluctance of the magnetic circuit of the motor.
  • By varying the applied voltage to the field circuit of the dc motor by keeping the voltage supplied to the armature circuit constant

i) Field Resistance Control:

In this method variable resistance is employed in series to the field circuit. As in this method when resistance value increases only field weakens. By weakening the field speed above the normal speed can be attained

ii) Reluctance Control Method:

This method requires motor to be constructed with special mechanical features such that reluctance of the magnetic circuit can be changed. This is more expensive and rarely employed

iii) Filed Voltage Control:

This method requires variable voltage source which is different from the voltage applied to the armature circuit.


    0 of 8192 characters used
    Post Comment


    This website uses cookies

    As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

    For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

    Show Details
    HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
    LoginThis is necessary to sign in to the HubPages Service.
    Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
    AkismetThis is used to detect comment spam. (Privacy Policy)
    HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
    HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
    Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
    CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
    Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
    Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
    Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
    Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
    Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
    Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
    VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
    PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
    Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
    MavenThis supports the Maven widget and search functionality. (Privacy Policy)
    Google AdSenseThis is an ad network. (Privacy Policy)
    Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
    Index ExchangeThis is an ad network. (Privacy Policy)
    SovrnThis is an ad network. (Privacy Policy)
    Facebook AdsThis is an ad network. (Privacy Policy)
    Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
    AppNexusThis is an ad network. (Privacy Policy)
    OpenxThis is an ad network. (Privacy Policy)
    Rubicon ProjectThis is an ad network. (Privacy Policy)
    TripleLiftThis is an ad network. (Privacy Policy)
    Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
    Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
    Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
    Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
    ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
    Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)