{"id":2725,"date":"2024-08-24T21:12:06","date_gmt":"2024-08-24T21:12:06","guid":{"rendered":"https:\/\/workhouse.sweetdishy.com\/?p=2725"},"modified":"2024-08-24T21:12:06","modified_gmt":"2024-08-24T21:12:06","slug":"characteristics-of-shunt-motors","status":"publish","type":"post","link":"https:\/\/workhouse.sweetdishy.com\/index.php\/2024\/08\/24\/characteristics-of-shunt-motors\/","title":{"rendered":"CHARACTERISTICS OF SHUNT MOTORS"},"content":{"rendered":"\n

The conventional diagram of this motor is shown in\u00a0Figure 11.45. In these motors, the shunt field current\u00a0I<\/em>sh<\/sub>\u00a0=\u00a0V\/R<\/em>sh<\/sub>\u00a0remains constant since the supply voltage\u00a0V<\/em>\u00a0is constant. Hence, the flux in DC shunt motors is practically constant (although at heavy loads, somewhat flux decreases due to armature reaction).<\/p>\n\n\n\n

\"image\"\/<\/figure>\n\n\n\n

Fig. 11.45<\/strong>  Conventional diagram of a DC shunt motor<\/p>\n\n\n\n

    \n
  1. N<\/em><\/strong>\u00a0\u2212\u00a0I<\/em><\/strong>a<\/sub>\u00a0characteristics:<\/strong>\u00a0We know that,\u00a0\"image\"\u00a0Since flux is constant,\u00a0N<\/em>\u00a0\u221d\u00a0E<\/em>b<\/sub>\u00a0or\u00a0N<\/em>\u00a0\u221d\u00a0V<\/em>\u00a0\u2212\u00a0I<\/em>a<\/sub>\u00a0R<\/em>a<\/sub>. If the armature drop (I<\/em>a<\/sub>R<\/em>a<\/sub>) is negligible, the speed of the motor will remain constant for all values of load as shown by the dotted line AB in\u00a0Figure 11.46. However, strictly speaking, as the armature current increases due to the increase of load, armature drop\u00a0I<\/em>a<\/sub>R<\/em>a<\/sub>\u00a0increases and speed of the motor decreases slightly as shown by the straight line AC in\u00a0Figure 11.46\u00a0(neglecting armature reaction). Moreover, the characteristic curve does not start from a point of zero armature current because a small current, no-load armature current\u00a0I<\/em>a0<\/sub>, is necessary to maintain rotation of the motor at no-load.\u00a0\"image\"Fig. 11.46<\/strong>\u00a0\u00a0N-Ia<\/sub>\u00a0characteristics of DC shunt motorSince there is no appreciable change in the speed of a DC shunt motor from no-load to full-load, it is considered to be a constant speed motor. This motor is best suited where almost constant speed is required and the load may be thrown off totally and suddenly.<\/li>\n\n\n\n
  2. T<\/em><\/strong>\u00a0\u2212\u00a0l<\/em><\/strong>a<\/sub>\u00a0characteristics:<\/strong>\u00a0We know that,\u00a0T<\/em>\u00a0\u221d\u00a0\u0278 l<\/em>a<\/sub>. Since flux is constant,\u00a0T<\/em>\u00a0\u221d\u00a0l<\/em>a<\/sub>. Hence, the electrical characteristic (i.e.,<\/em>\u00a0T\u00a0<\/em>\u2212\u00a0I<\/em>a<\/sub>) is a straight line passing through the origin as shown in\u00a0Figure 11.47. It is clear from the characteristic curve that a large armature current is required at the start, if machine is on heavy load. Thus, shunt motor should never be started on load.\u00a0\"image\"Fig. 11.47<\/strong>\u00a0\u00a0T-Ia<\/sub>\u00a0characteristics of DC shunt motor<\/li>\n\n\n\n
  3. N<\/em><\/strong>\u00a0\u2212\u00a0T<\/em>\u00a0characteristics:<\/strong>\u00a0The\u00a0N\u00a0<\/em>\u2212\u00a0T<\/em>\u00a0characteristic is derived from the first two characteristics. When load torque increases, armature current\u00a0I<\/em>a<\/sub>\u00a0increases, but speed decreases slightly. Thus, with the increase in load or torque, the speed decreases slightly as shown in\u00a0Figure 11.48.\u00a0\"image\"Fig. 11.48<\/strong>\u00a0\u00a0N-T characteristics of DC shunt motor<\/li>\n<\/ol>\n\n\n\n
    <\/a>11.23  CHARACTERISTICS OF SERIES MOTORS<\/h5>\n\n\n\n

    The conventional diagram a series motor is shown in\u00a0Figure 11.49. In these motors, the series field winding carries the armature current. Therefore, the flux produced by the series field winding is proportional to the armature current before magnetic saturation, but after magnetic saturation flux becomes constant.<\/p>\n\n\n\n

    \"image\"\/<\/figure>\n\n\n\n

    Fig. 11.49<\/strong>  Conventional diagram of a DC series motor<\/p>\n\n\n\n

      \n
    1. N<\/em><\/strong>\u00a0\u2212\u00a0I<\/em>a<\/sub>\u00a0Characteristics:<\/strong>\u00a0We know that\u00a0\"image\"\u00a0where,\u00a0E<\/em>b<\/sub>\u00a0=\u00a0V<\/em>\u00a0\u2212\u00a0I<\/em>a<\/sub>(R<\/em>a<\/sub>\u00a0+\u00a0R<\/em>se<\/sub>). When armature current increases, the induced emf (back emf)\u00a0E<\/em>b<\/sub>\u00a0decreases, due to\u00a0I<\/em>a<\/sub>\u00a0(R<\/em>a<\/sub>\u00a0+\u00a0R<\/em>es<\/sub>) drop. While flux\u00a0\u0278<\/em>\u00a0increases as\u00a0\u0278<\/em>\u00a0\u221d\u00a0I<\/em>a<\/sub>\u00a0before magnetic saturation. However, under normal conditions,\u00a0I<\/em>a<\/sub>\u00a0(R<\/em>a<\/sub>\u00a0+\u00a0R<\/em>se<\/sub>) drop is quite small and may be neglected.Considering\u00a0E<\/em>b<\/sub>\u00a0to be constant,\"image\"Thus, before magnetic saturation, the\u00a0N\u00a0<\/em>\u2212\u00a0I<\/em>a<\/sub>\u00a0curve follows the hyperbolic path as shown in\u00a0Figure 11.50. In this region, the speed decreases abruptly with the increase in load or armature current.After magnetic saturation, flux becomes constant, then,\u00a0N<\/em>\u00a0\u221d\u00a0E<\/em>b<\/sub>\u00a0\u221d\u00a0V<\/em>\u00a0\u2212\u00a0I<\/em>a<\/sub>\u00a0(R<\/em>a<\/sub>\u00a0+\u00a0R<\/em>se<\/sub>)Thus, after magnetic saturation, the\u00a0N\u00a0<\/em>\u2212\u00a0I<\/em>a<\/sub>\u00a0curve follows a straight line path and speed decreases slightly, as shown in\u00a0Figure 11.50. From this characteristic, it is concluded that the series motor is a variable speed motor, that is, its speed changes when the armature current (or load) changes. As the load on this motor decreases, speed increases. If this motor is connected to the supply without load, armature current will be very small and hence speed will be dangerously high that may damage the motor due to heavy centrifugal forces.\"image\"Fig. 11.50<\/strong>\u00a0\u00a0N-Ia<\/sub>\u00a0characteristics of a DC series motorTherefore, a series motor is never started on no-load. However, to start a series motor, mechanical load (not belt driven load because belt slips over the pulley) is put on it first and then started.\"image\"Fig. 11.51<\/strong>\u00a0\u00a0T-Ia<\/sub>\u00a0characteristics of a DC series motor<\/li>\n\n\n\n
    2. T<\/em><\/strong>\u00a0\u2212\u00a0I<\/em>a<\/sub>\u00a0characteristics:<\/strong>\u00a0We know that,\u00a0T<\/em>\u00a0\u221d\u00a0\u0278 I<\/em>a<\/sub>. In series motors, before magnetic saturation\u00a0\u0278<\/em>\u00a0\u221d\u00a0I<\/em>a<\/sub>. Hence, before magnetic saturation, the electromagnetic torque produced in the armature is proportional to the square of the armature current. Therefore, this portion of the curve (OA) is a parabola passing through the origin, as shown in\u00a0Figure 11.51. However, after magnetic saturation, the flux\u00a0\u0278<\/em>\u00a0becomes constant.Therefore,\u00a0T<\/em>\u00a0\u221d\u00a0I<\/em>a<\/sub>Hence, after magnetic saturation, the curve (AB) becomes a straight line. It is seen that before magnetic saturation\u00a0T<\/em>\u00a0\u221d\u00a0\"image\". When load is applied to this motor at start, it takes large current and heavy torque is produced that is proportional to square of this current. Thus, this motor is capable to pick up heavy loads at the start and best suited for electric traction.<\/li>\n\n\n\n
    3. N<\/em><\/strong>\u00a0\u2212\u00a0T<\/em>\u00a0characteristics:<\/strong>\u00a0This characteristic is derived from the first two characteristics. At low value of load,\u00a0I<\/em>a<\/sub>\u00a0and torque are small, but the speed is very high. As load increases,\u00a0I<\/em>a\u00a0<\/sub>and torque increases, but the speed decreases rapidly. Thus, for increasing torque, speed decreases rapidly as shown in\u00a0Figure 11.52.\u00a0\"image\"Fig. 11.52<\/strong>\u00a0\u00a0N-T characteristics of a DC series motor<\/li>\n<\/ol>\n","protected":false},"excerpt":{"rendered":"

      The conventional diagram of this motor is shown in\u00a0Figure 11.45. In these motors, the shunt field current\u00a0Ish\u00a0=\u00a0V\/Rsh\u00a0remains constant since the supply voltage\u00a0V\u00a0is constant. Hence, the flux in DC shunt motors is practically constant (although at heavy loads, somewhat flux decreases due to armature reaction). Fig. 11.45  Conventional diagram of a DC shunt motor 11.23  CHARACTERISTICS OF SERIES […]<\/p>\n","protected":false},"author":1,"featured_media":2709,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[414],"tags":[],"class_list":["post-2725","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-dc-machines-generators-and-motors"],"jetpack_featured_media_url":"https:\/\/workhouse.sweetdishy.com\/wp-content\/uploads\/2024\/08\/dc.png","_links":{"self":[{"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/posts\/2725","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/comments?post=2725"}],"version-history":[{"count":1,"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/posts\/2725\/revisions"}],"predecessor-version":[{"id":2726,"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/posts\/2725\/revisions\/2726"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/media\/2709"}],"wp:attachment":[{"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/media?parent=2725"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/categories?post=2725"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/workhouse.sweetdishy.com\/index.php\/wp-json\/wp\/v2\/tags?post=2725"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}