EENG 70 Electrical Machines I PDF

EENG 70 Electrical Machines I Topic 1. DC Machinery Fundamentals  DC Machinery Fundamentals a. Commutation and armature construction in real DC machines b. Problems with commutation in real machines c. Internal generated voltage and induced torque...

EENG 70 Electrical Machines I Topic 1. DC Machinery Fundamentals  DC Machinery Fundamentals a. Commutation and armature construction in real DC machines b. Problems with commutation in real machines c. Internal generated voltage and induced torque equations of real DC machines d. Construction of DC machines e. Power flow and losses in DC machines IMENG Support204 this- O Environment, pportunity for aEnergy & Technology Management better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU  a. Commutation and armature construction in real DC machines The commutator in a DC machine : Is a cylindrical arrangement of insulated metal bars connected to the coils of a direct-current electric motor or generator. Reverses the current flow within a winding when the shaft turns. Ensures unidirectional current from the generator or a reversal of current into the coils of the motor. Collects current from the armature conductor and supplies it to the load using brushes. Provides uni-directional torque for DC motors. I Support this Opportunity for a better CvSU  a. Commutation and armature construction in real DC machines I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU  a. Commutation and armature construction in real DC machines Armature: Armature winding is the winding in an electric machine that carries alternating current and produces voltage as the conductors pass through a magnetic field. It can also generate a magnetic field when voltage is applied to it, causing the armature to rotate. The armature winding is housed in the slots of the core and is responsible for the production of flux3. In DC machines, the armature winding is placed on the rotor shaft I Support this Opportunity for a better CvSU  a. Commutation and armature construction in real DC machines I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU  a. Commutation and armature construction in real DC machines I Support this Opportunity for a better CvSU  a. Commutation and armature construction in real DC machines I Support this Opportunity for a better CvSU  Armature winding I Support this Opportunity for a better CvSU  a. Commutation and armature construction in real DC machines I Support this Opportunity for a better CvSU  a. Commutation and armature construction in real DC machines I Support this Opportunity for a better CvSU  Example: I Support this Opportunity for a better CvSU  Example: I Support this Opportunity for a better CvSU  b. Problems with commutation in real machines In real DC machines, commutation is not always ideal, and several problems can arise during the process, primarily due to the non-instantaneous nature of current reversal in the armature windings. These issues can affect machine performance, cause mechanical damage, and reduce overall efficiency. Below are the key problems associated with commutation in real DC machines: I Support this Opportunity for a better CvSU  b. Problems with commutation in real machines 1. Sparking at the Brushes: Cause: Sparking occurs when current reversal is not completed by the time the armature coil reaches the neutral plane. As a result, the current in the winding is still changing when the brushes switch contacts between different commutator segments. This delay is primarily due to the inductance of the armature coils, which resists rapid changes in current. Effects: Sparking can cause excessive wear on the brushes and the commutator, leading to reduced machine lifespan. It can also generate heat, which may damage the insulation and other machine components over time. I Support this Opportunity for a better CvSU  b. Problems with commutation in real machines 2. Delayed Commutation (Inductive Kick): Cause: Armature windings have inductance, and when the current in the windings is suddenly reversed (during commutation), the inductance opposes this rapid change. This opposition creates an "inductive kick," which delays current reversal, leading to incomplete commutation. Effects: The delayed current reversal results in sparking, uneven commutation, and can lead to damage to the commutator and brushes. Over time, the efficiency of the machine decreases due to energy loss. I Support this Opportunity for a better CvSU  b. Problems with commutation in real machines 3. Brush Wear and Tear: Cause: When there is poor commutation, brushes may experience uneven contact with the commutator due to misalignment or excessive sparking. This leads to increased friction and wear. Effects: The brushes, which are typically made of carbon, wear down faster, and this requires more frequent maintenance and replacement. Additionally, worn brushes may lead to poor electrical contact, reducing machine performance. I Support this Opportunity for a better CvSU  b. Problems with commutation in real machines 4. Commutator Surface Damage: Cause: Continuous sparking causes localized heating of the commutator surface, leading to roughness, pitting, and erosion. Over time, this can cause uneven contact between the brushes and commutator. Effects: This uneven contact worsens the sparking issue, creating a cycle of increasing damage. The commutator may need resurfacing or replacement, which is expensive and time-consuming. I Support this Opportunity for a better CvSU  b. Problems with commutation in real machines 5. Armature Reaction: Cause: Armature reaction refers to the distortion of the main magnetic field due to the current flowing in the armature windings. This distortion shifts the neutral plane (the position where no voltage is induced in the armature windings) away from its ideal location. Effects: The brushes may no longer be properly aligned with the neutral plane, which increases sparking and reduces commutation efficiency. Additionally, armature reaction can result in uneven torque production in a DC motor and ripple in the output voltage of a DC generator. I Support this Opportunity for a better CvSU  b. Problems with commutation in real machines 6. High Commutation Losses: Cause: Poor commutation results in higher energy losses due to sparking and heat generation. This is mainly caused by the resistive and inductive effects in the armature windings during the current reversal process. Effects: These losses reduce the overall efficiency of the DC machine, leading to lower output power and higher operating costs. I Support this Opportunity for a better CvSU  b. Problems with commutation in real machines 7. Insulation Damage: Cause: Sparking and excessive heating during commutation can damage the insulation around the armature windings. This is particularly problematic in older machines or machines operating under heavy loads. Effects: Insulation damage can lead to short circuits within the windings, resulting in reduced performance, increased current draw, and even catastrophic failure of the machine if left unchecked. I Support this Opportunity for a better CvSU  b. Problems with commutation in real machines 8. Vibration and Noise: Cause: Poor commutation, uneven brush contact, and commutator wear can cause mechanical imbalance in the machine. This imbalance, coupled with sparking, can result in increased vibration and noise. Effects: Over time, excessive vibration can lead to mechanical failure of components such as bearings, the commutator, or even the armature itself. I Support this Opportunity for a better CvSU  b. Problems with commutation in real machines 9. Electrical Arcing: Cause: In severe cases of poor commutation, excessive sparking can escalate to full electrical arcing between the brushes and the commutator. This happens when the potential difference becomes large enough to ionize the surrounding air, creating a continuous arc. Effects: Electrical arcing can cause significant damage to the commutator, brushes, and windings. It also poses a safety hazard due to the high temperatures generated, which can lead to fire or component failure. I Support this Opportunity for a better CvSU  c. Internal generated voltage and induced torque equations of real DC machines I Support this Opportunity for a better CvSU  c. Internal generated voltage and induced torque equations of real DC machines I Support this Opportunity for a better CvSU  Example: I Support this Opportunity for a better CvSU  Example: I Support this Opportunity for a better CvSU  d. Construction of DC machines I Support this Opportunity for a better CvSU  d. Construction of DC machines I Support this Opportunity for a better CvSU  d. Construction of DC machines I Support this Opportunity for a better CvSU I Support this Opportunity for a better CvSU  d. Construction of DC machines I Support this Opportunity for a better CvSU  d. Construction of DC machines I Support this Opportunity for a better CvSU  Example: I Support this Opportunity for a better CvSU  d. Construction of DC machines I Support this Opportunity for a better CvSU  Example: I Support this Opportunity for a better CvSU  d. Construction of DC machines I Support this Opportunity for a better CvSU  Example: I Support this Opportunity for a better CvSU  d. Construction of DC machines I Support this Opportunity for a better CvSU  Example: I Support this Opportunity for a better CvSU  d. Construction of DC machines I Support this Opportunity for a better CvSU  Example: I Support this Opportunity for a better CvSU  e. Power flow and losses in DC machines I Support this Opportunity for a better CvSU  e. Power flow and losses in DC machines I Support this Opportunity for a better CvSU  e. Power flow and losses in DC machines I Support this Opportunity for a better CvSU  e. Power flow and losses in DC machines I Support this Opportunity for a better CvSU ---end of presentation--- Thank you!!!