Motor Control Circuitry

Motor Maintenance Schedule

• A good maintenance program includes detailed records that empower operators and engineers to spot patterns and predict problems before they occur.
• The frequency of preventative maintenance on a motor depends on its age, usage, and criticality.

Causes of Motor Failure

• The most common reasons for motor failure are vibration, overheating, contamination, bearing failure, and incorrect voltage.

Vibration

• Vibration can damage motor parts and cause loose electrical connections.
• Vibration is especially harmful to motor bearings, reducing the ability of the bearing lubrication to reduce friction.
• Causes of vibration:
  • Damaged bearings
  • Unbalanced and poorly aligned loads
  • Poor-quality power supply
• Ways to reduce vibration:
  • Check the condition of the bearings and have the motor overhauled if necessary.
  • Ensure the motor and load are securely mounted and properly aligned.
  • Check that the voltage and current are within nameplate specs and that the phases are balanced.
  • Check and tighten electrical connections that may have come loose from vibration.

Overheating

• Overheating can reduce the motor's service life and is especially harmful to the winding insulation and bearing lubrication.
• Causes of overheating:
  • Running the motor at lower speeds
  • Bearing lubrication breakdown
• Ways to prevent overheating:
  • Conduct infrared thermography tests.
  • Keep the motor running within recommended service levels.
  • Fit the motor with a soft starter or a speed controller such as a VFD (Variable Frequency Drive).

Contamination

• Contamination can damage the motor and interfere with its cooling.
• Ways to prevent contamination:
  • Ensure the motor's environment is clean and well-ventilated.
  • Clean the motor regularly, including the cooling fins.
  • Check electrical connections to ensure they are not being interfered with by dirt and other contaminants.
  • Keep the motor free of moisture during operation and storage.

Bearings

• Ensure the motor bearings are always properly lubricated according to the manufacturer's specifications.
• Ways to maintain bearings:
  • Lubricate bearings according to the manufacturer's instructions.
  • Replace sealed bearings at the end of their service life.
  • Avoid overfilling bearings with lubricant.

Current and Voltage

• For maximum service life, the motor's voltage and current must be maintained within correct specifications.
• Ways to prevent current and voltage issues:
  • Ensure a strong connection to the power supply.
  • Detect and prevent voltage spikes and dips.
  • Use a line reactor if necessary to smooth out voltage fluctuations.

Motor Management Strategy

• Develop a motor management strategy to reduce downtime and avoid large repair or replacement costs.
• Consider the motor's lifecycle from receipt to repair to recycle.
• Implement a consistent motor maintenance plan to avoid potential issues.

Motor Inspection and Installation

• Inspect the motor for any damage that may have occurred during shipping or storage.
• Refer to the motor's operation manual for installation and maintenance instructions.
• Ensure the motor is installed in a clean, dry, and well-ventilated area.
• Perform periodic maintenance and vibration checks to determine the motor's health.### Motor Equipment Criticality
• Motor equipment is critical to an operation, and decreased intervals with more check points should be implemented in the maintenance schedule.
• Inspections should include checking the cooling system, ensuring fins are clear, cooling fans are not damaged, and outside factors are not increasing ambient temperature.

Considerations for Motor Repair and Replacement

• A repair or replacement plan is needed for each motor, which should include elements such as:
  • Decision to repair or replace the motor
  • Identifying a shop or location for repair
  • Having motor winding information on file to speed up the repair process
  • Purchasing a spare motor or identifying a replacement motor model

Maintaining Electric Motors

• Develop a general maintenance and cleaning routine to ensure motor performance and lifespan
• Check the motor's lubrication, as overlubrication can lead to internal problems
• Regularly inspect the bearings, ensuring proper alignment and lubrication
• Reduce or eliminate vibrations, which can cause serious damage to the motor
• Inspect the rotor and stator, measuring gaps and diametrical clearance
• Record findings to monitor motor longevity and wear and tear

Motor Types

• Series motor: has high starting torque but a speed that varies with load, suitable for direct coupling to a load, and is often used in electric trains, cranes, and hoists
• Shunt motor: has constant speed characteristics, is desirable for driving power tools, and reversal of rotation can be achieved by reversing connections to either the field or armature winding
• Compound motor: has the characteristics of both series and shunt motors, is suitable for electric motors in steel rolling mills, and has a constant speed under varying load conditions

Motor Faults and Rectification

• Fuses or overcurrent trips operating at start: possible causes include premature operation of protective gear, overload, reversed field coil, short circuit or earth fault on field winding, and rectification involves checking and correcting these issues
• Motor will not start: possible causes include faulty supply or control circuit, faulty brushes, open circuit in field windings, and rectification involves checking and correcting these issues
• Overheated bearings or noisy operation: possible causes include bearing or mechanical defects, and rectification involves checking and correcting these issues
• General overheating of the case: possible causes include faulty ventilation, mechanical or electrical overload, short circuit, open circuit, or earth fault on armature, and rectification involves checking and correcting these issues### Electrical Maintenance and Installation
• Electrical maintenance is the process of ensuring that electrical equipment is kept in good working order to prevent problems that could lead to a loss of power or an electrical fire.
• It includes inspecting, testing, and repairing electrical equipment as necessary.
• Electrical maintenance is important for both businesses and homeowners, as it helps to ensure the safety of employees and residents and prevents expensive equipment repairs or replacements.

Electrical Installation and Maintenance Process

• Installing electrical systems and equipment correctly is vital to ensure the safety of those working with or near the equipment and to prevent any damaging electrical fires.
• Maintenance is equally important, as it helps to keep equipment running safely and efficiently.
• By inspecting electrical systems regularly and making any necessary repairs, potential electrical hazards can be addressed before they become more serious.

Who Can Do Electrical Maintenance?

• Electrical maintenance can be hazardous work, which is why it is essential for those who undertake it to be fully trained and qualified.
• Responsibilities of those who carry out electrical maintenance include:
  • Inspecting and testing equipment
  • Fixing faulty wiring and components
  • Replacing worn parts
  • Maintaining records of all work carried out

Steps to Ensure Electrical Safety

• Use proper safety equipment
• Shut off power
• Beware of standing water
• Inspect electrical equipment for damage
• Schedule periodic inspections

Electrical Maintenance Techniques

• Predictive and proactive care
• Preventive maintenance
• Corrective maintenance
• Inspecting electrical components and systems for damage or wear
• Testing electrical components and systems
• Cleaning electrical components and systems
• Repairing electrical components and systems

Electrical Safety Hazards

• Fires
• Electrical shocks
• Electrocution
• Explosions
• Injuries
• Death

Benefits of Electrical Maintenance

• Improved safety
• Reduced downtime
• Improved efficiency
• Reduced risk of electrical fires
• Reduced risk of electrical shocks, electrocution, and explosions
• Improved electrical system efficiency
• Improved equipment lifespan

Electrical Contractors

• An electrical contractor is a professional who installs, maintains, and repairs electrical systems.
• They are licensed and insured to work with electrical equipment and systems.
• Skills required for success as a certified commercial electrician include:
  • Ability to read and interpret electrical plans and blueprints
  • Ability to safely install, maintain, and repair electrical systems
  • Ability to troubleshoot electrical problems
  • Ability to use electrical testing equipment
  • Ability to work in confined spaces