New Efficiency Standards and Efficiencies
Electrical motor efficiency is the ratio between the shaft output power -
and the electrical input power.
Energy Standards are given from International Standard IEC 60034-30
Efficiency classes:
• IE1 (Standard Efficiency)
• IE2 (High Efficiency)
• IE3 (Premium Efficiency)
• IE4 (IEC 60034-31:2010)
New IE1-IE3 Efficiencies:
• Additional loses are no longer assumed as fixed percentage
values(0,05%) but are determined by making measurements(IEC
60034-2-1:2007)
ElectricMotorLossesandefficiency
Type of loss | Cause | Can be increased by |
Stator core | · Energy used to magnetize core material · Losses due to magnetically induced circulating currents in the stator core | · Overheating the stator core during winding removal · Grinding or filling stator slots · Sandblasting the core |
Friction and winding | · Energy to overcome bearing friction · Energy to overcome air movement from rotor and cooling fan | · Installing incorrect bearings · Damaging or improper installation of bearings · Use of wrong size or type of fan |
Stator winding | · Heating that occurs as current flows through the resistance of the stator winding | · Wrong type of seals · Change of winding design |
Rotor | · Heating that occurs as current flows through the resistance of the rotor bars and rings | · Damage to rotor cage · Poor connection between bars and end rings |
Insulation Class
Insulation is rated according to maximum allowable
operating temperatures
Insulation Class
Example - a motor operating at 180 Degrees C will have an estimated
life of:
• 300 hours with a Class A insulation
• 1,800 hours with Class B insulation
• 8,500 hours with Class F insulation
• 10.000 Hours with Class H insulation
Insulation Class F is the most common for international use
Motor Protections
• Based on operating temperature
Continuous duty motors must be protected from overload either by a
device integrated into the motor or via an independent protection
system, usually a thermal relay.
• PT-100
There are temperature detectors with operating principle base on the
properties that some materials vary the electric resistance with the
variation in temperature. They are also allowing continuous reading of
motor operating temperature through a monitoring display.
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• PTC-NTC
These are thermal protectors consisting of semiconductor detectors
with sudden variation of the resistance when reaching a certain
temperature. PTC are consider a thermistor. This sudden resistance
variation blocks the PTC current, causing the output relay to operate.
PTC does not allow continuous reading of motor operating
temperature.
• Thermal Relay
These are silver-contacts thermal sensors normally closed, that
operate at certain temperature
• Based on operating current
Overloads are processes that usually make the temperature increase
gradually. To solve this problem, the thermal protectors are quite
suitable. However, the only way to protect motors against short-circuit
currents is the application of fuses or breakers.
FORMS OF ENCLOSURE
The most common form of enclosure is "drip-proof" which by definition ensures protection of the windings, commutator and terminals not only from falling liquids but also any other particles. Drip-proof protection as applied to motors in ship requires a slightly different interpretation from that applied to motors ashore, owing to the motion of the ship. It is therefore for ship's motors extended to provide protection from falling water or dirt when the machine is tilted 22 ½ degrees in any direction. Protection must also be provided against liquids striking a surface and running into the machine or being drawn in by the ventilating air.
Another type of enclosure commonly used is "watertight", the standard requirement for which is that they will withstand complete immersion in water to a depth of not less than three feet for a period of one hour. "Watertight" must not be confused with "submersible". The essential difference is that a watertight motor is only intended to be suitable for immersion under a comparatively low head of water and for a limited period, whereas a "submersible" motor may be submerged under a considerable head for an indefinite period. Submersible motors are necessary for statuary bilge pumps.
Totally-enclosed motors may also be used, but for D.C. they suffer from the disadvantage that carbon dust from the commutator brushes is deposited on the windings, core-ducts, and brush gear insulation. Pipe-ventilation or duct-ventilation is sometimes used for large motors to enable clean cool air to be drawn from suitable places outside the engine room.
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Water cooling is seldom used for motors, except propulsion motors, though it is sometimes used for generators.
Axis of Rotation. Horizontal-shaft motors should be placed with the axis of rotation in a fore-and-aft direction. If it is unavoidable for it to be athwart ships, provision should be made to take end thrust and to reduce end- play which may arise
due to rolling of the ship.
TASK 3Motor Protection (fill in the missing words)
Word bank: be, apply, use, cause, detect, prevent, require
Protection of motors _____ required mainly to _______ overheating which can ________deterioration of winding insulation and burnout, if severe. Overheating as the result of overloading, stalling, single-phasing or prolonged starting period can be _______ by a rise in line current and by temperature change. Overheating as the result of high ambient temperature or poor cooling due to blocked air passages can only be detected by temperature rise within the windings.
Overload protection is _______ for all motors of more than 0.5 kW although different rules _______ to steering gear motors and others essential to safety or propulsion.
We ______ overload relays, thermistors (a thermal device which can be used in conjunction with an electromagnetic overload trip).
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