Showing posts with label Electrical. Show all posts
Showing posts with label Electrical. Show all posts
Saturday, 1 July 2017
Sunday, 11 April 2010
Saturday, 29 August 2009
Shortcoming in Maintenace ; Motor Control Panel (MCP)
a) Externnaly, most MCPs are messy with peeled paint, oil and dirt.
b) Internally, the control wirings and power cables are not strapped and rounted properly.
c) MCPs are ussualy set upon by water, oil and fibre. Little is done to improve the situation.
d) Screws are usually not complete or totally absent from front and back covers. As such many covers are seen..
e) Contactors are not opened up for servicing. They are left to operate until failures sat in.
f) Power fuses are sometimes replaced not according to connected load but what are available in stock. This can lead to single phasing.
g) Defective indicating lights and starts/stop push buttons are commonly found. Replacement are normally by cannibalising from spare starter boards.
b) Internally, the control wirings and power cables are not strapped and rounted properly.
c) MCPs are ussualy set upon by water, oil and fibre. Little is done to improve the situation.
d) Screws are usually not complete or totally absent from front and back covers. As such many covers are seen..
e) Contactors are not opened up for servicing. They are left to operate until failures sat in.
f) Power fuses are sometimes replaced not according to connected load but what are available in stock. This can lead to single phasing.
g) Defective indicating lights and starts/stop push buttons are commonly found. Replacement are normally by cannibalising from spare starter boards.
Shortcoming in Electrical ; Maintenance
1. Alternator
a) Insulation resistance of windings are not checked and recorded. Deterioration of cannot be ascertained.
b) Cable terminal box is seldom opened up to inspect for loose connections and heating.
c) Electric heater or carbon lamp is not used to heat up windings to remove moisture when alternator is not in operation.
d) Blowing of windings is only done at overhangs. Little attempts are made to remove dust and dirt in other areas of alternator's windings.
e) Lubrication of bearings are not properly recorded to maintain standard time for greasing.
f) Diode connections to rotating disc are not, checked by torque wrench and as such under and over tightening occur. Both can lead to failure of rotatinz diode assemblies.
2. Main Switchboard
a) Arrangement is not made to re - calibrate the overcurrent and earth fault relays periodically.
b) Defective meters, indicating lights, switches and lighting fittings are commonly found. This shows lack of maintenance.
c) Cleaning of trench is not done. Water, debris, cockroaches and rats are coomon sight.
d) Front, side and back covers are not close tightly. Gaps are left behind inviting the entry of vermin.
e) Defective power and control fuses are not replaced but instead shorted with 'cooper wires . This can lead to fire hazard.
f) Main switchboard is seldom being coened uo to check for loose connections and excessive heating.
g) The top of main switchboard is dirty and couple with rain water through leaking roof has caused rust tc set in. -This leads to entry of water inside main switchboard and probably short-circuits.
a) Insulation resistance of windings are not checked and recorded. Deterioration of cannot be ascertained.
b) Cable terminal box is seldom opened up to inspect for loose connections and heating.
c) Electric heater or carbon lamp is not used to heat up windings to remove moisture when alternator is not in operation.
d) Blowing of windings is only done at overhangs. Little attempts are made to remove dust and dirt in other areas of alternator's windings.
e) Lubrication of bearings are not properly recorded to maintain standard time for greasing.
f) Diode connections to rotating disc are not, checked by torque wrench and as such under and over tightening occur. Both can lead to failure of rotatinz diode assemblies.
2. Main Switchboard
a) Arrangement is not made to re - calibrate the overcurrent and earth fault relays periodically.
b) Defective meters, indicating lights, switches and lighting fittings are commonly found. This shows lack of maintenance.
c) Cleaning of trench is not done. Water, debris, cockroaches and rats are coomon sight.
d) Front, side and back covers are not close tightly. Gaps are left behind inviting the entry of vermin.
e) Defective power and control fuses are not replaced but instead shorted with 'cooper wires . This can lead to fire hazard.
f) Main switchboard is seldom being coened uo to check for loose connections and excessive heating.
g) The top of main switchboard is dirty and couple with rain water through leaking roof has caused rust tc set in. -This leads to entry of water inside main switchboard and probably short-circuits.
Motor ; Maintenance Programme
1. Induction Motor
a) Complete Overhaul 5 years
b) Greasing 6 months - I year
c) Insulation Test 3 months - 6 months
d) Vibration, Noise Alignment Check including Ventilation Fan check 2 months
e) Clean & Dry Motor Frame 1 month
f) Service Slip Ring & Carbon Brush 1 month
2. Motor Starter
Service starter & check operation of protection Relays 1 month 2 months
3. Sampling check by Maintenance Engineer 1 week
Motor ; Faalures by External Influence & Opreational
Causes
a) Ingression of liquid
b) Motor flooded
c) Chemical erosion
d) Attacks by rodent,
Results
Leading to short-circuit or open-Circuit of windings
Prevention
a) Provide cover for motor
b) Install motor at safe location.
c) Apply rat bait at infested areas.
Operational
Cause
Frequent start and stop to remove choking at machinery.
Results
Windings overheat.
Prevention
a) Change working habits of operator.
b) Improve supervision by MA.
c) Install thermal switch at windings.
a) Ingression of liquid
b) Motor flooded
c) Chemical erosion
d) Attacks by rodent,
Results
Leading to short-circuit or open-Circuit of windings
Prevention
a) Provide cover for motor
b) Install motor at safe location.
c) Apply rat bait at infested areas.
Operational
Cause
Frequent start and stop to remove choking at machinery.
Results
Windings overheat.
Prevention
a) Change working habits of operator.
b) Improve supervision by MA.
c) Install thermal switch at windings.
Motor ; Failures by Mechanical Defects
Causes
a) Defects at bearing or shaft.
b) Wrongalignment
c) Problems in driven machinery
d) Vibration
Results
a) Rubbing of stator and rotor leading to snort-circuit
b) Roasting of winding - overload
Prevention
a) Perform regular inspection of motor, drive system and driven machine.
b) Ensure thermal overload relay is working .
c) Install motor away from vibrating areas.
a) Defects at bearing or shaft.
b) Wrongalignment
c) Problems in driven machinery
d) Vibration
Results
a) Rubbing of stator and rotor leading to snort-circuit
b) Roasting of winding - overload
Prevention
a) Perform regular inspection of motor, drive system and driven machine.
b) Ensure thermal overload relay is working .
c) Install motor away from vibrating areas.
Motor ; Single Phasing / Starter Defects
Meaning
Running on two phasing
Causes
a) Defective contacts at starter's isolator or contactor
b) 1 No. power fuse open-circuit
c) Wiring to one phase open-circuit
d) Loose connection, loose bolts.
Results
Two sets of windings are overloaded
Prevention
a) Ensure starters are well serviced
b) Correct size oE power fuse is being used.
c) Ensure all screws are tightened.
d) Install electronic phase breaking relay.
Running on two phasing
Causes
a) Defective contacts at starter's isolator or contactor
b) 1 No. power fuse open-circuit
c) Wiring to one phase open-circuit
d) Loose connection, loose bolts.
Results
Two sets of windings are overloaded
Prevention
a) Ensure starters are well serviced
b) Correct size oE power fuse is being used.
c) Ensure all screws are tightened.
d) Install electronic phase breaking relay.
Motor ; Poor Insulation
Causes
a) Overload
b) Overheat
c) Aging
Note An increase of 5 degree C over its maximum operating temperuter will shorten its life spar. by half.
Improvement Could be improved by:
a) Cleaning, re-varnishing and baking
b) applying aerosol insulator spray.
a) Overload
b) Overheat
c) Aging
Note An increase of 5 degree C over its maximum operating temperuter will shorten its life spar. by half.
Improvement Could be improved by:
a) Cleaning, re-varnishing and baking
b) applying aerosol insulator spray.
Motor ; Short Circuit
types
a) Turn to turn short
b) Phase, to Phase short
c) phase to frame short
Causes
The insulation of conductor is caused to be removed by:
a) Overload
b) Overheat
C) Rubbing of stator and rotor (bearing defect)
d) Ingression of liquid
defective rubber lining or gasket or wrong installatio:
terminal cable box
e) Vibration and thus movement of coil windings
Prevention
a) Ensure thermal overload relay is in good working condition.
b) Do not start and stop too frequently.
c) Bearing and alignment is good
d) Rubber lining or gasket is properly installed.
e) Ventilation ducts are not clogged.
a) Turn to turn short
b) Phase, to Phase short
c) phase to frame short
Causes
The insulation of conductor is caused to be removed by:
a) Overload
b) Overheat
C) Rubbing of stator and rotor (bearing defect)
d) Ingression of liquid
defective rubber lining or gasket or wrong installatio:
terminal cable box
e) Vibration and thus movement of coil windings
Prevention
a) Ensure thermal overload relay is in good working condition.
b) Do not start and stop too frequently.
c) Bearing and alignment is good
d) Rubber lining or gasket is properly installed.
e) Ventilation ducts are not clogged.
Motor ; Overload
Overload
1.1 Causes
a) Motor undersize.
b) Restriction in turning
1.2 Results
a) Insulation of conductors is darken,
b) Brittle and easily peel off.
This is called roasting of windings
1.3 Can cause short-circuit between turnss
1.4 Prevention
a) Mainly due t0 wrong setting cf themal overload relay (TOR)
b) Defective ther-mal overload relay check by reducing the setting to minimum level.
c) $Thus ensure thermal overload relay is working.
1.1 Causes
a) Motor undersize.
b) Restriction in turning
1.2 Results
a) Insulation of conductors is darken,
b) Brittle and easily peel off.
This is called roasting of windings
1.3 Can cause short-circuit between turnss
1.4 Prevention
a) Mainly due t0 wrong setting cf themal overload relay (TOR)
b) Defective ther-mal overload relay check by reducing the setting to minimum level.
c) $Thus ensure thermal overload relay is working.
Different Causes and Failures of Motors
1.Electrical
a) Overload
b) Overheat
C) Short-circuits
e) Open-circuit
f) Poor Insulation
g) Single Phasing
h) Starter Defects
2. Mechanical
a) Bearing Defect
b) Shaft Defect
c) Alignmen t
d) Driven -Machinery Jam
3) Fan
3. External
a) Dust & Dirt
b) Liquid Ingression
c) Submersion
d) Rodent Attack
e) Chemical Erosion
f) Vibration
4. Operational - Winding Overheat
5. Undefined
a) Overload
b) Overheat
C) Short-circuits
e) Open-circuit
f) Poor Insulation
g) Single Phasing
h) Starter Defects
2. Mechanical
a) Bearing Defect
b) Shaft Defect
c) Alignmen t
d) Driven -Machinery Jam
3) Fan
3. External
a) Dust & Dirt
b) Liquid Ingression
c) Submersion
d) Rodent Attack
e) Chemical Erosion
f) Vibration
4. Operational - Winding Overheat
5. Undefined
Selection of Starter
Example
Machine Blower Fan (With highs inertia)
Electric Motors 3 phase 415V 1500 rpm 20PP
Method of Starting
Use Auto- Transformer (for high power or inertia machine)
Initial Starting Current = 1.7 to 4- In (Say 3 In)
Usual Starting Time = 7-12 secs (Say 10 secs)
Rated Current (In) = Set Current (Ie) = 29A
Multiples of current setting Ile on starting = 3 Ie
Selection of Thermal Overload Relay
Try CT31-32• 23-32A Try CT3-45 25-32A
Tripping Time Tripping Time
Cold Start 25 secs (OK) Cold Start 50 secs (OK)
WaLw Start 7 secs (NO) Warm Start 12 secs (OK)
Machine Blower Fan (With highs inertia)
Electric Motors 3 phase 415V 1500 rpm 20PP
Method of Starting
Use Auto- Transformer (for high power or inertia machine)
Initial Starting Current = 1.7 to 4- In (Say 3 In)
Usual Starting Time = 7-12 secs (Say 10 secs)
Rated Current (In) = Set Current (Ie) = 29A
Multiples of current setting Ile on starting = 3 Ie
Selection of Thermal Overload Relay
Try CT31-32• 23-32A Try CT3-45 25-32A
Tripping Time Tripping Time
Cold Start 25 secs (OK) Cold Start 50 secs (OK)
WaLw Start 7 secs (NO) Warm Start 12 secs (OK)
ADVANTAGE & DISADVANTAGE OF STARTERS
Direct on line
a) Simple and Inexpensive
b) Starting cannot be regulated
dis
a) High starting current
c) Starting cannot be regulated
Star-Delta
a) Relatively inexpensive
dis
a) Low starting Torque
b) 6 terminal motor required
c)Break in line supply when changing (arc & loss of torque)
d) No adjustment of starting current
Primary Resistance
a) Possibility of adjusting starting starting current current
b) No break in line supply during starting
dis
a) small reduction in starting current
b) Require resistor
AutoTransformer
a) Good torque
b) Possibility of auto-transformer adjusting starting values
Dis
a) Requires a costly auto-transformer
Rotors Resistance
a) Very good torque
b) Low starting more expensive
current
C) Possibility of adjusting starting current
d) No break in line supply
dis
a) a slip ring motor more expensive
b) Requires resistors
a) Simple and Inexpensive
b) Starting cannot be regulated
dis
a) High starting current
c) Starting cannot be regulated
Star-Delta
a) Relatively inexpensive
dis
a) Low starting Torque
b) 6 terminal motor required
c)Break in line supply when changing (arc & loss of torque)
d) No adjustment of starting current
Primary Resistance
a) Possibility of adjusting starting starting current current
b) No break in line supply during starting
dis
a) small reduction in starting current
b) Require resistor
AutoTransformer
a) Good torque
b) Possibility of auto-transformer adjusting starting values
Dis
a) Requires a costly auto-transformer
Rotors Resistance
a) Very good torque
b) Low starting more expensive
current
C) Possibility of adjusting starting current
d) No break in line supply
dis
a) a slip ring motor more expensive
b) Requires resistors
ELECTRIC MOTOR STARTERS
Type of Starters
a) Direct-On-Line (DOL)
b) Star-Delta
c) Auto-Transformer (AT)
d) Rotor Resistance (RR)
e) Primary Resistance Not Cc nly U99
Selection of Starters
a) 1hp.- 5.5 hp use DOL starter -
b) 7.5 30hp use SD starter
c) 40hp and above use AT starter
d) Slip-Ring Induction motor use RR starter
a) Direct-On-Line (DOL)
b) Star-Delta
c) Auto-Transformer (AT)
d) Rotor Resistance (RR)
e) Primary Resistance Not Cc nly U99
Selection of Starters
a) 1hp.- 5.5 hp use DOL starter -
b) 7.5 30hp use SD starter
c) 40hp and above use AT starter
d) Slip-Ring Induction motor use RR starter
Sunday, 2 August 2009
Sunday, 14 June 2009
DIPOM ; Electrical Application > Motor
Cost Of Motor Failures
1. Electrical
1.1 Overload
1.2 Overheat
1.3 Short-circuit
1.4 Open - circuit
1.5 Poor insulation
1.6 Single phasing
1.7 Starter defects
2. Mechanical
2.1 Bearing defect
2.2 Shaft defect
2.3 Alignment
2.4 Driven machinery jam
2.5 Fan defect
3. External
3.1 Dust & dirt
3.2 Liquid ingression
3.3 Submersion
3.4 Rodent attack
3.5 Chemical erosion
3.6 Vibration
4. Operational - winding overheat
5. Undefined
1. Electrical
1.1 Overload
1.2 Overheat
1.3 Short-circuit
1.4 Open - circuit
1.5 Poor insulation
1.6 Single phasing
1.7 Starter defects
2. Mechanical
2.1 Bearing defect
2.2 Shaft defect
2.3 Alignment
2.4 Driven machinery jam
2.5 Fan defect
3. External
3.1 Dust & dirt
3.2 Liquid ingression
3.3 Submersion
3.4 Rodent attack
3.5 Chemical erosion
3.6 Vibration
4. Operational - winding overheat
5. Undefined
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