Transcript Slide 1

EKAS 2.19.36
Fault find- General Appliances
UEE31307 Certificate III in
Refrigeration and Air Conditioning
Stage 2A
Units: UEENEEPOO2B
Chris Hungerford
Wednesday, July 22, 2015
The two golden rules
• Test before you touch,
this
protects you physically, so you can have a good day!
• Test your work is electrically
safe when completed, tests include
insulation resistance, earth continuity, polarity, and
visual inspection, this protects you financially.
2.19.36.A
Safe Isolation of a Supply
• Test before you touch, this protects you physically,
so you can have a good day!
1.
2.
3.
4.
5.
6.
7.
2.19.36.A
Procedure to isolate a Supply
Notify all persons likely to be affected by the isolation.
Determine the method to isolating the supply.
Test the supply availability.
Isolate the supply.
Danger tag the isolation device.
Test that the supply is isolated.
Test the testing device.
WARNING
Are you working LIVE?
Using a voltmeter to measure low voltage is working live!
Electrical Safety Regulation 2002
11 Requirements for electrical work
(1) An employer or self-employed person must ensure that, unless
the circumstances required under this division for the performance
of live work apply, live work is not performed.
Maximum penalty—40 penalty units.
As per Regulation 12 “Requirement for performance of live work”, to perform live work you must satisfy the following
seven (7) questions:
1. Have you prepared a risk assessment?
2. Is your test equipment appropriate to perform live work? Minimum Cat III @ 500v ac.
3. Has your test equipment been maintained and confirmed that it is operating correctly? Regulation 18.2(b) “the instrument
4.
5.
6.
7.
is tested at least every 6 mths to ensure it is in proper working order”, and Regulation 12.1(f) “the instrument is tested immediately prior to
work to confirm that the instrument is operating correctly”
Have you the correct PPE, (Safety boots, long pants, long sleeved shirt, insulated gloves, safety glasses)? As per
AS/NZS 4836 Safe working on low voltage electrical installations.
Is the isolation point clearly identified?
Is the isolation point able to be reached without any obstructions?
Is the area where the electrical live work is performed clear of any obstructions?
Note: if you are not working within the requirements of the above laws then your inaction to comply threatens the following;
1.
Your right to claim workcover in the event of an accident
2.
Your right to claim any insurance benefits in the event of an accident
3.
You will be fined the prescribed penalty units for those laws that you have breached.
2.19.36.A
What’s the bottom line?
• If you work on power circuits, you
need a CAT III-600 V or CAT IV-600 V/
CAT III 1000 V meter.
• Look for the CAT rating and voltage
rating marked near the input jacks.
– CAT or voltage rating alone can be
misleading
• Look for independent certification.
CAT IV-600 V
CAT III-1000 V
2.19.36.A
Heaters & heating devices
• All heating devices are resistive, therefore:
– Current can be calculated using the power rule.
– Resistance can be calculated using Ohm’s Law.
Determine the current &
resistance of this
12kW 240V Duct heater.
I = P/V = 12000/240 = 50A
R= V2/P = (240 x240) / 12000 = 4.8W
2.19.36.B
Determine the unknown values of the heating elements
Volts Current
Resistance
240v
24W
4A
100v
60W
5
A
250W
3.6kW
48W
2.19.36.B
Power
1.2kW
Answers
Volts Current
Resistance
Power
240v
10A
24W
2.4kW
240v
4A
50v
100v
5
A
36A
60W
10W
960W
2.7W
3.6kW
240v
5A
48W
1.2kW
2.19.36.B
250W
Temperature control.
AS/NZS 3000:2007
4.11 ELECTRIC DUCT HEATERS
The electrical portion of any electric duct heater installation shall comply with the
requirements of this Standard.
NOTE: Attention is drawn to the fact that—
(a) such installations are within the scope of AS/NZS 1668.1; and
(b) safety requirements are contained in AS/NZS 3102; and
(c) compliance therewith may be required by the relevant regulatory authorities.
2.19.36.B
AS/NZS 3102:2002
7 PROTECTION AGAINST HEAT AND FIRE
7.1 Fixing of heating units
An electric heating unit incorporated in a duct heater shall be assembled and firmly
supported so that it will not introduce a risk of fire through displacement resulting from
loosening of fixings or other defects likely to be brought about by vibration or other
conditions of service.
7.2 Interlocking of supply to heater unit and blower motor
The electrical supply to the heating unit(s) shall be interlocked with the supply to the
associated blower motor such that interruption of supply to the blower motor will
automatically interrupt supply to the heating units.
7.3 Devices to prevent overheating
The duct heater shall be provided with both the following devices as a safeguard against
overheating under abnormal operating conditions:
a) A device to interrupt electric supply to the heating unit if airflow through the duct heater
ceases. This device may be a thermal cutout or an air supply failure switch. The device
shall comply with the test requirements of Clause 17.8.2.
b) A non-self-resetting thermal cutout, located within the duct heater casing or air duct
adjacent to the heating units, so that the air temperature in the immediate vicinity of the
heating units does not exceed 120°C under abnormal operation. The thermal cutout
shall comply with the test requirements of Clauses 17.8.1 and 17.8.2.
NOTE “immediate vicinity” is considered to be a distance of 25 mm. The devices mentioned
in a) and b) may interrupt the heating unit current directly or they may form part of a
system in which they interrupt the heating unit current indirectly via a component such
as a contactor. The device or system providing protection during abnormal operation
shall not operate during normal operation.
The devices or systems are not required if the air temperature in the immediate vicinity of
the heating units does not exceed 120°C under the abnormal operation conditions
described with the devices short-circuited.
2.19.36.B
Thermostat
Fluid operated bellows. These are not that common in
small appliances but often found in refrigerators, air
conditioners, domestic ovens, and so forth. An
expanding fluid (alcohol is common) operates a bellows
which is coupled to a set of movable contacts.
2.19.36.B
Thermostat
Expanding Tube thermostat
2.19.36.B
Thermostat
A
Thermostats are closed
Loop control
Liquid Filled
Bellows
Electrical
Contacts
2.19.36.B
Oven
Element
N
Liquid Filled Thermostat
2.19.36.B
Thermostat
Electronic thermostats. These typically use a
temperature controlled resistance (thermistor) driving
some kind of amplifier or logic circuit which then
controls a thyristor or contactor.
2.19.36.B
Thermostat
NTC Thermistors:
•Are non-linear
•Change resistance dramatically with
temperature (they have a very high sensitivity)
•Are not interchangeable
•Are not suited to wide spans
•Suffer from drift and decalibration at high
temperatures
•If the resistance of a thermistor is 5,000Ω at
room temp, it may drop to about 20Ω at 300C
and rise to about 200,000Ω at -50C.
RESISTANCE (Ohms)
200K
100K
40k
20k
0
-100
0
100
200
TEMPERATURE °C
2.19.36.B
300
Other temperature measuring devices
•
•
•
•
•
•
•
Thermocouples
Resistance Temperature Detectors(RTD’s)
Diodes and semiconductor IC’s
Gas expansion system
Mercury expansion system
Coiled bimetal strip
Radiation Pyrometers
2.19.36.B
Thermostat settings
Differential
Set
Point
Temperature
Differential
It is the difference between the turn-on
temperature and the turn-off temperature
of the thermostat.
20°C
Time
2.19.36.B
Simmerstat control
The simmerstat consists of a parallel
connected heater that causes a bimetallic switch to bend and open circuit.
Problems; No control, open circuit heater or welded switch
contact. No output, damaged switch contacts.
Load
Line
Load
N
2.19.36.B
Energy cut-outs
• They are not adjustable.
• Designed to cut off the supply before
the appliance damages itself due to a
failure of the thermostat.
2.19.36.B
2.19.36.B
Fault finding heating circuits
Fuse
A 240V
Thermostat
Blower
interlock
A
thermal
cutout
24kw
heater
A
Switchboard
N
N
Voltmeter
= 240v
Field (on heater)
Voltmeter = 240v
Client: Hello…..Heater does not operate!
Step 1. Test supply is available at heater terminals and element.
Caution: Working live….. All work as per regulation 12.
Fault finding heating circuits
Fuse
Thermostat
Blower
interlock
A 240V
thermal
cutout
24kw
heater
A
N
isolate
Ohmmeter = 20MW
R= V2/P = (240 x240) / 24000 = 2.4W
Ask yourself, “I have supply at the element, this heater should operate”?
Step 2. Isolate the supply and test to confirm isolation, tag, ……..supply isolated.
Step 3. Measure the resistance of the element, compare the value to your
determined value using ohm’s law.
2.19.36.B
N
Fault finding heating circuits
Fuse
Thermostat
Blower
interlock
thermal
cutout
A 240V
24kw
heater
A
N
These two values should be approximately equal
Ohmmeter = 20MW
R= V2/P = (240 x240) / 24000 = 2.4W
Remember;
Very high values of resistance = open circuit.
Very low values of resistance = short circuit.
Therefore the fault with this circuit is an open circuit element.
2.19.36.B
N
2.19.36.B
Fault finding heating circuits
Fuse
A 240V
Thermostat
A
Blower
interlock
thermal
cutout
24kw
heater
A
N
N
Voltmeter = 0v
Client: Hello…..Heater does not operate!
Step 1. Test supply is available at heater terminals and element.
Caution: Working live….. All work as per regulation 12.
Fault finding heating circuits
Fuse
Thermostat
Blower
interlock
thermal
cutout
A 240V
24kw
heater
A
E
Voltmeter = 240v
Ohmmeter
= 20MW
High resistance = open circuited fuse
This fuse has blow for a reason, do not
replace it until the reason for blowing has
been determined.
No supply available at heater!
Step 1. Check supply at switchboard.
Step 2. Check condition of fuse or circuit breaker.
2.19.36.B
N
N
Fault finding heating circuits
Fuse
Thermostat
Blower
interlock
thermal
cutout
24kw
heater
A 240V
A
N
N
120A
Reasons for a Fuse to blow
1. An overload.
2. A Short circuit.
3. A partial short circuit.
I = V/R = 240/1.5 =160A.
Ohmmeter = 1.5W
The calculated
value should be
less than the fuse
rating.
1. An overload.
Step 1. measure the resistance of the circuit.
Step 2. determine the current from the measured values.
Step 3. compare determined current to the size of the fuse.
2.19.36.B
Fault finding heating circuits
Fuse
Thermostat
Blower
interlock
A 240V
thermal
cutout
24kw
heater
A
120A
Ohmmeter = 0.005W
2. A Short circuit.
Step 1. Measure the resistance of the circuit.
Step 2. Break the circuit at the element and measure it’s resistance.
the ohmmeter scale should be set to the x1 scale.
2.19.36.B
N
N
Fault finding heating circuits
Fuse
Thermostat
Blower
interlock
A 240V
thermal
cutout
24kw
heater
A
N
N
120A
R= V2/P = (240 x240) / 24000 = 2.4W
Ohmmeter = 0.005W
The correct value of element resistance = 2.4W.
The measured value is very low therefore the
fault is a short circuit, look for loose or damaged
wiring, or replace the element.
Step 2. Break the circuit at the element and measure it’s resistance.
2.19.36.B
2.19.36.B
Fault finding heating circuits
Fuse
Thermostat
Blower
interlock
thermal
cutout
A 240V
24kw
heater
A
N
N
E
120A
Here the megohmmeter indicates a leakage to earth,
But which component of the circuit is faulty?
Step 3. Break the circuit in ½ and test each side.
3. A Partial Short circuit
Megohmmeter = 500W
This type of fault is commonly a leakage to earth fault.
-The fuse may or may not be blown, Safety switches will trip.
-The client may report shock tingles from the equipment.
Step 1. Isolate the supply and test to confirm isolation, tag, ……..supply isolated.
Step 2. Perform an insulation resistance test on the whole circuit between all
active conductor to earth. AS/NZS 3000 minimum value > 1MW
The meghommeter scale should be set to 500vDC
Fault finding heating circuits
Fuse
Thermostat
Blower
interlock
thermal
cutout
A 240V
24kw
heater
A
N
N
E
E
120A
Megohmmeter = 500W
Step 3. Break the circuit in ½ and test each side.
The insulation resistance of the heating
element is> 1MW, therefore is good. The
reading on the thermostat side of the circuit is
< 1MW, therefore faulty.
Step 4. Break the faulty circuit in ½ and test each side.
2.19.36.B
Megohmmeter = 120MW
Fault finding heating circuits
Fuse
Thermostat
Blower
interlock
thermal
cutout
A 240V
24kw
heater
A
N
N
E
E
120A
Megohmmeter
= 120MW
Megohmmeter = 500W
The blower interlock circuit is less than
1MW, Therefore the fault is within that
area of the circuit.
Step 4. Break the faulty circuit in ½ and test each side.
2.19.36.B
Electric Motors
The electric motor is an inductive device, ie,
it has coils of wire and principle operation
is due to the magnetic effect.
2.19.36.B
Iron core
Copper winding
2.19.36.B
The Stator
Mounting frame
The rotor
The rotor earns the name being the
moving part of the motor.
Rotor bars
Cooling fan
The rotor bars induce a current that sets up a
magnetic field that opposes the original
magnetic field, thus, set up a magnetic
repulsion-attraction action.
2.19.36.B
Testing motor windings
• Check the resistance of the motor
windings to determine
if a fault has occurred.
• On single phase motors measure: start
to common winding, run to common
winding, and start to run winding.
• Check phase to ground.
– Ohms reading between
S-R should be the total of both R &
S winding.
– High insulation resistance between
any winding conductor to ground
2.19.36.B
Typical resistance test on a 1 motor
Testing motors on the bench
•
•
•
•
•
•
•
•
Continuity of winding
Resistance of windings
Insulation resistance
At least 1MΩ
Mechanical check
Can it turn
Visual check
Vents, end shields, balance weights in place, key not
dangerous
2.19.36.B
Small domestic refrigerator
240v 25W
Lamp
Door switch
A 240V
A
N
N
E
240v 100W
Evaporator fan
Compressor
Thermostat
Current
Relay
Run
Thermal
overload
Issue: Refrigerator does not operate!
Refrigerator does not make any sounds!
Step 1. Remove plug top from socket outlet.
Step2. Using your voltmeter test socket outlet for a supply
Supply indicates 240V, therefore the fault
maybe with the appliance.
2.19.36.B
Start
Small domestic refrigerator
240v 25W
Lamp
Door switch
A 240V
A
N
N
E
Ohmmeter = 15MW
Thermostat
Current
Relay
240v 100W
Evaporator fan
Run
Thermal
overload
Issue: Refrigerator does not operate!
Refrigerator does not make any sounds!
Start
Step 3. Place an ohmmeter across the A & N pins on the plug top.
Step 4. Think..! At this point of time what should be operating within this refrigerator?
The evaporator fan and the compressor.
Now determine what value of resistance should the ohmmeter be indicating.
Compressor approx 20W, evap fan approx 80W = total resistance approx 16W
The ohmmeter indicates a high value of resistance therefore = open circuit, but where?
2.19.36.B
Small domestic refrigerator
240v 25W
Lamp
Door switch
A 240V
A
N
N
E
Ohmmeter = 0.5W
Good reading
Thermostat
240v 100W
Evaporator fan
Current
Relay
Run
Thermal
overload
Start
Compressor
Step 5. Remove compressor terminal cover and connect an ohmmeter between the
neutral pin of plugtop and circuit wiring.
Ohmmeter = 20W
Good reading
2.19.36.B
Small domestic refrigerator
240v 25W
Lamp
Door switch
A 240V
A
N
N
E
240v 100W
Evaporator fan
Thermostat
Current
Relay
Run
Thermal
overload
Ohmmeter = 15MW
Bad reading!
Start
Compressor
Step 6. Remove thermostat cover.
Attach an ohmmeter between A pin of plugtop and circuit
Fault identified as an open circuit of the Active conductor
2.19.36.B
Final Tests
1 Visual inspection, is the work as per AS/NZS-3760?
2 Earth continuity test, is the earthing circuit continuous?
AS/NZS-3760: 2003 < 1W, .
3 Insulation resistance test, is the conductors insulation
able to contain the operating voltage?
AS/NZS-3760 2003 > 1MW
4 Polarity, are the outlets correctly connected, are the
circuit actives switched?
2.19.36.C
Small domestic refrigerator
240v 25W
Lamp
Door switch
A 240V
A
N
N
E
240v 100W
Evaporator fan
Thermostat
Current
Relay
Run
Thermal
overload
Start
Compressor
AS/NZS3760
Don’t forget to perform your safety tests on the appliance!
1. Visual inspection.
2. Earth continuity.
One connection on the earth pin
The other on the metal frame.
2.19.36.C
< 1W
Small domestic refrigerator
240v 25W
Lamp
Door switch
A 240V
A
N
N
E
240v 100W
Evaporator fan
Thermostat
Current
Relay
Run
Thermal
overload
AS/NZS 3760
Start
Compressor
Don’t forget to perform your safety tests on the appliance!
1. Visual inspection.
2. Earth continuity.
3. Insulation resistance test
2.19.36.C
> 1MW
Work Record required by Regulations
Electrical Safety Regulation 2002
Part 2 Electrical work
14 Testing of electrical equipment after electrical work
(1) This section applies if electrical work is performed on electrical equipment.
(2) A person who performs part or all of the electrical work, and is responsible
for bringing the electrical equipment to a state of readiness for connection
to a source of electricity for use for its intended purpose, must ensure the
electrical equipment is tested, as required under subsections (5) and (6).
Maximum penalty—40 penalty units.
.Date of
inspection
Appliance
Visual
inspection
Earth
continuity
W
Insulation
resistance
a
RCD test current
30 MA trip time
Milliseconds
0h
180h Test butt
Polarity
= Correct
MW
2/7/09
Refrigerator ( LG model
R100020 Serial 1004039832)
O.K
0.3
75M
N/A
N/A
N/A
N/A
2/7/09
Safetypac (Clipsal mod 56B,
serial 9987987)
o.K.
0.8
187M
a
22
18
a
2.19.36.C
Work Record required by Regulations
Electrical Safety Regulation 2002 Part 2 Electrical work
15 Certificate of testing and safety
This section applies if a licensed electrical contractor performs electrical work that must be tested under
this division.
(2) The contractor must, as soon as practicable after the testing, ensure that the person for whom the
electrical work was performed is given a certificate complying with this section.
(5) A licensed electrical contractor must keep a copy of a certificate given under this section for at least
5 years after the certificate is given.
Maximum penalty for subsection (5)—20 penalty units
Certificate of Testing and Safety
As per Electricity Safety Regulation 2002,Part 8”Electricity Supply”, Division 2 “Testing”, Regulation 15,”Certificate of Testing & Work”
Electrical worker who tested the
electrical work.
Phone
Licence No:
Details of work
Contractors Licence
Details of Electrical Contractor
Inspection Certificate No:
Acts, Regulations,
Codes of Practices & Standards.
Electricity Act 1994 & Electricity Regulation 2006
Electrical Safety Act 2002 & Electrical Safety Regulation 2002
AS/NZS 3000:2000. Incorporating Amendment No. 1 (September 2001), Amendment No. 2 (April 2002), &
Amendment No. 3 (July 2003). The Wiring Rules.
AS/NZS 3008.1.1:1998, Electrical installations— Selection of cables Part 1.1: Cables for alternating voltages up to and
including 0.6/1 kV—Typical Australian installation conditions
I certify that the electrical installation work listed above has been tested in accordance with the prescribed procedures and that such work is electrically safe
and complies in every respect with the requirement of the Electricity Safety Regulation 2002, regulation 159.
Signature of Electrical worker:
Date of Certification:
2.19.36.C
Manufacturer Specifications of disconnected & replacement
equipment.
When replacing any load you should be sure that the new
item is suitable with regards to: Speed, Rotation, Power
rating, Voltage, Current, Physical size, Environmental
conditions & design of replacement, Dust & waterproof,
temperature, UV rating, touch proof, life span.
2.19.36.C
Energising supply
• Only after the visual inspections and safety testing as
per AS/NZS 3000:2007 has proven that the circuit is
fit for purpose are you to energise the circuit.
• Remove only your Danger tag. If another worker has
their danger tag on the isolated point then you can
not energise.
• If clear: Energise the circuit.
• Test for the correct and safe operation of the circuit,
i.e. rotation, system performance, current draw,
voltage, etc.
• Prepare all your safety and performance
documentation.
2.19.36.C
Further reading: Textbook
Questions: Workbook, Topic 5, Q1 – Q10