Heat Trace 030203f Flashcards
What are the 3 main reasons for using heat trace?
To prevent the freezing of liquids in a pipe or container.
To melt snow and ice.
To maintain a specific fluid temperature in a pipe or vessel.
Page 2
What are the 4 basic design approaches to electric heat trace systems?
Series fixed resistance.
Parallel fixed resistance.
Self-regulating variable resistance.
Skin effect.
Page 2.
What principle does a series fixed resistance system use?
A resistor in series with a supply voltage.
Page 2
What are the two main types of cables used for a series fixed resistance system?
Mineral insulated.
Polymer insulated.
Page 2.
What is used to make a mineral insulated (MI) cable?
The mineral insulation is either magnesium oxide or silicon dioxide.
The sheath is either copper or stainless steel.
Contains one or more bare conductors.
Page 2
When two-conductor single termination cables are manufactured, what are the two things that are changed?
Specific lengths.
Specific heat output.
Page 4
Can mineral insulated cables be repaired in the field?
Only by trained personnel with proper equipment and techniques.
Page 4
What does a one-conductor polymer insulated cable require?
Dual termination.
Page 5
What does a two-conductor polymer insulated cable require?
Single, one-end termination.
Page 5
How are three-conductor polymer insulated cables configured?
Three-phase wye heating cable with one-end termination.
Page 5
What length can polymer insulated cables get up to?
3500m long with a single end connection to a power source.
Page 5
What does the length of the cable in a parallel fixed resistance system affect?
The length of the cable will affect the current being drawn from the source.
Page 6
What does a self-regulating cable do?
Changes the resistance of the cable based on the temperature.
Page 7
What is the design of a self-regulating variable resistance cable?
Multiple parallel resistors between two bus conductors.
Page 7
What is the difference between parallel resistance cables and power limiting cables?
Both are constructed with parallel heating elements however with power limiting cables the heating elements are an alloy that changes resistance with temperature.
Page 7
What phenomenon does skin effect heat trace rely on?
That current flows only on the inside of a ferromagnetic tube.
Page 8
What distances can skin effect heat tracing be used for?
3 km up to approximately 15 km.
Page 8
What voltage is applied to the conductor in a skin effect heat trace cable?
2000 V to 5000 V
Page 8
What are the two main types of self-regulating cables?
Self-regulating polymer.
Power limiting.
Page 7
What are four common faults with heat trace?
Incorrect temperature settings.
Incorrect temperature sensing location.
Insulation breakdown.
Incorrect voltage applied.
Page 18
What are some methods of testing for troubles with heat trace?
Manually measure the temperature of a service.
Insulation testing the heat trace.
Check terminations and splices.
Ensuring the correct voltage is applied to the heat trace.
Page 18
How do you properly test the insulation of heat trace with a megohmmeter (megger)?
Disconnect both ends of the heat trace and perform an insulation test of the entire run.
If the test fails then move to a point in the middle of the cable.
Test in both directions to further pin point the fail location.
Continue to do this until the portion that needs to be replaced is found.
Page 18
What is a thermostat used to sense the temperature of for heat trace systems?
Outside ambient air temperature.
Temperature of the surface that it is heating.
Temperature of a fluid in a process pipe.
Page 10
How can a simple thermostat be connected in a heating trace system?
In series with the cable.
May also be connected in a control circuit of an electromechanical heating contactor.
Page 10
