What is an Electric Heater
What is an electric heater? Generally speaking they convert electricity to heat. For the purpose of our discussion, we refer to heater that is used in industrial applications.
How does an electric heater convert electricity to heat? The electric heater is basically a resistor. Base on ohms law. The power generated by the electric heater is single phase is the square of the voltage divided by the resistance of the electric heater.
In troubleshooting or calculating the duty of a 3 phase heater. The following formula is use calculate the resistance of an heater
R (ohms) = 2 x V^2 / ( Power (w) * 1.05)
Heater Troubleshooting
Do we have a bad heater? Following are our recommended troubleshooting steps to determine if you have a good electric heater
This entire test shall be performed with qualified personnel. As a minimum the power shall be off, proper process isolation, all lock-out procedures implemented, etc to ensure personnel safety.
Visual Inspection – Look inside the heater housing. Looks for signs of overheating, broken/damage wire, process leakage, corrosion and water damage. If the heater is removed from the vessel, perform a visual examination of the heater bundle to see signs of physical damage.
Electrical Resistance Test –
On a 3 phase electric heater. Take a phase to phase resistance reading. Resistance reading should be within 10% of the following calculated value. An extremely low reading will indicate a shorted heater and a high reading will indicate an open heater
The following formula is use calculate the resistance of an heater
R (ohms) = 2 x V^2 / ( Power (w) * 1.05)
Electrical Insulation Test –
Utilizing an insulation resistance tester set a 500 VDC. Perform test from phase to ground. A reading of 2 mega ohm and higher should be observered. A low reading will indicate a wet heater. A wet heater will require a heater bake out.
Why is my heater wet? It is a common terms use to described that the electrical moisture seal of the heater has failed and allowed water (water vapor) into the insulation of an electric heater. Electric process heater utilizes Magnesium Oxide as an insulator between the heating coil and outside sheath. Magnesium Oxide is a good head conductor and provides good dielectric properties when dry. However, Magnesium Oxide is hygroscopic and will absorb moisture from the environment if not sealed. Hence a heater that has low resistance to ground will indicate moisture contamination in the Magnesium Oxide insulation. Operating the heater at low resistance will cause a short to ground and permanently damage the heater elements.