1 Overview

Temperature controlled heating cable (referred to as cable) is also known as self regulating electric heating wire or self limiting temperature electric heating belt. It is a strip type temperature limiting heat tracing device that adjusts its electric heating power according to the system temperature. The cable itself has the function of automatic temperature limiting and can automatically adjust the heating power according to the temperature changes of the heated system, to ensure that the working system always operates normally in the set optimal operating temperature zone.

1.1 Job Characteristics

- Automatically limit the working temperature of the cable during heating;

- It can automatically adjust the output power according to the temperature changes of the heated system without the need for external equipment;

The cable can be cut short or extended within a certain range without changing its performance.

- Allow cross overlapping winding and laying without the worry of overheating and burning.

1.2 Job advantages

Temperature controlled heating cables have the following advantages when used for antifreeze and insulation:

- The temperature of the heat tracing pipeline is uniform, will not overheat, and is safe and reliable;

- Save electricity;

During intermittent operation, the temperature rise starts quickly;

- Low installation and operation costs;

- Easy installation, use, and maintenance;

- Easy to automate management

- No environmental pollution.

2 PTC working principle

2.1 PTC Effect and PTC Materials

The PTC effect, also known as the positive temperature coefficient effect, refers to the characteristic that the electrical resistivity of a material increases with temperature and sharply increases within a certain temperature range. The material with PTC effect is called PTC material, and the polymer PTC material of this cable is a blend of semi crystalline polymer and carbon black.

2.2 Working principle

The electric heating element of the temperature controlled heating cable is a core strip made of PTC material uniformly extruded between two parallel metal busbars. After the PTC material is melted, extruded, cooled and shaped, the dispersed carbon particles form countless fine conductive carbon networks. When they are connected across two parallel busbars, they form a PTC parallel circuit of the core strip. When the two busbars at one end of the cable are connected to the power supply, the current flows horizontally through the PTC material layer on one busbar to reach the other busbar, forming a parallel circuit. The PTC layer is a resistor heating element continuously connected in parallel between busbars, which converts electrical energy into thermal energy and provides heat tracing and insulation for the operating system. When the temperature of the core strip rises to the corresponding high resistance zone, the resistance is so high that it almost blocks the current, and the temperature of the core strip will reach the high limit and no longer rise (i.e. automatic temperature limit). At the same time, the core tape transfers heat to the heated system at a lower temperature through the sheath, and the heat transferred per unit time when reaching steady state is equal to the electrical power of the cable. The output power of cables is mainly controlled by the heat transfer process and the temperature of the heated system.

2.3 Cable working performance

2.3.1 Power Self Adjustment Performance

The electric heating power of the heating cable decreases automatically with increasing temperature or increases automatically with decreasing temperature.

2.3.2 Self limiting temperature performance

When the heating cable is energized, the temperature rises and the resistance increases. When the resistance reaches a maximum, the electric heating power tends to be extremely small, and the temperature rises to the high limit. This is the self limiting temperature characteristic of the cable. Temperature limited tracing refers to the process in which cables can be traced in a certain temperature zone below the upper limit of temperature.

2.3.3 PTC Memory Performance

The resistance of the heating cable increases with temperature, and if the resistance can return to its original starting point along the original heating path during cooling, it has PTC memory performance. Only cables with memory performance can be used repeatedly for a long time.

2.3.4 Temperature uniformity performance

The core strip of the temperature controlled heating cable is composed of a large number of PTC parallel units formed by a fine conductive network. When there are fluctuations in material temperature and energy consumption in any section of the heat tracing pipeline, each PTC element in the location can directly sense the temperature and independently respond. Automatically adjust their output power in the direction of eliminating fluctuations in real time, increasing power when the temperature is low and decreasing power when the temperature is high. Provide power amplitude modulation according to the magnitude of temperature fluctuations to maintain uniform and stable operating temperature in each section of the entire system. This is a micro area tracking, fully synchronized, and fully automatic heat tracing and insulation process.

3 Main parameter definitions

3.1 Nominal power

The nominal power refers to the steady-state electrical power output per meter of temperature controlled heat tracing cable at a temperature of 10 ℃ in a pipeline with cable heat tracing within a certain insulation layer under rated operating voltage.

3.2 Temperature Control Index

The temperature control index refers to the decrease in cable output power for every 1 ℃ increase in temperature, or the increase in cable output power for every 1 ℃ decrease in temperature (usually given as the lowest value).

3.3 Maximum Maintenance Temperature

The maximum temperature that can be maintained by a certain type of cable when heating a system is called the maximum maintenance temperature of that type of cable. Maintaining temperature is a relative parameter that is related to the magnitude of heat loss in the insulation system and the maximum surface temperature of the heat tracing cable. If designed properly, the system temperature can be maintained at any temperature between the highest maintenance temperature and the ambient temperature during use. 

3.4 Maximum exposure temperature

Exposure temperature refers to the temperature applied to the cable by an external heat source. When the exposure temperature exceeds a certain temperature, it will begin to damage the electrical heating performance of the cable. This temperature is the maximum temperature that the temperature controlled heating cable can withstand, known as the maximum exposure temperature.

3.5 Maximum surface temperature

The maximum electric heating temperature that can be achieved on the surface of a heat tracing cable operating under good insulation conditions and rated voltage. This parameter is important for situations with flammable materials and explosive atmospheres.

3.6 Maximum usable length

At the rated operating voltage of a single power source, there is a maximum length limit allowed for the use of heat tracing cables, which is the maximum usable length. The maximum usage length is related to the rated voltage, power, specifications, and ambient temperature. If the maximum usage length needs to be exceeded, an additional power supply should be connected.

4 Product Model and Structure

4.1 Product Model and Specification Representation Method

The product model and specification are represented as follows:

structural style

Rated voltage

Product code

Temperature level

Nominal power

From left to right

1) Nominal power: For example, "10" indicates a nominal power of 10Wm-1.

2) Temperature level: D represents low temperature; Z represents medium temperature.

3) Product code: WK stands for temperature controlled cable.

4) Rated voltage: "1" represents 110V; 2 "represents 220V; 3 "represents 380V.

5) Structural type: "J" represents basic type, "P" represents shielding type, and "F" represents protective type.

Example: 10DWK2-F

Indicating: Protective low-temperature temperature control heating cable (as shown in Figure 1), with a nominal power of 10Wm-1 and a rated voltage of 220V.

4.2 Product Model and Specifications

Product model specifications are shown in Table 1

Table 1 Product Model Specifications (220V)

Project basic type shielding type protective type nominal power W/m

Low temperature series DWK-J DWK-P DWK-F 10, 25, 35, 45

Medium temperature series ZWK-J ZWK-P ZWK-F 30, 40, 50, 60

4.3 Product Structure

(1) Conductor (Tin plated copper wire 1.0, 1.5, 2.5mm2)

(2) PTC core strip

(3) Modified polyolefin insulation layer

(4) Tin plated copper wire braided shielding layer

(5) Modified polyolefin or fluorocarbon resin sheath layer

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