Summary
Temperature-controlled hot cable (cable for short) is also called self-controlled hot cable or self-limiting temperature electric belt, with power adjusting along with system temperature. As the cable itself has the function of automatic limiting temperature, and the function of self-adjusting power along with the temperature of heating system, it can be guaranteed that the working system always in the best operating temperature.
1.1 Features:
ü Limit cable’s working temperature automatically during heating.
ü Adjust output power automatically but not other additional equipments along with the temperature of heated system.
ü May be shortened or lengthened with certain scope but the properties above do not change.
ü It is allowed to be crossed but not worry about being overheat or burned.
1.2 Advantages:
The temperature-controlled hot cable has following advantages if used for preventing frostbite and heat preservation:
ü Even temperature, not be overheated, safe and reliable;
ü Save electric energy;
ü Quick increase temperature during interim operation;
ü Convenient to install, operate and maintain;
ü Convenient for automatization management;
ü No pollution.
2 PTC working principle
2.1 PTC effect and PTC material
PTC effect, the positive temperature coefficient, means that resistivity of material increases with temperature increasing, and increases rapidly within certain temperature scope. The material that has PTC effect is called PTC material. The macromolecule PTC material of this cable is the mixture of semicrystal high polymer and carbon black.
2.2 Working principle
The electrothermal component is core belt made from PTC coated between two parallel metal generatrixes. After melting extrusion and refrigerated molding, the carbon particulates dispersed in PTC from lots of fine electrical carbon networks; if connect them across the two parallel generatrixes, PTC parallel circuit is constituted. Once the two generatrixes on one end of cable connect to power, electric current will transfer from one generatrix to the other through PTC layer and forms parallel circuit. PTC layer is the heating unit connected parallel between generatrixes. It transforms electric energy to heat energy for heat preservation for operating system. If rising to corresponding degree when high resistance almost interdicts current, the temperature of current will not rise again. (automatic temperature limiting). Meanwhile, the core belt will be heated up heated system that is much low in temperature through jacket; the unit transferred energy reaching to stability is equal to cable’s power which is mostly determined by the temperature in heating course and heated system.
2.3 working properties of cable
2.3.1 Property of automatic power adjustment
The heating power of hot cable reduces automatically as the temperature rising or increase automatically as the temperature reducing.
2.3.2 Property of automatic temperature limit
When the hot cable is heated, temperature rises and resistance increases; when the resistance rises to limit, the heating power will go small and the temperature will rise highest, which is the property of cable’s automatic temperature limit. Temperature limit & hot companion means that cable can be heated within the highest temperature limit.
2.3.3 Property of PTC memory
The resistance of hot cable increases with temperature rising; if the resistance can still fall back to start point along with original rising route when temperature is reduced, which is the property of PTC memory. The cable of PTC memory can be used repeatedly for long term.
2.3.4 Property of even temperature
The core belt of temperature-controlled hot cable is composed by parallel connecting PTC unit formed by lots of fine electric networks. When there is temperature and energy consumption fluctuation in any part of hot pipeline, every PTC component in this position can be affected directly and response independently; then adjust self output power automatically in the direction of eliminating this fluctuation. If the temperature is low, the power will be large, vice versa; besides, the amplitude modulation of power is given in terms of the range of temperature fluctuation to keep the whole system stable in temperature. This is a whole course of tracking, synchronous, and full-automatic heat companion and preservation.
3 parameter definition
3.1 nominal power
Nominal power is the stable output power of temperature-controlled hot cable every meter when it is 10℃ in rated working voltage in certain heat-preserved layer.
3.2 Temperature-controlled index
Temperature-controlled index is the reduced value of cable’s output power when temperature increases 1℃ or the increased value when temperature reduces 1℃. (Generally give out the minimum value.)
3.3 Highest maintaining temperature
Using certain model of cable to heat up one system, this system can be maintained to the highest temperature, which calls the highest maintaining temperature of this model of cable. Maintaining temperature is a relative parameter. It has something to do with the heat loss of the heat-preserved system and the highest surface temperature of hot cable. If designed right in use, it can maintain the system temperature in any one from highest maintaining temperature to environment temperature.
3.4 Highest exposition temperature
Exposition temperature is the one that external hot source acts on cable. When it is higher than certain temperature, the electrothermal property of cable will be damaged. This temperature is the highest one this cable can bear, called the highest exposition temperature.
3.5 Highest surface temperature
The highest surface temperature is the one on the surface of hot cable can reach to in good condition of heat insulation and in rated voltage. This parameter is very important to the place where is easy to burn and easy to explode.
3.6、Maximum using length
The maximum length allowed to be used in single power supply in rated voltage is called the maximum using length. It has something to do with rated voltage, power, specification and temperature. If it is longer than this length, additional power supply is connected.
4 model and structure
4.1 representation of model and specification
as follows
structure type
rated voltage
code name
temperature ratings
nominal power
from left to right
(1) Nominal power: Example: “10”means nominal power is 10Wm-1.
(2) Temperature ratings: D stands for low temperature; Z stands for mid temperature;
(3) Code name: WK stands for temperature-controlled cable;
(4) Rated voltage: “1” stands for 110V; “2”stands for 220V；“3”stands for 380V;
(5) Structure type: “J” stands for basic type; “P” stands for shielded type; “F” stands for protective type;
Example: 10DWK2－F means protective type low-temperature controlled hot cable (CharⅠ) with nominal power is 10Wm-1 and rated voltage is 220V.
4.2 Model and specification
TableⅠfor product model and specification
Item; Basic type; Shielded type; Protective type; Nominal powerW/m
Low temperature series: DWK－J DWK－P DWK－F 10、25、35、45
Mid temperature series: ZWK－J ZWK－P ZWK－F 30、40、50、60
4.3 Structure
(1) conductor (WTC, 1.0、1.5、2.5mm2)
(2) PTC core belt
(3) modified polyolefin insulated layer
(4) WTC shielded layer
(5) modified polyolefin or fluorocarbon resin protective layer.
5 parameters
5.1 Parameters of low temperature series
Standard color: black
Temperature scope: highest maintaining temperature: 65℃; highest exposition temperature: 85℃; highest surface temperature: 85℃;
Construction temperature: -60℃ at least;
Heat stability: After cycling for 300times between 10℃ and 99℃, the heat value of cable keeps more than 90%.
Bending radius: If room temperature is 20℃, it is 25.4mm; if -30℃, it is 35mm.
Insulation resistance: When the length of hot cable is 100m and the temperature is 75℃, the minimum insulation resistance is 20MΩ.
5.2 Power-temperature graph of DWK hot cable (power supply: 220Vac)
5.3 Parameter of mid temperature series
Standard color: brown;
Temperature scope: highest maintaining temperature: 105℃; highest exposition scope: 135℃; highest surface temperature: 135℃;
Construction temperature: -30℃ at least;
Heat stability: After cycling for 300times between 10℃ and149℃, the heat value of cable keeps more than 90%.
Bending radius: If room temperature is 20℃, it is 25.4mm; if -30℃, it is 35mm.
Insulation resistance: When the length of hot cable is 100m and the temperature is 75℃, the minimum insulation resistance is 20MΩ.
5.4 Power-temperature graph of ZWK hot cable (power supply: 220Vac) CharⅡ
5.5 TableⅡfor fuse type and maximum using length of single power supple
TableⅡfor fuse type and maximum using length of single power supple
Model of cable
Starting temperature
Fuse
10A 20A 30A 40A
— 6 Use:
ü the position or the place where need to prevent frostbite, melting and coagulation.
ü heat preservation, viscosity break and block prevention of pipeline, valve, pump, vessel, groove, pot and reactor which are easy to fluidify, solid, crystal and adhibit liquid, such as coal gas, chlorine, crude oil, heavy oil, edible oil, water pipe and so on, especially the above pipelines interim operate but not eject air completely.
ü branch pipe of measure instrument, not flow because of fineness.
ü agricultural sideline production processing and other uses, such as zymolysis, incubating and breeding, etc..
— 7 Instruction
ü Do not press, impact, bend again and again, as well as incursion of organic solvent or oil dirt in the course of transportation, storage and installment.
ü One end of the cable connects to power supply; wire core of the other end can not be short or contact with electric matters. It is supposed to be sealed closely with cooperative sealing head. Use cooperative anti-explosion terminal box in the place where is anti-explosion, with jacket not be damaged and core belt not be exposed.
ü The output power of hot cable has something to do with most factors of hot system. Heat engineering design is supposed to be done so that the best running effect can be got.
8 Simple heat engineering design
Electric tracing heat is to make use of the heat output by hot cable to compensate the heat consumed in pipeline, vessel, port and other storage and transport system to keep the operating system medium always in right temperature what this technics require. Therefore, it is supposed to make sure heat loss or heat consumption before heat engineering design, then cable’s power and length can be confirmed in terms of heat consumption.
8.1 Technical parameters need to be confirmed:
1) maintaining temperature: TV;
2) minimum environment temperature: (℃)，TA
3) outer diameter of pipeline: D;
4) surface area of vessel: S;
5) categories and thickness of heat-preservation material in pipeline:
6) Pipeline is indoor our outdoor.
8.2 calculation of hot loss in pipeline or plane
8.2.1 pipeline
The hot loss of heat-preservation pipeline is calculated in terms of formula(1). (30% safety factor)
Qt={[2π(TV-TA) ]/［( LnD0/D1）1/λ+2/( D0α)]}×1.3 ………(1)
8.2.2 plane
The hot loss of heat-preservation plane is calculated in terms of formula(2). (30% safety factor)
QP=[(TV-TA)/(δ/λ+1/α)] ×1.3 ……………………………(2)
Qt —hot loss of unit pipeline ,W/m；
Qp —hot loss of unit plane，W/㎡;
TV —maintaining temperature system requires for，℃；
TA —minimum environment condition ℃；
λ — heat conductivity coefficient of heat-preservation material
D1 —inner diameter of heat-preservation layer (outer diameter of pipeline)
D0 — outer diameter of heat-preservation layer
δ —thickness of heat-preservation layer
Ln —logarithm
α —heat transfer coefficient from exterior of heat-preservation to atmosphere, W/(㎡℃) has something to do with wind speed ω，(m/s)
αis calculated in terms of formula (3).
α=1.163(6+ω1/2) W/( ㎡℃ ) …………………………(3)
8.2.3 The reduction coefficient of different material is different. The needed power is also different in the same TV. Reduction coefficient refers to Table (4);
The value of Q t、Q P is that in the condition when it is steel, if material changes, it is supposed to multiple reduction coefficient. Example: formula(4);
Table3, reduction coefficient of common heat-preservation material
heat-preservation material, reduction coefficient
0.036 fiberglass
0.038 silicate cotton
0.054 calcium silicate
0.054 expanded perlite
0.084 vermiculite
0.043 mineral wool
0.024 polyurethane
0.031 polystyrene
0.042 foam
0.093 asbestos
Table 4, reduction coefficient of pipeline
pipeline material, reduction coefficient
carbon steel 1
copper 0.9
stainless steel 1.25
plastic 1.5
Q=Qt×kc W/m ………………………………………(4)
8.3 Choose right hot cable with Q; confirm length and lay mode need in every meter of pipeline.
8.3.1 length of hot cable partially used in pipeline
1) length of hot cable in every meter of pipeline: Lg
Lg=Q/QM m/m ……………………………………………(5)
In this formula, QM stands for output power when maintaining temperature is TV.
2) If Lg is less than 1, the hot cable used in every meter of pipeline can not be laid, so it is not allowed to be less than 1.
3) If Lg is equal to 1, 1m hot cable is applied in every meter of pipeline, so it is laid linearly with single cable.
4) If Lg is equal to n (n is integer), n hot cables are applied in every meter of pipeline, so it is laid linearly with n cables.
5) If Lg is more than 1 but not equal to n, it be laid spirally with space is LS.
LS=π（D+d）/（Lg2-1）0.5 m
D: outer diameter of pipeline; d: thickness of hot cable
6) length of hot cable partially used in pipeline,
L1＝total length of pipeline×Lg m
8.3.2 length of hot cable partially used in plane
1) length of hot cable laid in every square meter surface:
Lp=（Qp×Kc）/ QM m/㎡
2) Lp≥3, every square meter surface can not be laid more than 3m hot cable.
3) length of hot cable partially used in plane
L2=S×Lp m…………………………………………………(8)
S stands for area of heat yield; when diameter of pipe is more than 600mm, plane vessel treatment is allowed.
8.3.3 Hot loss of pipeline accessories can be calculated as that of pipeline of certain length and the same diameter, the cable has to be laid in corresponding accessories.
Length of hot cable used in pipeline accessories=heat extraction coefficient of accessories×length of the same cable in very meter pipeline
1) length of cable used in every valve Lf:
Lf=kf×Lg………………………………………………………（9)
In this formula, kf stands for heat extraction coefficient of valve, referring to Table 5
Table 5, heat extraction coefficient of valve
Categories of valve, gate valve, butterfly valve, ball valve, globe valve
Heat extraction coefficient: 1.5 0.9 1.0 1.4
2) Length of cable used in other accessory of every pipeline: Lj
Lj=kj×Lg …………………………………………………（10)
In this formula, Kj stands for heat extraction coefficient, referring to table 6
Table 6: heat extraction coefficient of pipeline accessories
Accessories: flange, angle bend, straight joint, T-type joint, bracket, hanging bracket
Heat extraction coefficient: 2 2 2 3 3 3
8.3.4 1) reserve 1m for power supply;
2) reserve 0.5m in the end;
3) reserve 0.5m in every straight or T-type connecting box;
4) spare parts (according to project need)
Total length of hot cable (30% safety factor), L = （L1+L2+Lf+Lj+L3）×1.3
8.4 Proceedings of choosing hot cable
8.4.1 Choose corresponding hot cable of high exposition temperature in terms of the highest temperature what pipeline can bear.
Make sure whether the pipeline appears incidental temperature increasing (such as steam, hot water, hot oil cleaning pipeline) and highest temperature, the highest exposition temperature of hot cable can not be lower than incidental increased temperature.
If the incidental increased temperature is higher than highest exposition one, you may adjust installing method after heat engineering design, just add proper thick heat-preservation layer between hot cable and pipeline to reduce incidental temperature increase effecting cable.
8.4.2 Choose right power of hot cable in terms of power-temperature curve.
Choose output power not in terms of nominal power but what hot cable must output while system maintains temperature.
It has direct something to do with system maintaining temperature to choose temperature rank and power. Choose the cable whose highest surface temperature is higher than system maintaining temperature (example: 20℃) and can compensate system hot loss.
8.4.3 Make sure the maximum length of single-power cable
The length of summation of every hot cable elicited from one junction box is the maximum length of single-power hot cable. According to this, choose over-current protective switch. Choose right cable in terms of pipeline distribution and length of branches. The low-power cable is adapted for longer branch.
8.4.4 Choose right structure in term of installing environment and condition.
1) Choose shielded type product for the vessel and pipeline on which is coated with oil paint but can not contact with ground reliably.
2) Choose shielded type product in the area where is easy to burn or easy to explode, or for the medium inside of the pipe is easy to burn and easy to explode.
3) Choose protective type product if the medium inside of pipeline is corrosive or the cable may contact with corrective chemical products.
8.4.5 Other
1) The section of power wire has to be larger than that of cable conductor.
2) Choose right fuse and air switch which are supposed to be more than starting current.
3) It is supposed to apply special junction box, middle junction box, terminal and other special accessories in the area easy to burn and explode.
4) Make sure whether apply single-phase power or three-phase power and voltage rank in terms of power supply, voltage and power network balance.
5) Make sure whether apply straight laying or spiral laying in terms of the pipeline condition.
9 chart of electric heating system
9.1 Principle of drawing electric heating system
1) Draw every electric heating system respectively for every system supplied by single power.
2) The electric heating system chart is supposed to be denoted with projection chart in terms of heated pipeline chart.
3) The electric heating system chart is a pictorial drawing not in pro rata.
9.2 Requirement
1) List series number, diameter, material, heat-preservation material and preserved temperature.
2) Line out the positions of valve, pipe, bracket and flange, as well as length of pipeline, position of junction box.
3) List name of interior medium, working temperature, maintaining temperature, highest temperature, lowest temperature, temperature difference, hot loss and danger area.
4) List specification and amount of hot cable, calorific power in maintaining temperature, as well as the amount, specification, model of electric equipment and other accessories.
10 Installment of electric heating facility
10.1 Preparation before installing
1) Test the properties of circuit continuous and insulation to all hot cables. That not confirms to standard can not be used.
2) Examine the appearance of electric equipments and controllers. That has deformation, crack and can not be repaired can not be used.
3) Check up series number, specification, technical condition, parameter and model of hot cable, specification and model of electric equipment and controller according to system chart before installing; after make sure there is no error, can start to install.
4) That has no brand name or not clear or can not identifiable can not be installed.
5) Make sure all heated pipelines have finished and are checked eligible in water pressure test or air test before installing this system.
10.2 Notes on installation
1) Do not drag on ground during installation to avoid being damaged by sharp objects; do not contact with high-temperature object to prevent welding slag from falling onto cable.
2) The hot cable has good flexibility but it is not allowed to be forced to bend; if there needs to bend, the bend radius can not be more than 6 time of hot cable’s thickness.
3) It is forbidden to be broken with heavy objects. If broker, the cable has to be tested electric properties again before use.
4) The hot cable has to be fastened closely with heated pipeline (or equipment) for improving heating efficiency. Use special nylon belt. Do not use metal wire to tie.
5) It is supposed to stick a layer of aluminum adhesive tape between the outer wall of nonmetallic pipeline and the hot cable to increase transferring area.
Chart3 cable twisting method on pipeline
1. tie; 2. pipe; 3. tie; 4. hot cable
Maximum distance between ties: 300mm
Chart 4 cable twisting method on flange
Chart 5 cable installation and fastness on pipeline
1.falnge; 2. pipe; 3. tie; 4. hot cable;
1. pipeline; 2. heat-preserved coated; 3. outer protective layer; 4. tie; 5. hot cable
6) It has to consider adequately the possibility of taking apart pipeline accessory or equipment during installation; and the cable need not be cut; make sure the joint airproof.
7) When the hot loss of every meter pipeline is larger than output power of every meter hot cable, you may lay the hot cable in terms of chart 4 for being convenient to take apart in maintenance.
8) It is easy to leak in flange, so it is supposed to avoid twisting under the cable as shown in chart 5.
Fix and fasten the hot cable on pipeline in terms of chart 6. Material of tie is chosen according to the temperature of pipeline.
10) Carry out electric test to every circuit after installing hot system; and then test the cable’s heating properties. After make sure it normal, can start heat preservation.
11) The heat-preserved material has to be dry, as wet material not only influence heating effect, also corrupt cable and shorten its service life. As for the heat-preserved pipeline not wrapped with protective layer has to be wrapped again if wet by rain and snow after air drying.
12) Make obvious electric heating mark on the outer protective layer after construction to remind of people’s attention.
13) Seal the other end with cooperative sealing cover before one end of the cable connects to power supply. Make sure no short circuit between generatrixes.
14) Make sure every generatrix insulated by insulation cover when multi-circuit hot cables connect out from one junction box to avoid short circuit.
15) The junction box has to be sealed to avoid rain.
10.3 typical hot cable installation drawing (chart 7~ chart 17)
图6 伴热电缆总装示意图chart 6 hot cable installation pictorial drawing
chart 7 installation of three-way hot cable
chart 8 installation of hot cable on valve
1. tie; 2. hot cable; 3. pipeline; 1. tie; 2. hot cable; 3. pipeline; 4.valve
Reel off hot cable to lay outside of angle bend.
Chart 9 installation of hot cable on angle bend
Chart 10 installation of hot cable on U-shaped pipe
1. tie; 2. pipeline; 3. hot cable; 1. tie; 2. hot cable; 3. pipeline; 4. U-shaped clip; 5. bracket
chart 11 installation of hot cable on flat conduit saddle
chart 12 installation of hot cable on bended conduit saddle
1. pipeline; 2. hot cable; 3. tie; 4. conduit saddle; 1. pipeline; 2. hot cable; 3. tie; 4. conduit saddle;
chart 13 installation of hot cable on conduit saddle and bracket
chart 14 installation of hot cable on pipeline hanging bracket
1. tie; 2. pipeline; 3. bracket; 4. hot cable; 1. hanging bracket; 2. sealing compound; 3. airproof cover; 4 heat-preserved layer; 5. pipeline; 6. hot cable; 7. tie
chart 15 installation of hot cable on pump
chart 16 installation of hot cable on liquid level controller
1. motor, 2. pump exist; 3. hot cable; 4. pump entrance; 5. pump body; 1. hot cable; 2. tie; 3. end sealing; 4. junction box
10.4 Locale test and examination of electric heating system
1) Examine the cable’s continuous and insulated resistance with 500V measure. The system which insulated resistance is more than 5MΩis eligible.
2) After installing heating system, the test result of every circuit has been recorded and reported.
3) The examiner has to carry out mid examination and terminal check during installation in terms of relative engineering rules, as well as may ask cable manufactory for cooperation.
Structure and material of temperature-controlled hot cable
PTC芯带是将PTC材料均匀的挤包在两根平行镀锡铜线上，形成并联回路。
1. core belt layer
PTC core belt is to extrude PTC material evenly and then wrap on two parallel WTC wires to form parallel circuit. The section of core belt may be dumbbells type or oblate.
2. insulated layer
The insulated material of cable has to be modified and other insulated material that conforms to the highest working temperature rank. Insulated material has to be wrapped closely on PTC core belt. Its surface must be smooth, tidy and even in color but not allowed to be adhibited with core belt. The insulation thickness is 0.6 mm±0.1 mm, but not be less than 90%-0.1mm of this value. Examine it according to GB/T 2951.1 8.1 Standard; and get three samples in every one meter at least. The insulated wire core must withstand 50HZ ruled in the test methods for determining electrical properties of electric cables and wires A.C.spark test of insulated cores. The voltage is 6KV.
requirement for the test of insulation mechanical physical properties
serial No., item, unit, standard
11.11.2 Mechanical tensile strength before aging, minimum elongation rate at break, Min. MPa% 12.5200
22.12.2 Air container mechanical properties after aging: time of temperature continuous, tensile strength, Max. elongation rate at break, Max. ℃d%% 135±37±25±25
33.13.2 Heat elongation test: air temperature, load time, mechanical load, elongation at load, Max. eternal elongation after refrigerating, maximum℃minMPa%% 200±3150.217515
44.1 Test for water absorption, condition for weight method:
55.1 Condition for shrinking test:
3、Shielded layer
The shielded layer must be twisted with WTC on the insulation layer. Max. diameter of WTC is as following table:
size of WTC
width of cable
maximum of WTC
b≤10.0mm 0.16mm
10.0mm＜b≤20.0mm 0.21mm
Twist coverage must be over 75%.
4、Jacket layer
The cable’s jacket may be modified polyolepine and other material. If the hot cable is of protective type, the jacket should be wrapped on insulation layer or metal shielded layer closely. The surface of jacket must be smooth, even in color and easy to peel off but not damage insulation and twist layer. Thickness of jacket is 0.75mm±0.1mm, or be less a little but not less than 85%－0.1mm. Get three samples in every 1m cable for examination in terms of GB/T 2951.1—1997.
Requirement for the test of jacket’s physical properties
Serial No., Item, Unit, Standard
11.11.2 Mechanical tensile strength before aging; Min. elongation at break; Minimum: MPa% 12.5200
22.12.2 Condition of mechanical properties treatment after air oven aging:
3 Content of carbon black, Minimum% 2
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