Structural and electric standards for basic cable types used on UTN

Following basic types of paired cables are used in UTN

- cables with airily-paper insulation|insulant| in metallic moisture-proof|metallical| covering |(ТГ);

- cables with insulation made of|insulant| solid polyethylene in a polyethylene moisture-proof| covering (ТПП).

Cables with airily-paper insulation contain conductors in diameters of 0.4; 0.5; 0.7 mm. The insulation is made mainly from paper strips 0.05 mm thick, which overlaid spirally with an overlap of 20..30 %. Taking into account calibration, the diameter of an insulated thread is d ₁= 1.0 mm, if the bare conductor diameter equals 0.5 mm.

Cables have pair twisting with a strand pitch of|footpace| 70..100 mm| and a layer twisting of core|triblet|.

Cables are produced both “bare” unarmored ones (ТГ) and cables with different armored coverings (ТБ, ТК).

The cables of ТГ type are produced with pair amount from 5 to 1600 pairs, and armored cables contain up to 600 pairs.

ТПП cables with polyethylene cable-core insulation are produced by capacity from 10 2 to 2400 2. Cable leads are made of copper in diameter of 0.32 mm; 0.4 mm and 0.5 mm.

Depending on thread diameter the insulation of solid polyethylene has thickness of D_ins = 0.18..0.4 mm for pair twisting and D_ins = 0.18..0.35 mm for star-quad twisting. Over the core there is a shield made from aluminum strip which is D_s = 0.1…0.2 mm thick.

Under the shield there is|tube-face| the copper|cooper| tin-plated wire with a diameter of 0.5...0.6 mm|; an external plastic jacket of polyethylene is 1.5...4.2 mm| thick depending on the capacity|C.| of a cable.

Electrical ratings, which are measured at direct current and vary depending on type|typestyluseduu of the cable used in UTN, are given in Tables. 9.1 and 9.2. All standards are reduced to the length|lenght| of 1 km and the temperature of 20°С|.

Table 9.1 – Electrical ratings for ТПП

Parameter	Value	Note
Insulation resistance, megaohm•km	No less than 6500 for 100% capacity of cable	Specification В 05758730.014-2000
Mutual capacitance, nanofarad/km	45.5 ± 5	Single thread capacitance is not normalized

 

A standard|standard| of screen|tube-face|-earth insulation resistance|holdout| |insulant||ground-to-air|for jacketed cables of ТПП type|typestyle|, which has protective jacket made of polyethylene, is 5000 megaohm×km.

A loop resistance of treads, which is reduced to|by| the temperature of 20°C| and cable length|lenght| of 1 km, for cables ТГ and ТПП should be:

- for a thread with a diameter of 0.4 mm – no more than 296 Ohm/km;

- for a thread with a diameter 0.5 mm – no more than 186 Ohm/km;

- for a thread with a diameter 0.7 mm – no more than 96 Ohm/km.

A value of|unsymmetry| ohmic disbalance of threads for cables ТГ and ТПП should be no more than 1% of thread loop resistance|holdout|.

ТГ cables should stand the 500 V of test voltage between |cellulatreads during|for| two minutes|mn| at alternating current with frequency 50 Hz as well as |couple|the same voltage (500 V) between the threads|cellular| and leaden moisture-proof| covering. ТПП сables should stand 1000 V between the threads|cellular| of a pair|couple| during 1 minute|mn|.

Balanced cables with a styroflex insulation of threads (МКС) or with polyethylene one (МКП). Capacity of such cables can be 1×4, 4×4 or 7×4 cables. These are cables with star-quad twisting of threads and layer twisting of the core. Leads of such cable have diameter of 1.2 mm and they are insulated by varicolored styroflexes with diameter of 0.8 mm and by polystyrene strip which is 0,05 mm thick with overlap of 25…30 %. The first pair of every quad contains red (a)and yellow (b) thread, while the second pair contains blue (a) and green (b) one. Inside each quad there is a centering core with a diameter of 1.1 mm. All quads are characterized by interconsistent leads of twisting which are in the range 125…275 mm. A wrapping for such cables is produced from a cable paper. A moisture-proof envelope can be both made of lead (МКСГ) and from an aluminum (МКСА) or steel (МКСС). An aluminum and steel moisture-proof envelope requires protecting from external influences; therefore cable is covered with polyethylene jacket (МКСАШп, МКССШп). A bituminous adhesive layer spread on the moisture-proof envelope to prevent the jacket sliding off.

Star-quad cables can have armor from two steel strips (МКСБ) or steel wires (МКСК).

 

In case cable-core insulation is polyethylene, a cable is marked as МКП. A thickness of solid polyethylene conductor insulation is ∆_ins = 1.1 mm. The moisture-proof envelope of such a cable is a two-layer plastic one.

Electrical ratings measured at direct-current for different types HF balanced cables are given in Table 9.2 (State Standard 52221-74). A factory length for conventional cables МКС is l_fl = 825 5 m.

All standards|standard| are given for UTN cables without|senza| the account of their connection to|by| network terminal equipment|EQP||net|. During measurement of cables connected to|by| the terminal equipment|EQP| (boxes, etc|CH|) norms|standard|, even insulation resistances|holdout||insulant|, should be calculated taking into account | terminal plinths.

Table 9.2 - Electric ratings for cables МК, МКС, МКП

Parameter	For paper insulation	For styroflex insulation	For polyethylene insulation
Insulation resistance (Mohm•km) between each conductor and other earthed wires at temperarure t = 20°C is no less than	10 000	10 000	10 000
Mutual capacitance (nF/km) between conductors of the basic circuit and other earthed wires is no more than	27 ± 1.1	24.5 0.8	34.5 0.5
Resistance of circuit (Ohm/km) with d0 = 1.2 mm at t = 20°C is no more than
Ohmic disbalance per l­fl is no more than	0.2	0.2	0.2
Insulating strength (V) between a cable core and earthed covering or shield is no less than
electric strength (V) between threads a and b respectivelyjoined to bundles is no less than

 

Laboratory work 2