Classification of faults and damages in power cables

10.02.2016

Depending on specific damages and faults, all power cables can be divided into two main groups: with sheath (shielding) (usually grounded at both ends) and without it.

Cables with shielding may or may not have an extra metal armor in the form of a spiral steel tape, which protects the cable from mechanical damages. These cables called armored.

The most common fault (and hardest to define) is a type of spark breakdown damage or short-circuit of one core to sheath. Such damage called single-phase damage.

Breakdown or short circuit between the two conductors is the rarest. Such damage called two-phase damage.

Single-phase cable fault is very common and, in most cases, occurs when cable loaded or during cable testing.

Fault point (FP) is characterized by a certain resistance (Rfp) and breakdown voltage (Ufp.). Depending on the ratio of Rfp. and Ufp., conventionally, this kind of fault can be divided into three types:

a) Rfp. = 0 - 1 Ohm; Ufp = 0-10 V.

In this case, the FP has "reliable" electrical contact between core and sheath, and therefore there is no spark.

Such damage called the solid single-phase short-circuit of cable conductor to its sheath (SSC).

b) Rfp 10-100000 Ohms; Ufp = 1-10 kV.

Only one core of cable damaged, and two others withstand the test voltage. FP is characterized by significant leakage currents (milliamps), but the voltage can be raised within the range 1-10kV, while the FP sparks or arcing. This type of damage called "single-phase leakage".

c) Rfp = 1-100 MOhm; Ufp = 10-50 kV.

In this case, almost no current leakage, but above a certain voltage cable breakdowns with a spark in a fault point.

This type of damage called "intermittent breakdown"

Thus, a common feature of the single-phase leakage and intermittent breakdown is the presence of a spark in a fault point during the presence of voltage in cable, and the sound of the spark. Both of these cases can be grouped under the title "sparked single-phase breakdown".