BS 5099:1992 download free.pecification for Spark testing of electric cables.
1 Scope
BS 5099 specifies requirements and test methods for a.c., d.c., high frequency and pulsed wave-form spark testing of the insulation and sheath of electric cables, but does not apply to telecommunication cables. The use of high frequency and pulsed wave-form testers is limited to cables rated less than 0.6/1 kV, unless referred to in the cable specification.
2 References
2.1 Normative references
BS 5099 incorporates, by reference, provisions from specific editions of other publications. These normative references are cited at the appropriate points in the text and the publications are listed on the inside back cover. Subsequent amendments to, or revisions of, any of these publications apply to this standard only when incorporated in it by updating or revision.
2.2 Informative references
BS 5099 refers to other publications that provide information or guidance. Editions of these publications current at the time of issue of this standard are listed on the inside back cover, but reference should be made to the latest editions.
3 Application
The spark test which is specified in this standard shall be applied at the stages of manufacture indicated by the cable specification.
NOTE 1 The test clauses of the appropriate cable specifications give details of the component. to which spark testing is applicable. NOTE 2 For guidance on the use of spark testing machines, see Annex A.
NOTE 3 For each type of spark test equipment, the ability to detect spark faults in lengths of insulated core may be confirmed by carrying out the procedures in Annex C.
4 High voltage source
4.1 General
To avoid the risk of electrical shock to personnel, for all types of voltage source the output shall be limited to less than 10 mA r.m.s. or equivalent. The high voltage source shall be supplied in one of the following forms.
a) Alternating current of approximately sine wave-form at a frequency of 40 Hz to 62 Hz.
b) Direct current with the positive pole earthed and the negative pole connected to the test electrode by means of a low capacitance unscreened lead,
The peak to peak value of ripple on the d.c. output voltage shall not exceed 5 % of the d.c. voltage.
c) High frequency current of aroximately sine wave-form at a frequency of 10 Hz to 106 Hz.
d) Impulsed current generated from a voltage wave-form consisting of a sharp rise pulse followed by a highly damped wave train.
The sharp rise of the impulse wave front shall reach 90 % of the specified peak value in less than 10 s and shall reach peak value in less than 20 ps. Fluctuations of the actual peak value, due to variations of input power into the generator, shall not exceed ± 2 % of the specified peak value. The peak value shall not show more than 5 % reduction in the event of an increase of capacitance load of 50 pF, during the operation, from an initial load of 25 pF between electrode and instrument ground. The pulse duration, including the damped portion of the wave, shall be between 40 ts and 50 us. The pulse repetition rate of the electrode shall be a minimum of 170 pulses per second and a maximum of 500 pulses per second. Visible or audible corona shall be evident in the electrode structure when operating at the specified voltage.
4.2 Voltage monitoring equipment
4.2.1 For a.c., d.c. and high frequency sources the electrode to earth potential difference shall be displayed on a meter either by connection direct to the output terminals of the high voltage source or by any suitable arrangement which gives a result ± 5 % of the direct reading. The meter shall be calibrated to read d.c. or a.c. (r.m.s.) as appropriate and shall conform to a standard not lower than that specified for class 1 instruments in BS 89-1:1990 and BS 89-2:1990.
4.2.2 For an impulse source there shall be a peak reading instrument voltmeter connected directly to the electrode head, indicating continually the potential of the electrode with or without a grounded test wire in the chamber. The peak reading voltmeter shall show full deflection at a peak value not exceeding 25 kV and shall have an accuracy of ± 3 % of the specified operating value. This meter shall be capable of maintaining this accuracy for an adequate period, and the calibration frequency set accordingly.
The impulse test equipment shall be calibrated by means of a peak detecting electronic voltmeter connected directly between the electrode head and ground. The impulse generator shall be energized and the voltage control of the impulse generator shall be adjusted until the reading on the calibration voltmeter is the specified potential, at which point the reading on the instrument voltmeter shall be observed and recorded; this calibration shall be repeated at each specified peak potential. The pulse wave-form shall he monitored by means of an oscilloscope connected to the electrode head at suitable test points.
NOTE Calibration may be accomplished without a test wire in the electrode head, in which case the voltage control on the impulse generator may require a different setting for each cable size in order to give the desired reading on the instrument voltmeter; or the calibration may be made with a load of 20 pF to 60 pF. The equipment may also be calibrated against an oscilloscope with a calibrated and compensated attenuator. The chosen method should have an accuracy of * 2 %.
5 Test voltage
5.1 Contact electrode
5.1.1 General
The high voltage supply to the test electrode shall be either alternating current, direct current, high frequency current or impulsed current as specified in 4.1.
For all types of testing, the conductor of the core under test, or the conductor, metallic sheath, screen or armour underlying the non-metallic sheath to be tested, shall be continuously earthed.
5.1.2 Insulation
Spark test voltage values given by the potential difference between the test electrode and the conductor of the core or cable under test shall be the values given in Table 1 unless otherwise specified in the cable standard.
5.1.3 Insulation/sheath
When spark testing of a combination of insulationlsheath is specified in the relevant cable standard, it shall be carried out using one of the voltage sources specified in 4.1 at the appropriate voltage given as follows:
a) a.c.: at 6 kV per millimetre of the combined tabulated radial thickness of insulation and sheath, up to a maximum voltage of 25 kV;
b) d.c. and impulse: at 9 kV per millimetre of the combined tabulated radial thickness of insulation and sheath, up to a maximum voltage of 38 kV for d.c. and 23 kV for impulse;
c) h.f.: at 7 kV per millimetre of the combined tabulated radial thickness of insulation and sheath, up to a maximum voltage of 14 kV.
5.1.4 Sheath
When spark testing of sheath of thickness greater than 0.5 mm is specified in the relevant cable standard it shall be carried out using one of the voltage sources specified in 4.1 at the appropriate voltage given as follows:
a) a.c.: at 6 kV per millimetre of tabulated radial thickness of sheath, up to a maximum voltage of 25 kV;
b) d.c. and impulse: at 9 kV per millimetre of tabulated radial thickness of sheath, up to a maximum voltage of 38 kV for d.c. and 23 kV for impulse;
c) h.f.: at 7 kV per millimetre of tabulated radial thickness of sheath, up to a maximum voltage of 10.5 kV.
7 Fault indicator
There shall be a failure detection circuit to give a visible or audible indication of insulation/sheath failure. The fault detector shall be arranged to operate a digital display counter such that one count per discrete fault is registered. The counter shall maintain the indication until either the next succeeding fault is registered or until the indication is manually cancelled.
8 Sensitivity
8.1 A.C., h.f. and d.c. electrode supply The sensitivity of the spark testing apparatus shall be such that the detector will operate when an artificial fault device, described in Annex B, is connected between the electrode and earth. The methods for assessing the sensitivity apply for a.c. and h.f. as specified in B.1 and for d.c. as specified in B.2.
8.2 Impulse wave-form electrode supply The detection circuit shall be sufficiently sensitive to indicate a fault when the electrode is arced to ground through a 0.5 M1 resistor and shall be capable of detecting a fault which lasts for the duration of only one impulse.
9 Calibration frequency
NOTE The efficacy test referred to in note 3 of clause 3 should be carried out upon initial installation of the equipment or upon any extension to the range of core or cable to be tested (see C.2.1).
9.1 The voltage calibration specified in 4.2.1 and 4.2.2 shall be carried out at least once a year, and after any repairs or major adjustments to the equipment.
9.2 The sensitivity test specified in clause 8 shall be carried out at least once a year, and after any repairs or major adjustments to the equipment.