IEC 60071-1-2019 pdf download.Insulation co-ordination — Part 1: Definitions, principles and rules
Coordination de I’isolement — Partie 1: Definitions, principes et règles.
In all the test procedures described above no disruptive discharge is tolerated on the non- self-restoring insulation. In the case of a fifteen-impulse withstand voltage test performed on equipment where both self-restoring and non-self-restoring insulations are involved, the IEC 60060-1 fifteen-impulse withstand voltage test procedure is adapted and used to verify that no disruptive discharge occurs in the non-self-restoring insulation, This two out of fifteen- impulse withstand voltage test adapted procedure is the following for each polarity: It could be taken as an indication that no failure has happened in the non-self-restoring insulation, when the last three impulses have not led to a disruptive discharge. In case of a disruptive discharge at one of the impulse numbers 13 to 15, up to three additional pulses can be applied (maximum 18). When no further disruptive discharge occurs, the test object has passed the test, if not otherwise specified by the relevant technical committee.
No statistical meaning can be given to the three-impulse withstand voltage test in which no disruptive discharge is tolerated (P is assumed to be 100 %). Its use is limited to cases in which the non-self-restoring insulation may be damaged by a large number of voltage applications.
When selecting a test for equipment in which non-self-restoring insulation is in parallel with self-restoring insulation, serious consideration should be given to the fact that In some test procedures voltages higher than the rated withstand voltage may be applied and many disruptive discharges may occur.
6.4 Alternative test situation
When it is too expensive or too difficult or even impossible, to perform the withstand voltage tests in standard test situations, the apparatus committees, or technical committee 42, shall specify the best solution to prove the relevant standard rated withstand voltages. One possibility Is to perform the test in an alternative test situation.
An alternative test situation consists of one or more different test conditions (test arrangements, values or types of test voltages, etc.). It is necessary, therefore, to demonstrate that the physical conditions for the disruptive discharge development, relevant to the standard situation, are not changed.
A typical example is the use of a single voltage source for the tests of longitudinal insulation, while insulating the base, instead of a combined voltage test. In this case, the demonstration mentioned above concerning the disruptive discharge development is a very stringent condition for the acceptance of the alternative.
6.5 Phase-to-phase and longitudinal insulation standard withstand voltage tests for equipment In range I
6.5.1 Power-frequency tests
For some equipment with 123 kV ≤ Urn ≤ 245 kV, the phase-to-phase (or longitudinal) insulation may require a power-frequency withstand voltage higher than the phase-to-earth power-frequency withstand voltage as shown in Table 2. In such cases the test shall be preferably performed with two voltage sources. One terminal shall be energized with the phase-to-earth power-frequency withstand voltage and the other with the difference between the phase-to-phase (or longitudinal) and the phase-to-earth power-frequency withstand voltages. The earth terminal shall be earthed.
Alternatively, the test may be performed:
— with two equal power-frequency voltage sources in phase opposition, each energizing one phase terminal with half of the phase-to-phase (or longitudinal) insulation power-frequency withstand voltage. The earth terminal shall be earthed;
— with one power-frequency voltage source. The earth terminal may be allowed to assume a voltage to earth sufficient to avoid disruptive discharges to earth or to the earth terminal.
NOTE It. during the test, the terminal earthed in service is carried to a voltage which influences the electrical stresses on the phase terminal (as occurs in compressed gas longitudinal Insulation having 11m 72,5 liv), means will then be adopted to maintain this voltage as close as possible to the difference between the test voltage of the phase-to-phase (or longitudinal) insulation and that of the phase-to-earth insulation.
6.5.2 Phase-to-phase (or longitudinal) insulation lightning Impulse tests
The phase-to-phase (or longitudinal) insulation may require a lightning impulse withstand voltage higher than the standard phase-to-earth withstand voltage as shown in Table 2. In such cases, the relevant tests shall be performed immediately after the phase-to-earth insulation tests increasing the voltage without changing the test arrangement. In evaluating the test results, the impulses leading to disruptive discharge to earth are considered as non- events.
IEC 60071-1-2019 pdf download.Insulation co-ordination