NB/T 42099-2024Guide to the synthetic testing of high-voltage alternating current circuit-breakers (English PDF)

Foreword

This document was issued on 24 May 2024 by the National Energy Administration of the PRC and takes effect on 24 November 2024.

It is a NB/T standard: recommended rather than compulsory, but it is the text a Chinese reviewer applies when assessing a submission.

It is classified under ICS 19.020, Chinese classification K 40.

It replaces NB/T 42099-2016, which is superseded.

This document was drafted in accordance with the rules given in GB/T 1.1-2020 Directives for standardization - Part 1: Rules for the structure and drafting of standardizing documents.

This document replaces NB/T 42099-2016 Guide to the synthetic testing of high-voltage alternating current circuit-breakers. Compared with NB/T 42099-2016, apart from structural adjustments and editorial changes, the main technical changes are as follows:

a) a requirement has been added for the initial instantaneous value of the power-frequency recovery voltage of the second and third breaking poles in the three-phase symmetrical current breaking test of the high-voltage stage, see 5.1;

b) Figure 9 has been modified and the requirements for the unit test have been modified, see 7.1 and 6.1 of the 2016 edition;

c) an explanation has been added of the additional test requirements and their implementation for circuit-breakers in medium-arcing and/or long-arcing tests, see 7.4;

d) the required values of the parameters of the last half-wave of current in the T100a test have been modified, see 7.6 and 6.6 of the 2016 edition;

e) a new Annex A has been added, giving the additional test procedure for abnormal breaking in three-phase synthetic tests, see Annex A;

f) Figures B.3 and B.4 have been added, giving examples of test circuits for capacitive current switching, and Annex C has been merged into Annex B, see Annex B and Annexes B and C of the 2016 edition;

g) the former Annex B, Conversion values of TRV and di/dt for test duty T100a, has been deleted, see Annex B of the 2016 edition.

Please note that some of the content of this document may be the subject of patent rights. The issuing body of this document assumes no responsibility for identifying patents.

This document was proposed by the China Electrical Equipment Industry Association.

This document is under the administration of the Standardization Technical Committee on Short-circuit Testing Technology of the Energy Industry (NEA/TC 10).

The versions of this document and of the document it replaces are as follows: first issued in 2016 as NB/T 42099-2016; this is the first revision.

1 Scope

NB/T 42099-2024 is the Chinese energy sector guide to synthetic testing of high-voltage alternating current circuit-breakers. It exists because of an arithmetic problem that no laboratory in the world can spend its way out of. To prove that a 550 kV breaker can interrupt a short circuit, the test has to impose the full fault current and then, microseconds after the arc goes out, the full recovery voltage across the contacts; a direct test would need a source of tens of gigavolt-amperes, which no test station has and no utility would build. The synthetic method separates the two demands: one circuit supplies the current while the arc burns, a second injects the voltage the moment the current passes through zero, and the breaker experiences something electrically equivalent to the real fault. That equivalence is exactly where the argument lies, because a synthetic test that is set up slightly differently is a different test, and a breaker certified on a lenient interpretation is a breaker that may not clear the fault it was bought for. This document is the interpretation that removes the ambiguity: it explains the technical requirements of GB/T 4473-2018 so that they are read consistently alongside GB/T 1984-2014, and it unifies the test and measurement methods so that reports issued by different laboratories mean the same thing. It covers the high-voltage stage and the current injection method for breaking tests, including the initial instantaneous values of the power-frequency recovery voltage for each breaking pole at first-pole-to-clear factors of 1.5, 1.3 and 1.2; the circuits for short-circuit making tests; and the special requirements attached to clauses 6.102 to 6.111 of GB/T 1984-2014, covering unit tests, multipart tests, T100s with a substitute operating mechanism, the setting and validation of arcing time, test duties T100s and T100a with the tabulated parameters of the last half-wave of current, short-line fault, out-of-phase and capacitive current switching tests. Two informative annexes give the additional procedure for abnormal breaking in three-phase synthetic tests and the synthetic test method for capacitive current switching. It was issued on 24 May 2024 by the National Energy Administration, took effect on 24 November 2024, and replaces NB/T 42099-2016.

This document specifies the procedure by which a laboratory tests high-voltage alternating current circuit-breakers in accordance with GB/T 4473-2018.

This document applies to the synthetic testing of high-voltage alternating current circuit-breakers under short-circuit and switching conditions according to the test methods given in GB/T 4473-2018, and to the issuing of a type test report.

This document is an interpretation of the technical requirements of GB/T 4473-2018, intended to ensure a consistent interpretation when GB/T 4473-2018 and GB/T 1984-2014 are used together, and to unify the test methods and the measurement methods.

2 Normative references

The contents of the following documents constitute indispensable provisions of this document through normative reference in the text. For dated references, only the edition corresponding to that date applies to this document. For undated references, the latest edition, including all amendments, applies to this document.

GB/T 4473-2018 Synthetic testing of high-voltage alternating current circuit-breakers

GB/T 1984-2014 High-voltage alternating current circuit-breakers

NB/T 42101 General guide to type tests and type test reports for high-voltage switchgear

3 Terms and definitions

No terms and definitions need to be defined in this document.

4 Type test certification procedure

When a circuit-breaker is tested using synthetic test techniques in accordance with GB/T 4473-2018 and with this document, a type test report may be issued in accordance with NB/T 42101 only if the provisions of the corresponding test of GB/T 1984-2014 are complied with at the same time.

5 Synthetic test techniques and methods for short-circuit breaking tests

5.1 High-voltage stage

If, because of a recovery voltage that is direct or a combination of alternating and direct (see Figure 2 of GB/T 4473-2018), a breakdown occurs after one eighth of a cycle following the current zero, the test may be repeated using a recovery voltage at rated frequency, either alternating or a combination of alternating and direct. In the repeated test the requirements relating to the TRV may be disregarded.

In a three-phase symmetrical current breaking test, apart from the first pole to clear, the other two phases do not extinguish the arc at the peak of the power-frequency voltage; the correction factor for the transient recovery voltage (TRV) therefore has to be adjusted, while the power-frequency recovery voltage does not need to be corrected.

Table 1 gives the initial instantaneous values of the power-frequency recovery voltage of the different breaking poles when the test is carried out.

Table 1 - Initial instantaneous value of the power-frequency recovery voltage of the different breaking poles

First-pole-to-clear factor kpp = 1.5: first pole to clear, 1.5 ur x root 2 / root 3; later poles, ur x root 2 / root 3.

First-pole-to-clear factor kpp = 1.3: first pole to clear, 1.3 ur x root 2 / root 3; third breaking pole, ur x root 2 / root 3; second breaking pole, 1.26 ur x root 2 / root 3.

First-pole-to-clear factor kpp = 1.2: first pole to clear, 1.2 ur x root 2 / root 3; third breaking pole, ur x root 2 / root 3; second breaking pole, 1.14 ur x root 2 / root 3.

In a three-phase breaking test with kpp = 1.5, if an abnormal breaking such as that shown in Figure A.2 is encountered, the additional test procedure described in Annex A may be used to verify it; if the circuit-breaker under test passes the additional verification test, the test is considered to have been passed.

5.2 Current injection method

The test circuits given in Figure 1 and Figure 2 cannot be used for short-line fault tests or for T100s(b) and T100a tests carrying ITRV requirements.

5.3 Other synthetic test methods

Examples of test circuits for short-circuit breaking tests are given in Figure 1 and Figure 2.

Figure 1 - Example one of a test circuit and waveforms using two voltage circuits in a breaking test.

6 Synthetic test techniques and methods for short-circuit making tests

6.1 General

The synthetic test techniques and methods used for short-circuit making tests are given below, together with examples of the corresponding test circuits.

6.2 Examples of test circuits

Figure 8 - Test circuit for short-circuit making and out-of-phase making tests: circuit in which two transformer voltage sources are applied separately to the two ends of the test object.

Key to Figure 8: St, circuit-breaker under test; CH1 and CH2, making devices; Sa1 and Sa2, auxiliary circuit-breakers; ut, test voltage; uc1, voltage of the first voltage circuit; uc2, voltage of the second voltage circuit; ucs, voltage of the current circuit; it, current flowing through St; L1 and L2, inductance of the current circuit; Tr, transformer.

Figure 9 - Test circuit for verifying the insulation performance to earth of the enclosure in a short-circuit breaking test of a dead-tank circuit-breaker.

Key to Figure 9: St, circuit-breaker under test; Cv1 and Cv2, charging capacitors; Sa, auxiliary circuit-breaker; Ch1 and Ch2, TRV adjusting capacitors; ucs, voltage of the current circuit; it, current flowing through St; uh1, charging voltage of the first voltage circuit; uh2, charging voltage of the second voltage circuit; SP, triggered gap; L, inductance of the current circuit; Lh1, inductance of the first voltage circuit; Lh2, inductance of the second voltage circuit.

7 Special requirements for synthetic tests of making and breaking performance

7.1 Unit test

In a unit test, if a unit that is not under test acts as an auxiliary circuit-breaker, that unit is considered not to be part of the test object; if the unit not under test fails to break during the test, this shall not be regarded as a breaking failure of the test object.

In a unit test of a GIS or of a dead-tank circuit-breaker, because the insulation performance to earth is not adequately assessed, it is necessary to demonstrate in the short-circuit breaking test that the insulation performance to earth can withstand the full voltage; Figure 9 gives an example of such a test circuit.

7.2 Multipart test

For extra-high-voltage and ultra-high-voltage circuit-breakers the time t2 is normally rather long. This document specifies a lower limit of 250 Hz for the injected current frequency, so obtaining the value of t2 in a test using a current injection circuit may be difficult.

When the thermal performance has to be verified, a current injection test circuit should be used for the first part of the test, that is the current zero and the first part of the TRV; a voltage injection test circuit may then be used for the second part.

7.3 T100s test with a substitute operating mechanism

Item 6.102.7 b) of GB/T 1984-2014 requires test duty T100s to be carried out both on circuit-breakers that have passed the complete type test verification and on circuit-breakers fitted with a substitute operating mechanism. In accordance with Annex N of GB/T 1984-2014, the mechanical travel characteristics in the breaking test with the longest arcing time have to be compared with the characteristics in the corresponding test of the circuit-breaker that passed the complete type test verification.

In the case of a three-phase common-enclosure GIS circuit-breaker, a three-phase synthetic test circuit shall be used for the test, and the TRV shall be applied to all three phases.

7.4 Explanation of the arcing time

In the test sequences Od-t-(Cd)Os or Od-t-CsOs given in Table 4 of GB/T 4473-2018, the arcing time of Od shall be set during the test using the minimum arcing time determined by the step-by-step method.

If the arcing time actually obtained in the Od operation is within plus or minus 2 ms of the minimum arcing time already determined, the test is valid.

If the circuit-breaker fails to break at the expected current zero in a medium-arcing and/or long-arcing test but breaks at the zero of the following half-wave of current, no other additional test is required. For example, if breaking fails in the long-arcing test, an additional test shall be carried out taking T/2 added to the long arcing time as the new long arcing time; if the circuit-breaker breaks in that additional test, no other additional test is required.

7.5 Test duty T100s

For the making operation Cs sym, in a single-phase test the test is valid if the current starts within plus or minus 15 degrees of the peak of the applied voltage. The actual peak of the first half-wave of current shall be not less than 0.74 per unit and not more than 1.26 per unit. These values are calculated on the basis of a making phase angle of plus or minus 15 degrees and a time constant greater than 45 ms. If the current starts earlier, between minus 30 and minus 15 degrees from the peak of the applied voltage, and the actual peak thereby reaches 1.5 per unit, the test is more severe than required; if the circuit-breaker passes the test, the test is valid.

7.6 Test duty T100a

The parameters of the last half-wave of current in the three-phase test are given in Table 2 and Table 3.

Table 2 - Parameters of the last half-wave of current at 50 Hz, for three-phase conditions with the first pole to clear in phase A and the required asymmetry in phase C. The table gives, for time constants of 45 ms, 60 ms and 75 ms and for ranges of minimum breaking time, the required values of the peak current, of the interval delta t and of di/dt for phases A, B and C, at first-pole-to-clear factors of 1.5 and 1.3. For a time constant of 45 ms and a minimum breaking time between 10.0 ms and 27.0 ms at kpp = 1.5, the peak current is 1.24 in phase A, 1.24 in phase B and 1.52 in phase C, delta t is 11.6, 10.6 and 15.0 ms respectively, and di/dt is 99.2, 82.2 and 82.2 respectively.