1. IEC Short-circuit current making and breaking tests Taiwan-European HVAC apparatuses Accreditation and Certification forum
Harethe El Ouadhane
IEC Expert: Member of MT14 of IEC
Testing, design & calculation / MVSG & MVCB
Expert for internal arc, making, breaking and STC

2. Content Requirements of IEC 62271-100 Basic short-circuit test duties
Single-phase fault tests
Double-earth fault tests
Technology of vacuum interrupters
Extension of the validity of test results and derivations
Conclusion

3. 1. Requirements of IEC
Mandatory Test Circuit-breakers shall be capable of making and breaking all short-circuit currents, symmetrical and asymmetrical, up to and including the rated short- circuit breaking currents: This is demonstrated, when the circuit-breakers make and break the specified three-phase symmetrical and asymmetrical currents between 10% (T10) and 100% (T100) of the rated short-circuit breaking current at rated voltage.
In addition Circuit-breakers shall be capable of clearing single-phase short-circuit currents which may occur in two different cases: – in effectively earthed neutral systems in case of single-phase faults or, – in non-effectively earthed neutral systems in case of double earth faults, i.e. earth faults on two different phases, one of which occurs on one side of the circuit-breaker and the other one on the other side.

4. 2. Basic short-circuit test duties
Number of test specimen a unique test specimen should be used. Where required, maintenance is allowed and should be performed as permitted, between each individual test- duty in the case of short-circuit tests The manufacturer shall provide a statement to the testing laboratory of those parts that may be renewed during the tests.
No-load test Before commencing making and breaking tests, no-load operations and no- load operating sequences (O, CO and O – t – CO) shall be made and details of the operating characteristics of the circuit-breaker recorded. Details such as closing time and opening time shall be recorded.

5. 2. Basic short-circuit test duties
Behavior of circuit-breaker during tests During making and breaking tests, the circuit-breaker shall not – show signs of distress; – show harmful interaction between poles and to earth; – show harmful interaction with adjacent laboratory equipment; – exhibit behavior which could endanger an operator. NSDDs may occur during the recovery voltage period following a breaking operation
Condition after a short-circuit test-duty After each short-circuit test-duty, the circuit-breaker shall be capable of making and breaking its rated normal current at the rated voltage, although its short-circuit making and breaking performance may be impaired.

6. 2. Basic short-circuit test duties
Frequency Circuit-breakers shall be tested at rated frequency with a tolerance of ±8 %. However, for convenience of testing, some deviations from the above tolerance are allowable; for example, when circuit-breakers rated at 50 Hz are tested at 60 Hz and vice versa, care should be exercised in the interpretation of the results, taking into account all significant facts such as the type of the circuit-breaker and the type of test performed.

7. 2. Basic short-circuit test duties
There are several requirements for the test circuit, test parameters and CB
arrangements in order to simulate the possible worst case switching of the
CB in real system.
In general, closing against the highest making current, opening with
various arcing times and recovery voltages, under the unfavourable
mechanical operating conditions.
The main ones are among others related to:
Operating sequence O – CO – CO, with or without auto-reclosing T10, T30, T60, T100s & only O for T100a, SPF & DEF
Factors for recovery voltages; first-pole-to-clear (neutral earthing) and amplitude factor (based on CIGRE), RRRV
Arcing time and arcing window: Depending on the point of mechanical contact separation, interruption with minimum, medium and maximum arcing time

8. 2. Basic short-circuit test duties

9. 2. Basic short-circuit test duties

10. 3. Single-phase tests Mandatory in effectively earth neutral systems.
The main requirements for the test duty are related to:
Breaking of the rated symmetrical short-circuit current with the maximum arcing time and with the recovery voltage based on phase-to-earth voltage
Outer pole under test to simulate the maximum stress in the coupling mechanism

11. 4. Double-earth fault
Mandatory in non-effectively earth neutral systems.
The main requirements for the test duty are related to:
Breaking of the 87% of the rated symmetrical short-circuit current with the maximum arcing time and with the recovery voltage based on phase-to-phase voltage

12. 5. Technology of Vacuum Interrupters
History:
1896: First analysis of electrical field breakdown in vacuum (theoretical 6MV per 1mm)
1930: Quantum mechanics describes the field emission in vacuum
1960: First commercial VI in the market
2012: Over 75% all MV CB uses VI to switch the current
VIs are currently commercially available up to 145kV. Prototypes of multiple switching units at 220kV or higher voltages are under development.
Development of VIs is continuing towards higher voltages and higher short-circuit currents with the employment of advanced arc control systems.

13. 5. Technology of Vacuum Interrupters
Main feature of VI technology:
High number of operations: Up to 100 of rated short-circuit interruptions and up to of rated current interruptions without any maintenance
Compact & Lightweight and High Reliability with extremely low failure rate
Contact materials with low welding tendency and low chopping current
Contact design with arc control for high interrupting capacity and for withstanding fast recovery voltages

14. 6. Extension of the validity of test results
Who? - Manufacturer Experts / Expert teams - Third party Experts
What? - Yes it can be extended / it may be extended - No, it can not be extended
Responsibility only manufacturer
Is not the task of test labs or accreditation institutes

15. 7. Conclusion
The design and technology of high-voltage circuit-breakers is continuously developing and will continue also in the future.
Type tests qualify the type of product series while the routine tests ensure that the manufactured series are always in accordance with the type tested sample
Circuit-breakers qualified according to the IEC are best suited for switching of short-circuit currents. They are able to switch currents with high asymmetry and fast rising TRVs without any maintenance throughout the lifetime
Most of the failures are due to inappropriate human behaviors either during the project management phase (wrong product definition) or during operations (installation, operation, maintenance, etc.)
Thus, considering additional regulation should not bring more safety.
On the other side deregulating a proven standard will reduce the safety level

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