Breaker Gas (SF6) Analysis

After performing a BGA® test on your SF₆ breaker, you will receive a condition rating. The recommended sampling interval ranges from ‘immediately’ to ‘24 months’, depending on the condition of your unit. Please refer to the scoring methodology or reach out to TJ|H2b for further explanation on recommended intervals.

BGA® condition codes, in general, indicate the following+:

• Code 1: All parameters within acceptable limits. Retest within 24 months.
• Code 2: Onset of fault activity, component wear, or gas degradation is evident. Retest within 6 months.
• Code 3: Substantial development of fault, component wear, and/or deteriorating gas quality. Retest within 3 months.
• Code 4: Serious fault activity, component wear, and/or very poor gas quality. Further investigative action required. Retest within 14 days.
• Code 4*: Urgent action required. Retest immediately. Subject to confirmation via repeat sample, an internal inspection may be required, proceed immediately and with caution.

+Some variations of the recommended mitigations or retest intervals may occur at the discretion of the laboratory based on information provided. With breakers, we are dealing with a complex subject involving a number of variables. As such, general “rules of thumb” with regard to sampling intervals cannot be applied in every case. A number of other factors must be taken into consideration, such as:

• Service history 
• Maintenance history
• Model type
• Age
• Criticality

As such, the appropriate action is up to the discretion of the Asset Manager who is best placed to take other influencing factors into account according to established internal procedures. Our codes and recommendations, while based on a vast amount of experience as well as guidelines published by IEEE and other standards bodies, are to be taken only as useful guides.

Breaker Gas Analysis (BGA®) includes a condition rating, diagnostics, and potential remediation actions where applicable. Upon receipt of the report from TJ|H2b, we recommend that results and diagnostics are reviewed promptly, following internal procedures. If further support is needed, TJ|H2b offers free, 24/7 consultation services to help you understand reports and provide guidance.

Obtaining a representative sample is essential for any analytical testing process to yield meaningful results. In SF₆ analysis, contamination of the sample with air and moisture or corruption of the sample by reactions with sampling equipment are critical issues. Special sampling equipment and procedures have been developed to address these issues. The containers are fabricated from stainless steel because of its chemical inertness to SF₆ decomposition products (Gas Sampling Collection Unit). These containers are dried and evacuated before being sent into the field. Special fittings are used for each type of equipment.

In the absence of an electrical discharge or extreme heat (>500°C), SF₆ is chemically inert. When a discharge occurs, fluorine atoms on the SF₆ may capture an electron and dissociate from the sulfur. When the discharge has ended, under ideal circumstances, each dissociated fluorine loses the captured electron and recombines with a dissociated SFx species to reform SF₆ (Figure 1). This is the ‘self-healing’ or regenerative property of SF₆. Regardless of circumstances, this is the predominate reaction occurring in SF₆ filled high voltage electrical equipment. A discharge does not result in each SF₆ in the discharge path being completely dissociated. Instead, a distribution of dissociation products is formed that looks something like the distribution shown in Figure 2. The amplitude of the distribution is determined by the duration of the discharge and the composition of the distribution is determined by the energy of the discharge. Discharge durations and energies can vary considerably (Figure 3).

For more details, please see: Using sf6 analysis for condition based maintenance of circuit breakers and gas insulated substations.

The circuit breaker in Case 1 is a 161 kV, 2000 amp, SF₆ single pressure, live tank unit with a true spring operating mechanism. The breaker is operated 2 to 3 times per day to connect a 168 MVAR capacitor bank. On September 20, 1997, a remote dispatcher operated the breaker. Pole 2 failed to clear, resulting in operation of the overcurrent and breaker failure relay. The operation of these relays isolated the bus section that feeds the circuit breaker. After the clearance, the dispatcher was able to remotely energize the bus section. This failure did not result in a rupture of the interrupter.

For details about the four case studies, please see: Using SF₆ analysis for condition based maintenance of circuit breakers and gas insulated substations.