Lifetime Management of FACTS Controllers

Abstract

A FACTS Controller is an important part of an integrated AC network. It is important that it continues to operate at high reliability and availability. This chapter provides information on operating and maintaining the equipment throughout its lifetime to achieve the required performance. Maintenance management philosophies are introduced. A brief description of maintenance tasks relating to specialized equipment used in FACTS controllers is provided. The training requirements for the operating, maintenance, and engineering staff are described. A methodology for measuring the operational performance is outlined. A process for life extension decisions, including spare parts is included.

Appendix

1.1 Calculation of Facts Controller Performance

CIGRE Advisory Group B4-04 has developed a protocol for calculating the performance of FACTS controllers (CIGRE TB 717 2018). The following is the summary of definitions and method of calculating the performance.

1.2 Definitions

1.2.1 Capacity Terms

Rated Capacity (Q_m) – The maximum capacity (+/−MVARS), excluding the added capacity available through means of redundant equipment, for which continuous operation under normal conditions is possible, is referred to as the rated capacity.

The rated capacity is equal to the sum of reactive (inductive and capacitive) ratings of the device.

For a station with more than one FACTS controller, the rating of each device is calculated on its own.

Note: When the maximum continuous capacity varies according to seasonal conditions, the highest value is to be used as the capacity for the purpose of reports prepared according to this protocol. However, this excludes over-load capability available during low-ambient temperature.

Outage Capacity (Q_o) – The capacity reduction (+/−MVARS) which the outage would have caused if the system were operating at its rated capacity (Q_m) at the time of the outage is called the outage capacity.

Outage Derating Factor (ODF) – The ratio of outage capacity to rated capacity is called the outage derating factor.

$$ \mathrm{ODF}={\mathrm{Q}}_{\mathrm{o}}/{\mathrm{Q}}_{\mathrm{m}} $$

Example:

• If the normal rating of an SVC = −60/+150 Mvar.

• Available rating after the forced outage = −40/100 Mvar

• Q_m = 60 + 150 = 210 Mvar

• Q_o = 210 – (40 + 100) = 70 Mvar

• ODF = 70/210 = 0.33

1.2.2 Outage Terms

Outage – The state in which the FACTS controller is unavailable for operation at its maximum continuous capacity due to an event directly related to the failure of one or more of its components. Failure of equipment where a back-up equipment (standby pump, etc.) is available, is not considered as an outage for purposes of this report. Outages related to AC system or failure of other equipment not part of the FACTS controller will be recorded but not included in FACTS controller reliability calculations. For the purpose of this report, outages taken for major reconfiguration or upgrading of the switching FACTS controller such as breaker additions, etc. are not reported.

Scheduled Outage – An outage that is either planned or which can be deferred until a suitable time is referred to as a scheduled outage.

Scheduled outages can be planned well in advance, primarily for preventive maintenance purposes such as the annual maintenance program. During such planned maintenance outage (PM), it is customary to work on several different equipment or systems concurrently. It is not necessary to allocate such outage time to individual equipment categories. Only the elapsed time is reported in Scheduled Outage Unavailability, SOU as “PM”.

Classified under the scheduled outage category are also outages for work which could be postponed until a suitable time (usually night or weekend) but cannot be postponed until the next planned outage. Equipment category code should be used for outages of this type.

Forced Outage – The state in which the equipment is unavailable for normal operation at its rated capacity (Q_m) but is not in the scheduled outage state is referred to as a forced outage.

• Trips – Sudden interruption in reactive power transmission by a protective action or manual emergency shutdown.

• Other Forced Outages – In general, other forced outages are unexpected FACTS controller equipment problems that force immediate reduction in capacity of the FACTS controller but do not cause or require a trip. Also in this category are outages caused by switch-on delays.

1.2.3 Outage Duration Terms

Depending on the design of the FACTS controller, it is possible that the FACTS controller may remain in operation in a de-rated status. The entire duration of the derating is to be reported as a Forced Outage using the ODF.

The outage time should be given in “decimal hours,” i.e., 6 h: 30 min = 6.5 h.

Actual Outage Duration (AOD) – The time elapsed in decimal hours between the start and the end of an outage is the actual outage duration. The start of an outage is typically the first switching action related to the outage. The end of an outage is typically the last switching action related to return of the equipment to operational readiness.

Equivalent Outage Duration (EOD) – The actual outage duration (AOD) in decimal hours, multiplied by the outage derating factor (ODF), so as to take account of partial loss of capacity is called the equivalent outage duration.

$$ \mathrm{EOD}=\mathrm{AOD}\times \mathrm{ODF} $$

Each equivalent outage duration (EOD) may be classified according to the type of outage involved:

• Equivalent forced outage duration (EFOD) and

• Equivalent scheduled outage duration (ESOD).

1.2.4 Time Categories

Period Hours (PH) – The number of calendar hours in the reporting period is referred to as the period hours. In a full year, the period hours are 8760, or 8784, in leap years. If the equipment is commissioned part way through a year, the period hours will be proportionately less.

Actual Outage Hours (AOH) – The sum of actual outage durations within the reporting period is referred to as the actual outage hours.

$$ \mathrm{AOH}=\sum \mathrm{AOD} $$

The actual outage hours (AOH) may be classified according to the type of outage involved:

• Actual forced outage hours (AFOH) and

• Actual scheduled outage hours (ASOH).

  $$ \mathrm{AFOH}=\sum \mathrm{AFOD} $$
  $$ \mathrm{ASOH}=\sum \mathrm{ASOD} $$

Equivalent Outage Hours (EOH) – The sum of equivalent outage durations within the reporting period is referred to as the equivalent outage hours.

$$ \mathrm{EOH}=\sum \mathrm{EOD} $$

The equivalent outage hours (EOH) may be classified according to the type of outage involved:

• Equivalent forced outage hours (EFOH) and

• Equivalent scheduled outage hours (ESOH).

  $$ \mathrm{EFOH}=\sum \mathrm{EFOD} $$
  $$ \mathrm{ESOH}=\sum \mathrm{ESOD} $$

1.2.5 Availability Terms

Outage Unavailability (OU) – A measure of the Mvar capacity of the FACTS Controller that was not available is referred as Outage Unavailability.

$$ \mathrm{Outage}\ \mathrm{Unavailability}\%\mathrm{OU}=\left(\mathrm{EOH}/\mathrm{PH}\right)\times 100 $$

$$ \mathrm{Forced}\ \mathrm{Outage}\ \mathrm{Unavailability}\%\mathrm{FOU}=\left(\mathrm{EFOH}/\mathrm{PH}\right)\times 100 $$

$$ \mathrm{Scheduled}\ \mathrm{Outage}\ \mathrm{Unavailability}\%\mathrm{SOU}=\left(\mathrm{ESOH}/\mathrm{PH}\right)\times 100 $$

Controller Availability (CA) – A measure of equivalent duration for which the FACTS controller was available at rated capacity.

$$ \mathrm{Controller}\ \mathrm{Availability}\%\mathrm{CA}=100\hbox{--} \%\mathrm{OU} $$

1.2.6 Equipment and Fault Category Terms

FACTS controller equipment is classified into major categories for the purpose of reporting the cause of capacity reduction or FACTS controller outages. Failure of the equipment resulting in an outage or loss of FACTS controller capacity is charged to the category to which the failed equipment belongs. Failures or outages of redundant equipment which do not result in a loss of FACTS controller capacity are not reported. The outage may be forced as a direct consequence of the failure or miss-operation, or the outage may be scheduled due to maintenance requirements. Only scheduled outages classified as deferred are categorized according to equipment type. In the interest of providing information which can be used to further describe problem areas and help to improve designs, major categories are divided into subcategories. These subcategories are described in the following subsections. The performance report should utilize these subcategories by appending the respective subcode to the major outage code when maintaining the outage log.

A.C. and Auxiliary Equipment (AC-E) – This major category covers all ac main circuit equipment of the FACTS controller. This includes everything from the incoming ac connection to the ac connection of the FACTS controller. This category also covers low voltage auxiliary power, auxiliary valve cooling equipment, and ac control and protection. This category does not apply to capacity outages resulting from events in the ac network external to the FACTS controller. The following subsections give the different subcategories of equipment included in this category and contain examples of each type of equipment.

• A.C. Filter (AC-E.F) – Loss of FACTS controller capacity due to failure of passive and active ac filters. Types of components included in this subcategory would be capacitors, reactors, resistors, CTs, and arresters which comprise the ac filtering.

• A.C. Control and Protection (AC-E.CP) – Loss of FACTS controller capacity due to failure of ac protections, ac controls, or ac current and voltage transformers is assigned to this subcategory. AC protections or control could be for the main circuit equipment, for the auxiliary power equipment, or for the valve cooling equipment.

• FACTS Controller Interface Transformer (AC-E.TX) – Loss of capacity due to failure of a FACTS controller interface transformer is assigned to this subcategory. Included in this subcategory is any equipment integral with the FACTS controller interface transformer such as tap changers, bushings, or transformer cooling equipment.

• Auxiliary Equipment and Auxiliary Power (AC-E.AX) – Loss of FACTS controller capacity due to failure or misoperation of auxiliary equipment. Such equipment includes auxiliary transformers, pumps, battery chargers, heat exchangers, cooling system process instrumentation, low voltage switchgear, motor control centers, fire protection, and civil works.

• Note: The cooling system for the Thyristor/IGBT valve is not included in this category.

• Other A.C. Switchyard Equipment (AC-E.SW) – Loss of FACTS controller capacity due to failure of ac circuit breakers disconnect switches, isolating switches or grounding switches is assigned to this subcategory. Also included are other ac switchyard equipments such as ac surge arresters, bus-work, or insulators.

Valves (V) – This major category covers all parts of the valve itself. The valve is the complete operative array forming an arm, or part of an arm of the FACTS controller. It includes all auxiliaries and components integral with the valve and forming part of the operative array. The valve category is divided into four subcategories.

• Valve Electrical (V.E) – Loss of FACTS controller capacity due to any failure of the valve except for those related to that part of the valve cooling system integral with the valve is assigned to this subcategory.

• Valve Cooling (V.VC) – Loss of FACTS controller capacity due to any failure of the valve related to that part of the valve cooling system at high potential integral with the valve is assigned to this subcategory.

• Valve Capacitor (V.C) – Loss of STATCOM controller capacity due to failure of either the main valve capacitor or any subcomponent of the capacitor where the capacitor is not a single element.

• Phase Reactor (V.PR) – Loss of FACTS controller capacity due to failure of the phase reactor.

Control and Protection Equipment (C-P) – This major category covers the equipment used for control of the overall FACTS controller system and for the control and protection of each Thyristor Switched Capacitor (TSC), Thyristor Controlled Reactor (TCR), Thyristor Controlled Series Capacitor, Voltage Sourced Capacitor, and STATCOM excluding control and protection of a conventional type which is included in “a.c. and auxiliary equipment.”

The equipment provided for the coding of control and indication information to be sent over a telecommunication circuit and the circuit itself is included.

Capacitor Banks (C) – This category covers fixed capacitors and thyristor switched capacitors. The capacitors related to STATCOM or Voltage Sourced Converters are not included in this category.

• Fixed Capacitor (C.F) – Loss of FACTS controller capacity due to failure of any fixed capacitor or any sub component of the capacitor where the capacitor is not a single element.

• Thyristor Switched Capacitor (C.S) – Loss of controller capacity due to failure of any thyristor switched capacitor or any sub component of that capacitor where the capacitor is not a single element.

Reactors (R) – This category covers fixed reactors and thyristor controlled reactors. The phase reactors related to STATCOM are not included in this category.

• Fixed Reactor (R.F) – Loss of FACTS controller capacity due to failure of any fixed reactor or any subcomponent of the reactor where the reactor is not a single element.

• Thyristor Controlled Reactor (R.S) – Loss of FACTS controller capacity due to failure of any thyristor controlled reactor or any subcomponent of that reactor where the reactor is not a single element.

Human Error (H) – Loss of FACT controller capacity or extension of outage duration due to human error is assigned to this category. If, after an outage due to an event in another category, the outage duration is extended due to human error in maintenance or operation, the consequential extension in outage time is charged to this category.

Other (O) – Loss of FACT controller capacity or extension of outage duration due to unknown causes is assigned to this category.

Outages due to act of nature (storm, flood, etc.), small animals, and bird nesting are also included in this category.

External AC System (EXT) – Loss of FACTS controller capacity due to faults or events in the ac network external to the FACTS controller is charged to this category.

Note: The outages due to this category are not included in the calculation of forced outage unavailability.