Preventive maintenance of power plants, GIS substation bushings, and insulators

This article aims to bring your attention to the importance of preventive maintenance of polluted Power Plant GIS Substation bushings/insulators.

The user resolves the maintenance issues with cold washing/cleaning maintenance works, requiring a few days of power outage, typically one bay/circuit at a time.

Fog, mist, humidity, or light rain usually formulate conditions that produce a conducting film on the dirty insulator surface without washing the impurities from the surface.

When the polluted insulators become wet, a conductive layer is formed on the contaminated insulator surface, initiating current leakage.

Outdoor bushings/insulators are subjected to surface dirt deposits to some degree, and in all the operational areas.

To prevent ‘power outages’ when a contaminant related failure takes out a line, rather than running the risk of having multiple flashovers, repeated relay operations that are hard on the circuit breakers and substation equipment.

We recommend installation of a hotline insulator’s AUTOMATED washing system (AWS-PP) so as to increase power supply reliability towards achieving uninterrupted performance and higher productivity, and financial efficiency, among the other key significant factors.  

However, outdoor bushings/insulators are subject to surface dirt deposits to some degree and in all operational areas. Most encountered contaminants in the course, have a minimal effect on insulator’s performance if the surface is dry. 

These pollutants gradually build up on the insulators but they don’t decrease the insulation strength while the insulators are dry. 

Power plants installed in coastal and inland T&D power grids with climatic areas are subject to dry weather periods, followed by fog, mist, light rains. The surface of polluted insulators becomes wet in the proximity of contaminants sources like coal, cement factories, industrial/agricultural, dust, cooling tower effluent pollutants, among the others.  

A conductive layer forms a current leakage, which will ultimately cause a flashover; and in most cases, several arcing periods may precede an actual flashover.

Fog, mist, or light rain create circumstances that cause a conducting coating to form on the filthy insulator surface if impurities are not removed from the surface.

To solve or contain such pollution side effects, the users start installing the composite and polymer insulators. These equipment (Composite and Polymer bushings/insulators) are sold emphasising hydrophobicity as one of the main features, and claimed that the hydrophobic feature is a crucial factor in controlling the leakage currents. 

Moreover, preventive maintenance is often emphasised as minimal and ultimately unnecessary.

Because the contaminants settle in dry periods, the pollutant layer cover the hydrophobicity feature; therefore, the paramount quality of being hydrophobic is voided.

The marketing and sales strategy of the composite and polymeric bushings/insulators, all claim themselves to be maintenance free: with all due respect to the claim that composite and polymer insulators require minimal and ultimately unnecessary maintenance, sooner or later, they must be cleaned. (In climatic areas as stated above). The same fact is applicable to bushings/insulators RTV coated.

The RTV silicone coatings are generally being sold, emphasising hydrophobicity as the main feature, and claiming that (hydrophobic quality) is crucial in limiting leakage currents. These coatings are designed to replace silicone grease and water washing, and claims to have the ability to eliminate the maintenance cost.

Within a variable length period (time depends on the climatic conditions), RTV coatings degrade with the coating peeling off, forcing a power outage to resolve issues.

The aim and the challenge of a preventive maintenance program: clean insulators without a power outage.

A preventive maintenance program based on an “Automated Washing System” reduces network outages, eliminates repair time and maintenance costs, grants zero flashovers (caused by polluted insulators), can obtain operational excellence, reduces downtime risk, ensures personnel safety, and achieves financial efficiency by optimising the maintenance budget. 

• The AWS PP system for the above projected entire substation is divided into 17 washing zones. 
• Each washing zone is typically created by three insulators/bushings of the same type. 
• Washing time of each washing zone is approximately 15-25 seconds. Further to this, all bushings/insulators are cleaned in 34 minutes. 
• All the insulators of each wash zone are washed at the same time. 

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The kV rating dictates the washing water requirement.
• Demineralised water required quality for 400 kV rating is ≤ 20 µS/cm. 
• The wind direction dictates the washing sequence. 
• The User selects a custom washing frequency and decides to wash one specific bay, all bays, or the entire substation (4 bays) daily, weekly, monthly, as needed.

Clean bushings and insulators without a power outage:

• SF6 – Air Bushings; 
• LA – Lighting Arresters; 
• CVT – Capacitive Voltage Transformers; 
• TI – Tension Insulators (Gantry); 
• SI + LT Suspension Insulators (Gantry-side).

Clean without a power outage pros:
Reduces: 

• Voltage drops – Leakage currents; 
• Short circuit trips – Relay operations; 
• Flashovers – Power supply interruption; 
• Line outage events; 
• Eliminates cold washing outage; 
• System Average Interruption Duration Index (SAIDI); 
• System Average Interruption Frequency Index (SAIFI); 
• Customer Average Interruption Duration Index (CAIDI); 
• Customer Average Interruption Frequency Index (CAIFI). 

Increases: 

• Uninterrupted performance; 
• Overall system reliability; 
• Assets’ efficiency; 

Optimises: 

• Maintenance budget; 
• Operating cost; 
• Management cost; 

NOTE: The Preventive Maintenance plans are chronically suffering a shortage in funds with limited budgets allocation and are often mistakenly squeezed to the minimum. A customised preventive maintenance program should be adopted and seasonally adjusted. 

The washing frequency, seasonally programmable, is dictated by the type of contaminant and its buildup rate on the bushings/insulators. 

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