Thoughtful considerations to design MV/LV distribution substations for extended service life

Lifetime of MV/LV Equipment

The installation of a new MV/LV electrical substation is often part of a more global project, and it is not always the subject of very detailed attention. However, the consideration of simple and practical criteria is not always dictated by standards, but it can significantly increase the equipment lifespan and operator or public safety.

In this article, we will explore factors impacting MV Equipment Maintenance, Designing for Service Conditions and Extending Equipment Lifespan, and the Importance of local environmental conditions on maintenance schedules and equipment lifespan.

According to data from 2011, arc flash and arc blasts cause 80% of electrically related accidents and fatalities. It is crucial for employers and workers to be aware of the risks associated with electrical work and to take the necessary precautions to ensure their safety.

One of the ways to reduce the risk of arc flash and arc blasts is by designing safe MV/LV distribution substations.

Table of Contents:

1. 1. Factors Impacting MV installation environment and substation design
      1. Mechanical factors affecting MV equipment
      2. Electrical factors affecting MV equipment
      3. Additional design considerations and precautions for MV substation ventilation
   2. Designing for Service Conditions and Extending Equipment Lifespan
      1. Utilizing guidelines from IEC 6222-1 and IEEE C37.100.1 standards for outdoor service conditions
      2. Explanation of IEC or ANSI/IEEE certification and how it affects operation in varying humidity conditions
   3. Importance of local environmental conditions on maintenance schedules and equipment lifespan
      1. Utilization of algorithms and AI for proactive alerting and predictive maintenance planning
      2. Real-time Monitoring and Predictive Maintenance benefits
      3. Implementation of continuous monitoring for real-time condition reporting

1. Factors Impacting MV installation environment

Designing an installation environment is incredibly important to the overall effectiveness and longevity of the equipment being used. When it comes to creating a distribution substation, for example, particular precautions must be considered to ensure that maintenance can be performed smoothly, and that circuits can be easily de-energized.

Two factors to consider when designing a substation are the mechanical environment in which the MV equipment will be installed and the electrical factor which can lead to deterioration of insulation and disrupt the overall efficiency of the substation.

1.1 Mechanical factors

Mechanical factors are closely linked to the environment in which the MV equipment is installed. For instance, environmental conditions such as heating and cooling, or vibrations due to local or seismic activity can have a mechanical impact on substation design.

When designing an MV/LV distribution station, it is essential to consider the impact of mechanical factors on the equipment.

Moreover, some of those scenarios could be associated with incorrect work practices, operating staff must follow strict rules and precautions to ensure the safe installation and operation of cable terminations/bushings. For example, the manufacturer’s guidelines should be followed for proper installation, and the insulation resistance should be tested before and after installation to ensure proper installation and avoid the risk of arc flash¹.

Additionally, proper labeling and signage should be used to identify the specific hazards associated with cable terminations/bushings, and personal protective equipment should be worn by qualified workers when working on or near these components².

Figure 1 – Cable connection is a sensitive part of the MV installation which must follow strict rules and precautions. Excessive mechanical stress on the cable during installation can have a long-term impact on the bushing.

The majority of design-related mechanical issues relate to Busbars and Vacuum Interrupters, paying specific attention to these areas will reduce the risk of incidents.

Go back to Content Table ↑

1.1.1 Busbar Faults due to design issues

Busbars are common components in distribution substations and switchgear; however, issues could be generated by design error rather than failure. When a substation faces busbar faults, a high current level often results in a flashover. The majority of busbars are left without dedicated protection due to high reliability and the belief that upstream protection will be adequate.

Therefore, when designing busbar arrangements, always ensure that adequate clearances are respected.

Precautions to take when designing MV substations containing busbars:

1. Manufacturers could offer copper busbars, encapsulated in epoxy cast resin, or shrink-heat-tube to provide a degree of safety and help reduce flash-over.
2. Manufacturers can offer windows for thermal monitoring.
3. If you need to relocate your cubicle or extend the switchboard, you can easily anticipate the extension or modification of the switchgear design to easily accept an extension. Such anticipation can avoid busbar or panel adaptations with a preventive measure to reduce the number of busbar faults.

Go back to Content Table ↑

1.1.2 Effective switching of Circuit Breaker

Circuit breakers can also be affected by the same mechanical factors as busbars, resulting in the misalignment of the circuit breaker. Mechanical wear is a factor on any circuit breaker in both the mechanisms and vacuum interrupters and the number of operations is a well-known maintenance indicator.

Corrosion from harsh environments can also affect operation of circuit breakers e.g. mechanisms or operating coils.

Precaution to take when designing MV switchgear with vacuum circuit breaker:

• When selecting vacuum circuit breakers, mature products produced by reputable manufacturers must be selected that are suitable for harsh environments
• Selection of devices tested for a minimum of 10,000 closing & opening operations provides a good baseline for long lasting equipment, however devices are now becoming available with up to 30,000 tested operations, lengthening service life and reducing total ownership costs.

Go back to Content Table ↑

1.2 Electrical factors

Environmental conditions such as heat, humidity, and contamination (such as pollution or salt) can lead to premature electrical deterioration of insulation or connections. Degraded insulation increases failure risk because electric field stress overcomes the insulation properties and eventually incident occurs.

The example commonly associated with this phenomenon is the damage to cables and installations.

Go back to Content Table ↑

1.3 Additional considerations and precautions to take when designing MV substation

When designing an MV substation, it is important to take additional precautions and considerations into account. One such consideration is MV substation ventilation. Though ventilation is necessary, it’s important to note that excessive ventilation has been shown in studies to increase the occurrence of condensation.

Precautions to take when designing MV Substation ventilation:

It is therefore critically important that the ventilation within the substation is optimal. Ventilation should therefore be kept to the minimum level required. When forced ventilation is not enough to assure the indoor service condition of the switchgear or when the installation surrounding is a hazardous area, the HVAC unit will be necessary to separate the indoor service conditions from the outdoor environmental conditions.

Furthermore, ventilation should never generate sudden temperature variations that can reach the dew point.

For this reason, natural ventilation should be used whenever possible. If forced ventilation is necessary, the fans should operate continuously to avoid temperature fluctuation.

Figure 2 – Dry cast resin transformer requiring natural ventilation

To extend the lifespan of MV equipment where the electrical insulation and operating parts are exposed to atmospheric conditions, it is recommended to design the operating area to respect the normal service conditions as defined by IEC 62227-1 Standard to all outdoor services conditions.

In the early phase of substation design, ensuring that the products meet international standards such as IEC 62271-200 is important⁴. This standard defines the requirements for medium voltage equipment, including the impact of environmental and operational conditions on the performance of the equipment.

Figure 3 – Windfarm LV/MV substation submitted to a high variation of thermal conditions

Go back to Content Table ↑

2. Designing for Service Conditions and Extending Equipment Lifespan

Distribution systems around the world have evolved into different forms. The two main designs are North American and European. IEC For global and ANSI/IEEE for USA are the main standards for MV installations. Thus, for manufacturers, IEC and ANSI/IEEE are becoming more harmonized on performance and testing requirements

Local service condition

The various service conditions are linked to the design of the installation, the design of the operating room, the site and the application surrounding the installation, and finally, the seasonality. In recent years, the majority of local conditions have experienced volatility, whether in rainfall, humidity, or maximum temperatures.

Therefore, it remains a critical point to assess and prepare for all possibilities of environmental conditions. In such situations, conditions should be specified by the user by referring to the IEC 60721 or IEEE C37.100.1 series of standards.

Figure 4 – LV/MV substation situated in a tropical area near the sea

The environmental conditions, including high humidity, elevated ambient temperature, and the presence of salty air, pose a significant risk of severe deterioration.

You can refer to Schneider Electric’s medium voltage technical guide if you would like to learn more about international standards and how you can transform outdoor conditions to normal indoor service conditions that are within standard specifications.

Go back to Content Table ↑

3. Importance of local environmental conditions on maintenance schedules and equipment lifespan

Local environmental conditions dictate the maintenance schedules and lifespan expected. As local environmental conditions have a direct correlation with the maintenance Let’s look at an example of how continuous monitoring can report real-time environmental conditions, and how algorithms and AI can interpret that data to do two things.

Thing No.1 – Unexpected issues by alerts

Deal with any unexpected issues by alerts to inform you of the problem before it results in outages. Insulation of equipment in a distribution substation is affected by ambient conditions, as seen above, it accelerates the degradation of equipment and insulation.

Example of extreme weather: Very hot climates as high as 45 °C in Florida, USA where ambient conditions could directly affect the insulation of equipment. With extreme temperature variations, the need to monitor equipment insulation is accelerated.

Installing environmental sensors connected wirelessly can help to easily monitor ambient factors affecting the normal operation of the equipment and detect drastic variations that can cause early failures. This allows us to anticipate abnormal conditions and so prevent them with maintenance checks or actions.

Figure 5 – Thermal sensors installed on cable connection

Thermal monitoring sensors can provide either periodic or continuous monitoring of busbars, cable, or breaker connections to detect rises in temperature before it is too late. A simple wireless, self-powered sensor can remove the need to design-on IR windows for thermal scanning, and also be used to focus on excessive heat generated from poor connections or alignment of circuit breakers.

Suggested Video – Thermal Sensors Installation in MV switchgear

Partial Discharge monitoring can also be deployed to detect insulation damage across a broad range of components and is often detectable long before other signs of failure.

Jump here to learn more about connected systems equipped with sensors.

Thing No.2 – Predictive maintenance

Predictive maintenance, by replacing those traditional estimations that we know are conservative. Predictive maintenance allows us to extend the lifespan of aging installations. The traditional approach to maintenance involves routine inspections and tracking depreciation values every three months.

Unfortunately, following a strict calendar-based approach can lead to maintenance being performed either too late leading to costly failures or unnecessary expenses.

When it comes to maintaining the availability and reliability of equipment, condition monitoring is the process of systematically collecting and analyzing data to identify changes in performance or condition, so that cost-effective corrective action may be planned. Reduced equipment downtime, increased reliability, and lower operating and maintenance costs are just some of the benefits of a condition-based maintenance program that also helps with the aforementioned difficulties.

Discover White Paper about traditional to condition base monitoring.

Figure 6 – Thermal sensors installed on circuit breaker arms monitoring connection temperatures

Making use of these technologies can save time and money down the line and ensure the peak performance of your equipment. It is important to detect these types of risks early to reduce potential damage, minimize wasted energy and, most importantly, minimize unplanned downtime.

We have discussed some of the potential ways that local conditions may affect equipment health and longevity. The combination of digital sensors with cloud-connected maintenance alerts offers a unique opportunity to detect abnormal conditions before they contribute to failure risk, examples such as high humidity due to failed HVAC, or busbar connection issues that fall outside of regular maintenance schedules.

If you want to go further, you can find more on condition-based maintenance and design of MV installation by downloading the MV Technical Guide from Schneider Electric.

Go back to Content Table ↑

References:

1. Rockwell Automation (2021), Installation Guidelines for Medium Voltage Arc Plenums and Chimney Systems: https://literature.rockwellautomation.com/idc/groups/literature/documents/at/mv-at001_-en-p.pdf
2. Workplace Safety Awareness Council, Understanding Arc Flash : https://www.osha.gov/sites/default/files/2018-
   12/fy07_sh-16615-07_arc_flash_handout.pdf
3. Bouvier, Fault arcs on busbar sets and switchboard
   https://www.studiecd.dk/cahiers_techniques/Fault_arcs_on_busbar_sets_and_switchboards.pdf
4. Medium Voltage Design Basics: Environmental & Operation Conditions: https://blog.se.com/energy-managementenergy-efficiency/energy-regulations/2017/10/25/medium-voltage-design-basics-environmental-operation-conditions/