Electrical Power & Protection

Prevent unplanned outages

November 2018 Electrical Power & Protection

Air insulated (AIS) and gas insulated switchgear (GIS) are important elements in transmission networks. It is crucial to evaluate and understand their current condition in order to know when and where maintenance activities may be required before a fault causes a disruption in the grid. With its new and economical Onsite Condition Assessment Solutions, Siemens ensures the smooth operation of its customer’s assets.

There are many challenges for high-voltage switchgear: increasing load requirements, high demands from customers and processes, and limited backup power. But the number of these high-voltage components over 30 years old is increasing, making defects or failures more likely. In order to prevent major damage due to ageing devices, it’s crucial to properly monitor and service high-voltage switchgear regularly with as little downtime as possible.

Analyse the past, assess the present, and predict the future

Siemens offers a broad range of proactive services for all phases of AIS and GIS lifecycle management. Deviations from the specified conditions are identified by condition assessments, and maintenance and spare-part services bring the asset back to optimal condition. “Siemens’ Customer Services have a strong heritage of expertise across transmission and distribution equipment, with highly skilled technical experts globally available,” says Armand Tsague, field service engineer at Siemens. “With our Onsite Condition Assessment packages, we analyse the past, assess the present, and can predict the future of the asset’s condition. This significantly enhances the reliability and availability of the switchgear.”

High flexibility and accuracy with portable equipment

Siemens’ service technicians use a variety of assessment methods. Of course, each method can stand alone, but the company prefers a combination of assessments in order to provide a holistic view of the condition of the equipment and help increase the accuracy of the diagnostics. “Performing measurements frequently and using trend analyses can also help predict the future condition of the asset,” says Tsague. “Using portable measurement equipment, our experts take an in-depth look at a customer’s high-voltage equipment wherever necessary.”

Levels of condition assessment

The company’s condition assessment portfolio is split into three levels. The first and second levels are performed while the asset is running (no switch-off required). The most important is the partial-discharge measurement. For temporary monitoring, the experts prefer to use ultra-high-frequency (UHF) methods to detect partial discharges in the switchgear. They might combine this method with acoustic partial discharge detection, a visual inspection that employs the audit tool SAFE, a thermography scanning of the entire substation, and a gas analysis to measure moisture, SF6 percentage, dew point, sulphur dioxide content, and other values. The third level comprises additional electrical measurements that can only be performed when the asset is out of operation: for example, dynamic contact resistance measurement (DCRM) of the breaker, timing tests, outdoor bushing measurement, and transformer current measurement.

Benefits to operators

“Our on-site partial-discharge monitoring offers a number of advantages to operators even if they aren’t using Siemens equipment,” Tsague explains. These benefits include precise failure prediction, access to real-time condition data by installing UHF sensors, an early warning of malfunctions, and keeping the asset healthy and in service for as long as possible – which delays the need for major investments in new equipment and avoids the high cost of repairing serious damage.

What is a partial discharge (PD)?

PD is a partial dielectric breakdown in an electrical insulation system under high voltage. It causes continuous deterioration of the insulating material that could lead to a complete breakdown and outage. Therefore, it is important to detect PD at an early stage in order to prevent unplanned downtime. The main causes of PD in GIS devices include moving particles, voids in solid insulation, floating electrodes, defective insulators and protrusions or corona.

Sensors for ultra-high-frequency (UHF) measurement

Partial discharges in a GIS generate current and acoustic signals, and they also produce UHF electromagnetic waves, which can be detected using special sensors. If the GIS is not pre-equipped with embedded sensors, external ones can sometimes be installed. Studies have confirmed that UHF measurement is very sensitive to partial discharge signals and it is becoming the dominant method for both commissioning tests and temporary and permanent monitoring.

For more information contact Jennifer Naidoo, Siemens Digital Factory and Process Industries and Drives, +27 11 652 2795, jennifer.naidoo@siemens.com, www.siemens.co.za


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