Online Bushing Monitoring System

Bushing Monitoring

Bushings have been identified as the cause of about 15{d985d444412a266f6028815d748e3bbbf46c6bab8291227b63da9f9cb54d1c3d} of all transformer failures.

According to Doble, the leading cause of >100MVA transformer failure is bushing failure (35{d985d444412a266f6028815d748e3bbbf46c6bab8291227b63da9f9cb54d1c3d}).

A Western Power survey of 2096 transformers in Australia and NZ found that bushing were only second to OLTC as the component initially involved in failure.

For decades, the only method for determining the quality of HV bushings has been to performa periodic off-line test (transformer off-line).

Because it requires an outage, it is only performed every 2 to 5 years, and at best every year.

Why on-line bushing monitoring ?

While most utilities periodically test their bushings, there is a solid argument that periodic testing is not enough:
• Periodic testing is not without cost: it takes time, ties up workers and requires an outage.
• It is performed at lower voltages and under very different temperature conditions (due to absence of load).
• Most importantly, periodic testing misses quickly progressing (over weeks to months) problems that can arise between tests.

On-line bushing monitoring systems can now continuously check for and detect developing faults at an early stage, enabling to schedule an outage for maintenance /replacement and prevent a catastrophic failure from occurring Intellix BMT 300 – Customer Presentation.

Why on-line PD monitoring?

• Partial Discharge (PD) is a localized electrical discharge (like a low-energy spark) which will result in a localized gradual erosion of the insulation system.
• If undetected, it will increase exponentially, eventually leading to insulation failure, arcing and loss of the transformer.
• Monitoring PD activity and its rate of change gives valuable information about deteriorating transformer insulation.
• It will also detect any bushing PD first, an advanced state of bushing decay.

Intellix BMT 300

What is it?

An On-line system that continuously monitors:

• The condition of transformer bushings.
• The presence of Partial Discharge (PD) activity in the main tank.

It will alert personnel of fault conditions at an early stage and provide vital health information on the bushings & the transformer.

Differentiated Value

• An integrated solution from a sole supplier.

• When the BMT 300 is integrated with a Transfix multi gas DGA unit, GE can offer a unique all-in-one solution that provides a more in depth view of the transformer’s health.

• Enabling more condition based maintenance, resulting in reduced maintenance costs.

BMT 300 - Features & Benefits

Feature  Benefit
Bushing monitoring (Capacitance and Power Factor) Advance warning of bushing needing
maintenance/replacement
Enables Condition Based Maintenance (CBM)
Avoids catastrophic bushing failure and often transformer loss
Partial Discharge detection Additional feature engineered using the same tap adaptor
Advance warning of possible arcing in main transformer tank
Correlation with main tank DGA results
Integration with TRANSFIX multi-gas DGA units Provides a complete transformer solution to effectively monitor
the majority of root causes of transformer failures.
Uses same PERCEPTION software to visualize data
Less vendors installing equipment in your switchyard
Single vendor integrated solution that works/communicates

BMT 300 – What it does

Bushing Monitoring
5 signals are digitized and recorded:

three current magnitudes from the test tap and two independent phase angles between the currents.

From these, the change in capacitance and in relative Power Factor can be measured to indicate a developing bushing fault.

Partial Discharge detection

High frequency signals detected are discriminated against external PD using the neutral CT and are used to detect internal PD activity. In time not only the main tank but the bushing itself can be detected for PD but this option is being tested in field at the moment and is not commercially available.

Count and intensity are both recorded and a total activity measure calculated.

BMT 300 – What it does

Bushing Monitoring
5 signals are digitized and recorded:

three current magnitudes from the test tap and two independent phase angles between the currents.

From these, the change in capacitance and in relative Power Factor can be measured to indicate a developing bushing fault.

Partial Discharge detection

High frequency signals detected are discriminated against external PD using the neutral CT and are used to detect internal PD activity. In time not only the main tank but the bushing itself can be detected for PD but this option is being tested in field at the moment and is not commercially available.

Count and intensity are both recorded and a total activity measure calculated.

BMT 300 – How it connects

The BMT 300 connects to the 3x HV bushing tapping points using custom made adaptors.

There is an option for both HV and LV bushings (6 bushings).

Using the same adaptor, it measures leakage current, power frequency signals and high frequency signals.

Additional sensors help deliver further
information:

  • Ultra precise GPS timing signal
  • Ambient temperature & humidity
  • Top and bottom oil temperature
  • CT on neutral

BMT 300 – View of an Installed Unit