Monitoring and evaluating the condition of bushings

The failure of bushings can cause major transformer failures. They are even the main cause for transformer fires. Since the requirements for availability and reliability of transformers used in networks are increasing, continuous monitoring and evaluation of the condition of bushings is imperative. The new MSENSE® BM helps you detect faults in bushings early on and to take action before your transformer is damaged.

Bushings can age prematurely due to transient overvoltages, increased temperatures or the ingress of moisture. This results in partial discharges, which can quickly lead to failure of the insulation or even to a major transformer failure.

The condition of bushings can be determined through regular time-based diagnostics. As bushing failures, however, tend to develop rapidly, immediate action must follow. In contrast to this, continuous status monitoring is possible with an online monitoring system. MSENSE® BM continuously measures the relevant variables directly at oil-impregnated paper bushings (OIP) or resin-impregnated paper bushings (RIP) with voltage levels of Um = 123...765 kV*.
*) Um > 420 kV available on request

Changes in the condition of the insulation are detected early on by MSENSE® BM. An innovative and field-tested algorithm monitors the condition of the inner capacitances per unit length of the bushing field grading in terms of changes in capacitance (C) and dissipation factor (tan δ) and compares them to limit values. The key aspect of this innovation is the 2/3 reference method: the algorithm continuously incorporates all three bushings into mutual monitoring.  In addition, just only the measurement data of potential transformers on the system are required to determine the symmetry of the grid voltage. This ensures a reliable and clear evaluation of the condition of the high-voltage bushings – regardless of network asymmetries or fluctuations in voltage. The method eliminates the critical temperature-dependence of other bushing monitoring concepts. 2/3 reference method means: If the bushing-measurements of one phase (C or tan δ) deviate from the values of the other two phases, the user will be notified using a two-stage limit-value process.

MSENSE® BM is based on the MR ISM® technology automation platform, which has been used successfully in the field since 2013. For reliable monitoring of high-voltage bushings, MSENSE® BM also features simple operation and a state-of-the-art graphical display.



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