IGS's Solution: Transient Voltage Surge Plant damage

Steep front voltage surges can cause damage to the insulation of electrical equipment to the extent that premature failure or even in some cases failure during very early plant life may occur.  Circuit switching is the main cause of such transients on industrial or power plant auxiliary supply systems. Equipment using dry type insulation such as motors and dry type transformers are commonly the equipment being effected. 

Motor insulation withstand capability

Although no clear international standard is available today, a wealth of information is available for engineers on the subject.  Perhaps  the most detailed publications came from the IEEE, where a committee studied and collected test results on a large volume of motors.  The interesting conclusion is that the over-voltage withstand capability reduces at higher frequencies or steep front waveforms as shown in the graph on  the right. 

The reason for this is that the higher frequencies contained in the steep front part of the waveform, appears across a few turns into the windings, placing enormous stress on this insulation normally running at a small fraction of the applied voltage under running conditions.  

As breakers open and close, various dynamic interaction with the associated electrical circuit occurs and the following conditions arise:

  • During closing the arc will be established before the contacts are fully closed, then may extinguish, and re-ignite even several times in one operation.  The surges generated stressing the motor/ transformer insulation.  This is called pre-striking.

  • A similar breaking and making of the current can occur during opening of the breaker and is called re-striking.

  • Sometimes higher frequency transient currents flowing in the breaker, may cause the current to intermittently interrupt generating multiple surges. 

  • These steep front  current and voltage waveforms generated during the above conditions propagate down the cable and reflect and refract as it approaches the motor or transformer load.  This is due to the fact that the characteristic impedance of the motor or transformer is much higher than that of the cable. 

Initially engineers realized that arresters, which at best would provide a flat response at higher frequencies, are unable to adequately protect dry type insulation loads such as transformers and motors. 

IGS offers the only comprehensive protection that matches the IEEE curve presented above.  Click here to read more on this. 

Our Solutions

IGS provides a service to survey surge over-voltage on your plant by testing, assessment of risk.  On repetitive failures or failure during early plant life we assess designs, carry out testing and advise on root causes and best technical and economical solutions.  Where maintenance costs are high due to frequent failure of items such as motors, we review failures, identify root causes and recommend cost effective solutions.  For older plants we review the old surge protection devices, maintain them, or upgrade to new more effective types that will assist in extending the life of the older plant to more cost effective operations. 

IGS developed a systematic process in our quality plans that are based on world best practices and knowledge in this field that we use to assess the risk of transient surges, entering equipment and resulting in damage and premature failure. 

The figure below show pre-striking and re-striking transients on a motor. Before the Zorc suppresors were installed is at the top and after the modification is at the bottom. This modification significantly increased the lifespan of the motor.