From Condition Monitoring of Rotating Electrical Machines

10.1 Introduction

Chapter 9 concentrated on the perturbations to current, flux and power at the terminals due to faults in the machine. However, there is another effect at work in high-voltage electrical machines and that is perturbations to the voltage and current wave fed to the machine as a result of electrical disturbances or discharges in the insulation system.

This chapter deals with a more specialised terminal analysis than considered in Chapter 9, which has the potential to detect those discharge activities present in the machine winding insulation, particularly in high voltage machines. One of the reasons this technique has received so much attention is because the insulation system lies at the heart of every electrical machine, as described in Chapter 2, and its deterioration can be relatively slow, as described in Chapter 3. Therefore it should be a good target for condition monitoring.

10.2 Background to Discharge Detection

Discharge behaviour is complex and can be categorised in ascending order of energy and damage as

  • corona discharge,

  • partial discharge,

  • spark discharge,

  • arc discharge.

A well-made insulation system will exhibit low-level corona discharge on the surface of the insulation at AC voltages above 4 kV rms to ground. If there are voids inside the body of the insulation system those voids will also exhibit partial discharges at the points in the voltage cycle when the local electric field strength exceeds the Paschen curve level for the gas in the void at that temperature. Neither that surface or body activity is necessarily...

Products & Services
Partial Discharge Monitors
Partial discharge monitors are used to monitor partial discharge activities in high voltage equipment.
Corona Treaters and Plasma Cleaners
Corona treaters and plasma cleaners generate and expose organic or polymer substrates to ionized gas to improve wettability of adhesives, paints, inks or other coatings.
Gas Discharge Tubes (GDT)
Gas discharge tubes (GDT) or gas tube arrestors (GTA) provide protection against voltage and current surges in electronic and electrical equipment. They include spark gaps, simple devices with two or three conducting electrodes separated by a gap filled with a gas such as air.
Electrostatic Discharge (ESD) Generators
Electrostatic discharge generators are machines used to generate electrostatic discharge (ESD) signals to test how much ESD a piece of electronic equipment can tolerate without damage.
Dielectric Greases and Insulating Fluids
Dielectric greases and insulating fluids are applied to electric terminals in high voltage equipment to minimize disharges, insulate and lubricate non-conductive surfaces, exclude moisture, and conduct heat.

Topics of Interest

11.1 Introduction In earlier chapters of the book we have presented various techniques for condition monitoring. It was seen that most faults do have predictable symptoms during their development,...

E. Gockenbach 17.1 Introduction A partial discharge (PD) is a localised electrical discharge that only partially bridges the insulation between conductors and which may or may not occur adjacent to a...

I. J. Kemp 4.1 Introduction Partial discharges are localised gaseous breakdowns which can occur within any plant system provided the electric stress conditions are appropriate. Because the breakdown...

Testing for Immunity against ESD     Two ESD testing techniques are used to check medical devices. The first is air discharge; the second is contact discharge. Testing by air discharge...

GENERATOR OPERATIONAL CHECKS (SURVEILLANCE AND MONITORING) Regular monitoring of the following parameters is required: Temperature of stator windings. Core temperature. Temperature of slip rings.