Partial Discharge Monitoring System for Electrical Equipment : An Introduction

 Partial Discharge Monitoring System for High Voltage Switchgear, Transformers, Motors , Generators and Cables becomes the most important indicator in the predictive and preventive maintenance scheduling. It is highly reliable method that can be used anytime to diagnose the insulation condition of an electrical asset that operate at 3.3 kV and above. It could be an online or offline system of which the basic component is the PD sensor attached to the HV equipment.

Partial discharge (PD) measurement has long been used as a test to evaluate different insulation system designs, and as a quality control test for new equipment. However,  it is now widely applied to diagnose the condition of the electrical insulation in operating apparatus such as switchgear, transformers, cables, as well as motor and generator stator windings.

Sample below as one of application from "Irispower" to HV Motors.

Typical Schematic Diagram for HV Motor Application

InfoDiagram based on IrisPower

How does it work?

Epoxy mica capacitive couplers are installed on the motor junction box, coupled into the cable terminals.

The couplers will have a connector with RF Coaxial Cable then to a terminal box near to motor with a converter before connecting to a local monitoring panel via a special cable. This local panel will convert and process all the "raw" input signals and send it to the remote monitoring in central system.

The above configuration and technology is one of the popular and proven technique for the past years. Nowadays, a lot of method or techniques emerge using the same philosophy. 

Why Partial Discharge?

Partial discharge (PD) activity is a display of weak spots in the insulation that leads to failure and damage to motors and generators.

When a partial discharge pulse occurs, the electrons from the inside of the gas-filled void flow close to the speed of light across a small distance, usually a few nanoseconds. The electrons carry charges which in turn creates current pulses . At the same time, positive ions flow in opposite direction. Thus, this condition creates a disturbance and results in pulse current and voltage.

What is partial discharge monitoring?

Partial Discharge (PD) monitoring is a highly reliable method that can be used anytime to diagnose the insulation condition of an electrical asset. It provides engineers with practical information which allows them to detect even the tiniest weak points in a system.

What causes partial discharge (PD) activity in electrical equipment?

A variety of stress, poor installation, manufacturing defects,  environ-mental impact and aging factors result in partial discharge (PD) activity in electrical equipment during its service life, which can cause defects and eventual dielectric failure in the equipment’s insulation. 

What is partial discharge insulation failure?

Partial Discharge Insulation failure is one of the principal causes of forced outages for generators, motors, switchgear and dry type transformers which result in considerable damage and lost revenues.

There are a lot of vendors who are offering this technology recently. The list as follows:

• Irispower
• Omicron
• HV Technologies
• PDIX (by Megger)
• LS Cables
• Siemens-Energy
• ABB
• HVPD

The above vendors were using different techniques. Each technique and method employs different components but have the same philosophy. We will explore it in future posts.