Whenever there are small voids or air gaps on the insulation surface of the stator windings, it causes high-voltage electrical induction.
This creates small electric sparks in the equipment which is termed Partial Discharges(PD). As the stator winding wears out due to the coil vibration occurring in the slot, the functioning at high temperatures, or the contamination, it causes an increase in partial discharge activity.
Hence, partial discharge monitoring can detect the major causes of failure in stator winding and offers usually 2-3 more years of warning for an equipment failure.
In this blog, we shall discuss everything about Partial Discharge Detection and management in detail.
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Getting to know about Partial Discharges
Partial discharge occurs whenever a small insulation area under a high-voltage environment cannot withstand the undesired breakdown and electrical stress.
While considering the two insulated electrodes, it doesn’t span the entire distance between them, hence they are termed ‘partial’.
The partial discharge might be generally small, but it can consequently transform into great damage with time, that finally ends up in failure.
If this remains unchecked, the insulation failure not only causes a loss of supply for the business processes or customers but also can challenge the staff.
The non-intrusive instruments leverage the power of electromagnetic and ultrasonic emissions for effective problem detection.
But, while entering a substation, you should check out for your senses. Check for the stress signs, and smell of ozone, or listen closely for any audible crackling sounds inside the switchgear, etc.
Any of the above indicators can prove to be a warning of severe PD and can be an insecure environment.
Understanding the Causes of Partial Discharge
The major factors behind the partial discharge include:
- Defects in the design
- Voids in the solid insulation due to the manufacturing defects
- Contamination through particles
- Undesirable substation environments
- Combination of all these factors if you have an aging asset
Classification of partial discharge
Partial discharge can be classified into three major types:
- Internal PD: It occurs inside the insulation
- Surface PD: It gets tracked across the insulation
- Corona PD: flows from a sharp electrode into the gas
Let’s take a deep dive into the types in detail:
Internal PD:
This refers to the silent defect with no smell, sound, or visual alert of the problem before the failure occurs. If you could see the consequence of a compound insulated cable box damage, you can understand how the pressure built up can end up in a serious explosion.
Surface PD:
Once the materials alternative to porcelain and the dry terminations started getting introduced to the switchgear, certain crucial aspects of the design and installation might not be fully encouraged. This causes a spike in failure rates and can also generate an ozone smell or crackling sounds once developed.
Corona PD:
This term is familiar with outdoor switchyards, especially while being humid. Corona isn’t usually harmful with switchyards at the sharp regions. But, when the corona activity happens within the enclosed chambers and there is no airflow to eliminate the chemical reactions, it can cause the onset of partial discharge problems.
How PD Detection & Management ensures safety & Reliability
Performing Partial discharge monitoring is an off-line quality control examination. This test is conducted during machine outages and also through online monitoring under normal operating conditions. Partial discharge monitoring involves the use of:
Partial discharge sensors,
Monitoring instruments,
Diagnostic software
These track the partial discharge and understand the ideal condition of the insulation.
Different methods used in partial discharge detection
While detecting PD in the High Voltage Switchgear, it is relatively easy if we can perform this life without interfering with the electric supply. The most reliable ways depend on the ability to detect various radio frequency signals. Here are the various ways of implementing partial discharge detection:
PD sensors
Having a combination of sensors makes sure that various types of PD can be detected readily. Partial Discharge produces Transient Earth Voltages (TEV), which are electromagnetic pulses with high frequency. TEV signals traverse around the interior surfaces of the switchgear and escape outside along the openings of the metalwork. Placing TEV sensors on the outer part of the switchgear helps to measure the pulses with the detection of PD activity.
Ultrasonic method
Finding internal PD is easier with the TEV method. Acoustic emissions following the PD activity are usually at a frequency too huge for our ears, which is ultrasonic. While PD gets worse, the frequency reduces to an audible range. With the help of an airborne ultrasonic mic, you can detect PD where there occurs an air path along the mic and source. Sealed chambers can be effective with the use of contact ultrasonic sensors. This method works best to find surface PD and corona PD.
PD instruments or Spot testers
The patented algorithms for signal processing help to identify discharge in the cables, switchgear, etc. It caters to high-end reliability, reduced false alarm rates, and quick acquisition times. Additionally, the advanced PD detection probes help with the integrated display features and data logging capabilities. It also emulates the specified idle noise levels of the applications. Nevertheless, it pinpoints the PD event location to make faster root cause analysis and effective troubleshooting.
PD monitoring systems
Permanent PD tracking is specifically designed for places with high-voltage networks, for example, substations. The system offers an assessment of diagnostic insulation conditions round the clock for the service plants equipment like transformers, switchgear cables, and rotating machines. It tracks the PD trends and transfers the data into a PD monitoring server to perform advanced data management and diagnostics that highlight the flagged discharge activity.
Consequences of PD on electrical equipment and Systems
Once started, PD produces the progressive deterioration of insulating components which eventually leads to an electrical breakdown.
The consequences of partial discharge in the high voltage cables and the systems could be dangerous, which lead to a complete failure.
The repetitive discharge can create irreversible deterioration of the insulating material chemically and mechanically.
The energy that high energy electrons or ions dissipate, UV light via discharges, ozone invading the void walls, or the chemical breakdown procedure liberating gasses at unbearable pressure causes these damages.
Chemical transformation through dielectric suddenly increases the conductivity of its material surrounding the voids.
This improves the electrical stress on the unaffected region in the gap which scales the breakdown process.
Factors to consider while choosing PD detection and management provider
While choosing the partial discharge detection and management provider, you need to consider the following factors:
- The early detection of emerging PD faults to eliminate GIS failure.
- Prevention of unwanted shutdowns that develop due to non-PD or non-critical signals.
- Modular service concept which gives the ideal solution to cater to all your requirements.
- Dedicated and experienced partial discharge experts at your service.
Ocean way of implementing PD detection and management for electrical systems
While considering partial discharge monitoring and management, you need to source the best providers who can offer cost-effective and early-stage analysis of equipment.
Read more about the IPEC PD Testing devices in Ocean’s way of operation.
The failure of cabling and high voltage in MV switchgear can cause high cost of repair fines and replacements.
However, most failures cannot occur immediately, they initially develop warning signs, mostly the partial discharge.
Detection of these issues with Ultrasonic partial discharge actions on MV gear at the early stage can avoid serious failures of equipment.
The help of a professional data interpretation from a reliable Engineering company in Oman can assist you with the periodic assessments of the systems.
With effective monitoring of your cables and switchgear, Ocean assists you through timely alerts on suspicious spikes and highlights the part of your HV systems that need sudden investigation and attention.