Condition Monitoring is one of the maintenance methods which are used to assess the health and condition of ASSETS (Cables) by absorbing, checking, measuring and monitoring several parameters. This is also called Equipment Health Monitoring (EHM).

The main objective of this condition assessment is to generate a report which gives the information to achieve the following tasks

  • To arrest the deterioration in performance
  • To improve the availability, reliability, efficiency and safety of equipment.
  • To regain lost capacity
  • To extend useful life beyond design life and save investment on new equipment.

Condition Assessment Technique will be implemented as per the following techniques listed below, which will assess the condition of the Machine Insulation System in total. The various techniques are detailed below.

1. Visual & Endoscopic Inspection
2. Insulation Resistance &  Polarisation Index
3. Tan Delta & Capacitance Test
4.  VLF Tan delta
5. Partial Discharge Analysis
6. DC/AC High Voltage Tests
 

Tan Delta & Capacitance Analysis

The Tan Delta test works on the principle that any insulation in its pure state acts as a capacitor. The test involves applying a very low-frequency AC voltage. The voltage is generally double the rated voltage of the cable or winding.

Tan delta testing is a diagnostic method of testing cables to determine the quality of the cable insulation. This helps create a systemized method to analyse the ageing of power cables in the long run. Tan Delta (TD), or Dissipation Factor, is an excellent diagnostic tool to evaluate both aged and new cable systems, particularly when evidence of moisture ingress into the cable is concerned. This can manifest itself as corrosion of the neutrals and/or tracking in splices, and as water tree degradation in cable insulation etc.

The cable or winding whose insulation is to be tested is first disconnected and isolated. The test voltage is applied from the Very Low Frequency power source and the Tan delta controller takes the measurements. The test voltage is increased in steps up to the rated voltage of the cable. The readings are plotted in a graph against the applied voltage and the trend is studied. A healthy insulation would provide a straight line.

        

Partial Discharge Analysis

Partial discharges are a consequence of local breakdown either as a result of an electric field enhancement within or on the surface of the insulation, or a region of low breakdown field. PDs appear as individual events of very short duration; are always accompanied by emissions of light, sound and heat, as well as electromagnetic pulses; and often result in chemical reactions.

The PD parameters that are usually measured during tests on installed cable systems are as follows:

PD inception voltage, PD extinction voltage, PD location, PD magnitude (q), PD repetition rate (n), Phase-resolved PD plot

PD magnitude vs. voltage plot.

Types of Partial Discharge Activities

  • Voids (or) cavities within the insulation (or) at interfaces between the insulation and semi-conducting shields.
  • Cavities between cable and accessory interfaces.
  • High resistance insulation shield (or) broken neutral.
  • Electrical trees are initiated from protrusions, voids & water trees
        

VLF TAN δ

VLF testing methods utilize AC signals in the frequency range from 0.01Hz to 1 Hz. Diagnostic VLF testing allows the determination of the relative amount of degradation of a cable system section and establishes, by comparison with figures of merit or accumulated data, whether a cable system section is likely to continue to perform properly in service. It should be noted that values of the diagnostic quantity measurements obtained during VLF tests may not correlate with those values obtained during power frequency tests, for example, the dissipation factor is much larger at 0.1 Hz than at power frequency and partial discharge (PD) may differ in terms of magnitude and inception voltage.

        

DC TESTS

Cable insulation is an important protective material for cable conductors. It is non-conductive, used to resist electrical leakage, prevents cable conductors from contact with other conductors, and protects the conductor from environmental threats such as heat, water, and chemicals. Poor or damaged insulation may result in short circuit, electric shock, or fire.

Because the insulation of a cable is so important in determining the cable’s safety and electrical conductivity, we ensure that all our cables are subject to passing the insulation resistance (IR) test.

An insulation resistance (IR) test measures the resistance to current flow across it on a completed cable; it applies a test voltage to determine how effective the insulation is in preventing the flow of electric current out of the insulation. This is analogous to how you would pump pressurized water in a water pipe to identify leaks.

        
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(456) 789 10 12

(456) 789 10 15

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Prognosys EMS(P) Ltd.,
1st floor, Subishi town center,
Mokila, Shankarpalle Road,
Hyderabad, Telangana – 501203.