Motor

Condition Assessment Study

In this condition assessment package, we will assess the condition of total insulation system of electrical rotating machine consisting of high voltage motors.

The main objective of this condition assessment is to generate a report which gives the information to achieve 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 following techniques listed below, which will assess the condition of Machine Insulation System in total. The various techniques are detailed as below.

1. Visual & Endoscopic Inspection
2. Insulation Resistance &  Polarisation Index
3. Tan Delta & Capacitance Test
4. Partial Discharge Analysis
5. Digital ELCID Test
6. DC/AC High Voltage Tests
7. Wedge Deflection/Mapping Test
8. DC Winding Resistance
9. Natural Frequency Test
10. Coupling Resistance Test
11. Rotor RSO Test
12. Rotor AC Impedence Tests
13. Exciter Tests
14. Diodes & Fuses Tests

Diagnostic Tests

Thermal, Electrical, Ambient (or environmental) and Mechanical (TEAM) stresses act on various components of a Rotating Machine, either singly or in combinations (thermo-mechanical, electro-thermal, electro-mechanical, etc), with varying intensities, depending on design, manufacturing, operating, maintenance and storage conditions, ultimately weakening (ageing, defect formation) the structure of the Rotating Machine component (winding, insulation, bearing, shaft, etc) and ultimately resulting in failure. Based on various international surveys and studies it has been concluded that winding insulation is found to be the one of the maximum potential areas of failures in Rotating Machines.

PROGNOSYS provides Diagnostic Testing services for Generators,Transformers,Motors,Switch gears,etc., includes following techniques listed below, which will assess the condition of Machine Insulation System in total.

1. Visual & Endoscopic inspection
2. Insulation Resistance & Polarisation Index
3. Tan Delta & Capacitance Test
4. Partial Discharge Analysis
5. Digital Elcid Test
6. DC/AC High Voltage Tests
7. Wedge Deflection/Mapping Test

8. DC Winding Resistance
9. Natural Frequency Test
10. Coupling Resistance Test
11. Rotor RSO Test
12. Rotor AC Impedence Tests
13. Exciter Tests
14. Diodes & Fuses Tests

Capacitance & Tan Delta Analysis

Measurement of winding capacitance can indicate problems such as thermal deterioration or saturation of the insulation by moisture within the bulk of insulation. Capacitance tip-up test is the indirect partial discharge test and is closely related to tan delta tip-up.

Dissipation factor or Tan delta provides an indication of the dielectric losses within the insulation. Certain deterioration such as thermal deterioration and moisture absorption will increase these losses. Power factor tip-up is also an indirect way of determining partial discharge occurring.

Tan d and Capacitance will be measured both below and above discharge inception voltage. Capacitance and tan delta measurements will be performed using a Tan delta measurement instrument. Maximum test voltage will be VL /Ö 3 r.m.s (VL – Machine Line Voltage ).

Test will be performed on each phase individually by shorting other phases to ground. Test will be performed on slot region and end winding region separately.

The results will be analyzed in order to assess the winding insulation with regard to:

  • Extent of De-lamination (if any)
  • Condition of the corona protection shield
  • Contamination
  • Aging of Insulation

Partial Discharge Analysis

Partial discharges have been known to accelerate the aging process. They cause erosion of insulating material and propagate through treeing mechanism eventually bridging the electrodes and causing insulation breakdowns. While the Capacitance & Tan Delta tests gives us the indication of presence of these discharges, this test records such pd signals.

Partial Discharge test will be done using Partial Discharge Analyser by applying voltage as applied for tan delta test. PD Analyser system is used for partial discharge test that includes analysis software that gives discharge patterns for defect identification and also quantifies the partial discharge in the winding for trend analysis.

We provide Phase Resolved Partial Discharge (PRPD) analysis which will enable us to identify different types of PD.

  • Internal Discharges
  • Surface Discharges
  • Slot Discharges

Natural Frequency Test (NFT)

The operating conditions and start up stresses on the endwindings could result in loosening of the support ties and blocks and may cause the coils on the endwinding to vibrate or move. This will result in a change in the stiffness of the endwinding supports, which will lead to a shift (lowering) of the natural frequency of the endwinding structure.

It may so happen that this shift in natural frequency might come dangerously close to the exciting frequency of the 2 X line frequency forces that are generated by the currents flowing in the endwindings, and result in large movement of the endwinding coils. The natural frequency of endwindings should not be matching with the system’s natural frequency, which may otherwise cause high amplitude vibrations due to resonance, increasing stresses on the machine. This test is thus conducted to identify the natural frequency of endwindings. The response of the end winding to the tap of a hammer is recorded using an accelerometer pickup strategically positioned, and analyzed to characterize the relevant end winding resonant properties.

We will able to distinguish the different types of NFT problems

  • End winding looseness
  • Wedge Looseness
  • Slot Corona due to Vibrations

Surge Comparison Test

The Surge Test is highly important. That’s because 80% of all electrical failures in the stator begin at weak insulation turn-to-turn. Regardless of an individual’s personal view of Surge testing, knowing that a motor’s turn-to-turn insulation is sound is crucial for safety and motor reliability.

During a Surge Test, the equipment will charge up a capacitor inside the unit and dissipate it into one phase while holding the other two phases to ground. Then, automatically, the test unit will slowly increase the voltage from 0 volts to the target test voltage. This generates a waveform, in a shape based upon the inductance of the coil that is displayed on the test equipment screen. If the target test voltage is attained without any frequency change in the waveform, the turn-to-turn insulation integrity has been realized.

Paschen’s Law states that two bare wires placed next to one another just a thickness of a hair away need a minimum of 325 volts to jump the air gap between the two conductors. These two concepts are the core reason why Surge testing is the natural choice for testing turn-to-turn insulation. The main reason is that if the test equipment doesn’t produce a potential difference between the turns above Paschen’s Law, the current cannot flow through the fault. If current can’t flow through the fault, it will continue through all the coils and not show a difference.

Surge comparison tests are widely applicable for AC motors, DC motors, transformers, coils, wires, cables, capacitors etc.

Recurrent Surge Oscillograph

A high frequency DC step voltage impulse (12 V) is repeatedly applied using Progno RSO Pulse generator to the rotor winding at positive slipring and the reflected weaveform is recorded using Digital Oscilloscope. The RSO technique uses time domain reflectometry theory to detect faults in Rotor Winding. The process is repeated for negative slip ring and the two waveforms are superimposed to check for rotor winding abnormalities like shorted turns, earth faults, interturn faults or rotor high resistance areas. The method is largely suited for 2 pole machines for effective detection of rotor winding interturn shorts or high resistance joints.
The results will be analyzed in order to assess the Rotor winding insulation with regard to:
 

  • INTERTURN SHORTS
  • HIGH RESISTANCE JOINTS
  • EARTH FAULTS
  • Contamination

Rotor & Exciter Tests

DC Winding resistance and AC Impedance Measurement

The rotor DC winding resistance and AC impedance is measured to check for electrical unbalance due to shorted turns or open circuit faults in the winding. Low resistance Micro-ohmmeter is used for winding resistance measurement where 10 amps DC current is applied and resistance is measured. To measure Impedence AC voltage is applied and current is measured.

Test on Exciter and PMG Machine

The following tests are conducted on exciter armature/field windings PMG stator/rotor windings.
 

  1. Winding resistance and impedance
  2. IR and PI at low voltages

Miscellaneous Tests

Diode and Fuse checks

A diode is reverse-biased when the positive (red) test lead is on the cathode and the negative (black) test lead is on the anode. The reverse-biased voltage of a good diode displays ‘OL’ on a multimeter. The diode is bad if readings are the same in both directions.

DC Tests

IR, PI and Absorption test

The IR / PI test is an excellent means of finding windings for contamination and moisture presence in stator and rotor windings. The test is also good for detecting major flaws where the insulation is cracked. In form wound stators with thermoplastic insulation systems, the test can also detect thermal deterioration. The test is performed by applying megger voltage and finding Insulation Resistance, Polarisation Index and Absorption ratios & graphs.

Winding Resistance Measurement

The stator DC winding resistance is measured to check for electrical unbalance due to shorted turns or open circuit faults in the winding. Low resistance Micro-ohmmeter is used for winding resistance measurement.

Online Partial Discharge Analysis

Partial discharges have been known to accelerate the aging process. They cause erosion of insulating material and propagate through treeing mechanism eventually bridging the electrodes and causing insulation breakdowns. While the Capacitance & Tan Delta tests gives us the indication of presence of these discharges, this test records such pd signals.

Partial Discharge test will be done using Partial Discharge Analyser by applying voltage as applied for tan delta test. PD Analyser system is used for partial discharge test that includes analysis software that gives discharge patterns for defect identification and also quantifies the partial discharge in the winding for trend analysis.

We provide Phase Resolved Partial Discharge (PRPD) analysis which will enable us to identify different types of PD.
 

  • Internal Discharges
  • Surface Discharges
  • Slot Discharges

Motor Current Signature Analysis

The Motor Current Signature Analysis (MCSA) is considered the most popular fault detection method now a days because it can easily detect the common machine fault such as turn to turn short circuit, cracked /broken rotor bars, bearing deterioration etc.. The Motor current signature analysis (MCSA) can effectively detect abnormal operating conditions in induction motor applications.

Motor Current Signature Analysis (MCSA) is a technique used to determine the operating condition of AC induction motors without interrupting production. MCSA techniques can be used in conjunction with vibration and thermal analysis to confirm key machinery diagnostic decisions.

Motor Current Signature Analysis (MCSA) is a system used for analyzing or trending dynamic, energized systems.

Proper analysis of MCSA results assists the technician in identifying: 

  • Incoming winding health
  • Stator winding health
  • Rotor Health
  • Air gap static and dynamic eccentricity
  • Coupling health, including direct, belted
  • and Geared systems
  • Load issues
  • System load and efficiency
  • Bearing health

Thermographic Inspection

The principle of Infrared Thermography is based on the physical phenomenon that any body of a temperature above absolute zero (-273.15 °C) emits electromagnetic radiation. There is clear correlation between the surface of a body and the intensity and spectral composition of its emitted radiation. By determining its radiation intensity the temperature of an object can thereby be determined in a non-contact way.Thermography has proven to be the best tool to find out the hotspots in machine.This technique uses Thermographic cameras to detect hot spots on stator core, temperatures of blocked teflon tubes in rotating machines.