Pakistan’s Journey: From Waiting on Calls to Standing Tall on the World Stage

For much of its history, Pakistan has often been judged by its relationships with major powers—how quickly it secured aid, how eagerly it was courted by Washington or Beijing, or how frequently its leaders sought validation. A Prime Minister of yesteryears was frustrated on not getting a call from White House despite repeated requests by Pakistani diplomats. That was a time when the very act of being hosted in the White House was celebrated as a diplomatic triumph; a Prime Minister would return home declaring, “I feel as if I’ve won the World Cup.” That mindset signified both the insecurity and the ambition of a young nation grappling with external dependencies.

But today, Pakistan stands at a different junction. A maturation is underway—not perfect, not complete, but significant. We are beginning to be seen (and must act) not merely as a country in need, but as a state with agency, capabilities, and a reputation to defend.

From Provocation to Response: When Words Began to Back Up Deeds

In recent years, Pakistan has faced aggressive provocations. False-flag operations in Occupied Kashmir, cross-border forays, and unilateral strikes have tested our limits. Yet the global narrative is shifting—not because of rhetoric, but because Pakistan has shown it can deliver.

When India flaunted Rafale and Sukhoi aircraft as symbols of aerial dominance, Pakistan’s responses demonstrated that high-tech gear does not guarantee immunity. Skilled pilots, modern electronics, strategic defense systems, and the resolve to act decisively have helped close the capability gap. The consequence? A blow to India’s confidence, and a recalibration in regional perceptions.

Military and Technological Leverage: The Tools of Sovereignty

To be respected, one cannot rely on rhetoric alone. Pakistan has invested in hard power: missiles, radars, unmanned aerial vehicles, and electronic warfare systems. Under the umbrella of strategic deterrence, we now possess credible second-strike capability. SIPRI reports that Pakistan maintains an active nuclear program and continues producing highly enriched uranium for its warhead stockpile.

Though India's military expenditure dwarfs ours—$86.1 billion in 2024 versus Pakistan’s $10.2 billion—the ratio does not tell the full story. Against that funding gap, Pakistan’s strategic posture is deliberately lean, optimized, and calibrated for asymmetric confrontations.

Economic Turbulence and Recovery: Avoiding the Abyss

One of the greatest tests of a nation is surviving near collapse—and Pakistan is doing exactly that. Between 2022 and 2024, Pakistan endured a full-blown economic crisis. Rising fuel costs, external debt burdens, runaway inflation, catastrophic floods, and political instability pushed us to the brink.

Yet, in this chaos, Pakistan has pulled itself back from default. Through macroeconomic adjustments, austerity measures, and structural reforms, the government is slowly stabilizing the ship. The IMF mission recently affirmed progress toward a Staff-Level Agreement, unlocking new disbursements. Reuters reported that Pakistan will soon finalize a staff-level deal worth $1.24 billion under its bailout program.

Diplomacy, Alliances & Strategic Positioning

Recognition is also earned in halls of diplomacy. Pakistan’s alignment with China continues to strengthen, with Vision 2035 and the China-Pakistan Economic Corridor (CPEC) as cornerstones of long-term economic and strategic engagement. Analysts note that while Pakistan engages with the U.S. and other powers, its structural ties with China constrain full strategic realignment.

In global terms, Pakistan is no longer viewed solely through the lens of conflict. It is increasingly seen as a linchpin in regional trade, energy corridors, and climate resilience efforts. The shift from being aid-dependent to being a regional stakeholder is gradual but discernible.

Diplomatic Reckoning: From Isolation to Engagement

Pakistan’s resilience is not confined to the battlefield or the balance sheet—it is increasingly visible in the realm of diplomacy. Only a few years ago, Pakistan risked diplomatic isolation, struggling to balance relations with Washington, Beijing, Riyadh, and global institutions. Today, under the current setup, there is a visible course correction.

Pakistan has successfully repositioned itself as a responsible player in regional and global affairs. The recent IMF agreements, the $20 billion World Bank framework, and renewed Gulf investment pledges were not secured by chance—they reflect a diplomatic strategy that blends pragmatism with persistence.

Diplomatic Successes: Credibility in Action

Pakistan’s voice on climate change, sustainable development, and regional peace has also gained recognition. After the devastating 2022 floods, Islamabad’s call for “climate justice” resonated globally, culminating in commitments at COP27 and beyond. The Geneva Donors Conference (2023) saw pledges exceeding $9 billion, demonstrating confidence in Pakistan’s international advocacy.

On the regional stage, Pakistan’s diplomatic corps has played a careful hand—cooling tensions in the Gulf, facilitating dialogues on Afghanistan, and strengthening OIC’s focus on Kashmir. Each of these represents a shift from the old image of dependency to a newer posture of mediation, responsibility, and assertive presence.

Internal Risks: The Fragile Front Within

Even as we bolster our defenses abroad, internal threats loom large. The enemies of a rising Pakistan now seek to strike from within: separatist groups (BLA, Majeed brigades), religious extremists (TLP), Taliban affiliates, and the distortions of radical ideologies. Their aim is to destabilize, provoke polarization, and derail progress.

The Narrative of Identity: From “Help Me” to “Don’t Mess With Me”

The symbolic shift matters. When a nation no longer begs for phone calls, it exercises choice. When treaties and visits are not markers of worth but tools of engagement, sovereignty gains respect. Pakistan is now carving that narrative—not as a pretender, but as a power with humility, with muscle, and with legitimacy.

Conclusion & Call to Resolve

Pakistan has come a long way—from waiting on calls to making them count; from relying on external sponsorship to crafting its own destiny. Yet this evolution is incomplete. The country’s true strength will emerge not from weapons or loans but from its people’s unity, integrity, and education.

If we can bridge divisions—ethnic, sectarian, class—we will withstand both missiles and misinformation. If we can empower institutions, the next generation will own this progress. If we uphold the values that make a nation more than lines on a map—honesty, civility, justice—then Pakistan’s ascent will be durable.

Let us write the next chapter not in reaction, but in aspiration. 🇵🇰

Generator Protection: Testing of protective functions ANSI 90, ANSI 46, and ANSI 59GN.

me . March 2013 Issue . Lessons Learned . Generator Protection

Generator Protection

Author: Torsten Schierz, OMICRON electronics Deutschland GmbH, Germany

Introduction

Generator protection systems are very complex systems with many different protective functions. The configuration of these systems depends on the rated power of the generator as well as on the power system structure, i.e. whether the generator is in busbar connection or connected to a unit transformer, as shown in Figure 4.  This article will describe solutions for testing selected protective functions effectively for the above connection configurations. As a starting point, experience recommends to structure the tests according to the following criteria:

Step 1:   Testing protective functions that only use voltage measurements (e.g. ANSI 59, ANSI 81, etc.)

Step 2:    Testing protective functions that only use current measurements (e.g. ANSI 50, ANSI 87, ANSI 46, etc.)

Step 3:   Testing protective functions that use both voltage and current measurements (e.g. ANSI 32, ANSI 90/40, etc.)

Test philosophy for overlapping protective functions

Generator protection systems can trip different breakers such as the network circuit breaker (CB), the generator CB, and the de-excitation CB. This so called trip command matrix depends on the activated protective functions, the technical philosophy as well as the power system structure.

Therefore it is recommended to test the correct behavior of each protection function. This is only possible without deactivating any protective functions during the tests.

Application examples

For the following protective functions, the relevant technical background will be explained and practical settings for testing will be derived:

• Testing the ANSI 90 protective function (underexcitation)
• Testing the ANSI 46 protective function (negative sequence / unbalanced load)
• Primary testing of the ANSI 59GN protective function (directional 90% stator ground fault)

Testing of ANSI 90

A synchronous generator always requires a sufficient DC voltage and thus a DC current flow through the excitation winding. This is necessary to maintain the synchronization to the connected power system. 

The generator capability diagram defines the limits of active and reactive power resulting from the physical parameters of the turbine and the generator, see Figure 2.

The underexcitation area is especially critical for the stability of the generator. In this area, the generator can lose its stability, e.g. as a result of a short-circuit in the connected power system or a malfunction of the automatic voltage regulator.

The protective function ANSI 90 protects the generator from asynchronous operation in case of these events.

Depending on the manufacturer of the protective devices, this function uses the impedance measurement or the admittance measurement.

Note: The impedance measurement method is not part of this article, because it is possible to transfer all necessary relay settings directly in the impedance plane of a distance relay (Figure 1).

On the one hand, for protection devices which use the admittance measurement method, the calculation of the relay settings is a lot easier than with the impedance measurement, because the admittance plane of the turbo generator can be used directly, see Figure 3.

On the other hand, testing the following characteristics in the admittance plane is rather complicated. Therefore, in the following, a more elegant method of testing admittance characteristics shall be introduced. The idea is to transform the admittance characteristics to the impedance plane to use automated distance test routines for testing the underexcitation protective function.

The admittance plane can be reproduced in the impedance plane using a mathematical transformation, as shown bellow.

The constant voltage  must be divided by the apparent power S. (equation 1)

                                                    (equation 1)

By using this formula any point in the admittance plane can be transformed to the impedance plane. However, for the automatic testing of the ANSI 90, it is desirable to transform the complete characteristic curve.

For this purpose the straight line equations must be inverted. According to Figure 5 and equation 2 the inversion of a straight line in the admittance plane results in a circle in the impedance plane.  

                                                                     (equation 2)

With   

Figure 6 shows the settings which are used in this example.

The following example shows the transformation of the trip time characteristic No. 1 to the impedance plane (equation 3) and the resulting impedance zone (Figure 7).

    

 (equation 3a)

                                                                 

 (equation 3b)

                                     

The same transformation applies to the trip time characteristic curves 2 and 3.  Figure 9 shows the results of this transformation.

Summary: With the transfer of the trip time characteristics from the admittance plane to the impedance plane, it is possible to use the same test philosophy as for a distance relay. In order to stabilize overlapping protective functions,such as the undervoltage protective function, it is required to use a constant test voltage, i.e. the rated voltage of the generator.

If the overcurrent protective function is active, its pick-up or trip may interfere for test points between 0 Ω and approximately -40 Ω in the impedance plane. For such cases the relay settings have to be checked.

Testing of ANSI 46

Unbalanced load conditions result in a positive and a negative sequence system, see Figure 8.

The negative sequence component rotates counter to the rotor movement and hence produces a flux which cuts the rotor at twice the rotational velocity. Thereby large currents with double frequency are inducted in the rotor causing severe heating.

According to the manufacturers it is possible to have different thermal trip time characteristics. This example is based on protective devices which use the ratio between the negative sequence current and the generator nominal current (I2/In). This function works with the current of only one side (side 1 or side 2) as well.

In multifunctional machine protection relays, all necessary protective functions, including differential protection are implemented in one device.

This can cause problems, because some protective functions may overlap during the test of the unbalanced load protection function.

One philosophy for testing this protective function is to deactivate the differential protective function before starting the test. The disadvantage of this method is that it is not possible to discover logic errors, e.g. in the trip command matrix or overlapping protective functions. Therefore it is recommended to test without deactivating any protective function.

Without a unit transformer in the protection zone, testing ANSI 46 with active differential protection is not too complicated. There is just a phase shift of 180° between the currents of side 1 and side 2.

Note:   The phase shift between side 1 and side 2 depends on the position of the CT starpoint grounding.

The situation is different, however, if there is a unit transformer in the same protection zone, as shown in Figure 11.

In this case, the vector group and the transformation ratio of the unit transformer must be considered. Also the different CT ratios will have an influence on the calculation of the test currents for side 1 and side 2.

The phasor diagrams in Figure 10 (a and b) display the phase shift of the test currents between side 1 and side 2 for a unit transformer with the vector group Ynd5.

The transformer ratio and the CT ratios are not considered in this diagram.

Note: For the positive sequence current the phase shift is 150° clockwise (transformer vector group 5 times 30°). The phase shift for the negative sequence current is 150° counter clockwise!

Summary:  As a conclusion, the physical behavior of the symmetrical components depends on the transformer vector group. It was shown that it is possible to test protective functions which only use one current measurement system (side 1 or side2) while the differential protective function is active.

Primary testing of ANSI 59GN

For generators with a maximum rated power lower than 50 MVA and busbar connection, the directional 90% stator ground fault protection (ANSI 59GN) is the standard protective function.

An alternative solution is the ground differential protective function with the displacement voltage as pick-up criterion and two cable-type transformers for ground current measurement, as shown in Figure 12.

Note: This solution is only possible, if the generator is connected via cable and the star point is accessible.

Secondary tests alone do not guarantee the correct function of the stator ground fault protection, because all settings were calculated based on theoretical grounding conditions.

It is therefore necessary to confirm the theoretical values with primary tests.

For this function the very first commissioning test is to check the secondary current transformer ground connection. Only one CT must be grounded.

The two primary tests (Figures 13 & 14) will check if the ground fault current is higher than the set pick-up value, and if the stability of the 90% stator ground fault protection function is ensured.

In this example, the settings of a 2.5 MVA generator (IEE > = 4 mA; Ven > = 4.9 V) were used.

Primary test with a ground fault inside the protection zone:  A ground electrode is connected to the generator terminal, the voltage regulator is deactivated and the trip command is blocked. When the generator runs at nominal speed the terminal voltage must be increased manually to the rated generator voltage. The next step is to measure the ground fault current (IEE) and the displacement voltage (Ven), as shown in Figure 13.

Primary test with a ground fault outside the protection zone (stability test): A ground electrode is connected to the feeder grounding point. The remaining test steps are the same as for the previous test. Figure 14 displays the test for this example.

Summary:  The comparison between the measured ground fault values for both primary tests confirms that the relay settings for the ground fault protection in this example are correct. With a ground fault which is located inside the protection zone, the flowing ground fault current (IEE) and the displacement voltage (Ven) are high enough to protect approx. 90% of the generator stator.

For the ground fault in the power system (outside the protection zone) this protective function is stable (no trip) and the difference between the parameterized pick-up value and the measured ground fault current (IEE) is high enough.  The theoretical value ∆I = 0A is not possible, because the cable-type transformers have different magnetizing characteristics.  If the comparison between the measured and the calculated values reveals potential malfunctions, the settings need to be adapted based on the measured values.

Conclusions

In this article, solutions for secondary and primary testing of the protective functions ANSI 90, ANSI 46 and ANSI 59GN were introduced.   These solutions have shown that secondary testing of complex multifunctional relays is possible even without deactivating overlapping protective functions. 

Furthermore, it was pointed out why the additional primary test of ANSI 59GN to verify the calculated settings is essential.

The presented approaches are illustrated in a way that allows for their application to similarly configured protective functions in relays of completely different manufacturers.  

Biographies

Biography:

Dr.-Ing. Torsten Schierz worked for 7 years at the University of Applied Sciences Zittau/Görlitz in the area of research and teaching. Since 1996 he has been an employee of OMICRON electronics Deutschland GmbH in the business fields Training, Commissioning and Technical Consulting. He has more than 16 years of experience in power system and rotating machine protection, especially in calculation and commissioning, as well as more than 24 years of experience in teaching electrical engineering. At present he is a Senior Consultant.

Torsten is member of the VDE (Federation of Electro Technology Electronics Information Technolog

The shifting asset management paradigm for Electrical Utilities

The shifting asset management paradigm

by Dr. Siri Varadan, UISOL

Ensuring that an asset performs to its full potential throughout its life is fundamental to effective asset management. Various factors make this objective difficult to accomplish, however. Tight budgets, vying priorities and a strict regulatory regime pose constraints that force utilities to do-more-with-less. Utilities are, as a result, shifting their thinking and moving to a paradigm where:

• Risk is no longer avoided, but managed;
• Costs are no longer minimized, but optimized; and
• Performance is no longer maximized, but adjusted to achieve thresholds.

In the context of electric utilities and ongoing smart grid efforts, this shifting paradigm means that asset management needs to be understood in terms of the following simple high-level questions: What work should be done? When and how do you do it correctly? While these questions are simple, they provoke thought on a variety of subjects throughout the asset management process shown in Figure 1. Going through the asset management process and focusing on the correct work answers the question: "Where should a utility invest its money to obtain the best return?"

Asset management, at a high level, addresses the following questions:

1. What assets does the utility own?
2. Where are these assets?
3. How important are these assets?
4. What is the condition of these assets?
5. What is the performance level of these assets?
6. Are these assets' conditions and performances satisfactory?
7. If not, should action be taken to restore the asset to its original performance or health?
8. If yes, what are the proper actions and how do you choose from a diverse set of actions so that corporate objectives, including customer satisfaction and regulatory approval, are satisfied?

While the first two questions almost sound trivial, they are fundamental to asset management and may be addressed by the implementation of a geographic information system (GIS) or an asset registry. A common thread in all of this is the availability and use of quality asset data.

Asset Criticality

Common sense dictates that the "squeaky wheel gets the grease." An asset that is of consequence should get more attention. In a recent asset management survey conducted by UISOL, released in May, utilities equated the word consequence to loss of revenue, system reliability and performance. Consequence may also be understood as the impact caused by the absence of an asset on the system, the customer, other assets and socio-economic factors. Risk is one of the better measures of asset criticality because it describes the impact of the failure of the asset by combining probability of asset failure and impact. Depending on the factors considered in its calculation, risk may take various forms—operational risk, environmental risk, public safety risk and so on.

Asset criticality in the electric utility industry is typically calculated per asset or by asset type and prioritized based on the asset's geographical and topological location. Figure 2 shows an example of asset prioritization for a utility with transmission assets. Value refers to the total sustainment expenditures and risk is a measure of the asset's loss consequence. To clarify, the loss of an asset in the category P1 has the greatest business impact.

Asset Health

Asset health is often considered subjective. All factors that determine asset health are not quantifiable and, hence, asset health is different from asset performance. Despite this, several efforts are used in the industry to quantify asset health. A score from 0 to 100 is sometimes used with the understanding that 0 means the asset is at end of life and requires immediate attention, repair or replacement. A score of 100 means the asset does not need attention for the next several years.

As a starting point, asset health can be conceived as a weighted average of several components, which is a measure of an attribute of the asset that could potentially lead to failure or result in a situation that could cause a failure condition. The asset health indicator should allow peer comparison, provide a sense of remaining life and indicate how soon intervention is required to avoid failure.

Identification of failure modes and the effects of these failure modes is important to health determination in reliability centered maintenance (RCM) analysis. Failure modes effects and criticality assessment (FMECA) focuses on evaluating a failure's impact. In doing so, a reliability engineer might focus on addressing failure modes that bear higher consequence. To eliminate human experts' subjective variations in asset health when selecting the weighting factors used to compute asset health indices, it is best to rely on statistical data and RCM studies that establish failure rates for each failure mode.

Asset Performance

Asset performance is a quantitative concept and correlated to asset health. The nature of the correlation, however, is a topic of further study. At a simple level, one might ask: How well is an asset performing with respect to its peers? The same question might be asked when comparing performance with other assets at other locations, perhaps owned and operated by neighboring utilities. As a result, it is important to understand benchmarking and utility best practices. It is also important to understand the role and nature of standards in evaluating asset performance.

Several measures for asset performance exist. These measures are mostly based on failure frequency and duration. Other metrics commonly used include restoration time, maintenance costs and time between failures. Financial metrics such as replacement costs, O&M costs and return on investment may also be included. Selecting and defining the metrics to use, and the logistics of data collection for calculating metrics are important when implementing an asset management project. It is difficult to calculate an individual asset's performance due to the lack of monitoring. It is possible, however, to make valid inferences about asset performance by considering data from a variety of sources. This is typically an area where data integration helps the most.

Data collected through online monitoring of electrical and non-electrical devices is common with smart grid. This new data can be used to assess asset health and performance when the systems are integrated effectively.

Asset Investment

Actions that restore problem assets to their original performance and health are necessary. These actions or projects could include asset maintenance, repairs, refurbishments or replacements. Each action has its pros and cons. Understanding the cost of these actions and their benefits over time is important when deciding which projects to implement. This science of decision making is at the core of asset investment planning (AIP).

Integrated AIP tools can assist in decisions making using a combination of objective functions, as well as constraints. AIP takes a list of projects and prioritizes them according to an established set of objectives. The rankings indicate projects' importance, their expected return and the time frame in which each project must be executed. AIP also provides information about risk associated with each project.

Asset management is a cradle-to-grave concept that requires careful asset planning, operations, maintenance, performance measurement and corrective actions to improve and maintain performance. Asking the right questions along each step of the asset management process is the best way to ensure goals are met. Internalizing the responses to each of these questions will enable a utility to transform to the new paradigm. A question can have more than one correct response. It is important to ensure that the answers work in concert to achieve asset management's overarching goal of identifying the correct work.

Present efforts at asset criticality, health and performance assessments combine data from various sources to provide quantifiable metrics that provide a sense of remaining life, when to take action and which action yields the most benefit. Correctly performing the work requires incorporation of best utility practices, tight integration of online monitoring, implementation of an asset management culture and personnel training. Leveraging smart grid efforts will be a key factor in the future of asset management.

M7100 - Test Complete Transformer, Generator,... - Power Plant Professionals

M7100 - Test Complete Transformer, Generator,... - Power Plant Professionals:

'via Blog this'

An All Purpose Utility Tool for the Power Grid
Tackling two major concerns for utility workers—safety and time—Doble’s M7100 will revolutionize the way offline testing is done.
The M7100 automates multiple tests, previously performed by several pieces of equipment, cutting down testing time from seven hours to one and a half hours. By dramatically reducing testing time, utilities can now maximize their outage periods by performing more maintenance during the hours previously devoted to testing.
HV Power Factor/Tan-Delta
HV DC Resistance
Polarization Index
Tip-Up
HV 3 Phase 10 kV Iex
DFR
3 Phase LV TTR
3 Phase LR
3 Phase WRT
Primary Injection
Secondary Injection
Ductor
uOhm Meter & more…

Power Distribution System Reliability and Dependability in Process Industries

By Irfan Akhtar, MSEE, BSEE, MISA, MIEEE

Part I
For process industries including chemical, petrochemical, fertilizers, oil & gas plants, reliable delivery of electricity to run the various pumps, compressors, fans, & critical machinery is all the very important. A loss of supply is simply not a trip of the plant where you can restart and you lose just for the time plant remained offline. In certain industries, material in the pipelines and vessels is not just lost but its removal and restart of the plant implies more time and cost.

Therefore, availability, reliability and dependability of electric distribution system is vital and maintenance department has to be proactive. Simple dependence on corrective or preventive maintenance would not work. In this blog, i would like to draw your attention towards condition based maintenance techniques for individual electrical assets of the plant.

Generator:
Generally a plant will have a power supply: either through its own power generation or from the grid through a substation. However, generators will also be part of the supply for most medium to large sized process plants as standby power sources.

Generator is the most neglected part of the power supply network. I have deliberately started with generator and included it in power distribution system in a plant. For Low voltage small generators, it is important to keep the filters and hence the windings clean. Alternator winding should be kept clean and dry. If machine remains off for more than 4 or 5 days, perform insulation resistance test at 500 V before starting again. If you have got RTDs installed, then make sure that the winding temperature is around 2 to 3 C more than ambient to avoid condensation of moisture on winding that may cause flashover. When machines is off, winding heaters should be turned on.

If there is excessive dust on the winding along with oil seepage from bearings forming a think slag on the winding, windings should be cleaned. For ordinary contamination, low pressure instrument air can be utilized along with a nylon brush. For removing oil, apply a solvent which should not damage the insulation. Isopropyle alcohol known as propanol is a good choice. If contamination is too much, winding should be washed either with distilled water or dry ice blasting can also be employed. Advantage of dry ice blast cleaning method is that the dry ice will evaporate by itself. Reference d mentioned below is an excellent resource for inspection checklists and forms whereas reference b gives account of different types of winding insulation system being used by different manufacturers.

References:
a. Handbook of Large Turbo-Generator Operation and Maintenance (IEEE Press Series on Power Engineering)
b. Electrical Insulation for Rotating Machines: Design, Evaluation, Aging, Testing, and Repair (IEEE Press Series on Power Engineering)c.Condition Monitoring of Rotating Electrical Machines (IET Power and Energy)
d. Inspection of Large Synchronous Machines - Checklists, Failure Identification, and Troubleshooting (IEEE Power Engineering Series)


There is of course no substitute to monitor parameters of the running equipment. For generators, keep an eye on temperatures of the windings, cooler inlet, current, load, field current, vibrations. The trends over a longer period of time showing seasonal, load changes can give useful information. During major outages, physical inspection should be carried out with utmost care before any kind of cleaning is carried out. Look for signs of dust, fretting, partial discharge, overheating, puffiness of coils, braces, ties, blocked cooling ducts, end wedges, wedge fillers. It is also good to carry out boroscopy analysis of stator core and rotor if rotor is not removed.

For medium voltage rated alternators, a complete testing regime with online monitoring of key parameters is the order of the day. Though at the minimum, manufacturer's recommendations are to be followed, but following condition assessment tests should be performed every 3 to 5 years with one set o reading taken just after installation to form a baseline:

1. Insulation Resistance / Polarization Index - For routine diagnostics, 1 KV insulation resistance test set can be utilized. Depending on voltage 5 KV can also be utilized. PI values greater than 2.0 are considered excellent, 1.5 - 2.0 considered good, 1.25 - 1.5 fair and below 1.25 not acceptable. It is pertinent to mention that performing this test tells you only about cleanliness & dryness of the windings. Many people think that 5 or 10 KV IR test set can be used to find insulation faults but remember IR test set has very low leakage current capability and hence cannot be used a substitute for DC Hipot or DC ramp test. Note: I am not endorsing DC Hipot here. IEEE std 43 gives a detailed account of insulation resistance testing. IEEE std 4, std 1415 and std 95 also cover the subject in depth.

2. Power Factor - Power factor test is also known as C&DF, tan delta or just dissipation factor. An AC voltage is applied across winding and ground or other winding, leakage current is measured. Cosine of the angle between applied voltage and measure leakage current is called Power Factor. It gives useful information on the overall health of the winding. Major defects as against minor can be detected more easily. This test is part of quality assurance during manufacturing as well as important condition assessment test. Test is performed from 20% of rated voltage upto 120% of the rated voltage. Difference of these readings and also successive (at 20% intervals) is  known as tip up. Tip up of more than 1% is considered bad for winding insulation. A starting value (at  20% of Uo) of less than 0.5% is good. This value greater than 0.5% shows issues of quality of manufacturing and winding curing process initially. During the application of AC voltage Partial Discharge also take place after PD inception voltage (PDIV) and it is prominent in the graph of power factor plotted against voltage esp when machine has PD. Graph generally rises after the onset of PD. If slope is too steep then it shows problems and definitely will show higher tip up values. Another parameter for which tip up is measured is the capacitance of the winding insulation. More capacitance tipup shows higher voids or cavities in the insulation. A detailed account, procedures and limits of this test can be found in IEC 60034 and IEEE 286 standards.

To be continued...