- July 4, 2022
- Posted by: Anand Borad
- Categories: Condition Monitoring, Remote Monitoring
Power transformers are an integral part of any power distribution system.
Power generation at low voltage is very economical, but transmission at low voltage incurs power losses. In order to solve the power loss problem, step-up transformers increase voltage levels at the beginning for better power transmission application.
Again, high voltage power shouldn’t be distributed to consumers as it would destroy electrical equipment. Step-down power transformers are used to convert high voltage power into low voltage power.
In that way, it makes the power transmission and distribution ecosystem much more practical and efficient.
But what if they fail?
A power transformer failure would badly damage an asset. It also puts human health and life in danger.
Even a small fault in the transmission transformer can cause a power outage on a large scale. Also, it increases the possibility of fire and explosions to a greater degree as it has a large amount of oil very near to high voltage equipment.
Causes of transformer failure
According to a power transformer fault analysis study published at the International Symposium on High Voltage Engineering conference, in as many as one-fourth of cases, the root cause of power transformer failure is unidentified.
Of the known causes, 17.9% of failures are due to equipment aging, 2.7% of failures are due to improper maintenance, and 1.8% of failures are due to overheating. Refer to the chart below for more details:
One thing to note here is that these data cannot represent all power transformer failures as the data was collected from only 20 utilities in Germany, Swiss, Austria, and the Netherlands, but it gives a fairly good idea about what’s happening.
According to another study presented at the International Association of Engineering Insurers, 35.1% of failures are seen due to insulation failure, oil contamination, and improper maintenance/operation.
Here, in this study, they didn’t consider the age of the transformer as a separate factor. But as we have seen in the previous study, aging has a correlation with power transformer failure.
If we go through the studies mentioned here, there are various factors that lead to failure. Here, we only mentioned statistics about aging, improper maintenance, insulation failure, overheating, and oil contamination.
Why? Because these five factors can be managed better.
How? With a proper condition assessment using health and diagnostic tests.
The condition assessment and health checks of power transformers are a must for the security and stability of power system operation.
Let’s dive right into widely used health tests.
Widely used transformer condition assessment tests
- In the dissolved gas analysis (DGA) test, an oil sample is obtained from the transformer. Further, the sample is used for extracting the gases and detecting various faults based on the gas concentration in the lab.
- In order to test the insulating properties of dielectric transformer oil, a sample of the oil is taken and oil breakdown voltage is measured. The lower breakdown voltage signifies the poor quality of the transformer oil.
- The furan test measures insulation degradation byproducts deposited in oil using the oil sample taken from transformer oil.
- Partial discharge (PD), as the name suggests, partially bridges the insulation. During a partial discharge test, a high voltage is applied and electrical PD signals are measured using advanced sensors and data acquisition.
- The acoustic emission (AE) Test is carried out with acoustic sensors placed around the transformer tank. Sensors detect and monitor the release of ultrasonic stress waves. This is used as a follow-up test to locate sources of partial discharge if DGA flags for PD.
- Transient Earth Voltage (TEV) detection is another form of partial discharge test that can find hidden defects inside the insulating components of a transformer.
- In a heat run test, conditions of continuous rated load and overload are simulated in a lab environment in order to analyze temperature rises in extreme conditions.
- Degree of Polymerization (DP) assesses paper degradation but requires opening the transformer to take a sample.
- The dielectric Frequency Response (DFR) test is used for measuring the dielectric properties of the insulation as a function of frequency.
- Sweep Frequency Response Analysis (SFRA) evaluates the mechanical integrity of transformer structures such as core, windings, and clamping structures.
The frequency of these health tests depends on the criticality and the age of transformers. These maintenance tests are scheduled monthly, quarterly, semi-annually, annually, or bi-annually. The frequency of checkups and attention needed can increase as the age of the transformer increases.
Downsides of scheduled maintenance
Most of these assessment tests require the transformer to operate under the normal condition as usual to collect valid quantitative data.
And this requirement creates some safety concerns for personnel involved in data measurement and inspection.
If any of these health check tasks require opening the doors or covers of the transformer (such as the degree of polymerization test), then the personnel involved face an increased risk of electrocution or arc flash.
For transformers, the risks of an arc flash can be significant and make it very difficult to conduct inspections and collect the data.
Another downside of scheduled maintenance is that you have almost zero visibility of an asset between two scheduled maintenance.
For instance, if DGA tests are done quarterly and some anomaly happens in-between, it may go unnoticed.
Things may escalate quickly and may cause serious damage before the scheduled test, maybe in some cases, transformers could fail.
Sometimes, we need such health checks way before the scheduled timeline to avoid the transformer repair and replacement costs. (This cost may range from a few thousand USD to sometime USD 1M+).
Also, each scheduled maintenance comes with costs related to service, maintenance, and site visit. The site visit costs are significant as most power transformers are located in remote places.
The problem is that many times transformers don’t need such health checks as they are working fine, but it is required for precautionary measures.
How do remote monitoring and condition-based maintenance solve these problems?
To solve all three problems discussed above, a condition-based maintenance strategy could be implemented.
This maintenance strategy suggests monitoring the actual condition of an asset to conclude when and what maintenance needs to be done.
Now, with this strategy, the only time maintenance should be performed is when certain indicators indicate declining performance or upcoming failure.
The discussed checks/tests are still required but instead of doing it periodically, service teams can strategize the frequency of these tests. This will help in avoiding non-required tests and also identify if tests are required before the schedule.
To make things smoother, multiple smart IoT sensors can be attached to transformers. These sensors can track transformer temperature, oil quality, voltage level, current supply, KVA and power factor, humidity, oil level, and more. Contrary to the popular belief, these sensors are quite affordable and very easy to maintain, access, and analyze.
These sensor data are also accessible on the web and mobile applications on a real-time basis.
Compared to preventive maintenance, this results in a longer time between maintenance repairs, since repairs are done on a need basis.
Here are a few benefits of implementing remote monitoring of transformers:
- Data collection is on a real-time basis using sensors, so there are minimal chances of disruption to normal operations
- Minimizes time spent on maintenance
- Reduces the cost of asset failures
- Error-free sensor data
- Improves equipment reliability
- Minimizes unscheduled downtime due to catastrophic failure
- Better inventory management minimizes emergency spare parts requirements
- Optimizes maintenance intervals
- Improves worker safety
The transformer manufacturing industry has started adopting digital technologies for solving these challenges. Not just because of competitive pressure, but it also adds to their bottom line with cost reduction and more efficient operations.
Remote transformer monitoring and condition-based maintenance are just not a feature, it is the strategy to grab a greater market share in this industrial world.