While on-line DGA is now widely accepted as the most effective method of assessing the condition of a transformer, it does not cover all the possible sources of issues. Subsystems like the tap changer, the cooling system or the bushings can generate their own problems if they are left unmonitored.

It is most suited for monitoring large, mission critical transformers or compromised transformers with a view to extending their life and preventing any unexpected failure.

Industrial processes where an OLTC Transformer is seen as a manufacturing tool, often dependent on an uninterruptible power supply as part of the process.

Preventing unplanned outages is vital to maintain the manufacturing process output, where failure would result in costly downtime or waste. The OLTC transformer is often used within renewable power generation where varying output needs to be compensated.

Dissolved Gas Analysis (DGA) and moisture measurements of insulating fluids are recognized as the most important tests for condition assessment of transformers. In previous years, multi-gas DGA was traditionally confined to a laboratory environment, with infrequent yearly off-line manual sampling aiding time-based maintenance strategies.

However, as the global average age of transformers continued to rise, the possibility of rapid aging and even catastrophic failure between off-line tests also increased, leading many asset owners to adopt on-line DGA monitoring to provides remote alert and multi-gas diagnostic of deteriorating transformer condition.

This facilitated operational decisions without needing to go to site for manual oil sampling. It avoided unplanned outages, increased network reliability and enabled the move to condition-based maintenance.

In the early 2000’s, GE Vernova’s original Kelman™ range of on-line multi-gas DGA analyzers brought Photo-Acoustic Spectroscopy (PAS) measurement technology to the market. GE Vernova is now proud to introduce the Kelman DGA 900, its next-generation multi-gas on-line DGA and moisture analyzer. At its heart lies an evolved implementation of GE Vernova’s proven PAS technology, providing laboratory challenging levels of precision and repeatability with no consumables (carrier or calibration gases) and no need for frequent re-calibration. It also has enhanced computing power and scalable I/Os for future proofing and adding functionalities to grow each analyzer into a flexible transformer monitoring solution.

Transformer issues can now be detected in their infancy, making sure that they are fixed early so that the nominal expected life of the transformer can be achieved. Maintenance interventions can now be planned, reducing their length and their cost and causing less disruption to the network and customers. In addition, aging asset replacement strategies can be anchored on hard health condition data and not purely based on the age of the transformer.

Kelman DGA 900 PLUS further incorporates on-board calculations based on the very latest IEC®/ IEEE® thermal and moisture models standards and computed from the specific transformer characteristics obtained from the name-plate and test reports of the transformer.

The integrated Kelman DGA 900 PLUS comes with optional Input/Output (I/O) cards so that additional sensors can be attached to increase its measurement scope. With this add-on, the DGA 900 can continuously measures other critical parameters such as oil temperatures, load current, water content in oil, and cooling status which are complementary to the DGA information.

These models convert raw data into additional intelligent information to monitor the state of the transformer’s insulating system every 10 minutes and determine its long term aging profile. This information can also assist system operators in making critical operational decisions, particularly when it comes to safely overloading aging transformers by calculating the dynamic loading capacity. The aim of all the models is to aid in optimizing the transformer’s life (which is dictated by the state of its insulating system) and in deriving the optimum operating profile to maximize operational effectiveness.

It continuously measures the change in Capacitance C1 compared to the original nameplate value. It also measures the relative Power Factor (Tan Delta) change compared to the original nameplate value. If the reference voltage from a voltage transformer (phase to ground) information is available, then the real PF induced by the bushing can be calculated and displayed. This provides information similar to that obtained during off-line tests.

PD is a localized breakdown of a small portion of a solid or fluid electrical insulation system that is under high voltage stress, which does not completely bridge the space between two conductors. PD on solid dielectrics results in localized gradual erosion of the insulation system that eventually leads to failure of critical insulation.

Using the same bushing adaptors, the DGA 900 PLUS offers the added advantage of measuring high frequency signals in order to monitor PD activity, giving an added level of protection for the main tank of the transformer. The amplitude of the PD pulses are recorded and used to calculate an overall measure of PD activity. Several methods are used to discriminate between internal PD and external noise (corona discharge). The BMT 330 also provides Partial Discharge Phase Resolve (PDPR) diagnostics.

Graphical Visualisation of the monitoring data generated using the backend analytical engine, provides clear diagnostic trends.