變壓器油中氣體線上監測診斷系統 – 可擴展為變壓器監測系統 (TMS)

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.

A typical On-Line Tap Changer

On-Line Tap Changers (OLTCs) are complex mechanical devices with moving parts that wear over time due to the current they switch (contact wear) and the number of switches they perform (mechanical wear). An OLTC can operate many times a day, switching thousands of amps on each switch and sometimes over-using a limited set of contacts. This repeated use means that OLTCs require careful attention through inspection, replacement and refurbishment.

By monitoring the current position, the number of switching operations by position and the cumulated switched current load by position, an estimation of the contact wear can be obtained. In addition, the current consumption of the OLTC drive motor can be used to detect an increased difficulty in switching positions.

Finally, coking of the contacts will lead to increased arcing, to an elevated oil temperature in the OLTC compartment and thus can be detected by an oil temperature delta to the main tank. By monitoring these additional parameters, Condition Based Maintenance can be used on this key electro-mechanical component and an OLTC failure can be avoided, along with its usually not insignificant ensuing disruptions.

Bushing

Bushing failures account for a large proportion of substation events that result in severe and costly damages and unfortunately even sometimes fatalities. Preventive maintenance, early bushing replacement and regular off-line testing have been employed to address this issue in the past. Monitoring transformer bushings is critical because bushings are constantly under high stress due to the line voltage and heat effect of the current flow. These stresses can be further aggravated by the presence of micro cracks from manufacturing, loss of mechanical strength due to aging, repeated thermal cycling (load + sun), pollution and external flashover eroding the porcelain, sludge and moisture in the insulating oil, and by the fact that new bushings have been made closer to design limits in order to reduce cost, size and weight.

The Kelman DGA 900 PLUS with bushing monitoring is an integrated on-line system that continuously monitors the condition of up to 6 bushings (3x HV and 3x LV). It uses custom bushing adapters (specifically designed for each bushing type).

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.