Transformer health check

 

Transformer failure is a time-consuming and costly problem to deal with. A new service from ABB helps identify potential problems early on and prevent them developing into something more serious and costly.
ABB’s transformer diagnostic service uses state-of-the-art electronic equipment which, combined with the expertise of experienced and highly skilled test engineers, is providing utility and industrial customers with a fast, non-invasive, internal health check for power transformers rated up to 400kV. The service is designed to keep transformers from any manufacturer operating at maximum load and energy efficiency, without compromising reliability or safety. It can be applied at any stage of the asset’s life, from installation and commissioning, as part of a condition-based asset maintenance programme, and right through to diagnosing and locating a potential problem.
The transformer diagnostic service uses three main techniques – Sweep Frequency Response Analysis (SFRA), Frequency Domain Spectroscopy (FDS) and winding resistance measurement.

SFRA
The SFRA test, carried out by a Pax FRAX-101 system, diagnoses the condition of the transformer windings and magnetic core. It is performed by injecting a variable frequency AC voltage to each winding and plotting the responding current as a curve. Typically, these ‘finger print’ reference curves are captured either when the transformer is new or when it is known to be in good condition. They are then used as a baseline during maintenance tests or when there is a reason to suspect a problem.
In the hands of ABB’s team of transformer test experts, the SFRA test is an excellent way of checking for movement or displacement of windings and can even locate the exact position of a fault.

FDS
FDS, carried out by a Pax IDAX-206 system, is used to assess the integrity of a transformer’s insulation system by measuring its dielectric properties as a function of frequency over the 1MHz to 1000MHz range. This test provides information about the volume of moisture and presence of contaminants in the solid insulation, as well as the conductivity and power factor of the oil.

Winding Resistance Measurement
The Omicron CPC 100 winding resistance measurement equipment is used to inject a DC current of up to 2kV through the transformer windings and then measure the voltage drop across the winding to enable the resistance to be calculated. This test helps to check that the transformer connections are correct and that there are no severe mismatches or open circuits. LiamWarren of ABB’s UK power service operation says: “Power transformers are mission-critical for many industrial, utility and power generation customers. Failures can result in lengthy downtime, with consequent loss of operating revenue, and expensive repairs. Planned maintenance is the best insurance against transformer failure and that’s where this new service comes in. It offers an efficient, costeffective way of assessing the overall condition of a transformer fleet so that areas of potential concern can be flagged and action taken well before a potential failure develops into a serious fault.
“Furthermore, if a customer has a transformer that is already causing concern, our diagnostic team can establish the severity of the problem, locate the fault and provide expert advice on what action to take. For example, with regular testing it might be possible for the transformer to continue in service, while operating under a safe, reduced load, until a planned service interval is reached. ABB can then provide a comprehensive repair and refurbishment service to restore the transformer to full working order.”