Ageing

In service, fluids are usually submitted to temperatures ranging from 60°C to 120-140°C. Temperature can degrade the chemical matter and solid and liquid insulation. Oxidation stability is an important characteristic to measure and monitor.

Acidity is also an indicator of the fluid’s health – the lower the acidity levels, the longer the fluid will continue to perform optimally – not to mention the impact that it could have on the other components of the transformer.

NYCODIEL water compatibility offers an improvement in solid insulation protection, meaning less power loss and a longer shelf life for paper insulation.

Thermal oxidation stability

Testing at 500h is recommended by IEC 61099 but is not mandatory. Testing at 800h is neither required nor recommended, but was performed to illustrate how the different technologies resist to longer periods of stress.

IEC 61125 Method C

Test conditions:
– Temperature: 120°C
– Air flow: 0.15 l/h
– Metal: Cu
– Oil quantity: 25 g.

IEC 61125 METHOD C – RESULTS

Characteristics	Duration Hrs	Synthetic Ester			Vegetable Oil	Mineral Oil	Silicone Oil	IEC 61099 limit
		Nycodiel 1233	Nycodiel 1244	Nycodiel 1255 Nycodiel 1258
Acid number (mg KOH/g)	0	0.01	0.02	0.02/0.01	0.07	0.03	0.01
	164	0.09	0.08	0.09/0.01	2.84	0.40	0.01	Max 0.3
	500	0.16	0.14	0.20/0.01	ND	1.10	0.01
	800	0.23	0.23	0.23/0.01	ND	1.29	0.01
Deposit	164	0.004	0.005	0.005/0.004	0.5	0.10	0.01	Max 0.01
	500	0.004	0.005	0.005	ND	0.14	0.01
	800	0.005	0.005	0.003	ND	0.17	0.02
Appearance after 800hrs					N/A; product becomes solid between 164h and 500h.

•    NYCODIEL fluids exhibited very good resistance to oxidation and corrosion. They resist high temperatures and have a long shelf life.
•    Other tests were run to show additional results. See Nyco Presentation – EFIL 2013 paper.

Water Influence

Ester oils absorb water owing to their structure. Once absorbed, water is not free but “inactive”. Water links to ester molecules by hydrogen bonds and Van der Waals links.
This property means that they can dehydrate insulating paper, and it is a considerable advantage in the case of retro-filling: dehydrating insulating paper can extend transformer lifetime without power loss.

In-service fluid survey

IEC 61203 is the service survey-fluid maintenance standard to be used to determine conformity of a fluid in service.
The in-service survey is carried out as for conventional dielectric fluids:
•    Water content
•    Acidity
•    Fire point
•    Dielectric breakdown voltage
•    Dielectric dissipation factor

Other analyses like viscosity, density, dissolved gas content, should be done to evaluate the main product characteristics.

NYCODIEL properties

Safety     Environment     Insulation      Cooling      Retro filling and compatibility