Feature sponsored by Test & measurement
faults results in the accumulation of dissolved gases in the transformer oil, so this oil is routinely tested as part of a preventative maintenance program. Eneco’s transformer gas monitor was installed to provide continuous data and reduce the requirement for periodic oil sampling and laboratory analysis. “We discussed our requirement for the early detection of potential issues with our local service provider, Flux Transformer Services,” explains Laurens Freriksen, a project manager and maintenance specialist for Eneco. “They suggested that we should consider using one of Vaisala’s online monitors to support the planning and optimisation of preventive maintenance; to extend
T
ransformer materials can deteriorate over time, resulting in the potential for costly faults, repairs and downtime. However, the development of transformer
the lifespan of our transformer, and reduce the risk of unexpected and costly outages.” Vaisala’s Andreas Hilgers then visited the site to demonstrate two options; the MHT410 which monitors a single gas (hydrogen), and the OPT100 which is a multi-gas DGA (dissolved gas analysis) monitor. Subsequently, the MHT410 instrument was installed by Flux TS, and Freriksen says: “We have benefited from online measurements for around one year now, and it has been very reassuring to see low hydrogen levels in the transformer oil, irrespective of the transformer load.”
BIO GOLDEN RAAND POWER STATION
Laurens Freriksen, project manager and maintenance specialist for Eneco
Biomass is used as a feedstock at the Bio Golden Raand plant to generate energy from wood waste. This form of power generation helps to reduce the consumption of fossil fuels. The plant uses non-hazardous Grade B waste wood. This type of waste may contain Grade A wood (mainly from packaging waste, scrap pallets, packing cases and cable drums, and process off- cuts) together with other waste wood sourced from construction and demolition activities, transfer stations, civic amenity sites and the manufacture of furniture from solid wood. Every year, the plant processes approximately 300,000 tons of waste wood that arrives in Delfzijl by ship and truck from the Netherlands and surrounding countries. The wood is passed to a boiler fitted with a circulating fluidised bed furnace operating at 900°C. Flue gases from the furnace pass through three heat exchangers to a water steam circuit, where steam at 90 bar with a temperature of 520°C is produced. This steam can be delivered directly to local industry, or it can be used to drive a steam turbine, which in turn drives a generator that produces electricity. Generator step-up transformers provide the critical link between a power station and the
transmission network. These transformers step up the voltage from generator level to the transmission voltage level, which steps down the current and thereby reduces the loss of energy as heat and ensures efficient power transmission over long distances. Typically, generator transformers operate continuously 24/7 so they need to be extremely reliable.
TRANSFORMER OIL Generator transformers are generally oil-filled to provide insulation and cooling. The transformer at Bio Golden Raand, for example, contains around 20 tonnes of oil. A special mineral oil is used for its chemical properties and dielectric strength, and this is routinely tested as part of an effective preventative maintenance programme for the transformer. Oil degradation occurs when its molecules
break down under the influence of thermal and electrical stresses due to transformer faults such as discharges or hot spots, for example. This degradation raises the levels of hydrogen, carbon oxides and hydrocarbon gases in the oil. Hydrogen concentration increases with all fault types, but the ratio of hydrocarbons depends on the fault type.
TESTING AND MONITORING TRANSFORMER OIL Traditionally, transformer oil samples are collected once or twice per year and sent for laboratory analysis to determine the level of gases. This spot sampling method provides an indication of dissolved gases and oil quality at one moment in time. The main advantages of continuous monitors therefore, are that they are able to reveal trends so that users can correlate gas levels with transformer load, for example. Importantly, by measuring continuously, DGA monitors can provide early warnings of faults. The levels and trends of dissolved gases can be
Protecting a key power station transformer
38 September 2022 Instrumentation Monthly
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82
