闪点（最低）和倾点（最高）分别是140 °C 和 −6 °C。没有处理过的新油节电强度是12 MV/m (RMS)，处理后应该高于24MV/m (RMS)
室内使用的大型变压器必须使用干式变压器（不含油液）或者使用抗燃油。
油质量和测试：
在变压器工作时，变压器油会承受电和机械压力。此外还有因为绕组和固体绝缘物化学反应，或者高温催化下产生的污染物。变压器油的化学性质会随之慢慢改变，累积多年后会使得其应当发挥的功用失效。因此应该定期检测以获知油的基本电气参数，确保其适宜继续使用，确认是否需要进行过滤/再生等操作。检测可以分为如下方面：
含气量分析
呋喃分析
PCB（多氯联二苯）分析
一般电气和物理测试
颜色和外观
击穿电压
水分含量
酸度（中值）
介质损耗因数
电阻
沉积物和污泥
表面张力
闪点
倾点
密度
运动粘度
具体控制参数可以在IEC, ASTM, IS, BS等标准中查询，可以使用各种方式测得。呋喃和DGA测试并不是用来判定变压器油质量的参数，而是判断绕组内部是否有异常或者变压器绝缘纸是否有异常，因此这两项需要在整套变压器大修时测量。建议检测时间间隔如下：
一般测试和物理测试：两年一次。
含气量分析：一年一次
呋喃测试：变压器工作满5年后，每两年一次。
Oil transformer filter
Oil dehydration equipment
Oil tester
Water oil separator
dielectric oil filtration machine
The flash point (min) and pour point (max) are 140 °C and −6 °C respectively. The dielectric strength of new untreated oil is 12 MV/m (RMS) and after treatment it should be >24 MV/m (RMS).
Large transformers for indoor use must either be of the dry type, that is, containing no liquid, or use a less-flammable liquid.
Testing and oil quality
Transformer oils are subject to electrical and mechanical stresses while a transformer is in operation. In addition there is contamination caused by chemical interactions with windings and other solid insulation, catalyzed by high operating temperature. As a result the original chemical properties of transformer oil changes gradually, rendering it ineffective for its intended purpose after many years. Hence this oil has to be periodically tested to ascertain its basic electrical properties, make sure it is suitable for further use, and ascertain the need for maintenance activities like filtration/regeneration. These tests can be divided into:
Dissolved gas analysis
Furan analysis
PCB analysis
General electrical & physical tests:
Color & Appearance
Breakdown Voltage
Water Content
Acidity (Neutralization Value)
Dielectric Dissipation Factor
Resistivity
Sediments & Sludge
Interfacial Tension
Flash Point
Pour Point
Density
Kinematic Viscosity
The details of conducting these tests are available in standards released by IEC, ASTM, IS, BS, and testing can be done by any of the methods. The Furan and DGA tests are specifically not for determining the quality of transformer oil, but for determining any abnormalities in the internal windings of the transformer or the paper insulation of the transformer, which cannot be otherwise detected without a complete overhaul of the transformer. Suggested intervals for these test are:
General and physical tests – bi-yearly
Dissolved gas analysis – yearly
Furan testing – once every 2 years, subject to the transformer being in operation for min 5 years.
Source: http://en.wikipedia.org/wiki/Transformer_oil
