Measurement of insulation resistance on a power transformer

Measurement of insulation resistance

These measurements aimed to determine the condition of insulation between the windings to ground or between two windings. A common method is to provide a dc voltage and represents the condition of the unit megohm insulation. Measured insulation resistance is a function of leakage current that penetrates through the insulation or through the leak in the external surface. Insulation resistance testing may be influenced temperature, humidity and leakage paths on the external surfaces such as dirt on the bushing or insulator. Megaohm meters typically have a capacity of testing 500, 1000 or 2500 V dc.

Mega Ohm meter gauge

Polarization Index Test

The purpose of the polarization index test is to ensure the equipment is operated or even feasible to do overvoltage test. Polarization index is the ratio of insulation resistance at the 10th minute by minute to 1 with a constant voltage.

Total current that arise when providing a dc voltage steady state consists of: 

1. Charging current due to the nature of the measured capacitance of the insulation. This flows down from the maximum value to zero very quickly.
2. Absorption of molecular charge current due to shifting in isolation. These transient currents disappear to zero more slowly
3. leakage current is a conduction current in insulating concrete. Leakage current varies depending on the test voltage. Also includes a leakage current due to leakage at the surface due to contamination.

 

Description:
R = insulation resistance (MΩ)

C = 1.5 for oil filled transformers at a temperature of 20o C 30.0 to untanked oil-impregnated transformers

E =  voltage rating (V) on the inter-phase delta connection, the phase neutral star connection

kVA = rating capacity of the tested winding.

Insulation condition based on the index of polarization

Dissolved Gas Analysis (DGA) on power transformers

Transformer as a high-voltage equipment can not be separated from the possibility of having an abnormal condition, where the trigger can come from internal or external transformer. These abnormalities will have an impact on the performance of the transformer. In general, the impact / result can be overheating, corona and arcing.

One method to determine the presence or absence of abnormalities of the transformer is to determine the impact of abnormalities of the transformer itself. To determine the impact of abnormalities in the methods used transformer DGA (Dissolved gas analysis).

In the event of abnormalities of the transformer, insulating oil as the hydrocarbon chain will break down due to the amount of energy will shape abnormalities and hydrocarbon gases are soluble in oil insulation itself. DGA is basically a process to calculate levels / values ​​of the hydrocarbon gases are formed due to abnormalities. From the composition of the content / value of the gases that can predict what the effects of abnormalities in the transformer, if overheating, arcing or corona.

Gas gas detected from the test results DGA is H2 (hydrogen), CH4 (Methane), N2 (Nitrogen), O2 (Oxygen), CO (Carbon Monoxide), CO2 (Carbondioksida), C2H4 (Ethylene), C2H6 (Ethane), C2H2 (Acetylene).

Broadly speaking, the gas dissolved gases in transformer insulating oil will be extracted / separated from the insulating oil itself first so that the gas will be described and known levels.

Type of head space gas extractor

After separate between the gas with oil, gas will be described again by type of its gas by using chromatography methods.

Power Transformers Part

Power Transformers Part

1. Refrigerant

The temperature at which the transformer is operating will be influenced by the quality of the network voltage, losses in the transformer itself and the ambient temperature. High operating temperatures will cause damage to the transformer insulation paper. Therefore, effective cooling is needed.

Transformer insulating oil in addition to the isolation medium also serves as a coolant. At the time of the oil circulates, the heat emanating from the entanglement will be brought by the oil circulation on track and will be cooled on the fin - fin radiator. The cooling process can be aided by a fan and circulation pump in order to improve cooling efficiency.

Power Transformers Radiator

2. Oil preservation & expansion (Conservator)

When the operating temperature rise in transformer oil, insulation will expand so that its volume increases. Conversely when the operating temperature decreases, then the oil will shrink and the volume of oil will go down. Conservators used to accommodate the transformer oil at mengalamui temperature rise.

Power Transformers Conservator 

Silica gel

To avoid the transformer oil does not deal directly with outside air, then the current conservator designed using brether bag / rubber bag, which is a kind of rubber balloon that is placed inside the conservator tank.

Part of the Bushing

Broadly speaking, the bushing can be divided into four main sections namely insulation, conductor, clamp connections, and accessories. Isolation of the bushing consists of two types of oil impregnated paper and resin impregnated paper. In this type of oil impregnated paper insulation used is insulating paper and insulating oil while in the type of resin impregnated paper insulation used is the paper insulation and resins.

Paper insulation on the bushing (oil impregnated paper bushings)

Bushing conductor insulation coated paper

There are other types of conductors on the bushing is a hollow conductor in which there is an iron binding or hole in the middle penegang main conductor, solid and flexible conductor leads.

Is a means of fastening clamp connection between the stud bushing with a conductor Conductor bushing out.

Section - parts transformer and its function

Iron core

1 Electromagnetic Circuit (iron core)
Iron core is used as a medium course of flux caused by the induction of alternating current to the coil that surrounds the iron core so as to induce a return to the other coil. Formed from the plate - a thin iron plates insulated in such a way that the stacking.


2 Current carying circuit (Winding)
Winding consists of insulated copper rod that surrounds the iron core, which when alternating current flows

Types of Electrical Plugs and Sockets

Electrical plug and socket 2 pin was originally invented by Harvey Hubbell and patented in 1904. Hubbell's work is also a reference to the manufacture of plug and socket and by the year 1915 after its use more widespread, although in the years 1920s home and commercial appliances still use a screw-type lamp socket base Edison.

Then plug 3 pin was created by Albert Büttner in 1926 and obtain patents from German patent agency (ED 370 538), his work is known as "Schuko". But there is also the creator of this 3 pin plug, which is Philip F. Labre, during he was still studying at Milwaukee Vocational School (MSOE) and obtain patents from the United States on June 5, 1928. Anyone penenmunya, discovery 3 pin plug or plugs this is something that is very unusual, because the aspect of human safety, so that the plug or electrical outlet of this type became the standard in almost all countries to date.

Types of Plug and Socket

The types of plug and socket are classified based on the voltage and frequency used in a country, so it can be said there are only two types are based on this classification, namely:

• For voltage 110-220 volts at a frequency of 60 hz

• For voltage 220-240 volts at a frequency of 50 hz

There are also some countries that use the plug and socket for both, see the map of the use of voltage and frequency of electricity in the world below. (Click image to view larger map)

While based on the safety plug and socket are classified into:

• Without grounding, ungrounded. Usually for a 2 pin plug, and according to the IEC standard is a class-II

• With grounding, grounded. Usually for a 3 pin plug, and according to the IEC standard is the class-I

• With grounding and fuses, fuse and grounded. Usually for a 3 pin plug.

Based on the above classifications, then the plug and socket of each state may vary, and generally the type and standard of the plug and socket are:

POWER TRANSFORMERS

1. Definition and function POWER TRANSFORMERS

The transformer is an electrical device which serves to channel the power / energy from high voltage to low voltage or vice versa.The transformer uses the principle of faraday law of induction andthe Lorentz law in distributing power, where the alternating currentthat flows around an iron core iron core then it will turn into a magnet. And if the magnet is surrounded by a winding it on both ends of the windings is the potential difference will occur (Figure1.1).

Figure 1.1. Alternating current around an iron core

Current flowing in the primary winding will induce iron coretransformer that will flow in the iron core and the magnetic flux of this magnetic flux will induce a secondary winding secondarywinding so that at the end there

Transformer Tap Changer

The tap changer is a tool changer for voltage transformation ratio of secondary operations that are better than the network voltage / primary changes.

There are two ways of working tap changer:
1. Changing the tap in a state of no-load transformer. Tap changer that can only operate to move the transformer tap transformer in a state of no load, called "Off Load Tap Changer" and can only be operated manually

2. In a state transformer tap changing under load. Tap changer that can operate to move the tap transformer, the transformer under load condition, called "On Load Tap Changer (OLTC)" and can be operated manually or automatically

How to Bow Fire occurred in Circuit Breaker

How to Bow Fire Occurred in Circuit Breaker? At the time of termination or a circuit linking the power systems (circuit breaker) will occur arc, it happens because at the time of circuit breaker contacts are separated, the potential difference between the contacts will cause the electric field between the contact , as shown in the picture below.

The current that previously flowed to the contact will heat up the contacts and produce thermic emission at the contact surface. While the electric field of high field emissions led to contact the cathode (K). Both of these emissions are produced free electrons are very much and move toward the anode contact (A). These electrons hit the media a neutral molecule of positive isolation of the region, these collisions will cause the ionization process. Thus, the number of free electrons to the anode will be growing and emerging results of ionization of positive ions moving toward the cathode, transfer of free electrons to the anode current rise and heat the anode contact.

Positive ions arriving at the cathode contact will cause two different effects. If contact is made of high melting point materials, such as tungsten or carbon, then the positive ions will be cause heating at the cathode. As a result, emissions increased thermic. If contact is made from low melting point material, eg copper, positive ions will cause high field emission. The results of this thermic emissions and high field emissions will perpetuate the ionization process, so that the charge transfer between the contacts continued and is called the arc.