BUS BAR TESTING

The following test to be conducted  on bus bar.

1. Contact Resistance test
2. Insulation Resistance check  before H.V test
3. H.V test
4. Insulation Resistance check  after  H.V test

1. Contact Resistance test:

Contact Resistance measured by injecting the DC current through the busbar. With the feed back of voltage drop the resistance value will be arrived in the micro ohmmeter.


2. Insulation Resistance check before H.V test:

Insulation values measured between phase to earth and between phases with the help of 5 KV megger for 60 seconds.

3. HV for  BUS BAR:

The high voltage test is conducted to find the healthiness of the dielectric material supporting the bus bar. This is achieved by applying 24 KV AC between phase – Earth (remaining phases are shorted and earthed) for 1 minute. With the help of HV test kit.

The leakage current in milli amps will be measured and recorded for analyzing purpose the insulation should be withstand this test for the specified period.

H.V Testing for Bus bar

4. Insulation Resistance check after HV test:

Insulation value measured between phase to earth and between phases with    the help of 5 KV megger for 60 seconds.After HV test to find out any detonation of insulation material  after the HV test voltage stress. And to be compare with the IR values taken before the  HV test.

CURRENT TRANSFORMER TESTING METHODS

The following test to be conducted for a current transformer.

1. Insulation Resistance Test.
2. Winding Resistance Test.
3. Polarity Test.
4. Knee point Test.
5. Ratio Test.

1) Insulation Resistance Test:

To know the insulation value of CT windings. We will be applying primary to Earth 5kv for 60 seconds, primary to secondary 2.5 kv for 60 seconds & secondary to Earth 1000v for 60 seconds.


2) Winding Resistance Test:

To verify the winding resistance as specified by the manufacturer and to check for any damage in the CT winding resistance arrived by injecting DC current through the winding and measuring the voltage drop compare the reading with factory test report.

3) Polarity Test :  

This test is necessary to see the relative polarity of the primary and secondary terminals when terminals are not marked or to establish the correctness of the marking if already marked. This test is carried out with help of   9v (or) 12v DC battery. Apply the DC source between primary Terminals P1 (+) P2 (-) and measure the secondary side using Null deflection analog ammeter and check the correct deflection of meter & compare with polarity mark.

4) knee point voltage:

Saturation point of CT core is measured by applying voltage in secondary by keeping primary open the point where the exciting current increase by 50% for a 10% increase in secondary voltage is referred as saturation region.

5) Ratio Test:

To verify the ratio error of the CT this test is performed with help of primary injection kit. Inject the current through P1- P2 (primary of CT Terminals) and measure the corresponding secondary side output current and calculate the ratio error from actual and measured values.

Potential Transformer Testing Methods

The importance of transformer tests is often underestimated. Risks such as confusing instrument transformers for metering and protection, or mixing up connections can be reduced significantly by testing before initial use. At the same time, damages to the interior of an potential transformer, caused for example during shipping, can be recognized easily. Also changes in an instrument transformer, caused for example by aging insulation, can be identified at an early stage.

1. Insulation Resistance Test.
2. Winding Resistance Test.
3. Polarity Test.
4. Ratio Test.

1)Insulation Resistance Test:

To know the insulation value of PT windings we will be applying primary to Earth 5kv for 60 seconds, primary to secondary 2.5 kv for 60 seconds & secondary to Earth 1000v for 60 seconds.

2)Winding Resistance Test:

To verify the winding resistance as specified by the manufacturer and to check for any internal winding damage in the PT this test is carried out. Winding resistance is arrived by injecting DC current through the winding and measuring the voltage drop. Compare the reading with factory test report.

3)Polarity Test : 

This test is necessary to see the relative polarity of the primary and secondary terminals when terminals are not marked or to establish the correctness of the marking if already marked. This test is carried out with help of   9v (or) 12v DC battery. Apply the DC source between primary Terminals P1 (+) P2 (-) and measure the secondary side using Null deflection analog ammeter and check the correct deflection of meter & compare with polarity mark.

4)Ratio Test:

To verify the ratio error of the PT this test is performed with help of primary injection kit. Inject the Voltage through P1- P2 (primary of VT Terminals) and measure the corresponding secondary side output voltage and calculate the ratio error from the actual and measured values.

ELPLUS NT-111 High Voltage Insulator Coating

NT-111 High Voltage Insulator Coating is a new generation with nano-technology one-part   room   temperature vulcanizing silicone coating. The coating exhibits highly hydrophobic and arcing resistance and is designed to improve the performance of porcelain or glass insulator. The coating could significantly depress the leakage current and dry band arcing and totally prevents the tracking and flashover. It provides a virtually maintenance–free power system. The nano-technology additive extreme increase the strength of silicone coating that proves NT-111 not only have a long term performance but also will not be affected by ozone, UV light, temperature and corrosive environments(salt-fog, industry dust and mist of hydrochloric acid or sulfuric acid, etc.)

220 KV Ping-Shan Substation

Due to excellent properties of NT-111 the coating could eliminate or reduce the routine maintenance as the following:

• Regular insulator water washing.
• Periodic re-application of silicone grease or compound.
• Replacement of insulators damaged by flashover.

500 KV Ling-Dong Jia Line

*Applied unique nano-technology and exhibited highly hydrophobic and arcing resistance. It significantly depresses the leakage current and prevents flashover on insulators.

*Specially formula of one-part RTV silicone coating, designs for easy application on both substation and transmission line.

*Stable weatherability, proves coating will not be affected by ozone, UV light, temperature and corrosive environments.

*Provide highly protection for all kind of contaminations that include heavy salt-fog, industry dust and chemical mist.

*correspond to IEC60587 Class 1A 4.5.

Application

The surface of insulator must be thoroughly clean and dry. In general that use high pressure water washing will be enough for most case. If insulator have previously been coated with silicone greases or other type of compounds, it would be hard to get it off by only water washing. The workers should scrape the greases off by scraper first and then hand wiping the residual grease film with paraffin and naphtha. If the surface contaminated cement like material, the dry abrasive have to be applied with crushed corn cob.

The methods of coat  on insulator include brushing, dipping and spraying. Usually the coating has to be applied from one to three layers that depend on the coating methods. When applied by brushing or dipping, usually one coat is sufficient to obtain complete coverage. When applied spraying it needs two or three coats and depends on the equipment we use. Each coat can be applied after the surface of previous coat is tacky.

According to IEEE std 1523-2002 the thickness of dry layer is about 15 mil to 20 mils (0.4 mm to 0.5 mm). When apply coating for only few insulators, we can coat by the way of brushing. If we try to apply coating on suspension insulator, dipping is the best way. If we try to apply coating on an entire substation, spraying is the best way. It is also  cost efficiency and will form a smooth silicone elastomer surface. The details about how to apply the coating on insulators please refer to the HVIC Field Application Guide.

NT-111 High Voltage Insulator Coating can be sprayed for live line application but must be used high-flash point carrier solvent. It could keep it off the fire. The application has to be operated by professional workers with a special design tool.

Packaging

ELPLUS NT-111 is available in 4 kg (1 gallon can), 20 kg (5 gallon pail), 10 lb (1 gallon can) and 45 lb (5 gallon pail).

Colors

ELPLUS NT-111 standard colors are dark grey and white. Other colors are available by request.

Storage

ELPLUS NT-111 when store at or below 32 oC in original unopened container has a shelf life for 12 months from date of production.

Safety precaution

Adequate ventilation should be provided when apply HVIC in closed type environment. Contact uncured coating may irritate eyes. Flush well with water and call a physician. The details please refer to Material Safety Data Sheet.

Uncured

Type                               One-Part Silicone

Appearance                    Smooth Paint

Specific                          Gravity 1.22

Cure System                   Oxime

Tack-free                        30 minutes

Solid Content                 72%

Viscosity                        10000±1000cps

Cured – at standard condition* for 7 days  

Dielectric strength            455 V/mil 

Dielectric constant            3.8(at 100Hz)

Volume Resistivity            3.75 x1015Ω/cm 

Dissipation Factor            0.022(100Hz)

                                           0.016(100KHz)

Dry arc resistance              Track > 180s

                                           Burn out > 420s

IEC 60587                         1A4.5

*Standard condition is at 25 Degree Celsius and 50% R.H.