substation preventive maintenance - pea€¦ · 1) a kind of substation 2) electrical equipment...

PROVINCIAL ELECTRICITY AUTHORITY

Substation Preventive Maintenance

DR.URAIRAT FUANGSOONGNERN : PEA

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Presentation Contents

1) A kind of substation

2) Electrical equipment details of AIS substation

3) Electrical equipment details of GIS substation

4) Preliminary operation before preventive maintenance

5) Preventive maintenance operation details of AIS substation and GIS substation

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A kind of substation

1) AIS Outdoor substation

2) GIS Indoor substation

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Electrical Equipment Details of AIS substation

1) 115 kV Switchyard1) Gas Circuit Breaker

2) Disconnecting & Earthing Switch

3) Current Transformer

4) Voltage Transformer

5) Lightning Arrester

6) Protection Relay

7) Digital Multimeter

2) 115/22 kV Power Transformer

3) Station Service Transformer

4) Distribution Board4

5) 22 kV Switchgear1) Vacuum Circuit Breaker

2) Load Break Switch



5) Protection Relay


7) Bus Bar

8) Power Cable

6) Battery & Battery Charger

7) Grounding


Electrical Equipment Details of GIS substation

1) 115 kV Gas Insulated Switchgear

2) 115/22 kV Power Transformer

3) Protection & Control Board

4) Lightening Arrester/Surge Counter

5) Station Service Transformer

6) Distribution Board

7) Battery & Battery Charger

8) Grounding

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9) 22 kV Switchgear1) Vacuum Circuit Breaker

2) Load Break Switch



5) Protection Relay


7) Bus Bar

8) Power Cable


Preliminary operation before Preventive Maintenance

1) Visual inspection of electrical equipment inside substation

2) Thermo-scan an electrical equipment inside substation before and after preventive maintenance

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Thermoscan (Before – After)

Description : Probably poor connection

Classification : Minor. - > Normal

Recommendation : Should be checked and cleaned the indicated connection point.Criteria of temperature- Temperature normal : less than 40 ºC- Temperature dangerous : more than 40 ºC

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Before Visible Image After


Before Visible Image After

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Thermoscan (Before – After)


Preventive Maintenance operations details of AIS substation and GIS substation

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115 kV Disconnecting & Earthing Switch

Electrical Test- Insulation Resistance Test

Insulation resistance test of each pole to ground by energize voltage 2500 Vdc for 1 min with switch open, shall be exceed than 100,000 MΩ- Contact Resistance Test

It will be made across the main contact with switch close by energize 100 Adc, and value compare by factory test should be very less.- Operating Interlocking Check

When ground bar is closed, It should not operate to close with mechanic interlocking.

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96 kV , 108 kV Lightning Arrester

Visual Inspection- Support Structure - Seal and Body- Grounding System- Cleaning


Energize 5,000 Vdc for 1 min on each arrester, phase to ground. The value shall be exceed more than 100,000 MΩ- Counter Operation Test

Verify correct operation of surge counter by input about 100 Vdc (by capacitor 300mF) at top and bottom of surge counter and counter should count up- (Optional) DC Hi-Pot Test

Power frequency voltage test on the main circuit for 1 min at lease 62% of maximum test voltage, should have a few difference leakage current of each phases 13


115 kV Voltage Transformer & Current Transformer


Insulation resistance test of primary winding and secondary winding with respect to ground at voltage 2,500 Vdc for 1 min. The value shall be exceed more than 1,000 MΩ- Turn Ratio Test

Verification check by voltage method, measure a turn ratio of each phase and each tap by energize current following nameplate (such as 1000 A for CT, 150 A for VT) between HV and LV in every core Then, read the ratio value from a test instrument in A. analyze the value of turn ratio in the every core, the different value should be very less comparing by nameplate shall not deviate more than 0.5%

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115 kV Voltage Transformer & Current Transformer

Electrical Test- Winding Resistance Test

Measure a secondary winding resistance of each phase by energize DC current ( 1 A or 5 A follows its nameplate) between HV and ground in every core at full tap. Receive the value of V and calculate to R from a test instrument in Ω and analyze the value, the different value should be very less and/or comparing by factory test

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115 kV Gas Circuit Breaker (SF6)


Insulation resistance test at 5000 Vdcbetween top and middle, and between middle and case for 1 min, shall be exceed than 100,000 MΩ- Contact Resistance Test

It will be made between the upper fixed contact through the GCB to the lower contact points (top to middle) with GCB close at 100 Adc, the different value should be very less comparing by factory test- Operating Timing Test

Energize 125 Vdc at coil for operate GCB to change position to close and open and catch that time in use for compare with factory test.

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115 kV Gas Insulated Switchgear (115kV GIS)

Visual Inspection- Support Structure - Seal and Body- Motor Charging- Cleaning

Electrical Test- SF6 Pressure System Test

to measure pressure of each compartments by instrument (IR zero waste SF6 analyzer), compare with its nameplate and gauge (green zone)- SF6 Moisture (Dew-Point) and leakage

to measure dew point by analyzer and refer to moisture inside compartments, shall be less than -30ºC

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Standard H2O SO2 SF6 HF

IEC60480-1 750 ppm 12.0 ppm 97 % 25 ppm

115 kV Gas Insulated Switchgear (115 kV GIS)

Electrical Test- Contact Resistance Test

It will be made between the upper fixed contact through the CB at 100 Adc (at the terminal box), the different value in µΩ should be very less comparing by factory test- Operating Timing Test

Energize 125 Vdc at coil (in the terminal box) for operate CB to change position to close and open and catch that time in use for compare with factory test.- Insulation Resistance Test

It test between current transformer secondary and ground usually checked by use of megger test at 1000 Vdc (500 Vdc if required) for 1 min shall be exceed than 100,000 MΩ- Winding Resistance Test

Test with multi-meter, measure in Ω.- Alarm Circuit Check 18


115/22 kV Power Transformer

Visual Inspection- Bushing, Tank and associated device- Load Tap-changer- Oil Level Check- Replace Silica Gel- Cleaning

Electrical Test- Polarization Index Test

Perform polarization index on each winding (primary and secondary shorting 3 phases) to ground. Energize voltage at 2,500 Vdc (about 0.5 ampare) for 1 min and 10 mins. PI should be more than 2.0

PI=MΩ at 10 minsMΩ at 1 min

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Electrical Test- Winding Resistance Test

Measure a winding resistance of each phase by energize current 10 Adc between each phase in every primary taps and secondary tap in V and calculate to Ω. Analyze the value with each phases in the same tap, the different value should be very less comparing by factory test

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- Turn Ratio TestMeasure a turn ratio of each phase and each tap by

energize voltage 10 Vac (or auto mode) between HV and LV in every tap in V. Analyze the value of turn ratio in the every tap, the different value should be very less comparing by nameplate (including phase angle difference in degree)




Electrical Test- Oil Transformer Test

By IEC 60156 (ASTM if any) including Dielectric Breakdown Test at both main tank and OLTC.

- Water Content TestBy ASTM D1533, to sampling transformer

oil to test in the laboratory, shall be less than 25 ppm on main tank and less than 40 ppm on OLTC.

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Standard Type Gap No. of Test Acceptable

IEC 60156 Spherical 2.5 mm 6 > 60 kV

ASTM D877 Plate 2.5 mm 5 > 30 kV

ASTM D1816 Spherical 2.0 mm 5 > 50 kV



Electrical Test- Dissolved Gas Analysis (DGA)

By ASTM D3612, to analyze key gas in transformer oil such as O2 N2 H2 CH4 CO CO2 C2H4 C2H6 C2H2 C3H6 C3H8 of main tank and OLTC.

- Oil/Winding Temp.See a winding temperature at a gauge, shall be in

the length of setting* Normally Setting Fan : 70 C | Alarm : 95 C | Trip : 105 C- Tr. Fan (Motor/Fan)

See fan working by simulate all functions refer by temperature (on/off/work at high temp.), shall work by its setting 22

O2 N2 H2 CH4 CO

N/A N/A <100 <120 <350

CO2/CO CO2 C2H4 C2H6 C2H2

>3 <2500 <50 <65 <1


115 kV Protection & Control Board115 kV Protection Relay

Visual Inspection- Seal and Body- Setting Relay Recording- Cleaning

- Relay Feature (Operation) Check- Digital Multi-meter Check

Relay in testing27/59 – Under/Over Voltage Relay50/51G – Instantaneous/Inverse Time Overcurrent Relay21 – Distance Relay87 – Differential Relay

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22 kV Switchgear & Bus Bar

Visual Inspection- Support Structure- Seal and Body- Bus Bar Connection- Cleaning- Motor Charging (VCB)- Terminator (Power Cable)- Record Setting Relay (Relay)

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Item- Vacuum Circuit Breaker- Current Transformer- Voltage Transformer- Protection Relay- Metering- Power Cable


22 kV Switchgear & Bus Bar

Electrical Test (VCB)- Contact Resistance Test- Insulation Resistance Test- Operation Timing Test- Operation Test

Electrical Test (CT&PT)- Winding Resistance Test- Insulation Resistance Test- Turn Ratio- Contact Resistance Test

Electrical Test (Power Cable)- Insulation Resistance Test

Electrical Test (Protection Relay)- Secondary Injection Test 25


Station Service Transformer

Visual Inspection- Bushing, Tank and associated device- Oil Level Check- Cleaning

Electrical Test- Winding Insulation Resistance Test

Perform insulation resistance and/or polarization index on each winding to ground. Recommended minimum DC test voltage at 2500 Vdcfor primary and 500 Vdc for secondary.- Oil Transformer Test

By IEC 60156 (ASTM if any) including Dielectric Breakdown Test.

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Computerized Substation Control System (CSCS)

- Visual Inspection- Cleaning- Communication System Test

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AC/DC Distribution Board

- Visual Inspection- Cleaning- Insulation Resistance Test (Panel)

Test for 1 min on each bus, phase to ground and phase to phase with input/output off.

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Battery & Battery Charger

Visual Inspection- Seal and Body- Cleaning

Electrical Test- Insulation Resistance Test- Charger Operating- System Function Check- Voltage Battery Cell Check

Measure cell voltage compare by its nameplate and analyze its defect.- Impedance Test

Measure cell resistance (impedance) between pole + and pole - in Ω compare by nearby cell and analyze its defect.

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Grounding Systems

Visual Inspection- Grounding System Connection Check- Torque at joint

Electrical Test- Grounding Resistance Test

Performed the test by fall of potential method. The resistance of grounding point should less than 5 ohm.- Grounding Continuity Test

Performed the test by two points method. The resistance of ground and another ground should be very less

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Insulation Resistance and Polarity Index Test

1. Prepare a test instrument (such as Megger/MIT515) 2. Measure an insulation resistance of each core by

energize 5,000 Vdc between core and ground for 1 min and 10 mins with switch open

3. Read the value from a test instrument in MΩ4. Measure in every phases and cores, then analyze

the value compare by each phase in the same core, the different value should be very less but shall be exceed than 100,000 MΩ

5. PI (Polarization Index) is the value of Insulation Resistance at 10 mins divided by at 1 min, shall be above 2.00

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Contact Resistance Test

1. Prepare a test instrument (such as Megger/MOM200A) 2. Measure a contact resistance of each coil (status close

and open) by energize current 100 Adc in every phases3. Read the value from a test instrument in µΩ4. analyze the value with each phases, the different

value should be very less comparing by factory test

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substation preventive maintenance - pea€¦ · 1) a kind of substation 2) electrical equipment...

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