Importance of sub-station
Equipment Maintenance
Presented By
MD.GOLAM MOWLA
XEN(G&P)
Major Equipments of S/S
Inspection and maintenance of substation components
•Daily, Weekly, Monthly, Half-yearly & yearly maintenance
• Special and emergency maintenance and execution of annual
maintenance
•Maintenance of bushings and insulators
• Maintenance of transformer mounted ancillary equipment
•Maintenance and inspection of gaskets
• Checking tank and radiators for oil leaks
•Checking for oil levels in main tank and the LTC
• Changing silica gel in breathers
•Inspecting fan operation
•Inspection of LTC
• Maintenance of transformer firefighting system
Major Equipments of S/S
Isolator
Earth Switch
C.T./P.T.
Lightening Arrester / Surge Diverter
Switchgear / Breaker
Power transformer
Auxiliary Transformer
Bus bar
Battery and Battery Charger
Control Relay Panel
Remote Terminal Unit for SCADA
Importance of Maintenance
Reliable Power supply
Sustainable Energy Drawing
Quality power deliver
Un-Interruption
Durability
Risk free assurance
Importance of Maintenance
Free from Threat or Pressure
Cost Effective for future planning
Free from Electric Hazards
Economically Savings from unwanted or
unknown huge amount of cost for
restoration.
In a broad sense, savings annually 90
million Taka paying 10 million by
properly using.
Maintenance & Inspection of S/S Equipments
Maintenance of Substation Equipment
Preventive and Schedule Maintenance
Emergency or Break-down maintenance
Inspection of Substation Equipment
Daily Inspection
Weekly Inspection
Monthly Inspection
Quarterly Inspection
Half-yearly Inspection
Annual Inspection
Power Transformer
Power Transformer
Conservator
HT Buchholz
Bushing Relay
LT
Bushing Tap
Changer
Radiator
Silica Gel
Cooling fan
Operation of Power Transformer
Operation of
Operation of cooling breathing system
control system
Operation of
tap changer
Maintenance of A Power Transformer
Test oil sample of transformer main tank & tap changer tank
Check condition of oil gauges and oil level
Check for oil leakage & integrity of gasket joints
Check the tightness of nuts & bolts
Check the insulation resistance of bushing
Check that silica gel crystals are blue
Re-greasing of bearings of cooling fan
Check the performance of oil temperature & winding temperature meter
Change the oil of OLTC
Check the control system and driving mechanism of OLTC
Check insulation resistance between each winding and ground.
Calculate the Dielectric Absorption Ratio-
DAR = (I.R. of 60 sec)/(I.R. of 15 sec)
Test of Insulating Oil
Test/Parameter Reference value
Dielectric strength test: Minimum 30 kV at 2.5 mm gap between
two gloves with minimum mm dia
Acidity test: Acid value less than 0.02 mg KOH/g
Measurement of moisture
content in oil: 50-60 ppm
Gas analysis:
Viscosity at 20°C : 40 cst
Pour point maximum: -10°c
Flash point: 140°c
Dissipation factor or
Power Factor/loss tan delta: at 90°c 0.5%
at 20°c 0.1%
Volume resistivity : 5.7×1014 Ω-cm
Interfacial tension at 27°C: minimum 0.04 N/m
Dielectric constant: 2 to 2.5
Power Transformer Maintenance Form (132/33 KV)
Substation: Bashundhara 132/33 KV Grid Year of installation: 1995
Capacity: 50/75 MVA
Year of manufacture: 1993
Equipment: 132/33 KV Power Transformer. Tap Type: ONLOAD Maximum load: 315 Amps
(132 KV Side) Date 27.05.07
Identification Name:GT-1 Quantity of oil:39216 liters Date of Maintenance: 02 November 07.
Manufacturer:Hawker Siddeley Power Trans Ltd. Cooling type: ONAN/ONAF Winding Repair/Not repaired
Serial no. 901562 Repaired: 2003.
Checklist:
Sl Check point Checked Remarks
01 Test oil sample of main tank √ Yes No Tested from CERS, result satisfactory
02 Test oil sample of tap changer √ Yes No Replaced oil of tap changer
03 Condition of oil gauges and oil level √ Yes No Good
04 Condition of paint works √ Yes No Ok
05 All valve correctly open and close √ Yes No Ok
06 Silica gel condition & breather plugs √ Yes No Color degraded & should be changed.
07 All reservoir filled with oil √ Yes No Sufficiently filled
08 Pressure relief diaphragm intact √ Yes No Ok
09 Operation of the floats √ Yes No Ok
10 Earth connections √ Yes No Proper
11 Oil leakage and integrity of gasket joint √ Yes No Not good condition
12 Tightness of nuts & bolts on the top √ Yes No Ok
13 NER connection √ Yes No Ok
14 Force cooling mechanism & fan motor √ Yes No Ok
15 Auto/Manual of force cooling system √ Yes No Ok
16 Protection and control system √ Yes No Healthy
Test-01: Insulation resistance (Insulation resistance Ohmmeter,
Model: Megger BM 11D)
Winding 15 Sec. 60 Sec. P.I. Remarks
HT-LT 366 MΩ 434 MΩ 1.121 Oil Temperature
40 Deg Cen.
HT-E 352 MΩ 412 MΩ 1.170 Megger Voltage 5000 V
LT-E 210 MΩ 252 MΩ 1.200
Test-02: LT Winding resistance (Digital Low resistance Ohmmeter, Model: Megger DLRO 200)
Winding Resistance Remarks
R phase to Y phase 0.12 Ω Oil Temperature
40 Deg. Cen.
Y phase to B phase 0.12 Ω
B phase to R phase 0.12 Ω
Comments:
Transformer main tank oil is to be centrifuged as degraded P.I. ratio.
Service man: Supervised by:
Protection of power system
Requirement of protection:
Normal operation
Prevention of electrical failure
Mitigation of the effects of electrical failure
Protective device:
Switchgear
Fuse
Functional characteristics of protective relaying
Sensitivity, Selectivity and Speed
Reliability
Transformer Protection
Buchholz relay
Differential relay
Pressure relief relay
Oil surge relay for OLTC
Over fluctuation protection
Directional over current
High set over current
Earth fault protection
- Stand by earth fault
- Restricted earth fault
Thermal over heating protection
a) Winding temperature
b) Oil temperature
Testing and Commissioning
Transformer:
Visual check
Insulation resistance measurement
Vector group test
Measurement of winding resistance
Ratio test of Bushing CT
Magnetizing test of Bushing CT
Polarity test of Bushing CT
Dielectric test of oil
Short circuit test
Magnetic balance test
Oil / winding temperature meter test
Impedance test
Importance for Maintenance of
Isolator
Vital Part of S/S
Initial Power Point
Kept smooth for voltage receiving.
Power receiving and delivering point ,so
it must be proper dimension considering
demand side management.
Importance of Earth switch
Maintenance
When Earth switch is required?
During Sub-station Maintenance Period
During shut-down.
During new bay extension.
Why earth switch is required?
For maintenance of cable and breaker
must be kept under voltage free
condition. IN THESE CASE Earth switch
must be closed.
Momentary induced voltages comes if
cable and breaker is not close via earth
switch.
Henceforth, Grounding system must be
healthy under design consideration.
Importance of Earth switch
!Do not close earth switch of BUS when
BUS is under operational condition.
!Do not close earth switch of the Cable
when cable is under charging condition.
Proper earthing criteria
Mesh Network
Dedicated neutral Grounding.
Proper Boring of Copper Grounding Rod.
Proper size and quality ensure for
copper grounding.
Soil resistivity is more important.
Must have proper grounding design &
grounding equipment and connection.
Importance of Circuit Breaker
No maintenance is required before 10
years for GIS (a set of Bus, Isolator
,Earth switch, Circuit Breaker).
But AIS is not maintenance free.
Thank you
