OPERATION & MAINTENANCE OF 33/11 kV SUBSTATION

1. Presentation
on
Operation and Maintenance of 33/11 KV Sub-station
at Dhaka Palli Bidyut Samity-1
Presented by
Md. Muzahidul Haque
ID# 12305145
Program: BSEEE
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2. Overview
 Objectives
 Bangladesh Power Division Structure
 Organizational Overview
 33/11 kV DPBS-1 sub-station
 Sub-station single line diagram
 Sub-station equipments
 Sub-station operation
 Maintenance of sub-station equipments
 Findings
 Recommendation
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3. Objectives
• To know about sub-stations
• To learn about assemblage of substation equipments
• Study on switchgear equipments
• Operation of sub-stations
• Maintenance of Sub-stations
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4. Bangladesh Power Division
Structure
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5. Bangladesh’s Power Sector
 Generation capacity : 13,179 MW (March 2017)
 Power import : 600 MW from India
 Highest generation : 9,036 MW (30 June, 2016)
 Total consumers : 24.2 million (March 2017)
 Transmission line : 10,377 CKT. KM (February 2017)
 Distribution line : 3,89,000 km (February 2017)
 System loss : 13.10% (June 2016)
 Distribution loss : 10.69% (June 2016)
 Per capita generation : 407 kwh (August, 2016)
 Access to electricity : 80%
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6. Organizational Overview
 Rural Electrification Board (REB) is
established in 1978.
 13th December 1978, DPBS-1,
started its function.
 2nd June 1980, DPBS-1 started its
commercial operation.
Contribute in Agricultural, Industrial
and Socio-Economic Development.
Company Logo
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7. Organizational Overview
Mission:
Electricity for all by 2021
Vision:
Quality and Uninterruptible power supply.
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8. Basic Content of Electrical System
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9. Distribution Substation
The assembly of apparatus is used to change
some characteristic of electric supply.
 Its connected with grid
 Incoming voltage is 33 kV
 Outgoing voltage is 11 kV
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10. Dhaka PBS Substation
 Dhaka PBS-1 S/S supply power at
Savar area.
 Receive power from Kabirpur and
Savar grid.
 Capacity 35 MVA.
 There are six feeders.
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11. 11

12. Substation Equipment's
 Instrument Transformers
 Power Transformer
 Automatic Voltage
Regulator(AVR)
 Automatic Circuit Re-
closer(ACR)
 Insulator
 Lightning Arrester
 Bus bar
 Isolator
 Earth switch
 Protective Relay
 Auxiliary Transformer.
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13. Instrument Transformers
Instrument transformers is used for measuring and
protection purpose.
Instrument transformers are two types –
1. Current Transformer (C.T.)
2. Potential Transformer (P.T.)
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14. Current Transformer (C.T.)
A current transformer steps down the current.
 Used for current measurement.
 Step up transformer.
 It is connected in series
Specification
Primary 50-100 A
Secondary 5A
Frequency 50 Hz
Weight 75 kg
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15. Potential Transformer (P.T.)
It is used to step down the voltage.
 Used for voltage measurement.
 Step down transformer.
 PT is connected in parallel.
Specification
Primary 6350 V
Secondary 240 V
Frequency 50 Hz
Weight 70 kg
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16. CT & PT Meter Connection
Diagram
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17. Power Transformer
 A power transformer is used for
step-up or step-down the voltage.
 Transformer has two winding
namely primary and secondary.
 Operate at nearly full load.
power transformer
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18. In DPBS substation three types of transformers
are mainly used.
These are:
– Single Phase Transformer
– Three Phase Transformer
– Auxiliary Transformer
Power Transformer
Single Phase Transformer
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19. specifications
 Transformer Type OUT DOOR
 Type of Cooling ONAN/ONAF
 Rated MVA 5/6.25
 Rated KV
 HV 33 kV
 LV 11 kV
 Rated Line Current (amp)
 HV 87.5/109.3
 LV 249.9/312.4
 Vector Group Dyn-1
 No of Phase 3
 % Impedance HV/LV 6
 Standard Frequency 50Hz
 Year of Manufacturing 2011
 Core and Coil 6800 kg
 Tank and Fittings 3600 kg
 Mass of Oil 3400 kg
 Total Mass 13800 kg
 Volume of oil 3542 Liter
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20. Parts of Transformer
 Transformer Tank
 Conservator
 Buchholz Relay
 Oil level indicator Buchholz Relay
conservator
Transformer Tank
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Oil Level Indicator

21.  Bushing
 Breather
Cooling system:
 O.N.A.N- Oil Natural Air Natural
 O.N.A.F-Oil Natural Air Forced
Parts of Transformer (Cont’d)
Breather
Bushing 21
Cooling system
Bushing

22. Silica Gel
 Used for the absorption of
moisture in a transformer.
 Blue silica gel is fresh.
 Pink silica gel contains
moisture.
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23. Parts of Transformer (Cont’d)
 Tap Changer
 Oil Temperature Indicator
 Winding Temperature Indicator
Tap Changer Oil and Temperature level Indicator
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24. Auxiliary Transformer
Auxiliary transformer
used to supply the
substations own needed
power.
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Auxiliary transformer

25. Automatic Voltage Regulators
 Used to regulate the
voltage.
 It takes the fluctuate
voltage and changes them
into a constant voltage.
Rated power 416.5 kVA
Rated voltage 6350 V
Rated current 656 A
Cooling ONAN
Coil temperature rise 55 ̊C
Oil temperature rise 50 ̊C
Fase number 1
Total weight 2060 kg
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26. Automatic Circuit Re-closer
(ACR)
 This device where SF6 gas is used to arc
extinction
 There is a interrupter for each line.
Specifications
 Operating voltage : 240V AC or
24V DC
 Current ratio : 500:1
 Rated max voltage : 27 kV
 Rated continuous current : 630A
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Control panel
ACR

27. Lightning Arrester
 Use to protection of power
system equipment.
 Protection against lightning
stroke.
 Passed total voltage surges
to the ground.
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Lightning Arrester

28. Bus Bar
An assembly of conductors for collecting electric
power and distributing them to outgoing feeders.
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Bus Bar

29. Isolator
It is also known as
disconnecting switch.
It used to protect the
transformer and other
equipment in the line.
 Design to open a circuit
under no load.
Isolator
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Isolator

30. Distribution Transformer
 The final voltage transformation in the
electric power distribution system.
 Stepping down the voltage used in the
distribution lines to the level used by the
customer.
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31. 11 KV/440 V Power Distribution
System
In power distribution system they use
single phase transformer.
Commonly used 1-φ transformers are
rated as.
5 KVA
10 KVA
15 KVA
25 KVA
37.5 KVA
50 KVA
75 KVA
100 KVA
167 KVA distribution transformer
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32. Transformer Test
In DPBS-1 System they do six type of test
Insulation Test
Continuity Test
Ratio and Polarity Test
No Load Test
Full Load Test
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33. Transformer Test
SL. NO Insulation Test Ratio
1 HT/LT Bushing 1000 + MΩ
2 LT Bushing/Tank 1000 + MΩ
3 LT Bushing/LT Bushing 0
After the Insulation test we get this result
After the Continuity test we get this result
SL. NO Continuity Test Ratio
1. HT Busing / Tank 0
2. LT Bushing/LT Bushing 0
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34. Sl. No Ratio and Polarity Test Ratio
1. Obtained Voltage in (HT) Side 240 Volt.
2. Obtained Voltage in (LT) Side 9.07 Volt.
3. Ratio of HT and LT Side 26.461 Volt.
4. Polarity Additive
After the Ratio and Polarity test we get this result
Sl. No No Load Ratio
1 Applied Voltage in LT Side 240 Volt.
2 Obtained Current 0.26 Amp.
3 Loss 24.12 Watt
Sl. No Full Load Ratio
1 Induce Volts 160.1 Volt.
2 Obtained Current 1.74 Amp.
2 Loss 190 Watt
4 Impedance 2.52%
After the No load and Full load test we get this result
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35. Maintenance of Substation
Daily maintenance:
 Make record of power (MW) flow in each hour
 Switchgear equipment’s inspection
 Load management
Emergency Maintenance:
Emergency maintenance is required when any uncertain hazard is
occurred in the electric system.
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36. Maintenance of Transformer
Steps for power transformer shutdown
 CB of the Transformer secondary side open.
 CB of the Transformer primary side open.
 Isolator opens from both sides.
 Grounding switch close from both sides.
 Make additional grounding if required.
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37. Transformer Faults and Failures
 winding failures due to short
circuits :
– Phase-phase faults,
– Phase-ground,
 Core faults :
– Core insulation
failure
 Lighting Surge
 On-load tap changer failures:
– Mechanical,
– Electrical,
– Short circuit,
– Overheating
 Abnormal operating
conditions:
– Over loading,
– Over voltage.
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38. Maintenance of Equipments
 Maintenance of Circuit Breaker
• For SF₆ circuit breaker, gas pressure should be checked.
• Leakage of gas should be checked
 Maintenance of Conservator
• Oil pressure should be checked.
• Oil leakage should be checked.
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39.  Remove all additional or local grounding
 Grounding switch open from both sides.
 Isolator close from both sides.
 Transformer primary side CB close.
 Transformer secondary side CB close.
After finish the maintenance work
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40. Protection of Substation
Protection scheme in substation are three parts:
1. Transformer protection scheme.
2. Feeders protection scheme.
3. Bus bar protection scheme.
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41. Findings
1. Most of the distribution transformers are overloaded.
2. Repairing division is slow.
3. System loss is more.
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42. Recommendation
1. More concentration is required to maintain the pricing
mechanism.
2. Number of distribution transformers should be increased.
3. Upgraded switchgear equipment’s are highly required.
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