difference between power and distribution transformer

Difference Between Power Transformer and Distribution Transformer

Power and distribution transformers are both essential components of electrical power systems, but they serve different purposes and have distinct characteristics. Below is a detailed comparison under various headings:

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Definition: Power and distribution transformer

• Power Transformer:

  A power transformer is used in high-voltage transmission networks to increase or decrease voltage levels for efficient power transmission over long distances.

• Power transformers are devices designed to transfer electrical power from one circuit to another without altering the frequency. They function on the principle of electromagnetic induction and are essential for transmitting power between generators and primary distribution circuits

• Distribution Transformer:

  A distribution transformer is used to step down voltage levels for distribution to end-users, such as homes, businesses, and industries.

• A distribution transformer is a type of electrical transformer that is used to step down the voltage from the primary distribution level to a lower secondary voltage level suitable for end-use by residential, commercial, and industrial consumers.

  

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  2.Location in the Power System

• Power Transformer:

  Located at generating stations (step-up) and primary transmission substations (step-down).

1. Generation Side (Step-Up Transformer)

• • Located at or near power generation plants.
  •  As a thermal, hydro, nuclear, or renewable energy plants.
  • Function:
  •  Steps up the generated voltage (typically 11 kV to 33 kV) to high transmission levels (132 kV, 220 kV, or 500 kV) to reduce losses during long-distance transmission.

2. Transmission Network

• • Located at transmission substations along the high-voltage transmission lines.
  • Function:
  •  It transforms voltage levels between different stages of the transmission network (500 kV to 220 kV) or steps down voltage for sub-transmission.

3. Distribution Side (Step-Down Transformer)

• • Located at distribution substations or near load centers (residential, commercial, or industrial areas).
  • Function:
  •  Steps down voltage from sub-transmission levels (33 kV or 11 kV) to lower distribution levels (400 V or 230 V) for end-use.

4. End-User Location

• • Located at the consumer premises (factories, homes, or offices)
    

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    .

  • Distribution Transformer:

  • Located at distribution substations and near end-user premises.

• • Pole Mounted Transformers:

  • Mounted on utility poles, especially in rural or suburban areas.
  • Used for serving small residential or commercial loads.

  • Pad-Mounted Transformers

  • Installed on ground-level concrete pads, often in urban or suburban areas.
  • Commonly used in residential neighborhoods or commercial complexes.

  • Underground Distribution Transformers

  • Placed in underground vaults or chambers, typically in densely populated urban areas.
  • Used where overhead lines are not feasible.

  • Distribution Substations

  • Located within distribution substations, where multiple transformers serve a larger area.
  • These substations are strategically placed to optimize power distribution.

  • Industrial or Commercial Facilities:

  • Installed on-site at factories, hospitals, or large commercial buildings to meet specific voltage requirements.
    

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  • Voltage Levels: Power and distribution transformer

• Power Transformer:
  Operates at high voltage levels (typically 33 kV and above) for transmission purposes.
• Distribution transformer.

• Advanced Voltage Table for a Distribution Transformer

Parameter	Primary Side (HV)	Secondary Side (LV)
Rated Voltage	11 kV, 22 kV, 33 kV	400 V (3-phase), 230 V (1-phase)
Voltage Tolerance	±10% (typical)	±5% (typical)
Tap Changer Range	±5% to ±10% (in steps of 2.5%)	–
No-Load Voltage Ratio	11 kV/400 V, 22 kV/400 V, etc.	–
Impedance Voltage (Z%)	4% to 6% (typical)	–
Phase Configuration	Delta (Δ) or Star (Y)	Star (Y) with neutral
Frequency	50 Hz or 60 Hz	50 Hz or 60 Hz
Voltage Regulation	2% to 5% (typical)	–
Insulation Level	28 kV (for 11 kV), 50 kV (for 22 kV)	3 kV (for 400 V)

• Detailed Explanation of Parameters:

• Rated Voltage:
• Primary (HV) side;  Typically 11 kV, 22 kV, or 33 kV, depending on the distribution network.
• Secondary (LV) side: 400 V for three-phase systems or 230 V for single-phase systems.
• Voltage Tolerance:
• Primary side: ±10% to accommodate fluctuations in the grid.
• Secondary side: ±5% to ensure stable output for end users.
• Tap Changer Range:
• Transformers often have tap changers to adjust the output voltage. For example, ±5% or ±10% in steps of 2.5% to compensate for voltage drops or surges.
• No-Load Voltage Ratio:
• The ratio of primary to secondary voltage under no-load conditions. For example, 11 kV/400 V means the transformer steps down 11 kV to 400 V.
• Impedance Voltage (Z%):
• The percentage impedance of the transformer (typically 4% to 6%). This determines the short-circuit current and voltage regulation.
• Phase Configuration:
• Primary side: Delta (Δ) or Star (Y) configuration.
• Secondary side: Star (Y) with a neutral wire for three-phase systems.
• Frequency:
• Typically 50 Hz in Europe and Asia or 60 Hz in North America.
• Voltage Regulation:
• The ability of the transformer to maintain a stable secondary voltage under varying load conditions. Typically 2% to 5%.
• Insulation Level:
• Primary side: Insulation level depends on the voltage rating 28 kV for 11 kV transformers.
• Secondary side: Lower insulation level 3 kV for 400 V transformers.
  

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• Size and Rating: Power and distribution transformer

• Power Transformer:

  Larger in size and has higher power ratings (usually above 200 MVA).

• Size of Power Transformers

• Physical Size:

• Depends on the power rating, voltage level, and cooling type.
• Larger transformers can weigh several hundred tons and occupy significant space.
• Distribution transformers are smaller, often pole-mounted or pad-mounted.

• Core and Winding Size:

• Determined by the magnetic flux and current-carrying capacity.
• Higher ratings require larger cores and thicker windings.

• Cooling System:

• Oil-immersed transformers are larger due to the oil tank and cooling fins/radiators.
• Dry-type transformers are more compact but limited to lower ratings.

• Rating of Power Transformers

• Power Rating (kVA or MVA):

• Represents the maximum load the transformer can handle without overheating.
• Common ratings:
• Distribution transformers: 25 kVA to 2500 kVA.
• Power transformers: 1 MVA to 1000 MVA or more.

• Voltage Rating:

• Specifies primary and secondary voltage levels.
• High-voltage transformers are used in transmission networks.

• Frequency Rating:

•       Typically 50 Hz or 60 Hz, depending on the region.
• Impedance Rating:
• Expressed as a percentage indicating voltage drop under load.
• Temperature Rating:
• Defines the maximum operating temperature.
• Cooling Class:
• ONAN (Oil Natural Air Natural) for smaller ratings.
• OFAF (Oil Forced Air Forced) for larger ratings.
• Factors Affecting Size and Rating
• Load Requirements: Higher loads require higher ratings and larger sizes.
• Efficiency: Larger transformers are often more efficient at higher ratings.
• Application:
• Distribution transformers are smaller and rated for lower power.
• Transmission transformers are larger and rated for higher power.
  

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• Distribution Transformer:

  Smaller in size and has lower power ratings (usually below 200 MVA).

• Size (kVA Rating):
  • Distribution transformers typically range from 16 kVA to 2500 kVA.
  • Common ratings include 25 kVA, 50 kVA, 100 kVA, 250 kVA, 500 kVA, 1000 kVA, and 2500 kVA.
  • Smaller transformers are used for residential or light commercial applications.
  • Larger transformers are used for industrial or heavy commercial loads.
• Voltage Rating:
  • Primary voltage: Typically 11 kV, 22 kV, or 33 kV (depending on the distribution network).
  • Secondary voltage: Commonly 400/230 V (for three-phase systems) or 230/120 V (for single-phase systems).
• Physical Size:
  • Smaller transformers (25 kVA) are compact and pole-mounted.
  • Larger transformers (1000 kVA or above) are ground-mounted and require more space.
• Cooling Type:
  • Smaller transformers are often oil-cooled or dry-type.
  • Larger transformers are usually oil-immersed with cooling fins or radiators.
• Efficiency:
  • Efficiency depends on the size and design, typically ranging from 95% to 99%.
  • Larger transformers tend to have higher efficiency due to lower losses.
• Load Capacity:
  • Designed to handle continuous load at rated capacity.
  • Can handle short-term overloads (e.g., 10-20% above rated capacity) for limited durations.
• Application-Specific Sizing:
  • Residential areas: Smaller transformers (16 kVA to 100 kVA).
  • Commercial buildings: Medium-sized transformers (250 kVA to 1000 kVA).
  • Industrial facilities: Larger transformers (1000 kVA to 2500 kVA).
    

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5. Load Fluctuations: Power and distribution transformer

• Power Transformer:
  Designed to handle consistent and high loads with minimal fluctuations.
• Distribution Transformer:
  Designed to handle varying loads as the demand from end-users fluctuates throughout the day.
• Definition: The load factor is the ratio of the average load to the maximum (peak) load over a specific period, typically expressed as a percentage.
• Average Load: The average power demand over a given period (daily, monthly, or annually).

• Peak Load: The maximum power demand during the same period.
• Importance of High Load Factor:
  • Indicates efficient utilization of the transformer.
  • Reducing losses and improving energy efficiency.
  • Extends the lifespan of the transformer by avoiding constant overloading.
  • Lowers operational costs by optimizing energy consumption.
• Low Load Factor Implications:
  • Indicates underutilization of the transformer.
  • Leads to higher energy losses relative to the energy delivered.
  • May suggest poor load management or oversized transformer capacity.
• Ideal Load Factor:
  • Typically, a load factor of 70-80% is considered optimal for distribution transformers.
  • Ensures a balance between efficient operation and avoiding overloading.
• Factors Affecting Load Factor:
  • Variations in consumer demand (residential, commercial, industrial).
  • Seasonal changes (higher demand in summer for cooling).
  • Time of day.
• Improving Load Factor:
  • Implementing load management strategies (peak shaving, load shifting).
  • Using energy storage systems to balance demand.
  • Encouraging consumers to shift usage to off-peak hours.
• Measurement:
  • Load factor is calculated using data from energy meters or monitoring systems over a specific period.
    

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6. Efficiency: Power and distribution transformer

• Power Transformer:
  Highly efficient at or near full load, as it operates at a constant load most of the time.
• Distribution Transformer:
  Designed for maximum efficiency at 50-70% load, as it operates under variable load conditions.
• Efficiency of Distribution Transformer:
• Lower Efficiency Range: Typically 95-98%.
• Designed for Lower Loads: Optimized for partial loads, often operating at 30-50% of full load.
• Core Losses: Lower no-load losses (core losses) due to continuous operation.
• Copper Losses: Higher load losses (copper losses) as they handle varying loads.
• Voltage Regulation: Focuses on maintaining voltage levels for end-users.
• Cooling: Often uses oil or natural air cooling.
• Cost-Effective: Designed for cost efficiency over high performance.
• Efficiency of Power Transformer:
• Higher Efficiency Range: Typically 98-99.5%.
• Designed for Higher Loads: Operates near full load most of the time.
• Core Losses: Higher no-load losses due to larger size and higher voltage.
• Copper Losses: Lower load losses relative to their capacity.
• Voltage Regulation: Focuses on bulk power transfer with minimal losses.
• Cooling: Uses advanced cooling methods like forced oil or water cooling.
• High Performance: Prioritizes efficiency and reliability for grid stability.
• Key Differences:
• Application: Distribution transformers serve end-users; power transformers handle transmission.
• Load Profile: Distribution transformers face variable loads; power transformers handle consistent, high loads.
• Efficiency Focus: Distribution transformers balance cost and efficiency; power transformers maximize efficiency for large-scale power
• 
  

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   Iron and Copper Losses: Power and distribution transformers

• Power Transformer:
  Optimized for low iron losses (core losses) since it operates continuously.
• Distribution Transformer:
  Optimized for low copper losses (winding losses) due to varying load conditions
• Iron Losses (Core Losses)
• Definition: Iron losses occur in the transformer’s core due to alternating magnetic flux.
• Types:
• Hysteresis Loss: Energy lost due to the repeated magnetization and demagnetization of the core material.
• Eddy Current Loss: Energy lost due to circulating currents induced in the core material.
• Characteristics:
• Constant at all load conditions (independent of load current).
• Depending on the core material, frequency, and flux density.
• Reduced by using high-quality laminated silicon steel cores.
• Distribution Transformer: Typically designed for lower iron losses as they operate continuously, even at low loads.
• Power Transformer: Iron losses are significant but optimized for efficiency at higher loads.
• Copper Losses (Winding Losses)
• Definition: Copper losses occur due to the resistance of the transformer windings when current flows through them.
• Characteristics:
• Vary with the square of the load current (proportional to I2RI2R).
• Higher under loaded conditions and negligible at no-load.
• It depends on the winding material (copper) and temperature.
• Distribution Transformer: Designed to minimize copper losses for better efficiency at partial loads.
• Power Transformer: Copper losses are significant at full load but optimized for high efficiency under heavy loads.
• Key Differences Between Distribution and Power Transformers
• Iron Losses:
• Distribution transformers prioritize low iron losses for continuous operation.
• Power transformers balance iron and copper losses for optimal performance at high loads.
• Copper Losses:
• Distribution transformers are designed for lower copper losses at partial loads.
• Power transformers are optimized for lower copper losses at or near full load.
• Efficiency:
• Distribution transformers aim for high efficiency at light loads.
• Power transformers aim for high efficiency at or near full load.
• Summary
• Iron Losses: Constant, core-related, and independent of load.
• Copper Losses: Load-dependent, winding-related, and proportional to the square of the load current.
• Design Focus: Distribution transformers prioritize low iron losses, while power transformers balance both losses for high-load efficiency.
  

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• Cooling System: Power and distribution transformer

• Power Transformer:
  Equipped with advanced cooling systems (e.g., oil-immersed, forced air, or water cooling) due to high power handling.
• Distribution Transformer:
  Typically uses natural cooling (oil-immersed or air-cooled) as it handles lower power levels.
• Cooling Systems of Distribution and Power Transformers
• Distribution Transformers
• Natural Air Cooling (ONAN):
• Uses natural convection for cooling.
• Oil-Immersed Cooling:
• Oil circulates naturally, dissipating heat through the tank walls.
• Radiators or Fins:
• Added to increase surface area for better heat dissipation.
• Compact Design:
• Smaller size allows for simpler cooling methods.
• Low Noise Levels:
• Cooling systems are designed to minimize noise.
• Power Transformers
• Oil-Immersed Cooling (ONAN, ONAF):
• ONAN: Natural oil and air circulation.
• ONAF: Forced air cooling with fans.
• Forced Oil Cooling (OFAF, OFAN):
• OFAF: Forced oil and forced air.
• OFAN: Forced oil with natural air.
• Water Cooling (OFWF):
• Forced oil and water cooling for high-capacity transformers.
• Radiators and Cooling Tubes:
• Enhanced heat dissipation with larger radiators or cooling tubes.
• Buchholz Relay:
• Monitors oil flow and gas accumulation for fault detection.
• Oil Pumps and Fans:
• Used in larger transformers to improve cooling efficiency.
• Directed Oil Flow:
• Ensures efficient cooling of the core and windings.
• Advanced Monitoring:
• Includes temperature and cooling system performance monitoring.
• Common Features
• Oil as Coolant:
• Both types use oil for insulation and cooling.
• Thermal Monitoring:
• Equipped with sensors to monitor temperature.
• Safety Mechanisms:
• Includes pressure relief devices and alarms.
• Key Differences
• Cooling Capacity:
• Power transformers require more advanced cooling due to higher loads.
• Complexity:
• Power transformers have more complex cooling systems compared to distribution transformers.
• Size:
• Power transformers are larger, needing more robust cooling solutio

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9. Applications: Power and distribution transformers

Power Transformer:
Used in transmission networks for stepping up voltage at generating stations and stepping down voltage at receiving stations.

• Distribution Transformer:
  Used in distribution networks to provide the final voltage transformation for end-users. Distribution Transformer
• Voltage Step-Down: Steps down high distribution voltage (11 kV, 6.6 kV, etc.) to lower levels (400/230 V) for end-use.
• Local Power Supply: Supplies power to residential, commercial, and small industrial consumers.
• Pole-Mounted or Ground-Mounted: Installed on poles for overhead lines or on the ground for underground systems.
• Low Power Rating: Typically ranges from 16 kVA to 500 kVA.
• Continuous Operation: Operates 24/7 with varying loads.
• High Efficiency at Partial Load: Designed for optimal efficiency at 50-70% load.
• Distribution Networks: Integral to power distribution networks, delivering electricity to end-users.
• Oil or Dry-Type: Uses oil for cooling or dry-type for indoor/urban areas.
• Load Fluctuations: It handles frequent load changes due to varying consumer demand.
• Power Transformer
• Voltage Step-Up/Step-Down: Steps up voltage for transmission or steps down for distribution.
• Transmission Networks: Used in generating stations and substations for high-voltage transmission.
• High Power Rating: Ranges from 1 MVA to several hundred MVA.
• Bulk Power Transfer: Transfers large amounts of power over long distances with minimal losses.
• Efficiency at Full Load: Optimized for high efficiency at or near full load.
• Large Size and Weight: Physically larger and heavier, requiring robust foundations.
• Oil-Immersed Cooling: Typically uses oil for insulation and cooling.
• Stable Load Operation: It operates under relatively stable load conditions.
• Grid Stability: Maintains voltage levels and ensures grid stability.
• Interconnected Systems: Links different voltage levels in interconnected power systems.
• Key Differences
• Application: Distribution transformers serve end-users; power transformers handle transmission and bulk power.
• Load Type: Distribution transformers handle fluctuating loads; power transformers handle stable loads.
• Size and Rating: Distribution transformers are smaller with lower ratings; power transformers are larger with higher ratings.
• Efficiency: Distribution transformers are efficient at partial loads; power transformers are efficient at full loads.
  

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10. Cost: Power and distribution transformers

    

• Power Transformer:
  More expensive due to higher power ratings, advanced cooling systems, and robust construction.
• Distribution Transformer:
  Less expensive due to its smaller size and lower power ratings.

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11. Design: Power and distribution transformers

• Power Transformer:
  Designed for high efficiency and reliability under continuous operation.
• Distribution Transformer:
  Designed for cost-effectiveness and efficiency under variable load conditions.

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12. Examples: Power and distribution transformers

• Power Transformer:
  Transformers are used in substations connecting generating stations to transmission lines.
• Distribution Transformer:
  Pole-mounted or ground-mounted transformers supply power to residential or commercial areas.

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Summary Table

Aspect	Power Transformer	Distribution Transformer
Purpose	Transmission of power over long distances	Distribution of power to end-users
Voltage Level	High voltage (33 kV and above)	Low voltage (below 33 kV)
Size and Rating	Larger, higher ratings (200 MVA+)	Smaller, lower ratings (below 200 MVA)
Load	Constant load	Variable load
Efficiency	High at full load	High at 50-70% load
Cooling System	Advanced cooling systems	Natural cooling
Cost	Expensive	Less expensive
Applications	Transmission networks	Distribution networks

13. Installation: Power and distribution transformer

• Power Transformer:
  Installed at generating stations, transmission substations, and receiving stations. Requires a dedicated foundation and space due to its large size.
• Distribution Transformer:
  Installed on poles (pole-mounted) or ground-mounted near residential, commercial, or industrial areas. Compact and easy to install.

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14. Operation Time: Power and distribution transformers

• Power Transformer:
  Operates 24/7, as it is part of the continuous transmission network.
• Distribution Transformer:
  Operates based on the demand of end-users, with load fluctuations throughout the day.

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15. Insulation Level: Power and distribution transformers

• Power Transformer:
  Requires high insulation levels due to the high voltage it handles.
• Distribution Transformer:
  Requires relatively lower insulation levels as it operates at lower voltages.

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16. Tapping: Power and distribution transformers

• Power Transformer:
  Equipped with on-load tap changers (OLTC) to adjust voltage levels without interrupting the power supply.
• Distribution Transformer:
  Typically, it has off-load tap changers, as voltage adjustments are less frequent.

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17. Magnetic Flux Density: Power and distribution transformers

• Power Transformer:
  Operates at higher magnetic flux density to handle high power levels efficiently.
• Distribution Transformer:
  Operates at lower magnetic flux density to optimize performance under varying loads.

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18. Maintenance: Power and distribution transformers

• Power Transformer:
  Requires regular and specialized maintenance due to its critical role in the power system.
• Distribution Transformer:
• Requires less frequent maintenance, but periodic checks are necessary to ensure reliability.
  

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19. Life Expectancy: Power and distribution transformers

• Power Transformer:
  Longer life expectancy (30-40 years) due to robust construction and continuous operation under controlled conditions.
• Distribution Transformer:
  Shorter life expectancy (20-25 years) due to exposure to varying loads and environmental conditions.

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20. Environmental Impact: Power and distribution transformers

• Power Transformer:
  Larger environmental footprint due to higher oil content and cooling requirements.
• Distribution Transformer:
  Smaller environmental footprint due to compact size and lower oil content.

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21. Voltage Regulation: Power and distribution transformer

• Power Transformer:
  Designed for precise voltage regulation over long distances.
• Distribution Transformer:
  Designed for local voltage regulation to meet end-user requirements.

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22. Connection Type: Power and distribution transformers

• Power Transformer:
  Typically connected in star-delta or delta-star configuration for transmission networks.
• Distribution Transformer:
  Typically connected in star-star configuration for distribution networks.

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23. Harmonics: Power and distribution transformers

• Power Transformer:
  Less affected by harmonics due to controlled loads in transmission networks.
• Distribution Transformer:
  More susceptible to harmonics due to the presence of non-linear loads (electronic devices) in distribution networks.

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24. Noise Level: Power and distribution transformers

• Power Transformer:
  Generates higher noise levels due to its large size and high power handling.
• Distribution Transformer:
  Generates lower noise levels, making it suitable for residential areas.

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25. Protection Systems: Power and distribution transformers

• Power Transformer:
  Equipped with advanced protection systems (Buchholz relay, differential protection) due to its critical role.
• Distribution Transformer:
  Uses simpler protection systems (fuses, overcurrent relays) due to its smaller size and lower voltage levels.

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26. Transportation: Power and distribution transformers

• Power Transformer:
  Requires specialized transportation due to its large size and weight.
• Distribution Transformer:
  Easier to transport due to its compact size and lighter weight.

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27. Failure Impact: Power and distribution transformers

• Power Transformer:
  Failure can lead to widespread power outages and significant economic losses.
• Distribution Transformer:
  Failure affects a smaller area and fewer consumers, with relatively lower economic impact.

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28. Testing: Power and distribution transformers

• Power Transformer:
  Undergoes rigorous testing ( impulse testing, partial discharge testing) due to its critical role.
• Distribution Transformer:
  Undergoes standard testing ( insulation resistance, turns ratio) to ensure reliability.

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29. Oil Quality: Power and distribution transformers

• Power Transformer:
  Requires high-quality insulating oil due to high voltage and continuous operation.
• Distribution Transformer:
  Uses standard-quality insulating oil, as it operates at lower voltages and under less demanding conditions.

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30. Replacement Frequency: Power and distribution transformers

• Power Transformer:
  Replaced less frequently due to its long life expectancy and high cost.
• Distribution Transformer:
  Replaced more frequently due to wear and tear from varying loads and environmental exposure.

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31. Temperature Rise: Power and distribution transformers

• Power Transformer:
  Designed to handle higher temperature rises due to continuous operation.
• Distribution Transformer:
  Designed for lower temperature rises, as it operates under varying loads.

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32. Overload Capacity: Power and distribution transformers

• Power Transformer:
  Limited overload capacity, as it operates near full load most of the time.
• Distribution Transformer:
  Higher overload capacity to handle peak demand periods.

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33. Standardization: Power and distribution transformers

• Power Transformer:
  Custom-designed based on specific project requirements.
• Distribution Transformer:
  Mass-produced and standardized for ease of deployment.

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34. Role in Grid Stability: Power and distribution transformers

• Power Transformer:
  Critical for maintaining grid stability and ensuring uninterrupted power flow.
• Distribution Transformer:
  Plays a secondary role in grid stability, focusing on local power distribution.

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35. Cost of Failure: Power and distribution transformers

36. Power Transformer:
    High cost of failure due to its critical role in the power system.
37. Distribution Transformer:
    Lower cost of failure, as it affects a smaller area and fewer consumers.