Power Factor Explained

Power Factor (PF) is the ratio of real power (P, in kilowatts, kW) used by a load to do useful work to the apparent power (S, in kilovolt-amperes, kVA) drawn from the grid.

  PF = P/S = cos φ = Active Power / Apparant Power

- φ = the phase angle between the waveforms of voltage and current.

• Real power (P) does the work (lighting, heating).
• Reactive Power (Q) (in kVAR) oscillates between source and load, creating magnetic fields (motors, transformers).
• Apparent Power (S) combines both - S² = P² + Q².

Layman’s Analogy - 

Imagine water flowing through a hose - 

• Real power is like the water you actually use (to water plants).
• Reactive power is when water flows back and forth in the hose without actually watering anything (only creating pressure).
• All of the water in the hose, both wasted and helpful, is known as apparent power.
• A good PF (near 1) means almost all water goes to your plants.
• A poor PF (low) means lots of water just sloshes and doesn’t water.

What Happens with Good v/s Poor Power Factor?

What can be done for Power Factor Improvement- 

• Use PF Correction Devices - Capacitor banks or smart PF controllers.
• Choose PF‑Certified Appliances - Look for motors and appliances with PF > 0.9.
• Regular Maintenance - Keep motors and compressors clean for optimal magnetics.
• Balance Loads Across Phases - (in three‑phase systems) to avoid neutral overloading.

- GGJ

Comparison between Dry-type copper wound and Dry-type aluminum wound Transformers

Dry Type Transformer

Dry-Type Copper Wound Transformer - A dry-type copper wound transformer is a transformer that uses copper conductors in its windings and relies on air or resin insulation instead of oil for cooling. Known for their high electrical conductivity, durability, and efficiency, these transformers are ideal for critical and long-term installations where performance and reliability are key.

Dry-Type Aluminum Wound Transformer - A dry-type aluminum wound transformer uses aluminum conductors in the windings and is similarly air- or resin-insulated, eliminating the need for oil. These transformers are lighter and more cost-effective, making them suitable for installations where budget and ease of handling are more important than maximum efficiency.

1. Conductor Material 

Copper

• Higher electrical conductivity (\~59.6 MS/m)
• Requires a smaller conductor cross-section

Aluminum -

•  Lower conductivity (\~36 MS/m)
•  Requires a larger conductor size for the same current

Best - Copper

2. Resistance

Copper -

•  Lower electrical resistance
•  Reduces I²R losses

Aluminum -

• Higher resistance
• More heat and power loss

Best - Copper

3. Heating & Thermal Performance -

Copper-

• Better heat dissipation
• Lower temperature rise
• Less thermal expansion

Aluminum -

• Heats up more
• Higher thermal expansion (can cause joint issues)

Best - Copper

4. Efficiency -

Copper -

• Higher energy efficiency
• Better for long-term power savings

Aluminum - 

• Slightly lower efficiency

Best - Copper

5. Losses - 

Copper -

• Lower copper (I²R) losses

Aluminum - 

• Higher copper losses

Best - Copper

6. Size and Weight - 

Copper - 

• Compact winding size
• Heavier due to high density

Aluminum - 

• Larger windings
• Lighter and easier to handle

Best - Aluminium (for weight-sensitive setups)

7. Life Expectancy - 

Copper - 

• Longer lifespan
• Stronger mechanical strength
• Less prone to oxidation

Aluminum - 

• Shorter lifespan
• Higher risk of connection issues over time

Best - Copper

8. Oil & Insulation (Dry-Type Specific)-

Both - Use air or resin for cooling, no oil required, environmentally friendly

Best - Equal

9. Indoor/Outdoor Suitability - 

Copper - 

• Excellent in harsh outdoor environments

Aluminum - 

• Acceptable, but more prone to corrosion

Best - Copper

10. Mechanical Strength & Reliability -

Copper -

• Stronger
• Withstands vibrations and short-circuits better

Aluminum - 

• Softer metal
• Lower mechanical endurance

Best - Copper

11. Cost Consideration

Copper - 

• Higher initial cost
• Lower lifetime cost due to durability and efficiency

Aluminum - 

• Lower initial cost
• Higher total cost due to greater losses

Best - Aluminium (when budget is a constraint)

12. Installation & Handling - 

Copper -

• Heavier and harder to move/install

Aluminum - 

• Facilitated transportation and installation owing to reduced weight

Best - Aluminum

13. Accuracy (Voltage Regulation)-

Copper -

• Lower voltage drop
• Tighter voltage regulation

Aluminum - 

• Higher voltage drop under load

Best - Copper

So, lets check in below-

Factors                   /                         Suitable

..................................................................................................................................

In Efficiency                             -           Copper        

Mechanical Strength & Life  -           Copper        

Heating & Thermal Stability -          Copper       

Price                                           -          Aluminum

Weight & Portability               -          Aluminum

Durability outdoors                 -         Copper  

Handling & Transport             -         Aluminum

Final Recommendation - 

• Choose a copper-wound transformer for high efficiency, long life, critical loads, and reliable performance.
• Choose an aluminum-wound transformer for budget-conscious applications, lighter installations, or temporary use.

- GGJ

Impact on electrical system if the Transformer is given 100 % Solar Load

    

The electrical system on the solar load

 Let us consider the case first - 

    I have a 100 KVA distribution transformer installed near my house (considering PF 0.9). The total solar load applied by households in that area is 90 kW, which will be fed through this 100 kva transformer. The parameters are -

1. Transformer rating = 100 kVA  
2. Power Factor = 0.9 (lagging, assumed typical for residential loads)  
3. Rated real power = 100 × 0.9 = 90 kW
4. Total solar load on system= 90 kW

    As per the condition, let's say all 90 kW solar generation is connected to feed into the transformer (i.e., export to the grid or supply local loads).

What Happens Technically When 90 kW Solar Is Connected?

1. Loading of Transformer - The transformer is rated 90 kW at PF 0.9. If all 90 kW solar starts generating at peak - 

1.  The transformer is operating at full real power capacity.
2.  But in real life, transformers also handle reactive power (kVARs), so apparent power can exceed 100 kva.

Risk Involved - If the local load is low (at night or on holidays), this full 90 kW might be pushed back to the grid, causing reverse power flow.

2. Reverse Power Flow - Transformers are usually not designed for continuous reverse flow unless specially specified.

- If generation > local consumption, surplus power flows back from LV to HV side, i.e., from 415 V to 11 kv in India.

Impacts -

• Overheating of the transformer due to reverse magnetisation.
• Protection malfunctions (relay settings typically designed for forward load).
• Can lead to overvoltage on the 11 kv feeder, especially if other transformers also have high solar.
• Utilities may limit solar penetration per transformer (usually 30-50 % of kva capacity); however, in JdVVNL, AVVNL, JVVNL, Rajasthan  norms its 80 % of the Transformer capacity.) 

3. Voltage Rise on LT Side -

• The LT line's voltage increases as a result of solar power.
• With 90 kW connected and minimal local consumption:
• LT voltage can exceed permissible limits (say > 240 V phase-to-neutral).
• May trip inverters due to overvoltage (anti-islanding protection).
• Uneven PV output can cause voltage fluctuations, especially if single-phase inverters are used.

4. Thermal Overload Risk -

• The transformer is designed for typical residential loads, with diversity and non-peak coinciding.
• 90 kW solar = non-coincident, simultaneous injection → actual load on transformer may exceed thermal limit.
• Temperature rise in windings, insulation degradation → shortens transformer life.

5. Power Quality Issues -

• If many inverters operate simultaneously - 
• It may introduce harmonics and voltage flicker.
• Also results in unbalanced loads (if solar is not equally spread across 3 phases), neutral heating, and voltage imbalance.

Solutions & Measures -

1. Limit Solar Capacity on DT -

• Follow solar hosting capacity guidelines and respective acts and norms to be followed with discipline. 
• Generally, max 30–50% of transformer capacity or as applicable by various discom norms of different states.
• For 100 kVA DT → limit solar to 30–50 kW (or as decided by the distribution company norms across states).

2. Upgrade Transformer -

- If demand justifies -

•  Upgrade to a 100 kVA or 160 kVA transformer.
•  Ensure it supports bi-directional power flow.

3. Install LT Side Voltage Regulation -

• Use on-load tap changers (OLTC) or line voltage regulators.
• Monitor and stabilise the voltage rise due to solar.

4. Install Reverse Power Relays or Limiters -

• Prevent dangerous export by tripping or curtailing excess generation.
• Or install net metering + export limiters.

5. Phase Balancing -

• Ensure solar connections are equally distributed across the 3 phases.
• Prevents overloading of a single phase and neutral heating.

6. Real-time Monitoring System -

IoT or SCADA monitoring of ----

•  Transformer loading
•  Voltage at the LT side
•  Solar injection
•  Reverse power

7. Energy Storage (Optional but Effective) -

• Use battery storage to store excess daytime generation.
• Reduces grid injection and stabilises voltage.