Important Points About Energy Conservation In Electrical Machines

Copper losses : They are nearly 55-60% of total losses, stator and rotor Cu losses are reduced by using copper conductors for winding in place of aluminium conductors , motor is operated near to synchronous speed which reduces rotor Cu losses.

Core losses : There are nearly 20-25 % total motor losses. Hysteresis loss is reduced by using low loss grade of silicon steel Flux density is reduced by increase in core length of stator and rotor. Eddy current losses are reduced by using thinner laminations.

Friction and windage losses are 8-12% of total losses. Due to reduction in copper and iron losses, heat generated is reduced, hence smaller fan is required for cooling. Also small diameter of fan reduces windage losses. Stray load losses are nearly 4 to 5% of total losses, they are reduced by proper selection of slot numbers, tooth/slot geometry and air gap.

Factors affecting energy efficiency :

1. Voltage variable
2. Unbalance in 3-phase currents.
3. Frequency variation.
4. Operation on under loading.
5. Temperature rise. 
6. Variable loads.
7. Power factor.
8. Maintenance.
9. Age.
10. Rewinding.
11. Space harmonic fields.

Energy conservation can be obtained by the following means :

1. By operating in star mode.
2. By improving mechanical transmission.

Energy efficiency in motors is obtained by the following ways :

1. Properly size to the load for optimum efficiency.
2. Use energy efficient motors.
3. Check alignment.
4. Check for under or over voltage.
5. Balance the 3-phase supply.
6. After rewinding demand for efficiency restoration.

Energy conservation in case of transformers can be achieved by reducing

1. Copper losses,
2. Iron losses and
3. Stray load losses of transformer.

• Iron losses are reduced by using low flux density in the core and using high resistive, low hysteresis loss CRGO material for core.
• Copper losses are reduced by using copper conductor in place of aluminium conductors and using large conductor sections.
• Stray load losses are reduced by two measures taken above and using standard conductors with insulation between strands.

Advantages of connecting transformers in parallel :

1. If one unit failed power supply can be maintained.
2. Units can be connected depending upon load condition so that maximum operating efficiency can be obtained.
3. Additional unit can be installed if load demand increases.
4. Cost of spares will be reduced if identical units are installed.

Conditions for connecting transformers in parallel :

1. Same voltage ratio.
2. Same percentage impedance.
3. Same polarity.
4. Same phase sequence and zero relative phase displacement in case of 3-phase transformers).  

Following energy conservation techniques are used in operating transformers :

1. In parallel transformer, it can be operated close to the maximum efficiency.
2. Transformers in parallel may be kept in service depending upon load, so that energy due to constant losses will be reduced.
3. When transformers are operating in parallel, it is necessary to remove and isolate some transformers when load demand is less, so that other transformers will supply energy at their maximum. 

Following are advantages of energy efficient transformer :

1. Less operating losses.
2. Less heat generated.
3. Longer life. 
4. Better cost effective.
5. Low field magnetization, reducing hysteresis loss 
6. High resistivity material reducing eddy current losses.
7. Amorphous metal strips, reduces problem of small thickness of core.
8. Low magnetizing current and low iron losses reduce no-load current.

Amorphous core transformer :

1. It is a energy efficiency transformer.
2.  Reduce transmission and distribution losses.
3. Losses are greatly reduced.
4. It reduces electricity generation and hence CO2, emission.
5. Losses due to heat and vibration of transformer are reduced.
6. Reduction in energy loss is about 70 % over conventional transformers.  
7. Have increased efficiency at low load condition also.

• Amorphous transformers are energy efficient transformers.
• Amorphous metal : It is a magnetic material having high permeability.
• Epoxy resin cast transformers : CRGO M-4 or M-3 grade toroidal cores are wound with secondary enameled copper wire which is distributed uniformly on the periphery of core to achieve minimum leakage reactance. Inter layer insulation is provided to avoid secondary winding short-circuiting in times of fault. Primary winding consists of flexible rope of copper and has required number of turns in one or more sections. 

Following faults may develop due to improper or poor maintenance :

1. Loose core bolts may result into vibration of stampings and more noise.
2. Improper supports and clamps for winding may result collapse of winding.
3. Bad soldering increases heating effect due to increased resistance of joint.
4. Oil leakage will increase temperature.
5. Dirt and dust deposited on the bushing may result into flashover.
6. If sludge is formed in transformer oil it blocks free circulation of oil, resulting into over heating of transformer.
7. Cracks or broken bushing may result into failure of transformer.
8. Loose connection in conducting parts results in overheating.