**2.3. Basic reduction of electric energy own consumption of power plants by setting voltage within Un±5%**

Subject of concrete project (Kostic et al., 2006) is reduction of electric energy own consumption of thermal power plant "Nikola Tesla" B, Obrenovac (Serbia), with 2 blocks.. The own consumption of the electric energy, with motors on medium voltage (6.6 kV), is about 90% and with motors on voltage 0.4 kV is about 10%, supplied by a transformer whose primary is directly connected to the generator bus. Nominal powers of the transformers (21 kV/6.6 kV) are approximately equal to total nominal powers of all installed motors which are about 140 MW. Active and reactive loads are about 70 MW and 60 Mvar. As the load of most motors is about 35–70% of full load, reduction of electric energy own consumption could be achieved by setting the voltage magnitude in the range Un±5%.

Application of this procedure results in reduction: of core losses (*PFe*), reactive loads (*Q*) and active power losses component *PCuQ=RIQ2*. Thereby, both active and reactive energy consumptions are decreased. Optimal voltage values are being determined according to appropriate calculations and analysis is based on motor catalogue data and its experimental verification at actual load regimes.

According to the effects of voltage magnitude on motor power losses (*Pγ*) and motor reactive loads (*Q1*), for overall own consumption, the following dependencies can be determined: restrictions:



132 Induction Motors – Modelling and Control

**setting voltage within Un±5%** 

verification at actual load regimes.


determined: restrictions:

change, and

Results of the author's research (Kostic, 1998, 2010) confirmed that there are significant possibilities for energy savings by setting voltage values within the voltage band (*Un*±5%), because more then 80% of induction motors, especially small and medium power (1 - 30

*Q1(u)* for motor of nominal power 2 MW, for *P1 /PN* 0% (no-load), 25%, 50%, 75% and 100%

*(UN) = ΔP1 = P1(Ui)-P1(UN)*, i.e. active loads

*(u)* and reactive loads

kW), operate at partial load (70%). Dependencies of power loss *P*

**Figure 3.** Dependencies of power losses and reactive loads on supply voltage

**2.3. Basic reduction of electric energy own consumption of power plants by** 

Subject of concrete project (Kostic et al., 2006) is reduction of electric energy own consumption of thermal power plant "Nikola Tesla" B, Obrenovac (Serbia), with 2 blocks.. The own consumption of the electric energy, with motors on medium voltage (6.6 kV), is about 90% and with motors on voltage 0.4 kV is about 10%, supplied by a transformer whose primary is directly connected to the generator bus. Nominal powers of the transformers (21 kV/6.6 kV) are approximately equal to total nominal powers of all installed motors which are about 140 MW. Active and reactive loads are about 70 MW and 60 Mvar. As the load of most motors is about 35–70% of full load, reduction of electric energy own consumption could be achieved by setting the voltage magnitude in the range Un±5%.

Application of this procedure results in reduction: of core losses (*PFe*), reactive loads (*Q*) and active power losses component *PCuQ=RIQ2*. Thereby, both active and reactive energy consumptions are decreased. Optimal voltage values are being determined according to appropriate calculations and analysis is based on motor catalogue data and its experimental

According to the effects of voltage magnitude on motor power losses (*Pγ*) and motor reactive loads (*Q1*), for overall own consumption, the following dependencies can be

> *= P(Ui)-P*

are given in Fig. 3, (Kostic et al., 2006 and Kostic, 2010).

for the voltage range *UUN* 0.955-1.045, i.e. for *U* 6300V-6900V (*UN* = 6 600V), Fig. 4.

**Figure 4.** Dependency of total power losses and reactive loads for own consumption

As was shown in Kostic et al. (2006), application of this procedure causes reduction of the electric energy own consumption. Changing voltage value (regulation at own consumption transformers 1BT and 2BT, and at common consumption transformer OBT) from 6.8 kV (1.03 *UN*) to 6.6 kV (*UN*) or 6.5 kV (0.985 *UN*) causes reduction of:


Power losses addition reduction in the own consumption network for 42.4 kW and 54.7 kW, respectively, due to of the above mentioned of reactive loads' reduction in the own consumption network.

According to values of reduced power losses, reactive loads and assumed operational plan of the thermal plant (estimated 6 000 h/years), savings in active and reactive energy have been determined and given in Table I, (Kostic et al., 2006, and Kostic, 2010).


**Table 1.** Reduction of the active and reactive energy own consumption of Power plant by voltage change, Kostic et al. (2006).
