Because the cost of electrical energy can be dependent on power factor, judicious selection of the techniques used to control electrical power to industrial process heating applications can result in significant savings. When SCR controllers are used to control the electrical power, power factor is effectuated. Learn how multiple SCR controllers can be used to improve the power factor and reduce electrical costs.

Power factor is the ratio of real power to apparent power; therefore, power factor is

If the voltage and current are in phase, as would occur with a resistive load, the power factor is unity because the real power and apparent power are equal. If the voltage and current are not in phase, as would occur with an inductive or capacitive load, no power is created and the power factor would be zero.

Because the utility company incurs additional costs when the power factor is less than unity, the rate per kilowatt of energy used often is increased as a function of the power factor. Numerous methods are used; however, a rather common technique is that if the power factor is lower than a specified value, then the rate per kilowatt hour will be increased by dividing the specified value by the actual power factor. For example, if the specified rate is 0.9 and the actual power factor is 0.8, the cost per kilowatt hour would increase by 12.5 percent. If a facility consumes 100 kW and the price per kW-hr is \$0.06, the annual cost would be \$52,560 if the power factor is 0.9. If the power factor is 0.8, the annual cost would increase by \$6,570 to \$59,130.

The power factor of an existing facility may increase or decrease as a result of adding a load that is controlled by solid-state devices such as SCR controllers. The power factor obtained with modern instrumentation of a load controlled by SCRs will be equal to the square root of the percent power applied. For example, if 50 kW is applied to a 100 kW load, the power factor would be 0.707. If the existing power factor was 0.9, the addition of the 100 kW load powered at 50 kW would reduce the total power factor. Conversely, the power factor of the 100 kW load would be unity if powered at 100 kW, which would improve the existing 0.9 power factor. Figure 1. In this example, there are three heating elements operating at 66.6 percent of the maximum power to maintain temperature. The power factor is 0.816 at operating temperature.
The power required to maintain the temperature of an electrical load such as a furnace often is significantly less than the maximum power that the load could provide. The maximum power is required such that the system can be brought up to operating temperature in an acceptable period of time. The power factor when the process is at the desired temperature will be proportional to the square root of the applied power divided by the maximum available power. Figure 1 depicts a conventional control technique using one load. If only 66 percent of the maximum available power is required to maintain the process temperature, then the power factor would be 0.81. Figure 2. In this example, two heating elements operate at 100 percent power to maintain operating temperature. One heating element is used to increase temperature. The power factor is at unity at operating temperature.
One method to improve the power factor and to reduce the power factor penalty is to use multiple loads as shown in figure 2: one sized to operate at 100 percent output to maintain the process temperature and the other providing the power to increase the process temperature. The power factor when the system is operating at the desired temperature would be unity.

The effects on the power factor of a facility resulting from using multiple loads is dependent upon the amount of existing power, the power factor of the existing power and the percent of power required to maintain the desired process temperature. The amount of savings that can be obtained by using multiple loads is dependent on the power factor and the power factor penalty. Figure 3. Using two loads, where one is sized to provide the power to maintain the temperature and the second is used to increase the operating temperature, can reduce operating costs by eliminating a power factor penalty.
Figure 3 shows the savings that can be achieved by the use of two loads where one is sized to provide the power to maintain the temperature and the second is used to increase the operating temperature. The data is based on an existing power factor of 0.9 and that the power factor penalty is based upon 0.9.

If the controlled load represents 25 percent of the existing load and is operating at 70 percent of the maximum power, then a savings of 4.3 percent could be realized by using multiple loads. If the same load represents 50 percent of the existing load, then a savings 6.3 percent could be realized by using multiple loads. If a 100 kW load that requires 70 kW to maintain the temperature is added to a facility with a 0.9 power that currently uses 200 kW, the savings per year by using multiple loads would be approximately \$7,000. The cost to implement multiple load control on existing or new applications is dependent upon the particular situation. However, the return on investment is often less than one year.

The cost of electrical energy will increase, the penalty for a low power factor will increase and the need for a greener environment will increase. Ask your supplier of electrical equipment to provide you with a cost savings analysis.