AN INTRODUCTION TO THE USE OF INVERTER POWER SUPPLIES IN GLOBAR APPLICATIONS HOW TO IMPROVE THE POWER FACTOR OF THE SYSTEM.

Transcription

1 AN INTRODUCTION TO THE USE OF INVERTER POWER SUPPLIES IN GLOBAR APPLICATIONS HOW TO IMPROVE THE POWER FACTOR OF THE SYSTEM. Stanley F. Rutkowski lll, Senior Applications Engineer, RoMan Manufacturing The Challenge Can an IGBT driven inverter power supply power the Globars in resistance heating applications to both improve the Power Factor of the system and use the same amount or less power. The Testing Process In order to test in free air the effects of AC and DC power onto the Globar, RoMan acquired silicon carbide Globars from a world branded manufacturer. Controlled Testing The illustrations shown below indicate the measured temperature on non-energized A/B/C Globar left hand view of the diagram and measured the temperature of a non- energized element next to it at position Z right hand view of the diagram. This was done for all five tests conducted in order to capture Conductive, Convective and Radiant heating. The calibrated current of the tested Globar is 60 Amps. 1

2 Results of Five Tests Test Notes Test #1: AC Three Phase A, B and C connections to the Globar 45.2 V A 3.45 kw C Test #2: AC Single Phase A-C connected to the Globar and B left open 68.2 V 57.9 A 4.0 kw C 62.8 V 54.2 A 3.4 kw C Test #3: DC Single Phase A-C connected to the Globar and B left open 68.4 V 58.6 A 4.0 kw C 63.3 V 55.1 A 3.5 kw C Test #4: DC Single Phase C-A (reversed polarity of Test #3) connected to the Globar and B left open 62.8 V 54.3 A 3.4 kw C Test #5: DC A and C connections Positive and B connection Negative 56.4 V 59.2 A 3.39 kw C During the testing process, connections of A-B and B-C were tested with all the outcomes being similar to A-C connections. As a result, only one set of data is presented. In addition, also 2

3 presented is data for forward and reversed DC connections that confirms there were no radical differences in the connections to determine a polarity on the Globar. Three phase Delta to Delta If we consider at 150 kw zone (40 elements in parallel), we can use a three phase Delta to Delta AC transformer with the ratings of: Tap Primary Secondary Secondary Turns Turns Volts

4 Test #1 indicated that the secondary voltage required is 45.2 volts and the current per Globar is Amps (for 40 Globars it would be Amps). Using tap two of the typical three phase power supply produces 70.2 volts on the secondary, or a margin of 1.5 (70.2 V / 45.2 V) Tap Primary Secondary Secondary Primary Primary Secondary Secondary Turns Turns Volts Phase Line Phase Line Considering an Inverter DC Application Current Current Current Current Test #4 indicated that the secondary voltage required is 62.8 volts and the current per Globar is 54.3 Amps (for 40 Globars it would be 2172 Amps). Tap Primary Secondary Secondary Primary TX TX Turns Turns Volts Phase Primary Secondary Current Current Current

5 Test #5 indicated that the secondary voltage required is 56.4 volts and the current per Globar is 59.2 Amps (for 40 Globars it would be 2368 Amps). This provides a margin of 1.5 (84.78 V / 56.4 V) similar to the AC unit. Comparisons Tap Primary Secondary Secondary Primary TX TX Turns Turns Volts Phase Primary Secondary Current Current Current Comparing the Three Phase AC system to test #4, the primary current per phase was reduced from Amps to Amps (28.3 Amps). This resulted in a 23.5 KVA (28.3 A x 480 V x Square Root (3)) reduction in Power in the application. Comparing the Three Phase AC system to Test #5 the primary current per phase was reduced from Amps to Amps (7.7 Amps) resulting in a 6.4 KVA (7.7 A x 480 V x Square Root (3)) reduction in Power in the application. Conclusions The Real Power of the application with the use of an IGBT system is similar to the existing three phase AC systems A typical power bill consists of five segments (Real Power, Reactive Power, Total Power, Power Factor and Peak Demand). -- The IGBT system will reduce Reactive Power (kvar) because of the DC in the secondary loop eliminating the inductance. -- Total Power (kva) as Reactive Power is a component of the Total Power. -- Power Factor as the wave form is modulated and not chopped as well as the reduction of the Reactive Power. -- Real Power and peak demand will be similar if not slightly reduced as indicated in the previous examples. Present systems employ a three pole (three phase AC System) while DC power is a two pole system. The IGBT system will work with the existing system, however, it would be optimized by a two pole system.* Heat on the pole is less with a DC system (measured with IR gun) however, the Radiant heat at the sample point was the same (what the load will see). 5

6 The Size and Weight of the transformer are reduced. *Tests conducted using the three pole system in order to obtained equitable test results 6

7 Copyright 2014, RoMan Manufacturing 7