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THEORY OF OPERATION |
FIGURE E.5 — SWITCH BOARDS AND MAIN TRANSFORMER.
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| MAIN |
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| TRANSFORMER | CURRENT |
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| SENSOR |
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| LEFT |
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| SWITCH |
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| BOARD |
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| PWM |
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| TERMINAL |
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| INPUT |
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| DRIVE |
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| CONTACTOR | RECTIFIER |
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| R | S |
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| E | W |
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| CURRENT |
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| E | C | VOLTAGE |
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| C | H | FEEDBACK |
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P S |
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O W |
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W I |
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E C | I | B |
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R H |
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| SWITCH |
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| U R |
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| OUTPUT | |
| T | D | CONTROL SIGNALS |
| PWM | CAPACITOR |
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| DRIVE | VOLTAGE |
| THERMOSTATS | |
| #1 AUX. |
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| FEEDBACK |
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| TRANS. |
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| 65VDC |
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| CURRENT FEEDBACK | |
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| CONTROL BOARD |
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AUX. |
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| VOLTAGE FEEDBACK |
RECONNECT | #2AUX. |
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| TRANS. | FAN |
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| MOTOR | POWER |
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| BOARD |
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| 40VDC |
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| STATUS |
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| WIRE FEEDER | RS232 | VOLTAGE | THERMAL | LIGHT |
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| 115VAC |
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| RECEPTACLE | CONN. |
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| RECEPTACLE |
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SWITCH BOARDS AND MAIN TRANSFORMER
There are two switch boards in the Power Wave 455, each containing an input capaci- tor and insulated gate bipolar transistor (IGBT) switching circuitry. Refer to Figure E.5. When the machine reconnect switches are configured for a lower input voltage (below 300 VAC) the input capacitors are connected in parallel. When the machine is configured for higher input voltages (300 VAC and above) the input capacitors are connected in series.
When the input capacitors are fully charged they act as power supplies for the IGBT switching circuit. The Insulated Gate Bipolar Transistors switch the DC power, from the input capacitors, “on and off” thus supplying pulsed DC current to the main transformer primary windings. See IGBT
Operation Discussion and Diagrams in this section.
Each switch board feeds current to a sepa- rate, oppositely wound primary winding of the main transformer. The reverse direc- tions of current flow through the main trans- former primaries and the offset timing of the IGBT switch boards induce an AC square wave output signal at the secondary of the main transformer. These primary currents are monitored by the current transformer (CT). If the primary currents become abnor- mally high, the control board will shut off the IGBTs, thus disabling machine output. The DC current flow through each primary wind- ing is clamped back to each respective input capacitor when the IGBTs are turned off. This is needed due to the inductance of the transformer primary winding. The firing of the two switch boards occurs during halves of a 50 microsecond interval, creat- ing a constant 20 kHz output.
POWER WAVE 455/POWER FEED 10
