4-4 Checking the Main Element 4-4 Checking the Main Element The quality of the main element can be checked using a tester. Preparation Make preparations for the check by following the procedure below. 1. Disconnect the cables (N, RB, P and P terminals), and the built-in resistor cable (RB and P terminals). 2. Prepare a tester. (Usable range is 1 Ω measurement resistance.) 4 Inspection and Maintenance Checking method The quality can be judged by measuring the conduction state of the N, RB and P terminals on the Regenerative Braking Unit terminal block (main circuit terminals) while alternating the tester polar- ity.
P FD (flywheel diode) RB IGBT (main element) N • First, measure the voltage between the P and N terminals in the DC voltage range. Then, make sure that there is no residual voltage before performing the check. • A nearly infinite value is shown in a no-conduction state. The value shown ranges from a few to a few dozen Ω in a conduction state. If the measurement result for each item is as listed below, the quality is judged as being acceptable. 4-5 Tester polarity Measurement results + (red) − (black) IGBT RB N Conduction N RB No conduction FD P RB Conduction RB P No conduction