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7.
An IGBT failure is usually also a result of an over voltage. Failures due to over current are rare since the
cell and system is much more capable of protecting itself from this condition. There are two types of IGBT
failures, catastrophic and non-catastrophic.
In non-catastrophic failures (those which do not result in case rupture), the root cause can often be found
by Product Development or the device manufacturer. Failures of this type during cell testing or early in the
commissioning cycle are often the result of infant mortality failures. These devices must be returned to
Product Development since they may be a result of insufficient process quality. In most cases, gate drive
and cell control circuits are left unaffected and can be presumed functional.
In catastrophic failures (those which result in case rupture), the root cause is more difficult to determine.
Failures of this type usually result in collateral damage to adjacent IGBTs, especially those IGBTs in the
same pole (for instance Q1/Q2 or Q3/Q4). These failures almost always cause damage to any connected
gate drive or gate circuit.
8.5 Component Re-use
It is often unnecessary to replace all components in a failed cell. Usually only failed components need replaced,
provided that the remaining components are determined re-usable.
8.5.1
Non-Catastrophic Rectifier Failures
If a non-catastrophic Rectifier failure occurs, it usually results in one upper diode and one lower diode failing short
circuit. This requires replacing two diode modules. The third diode module can be presumed OK if:
8
1.
Device passes a 3400VDC (for 1700V devices) HIPOT, all terminals to baseplate.
2.
Device passes A-K check.
3.
Device passes all specified in-circuit cell tests.
8.5.2
Non-Catastrophic IGBT Failures
If a non-catastrophic IGBT failure occurred in only one pole (i.e., Q1/Q2 or Q3/Q4), replace only the failed IGBT
module with an approved device with the same part number. The other IGBT module can be presumed OK if:
1.
Device passes a 3400VDC (for 1700V devices) HIPOT, all terminals to baseplate.
2.
Device passes G-E, C-E, and A-K check.
3.
Device passes all specified in-circuit cell tests.
The following tests can be performed to verify an IGBTs condition after a cell failure:
G-E Check
Short the collector to the emitter. Ohm check gate to emitter. Resistance should be 10M to infinite. A low resistance
indicates device destruction. Device must be replaced.
C-E Check
Short the gate to the emitter. Ohm check collector to emitter. Resistance should be 10M to infinite. A low resistance
indicates device destruction. Device must be replaced.
A-K Check
Use a diode checker to verify a small positive voltage drop (<1V) from emitter to collector (anode to cathode of the
FWD) and blocking from collector to emitter (cathode to anode of the FWD). If a short, or if >1V is measured, the
device must be replaced.
8-2
MicroHarmony Cell Sizes 40 - 260A Manual
s
19001467: Version 1.0
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