Velocity Edge GX440 Instructions d'exploitation télécharger pdf (Page 406)

Functions, monitoring, and protective functions

9.5 Monitoring and protective functions

Drive converter cabinet units

406 Operating Instructions, 10/2008, A5E00288214A

9.5.2 Thermal monitoring and overload responses

Description

The priority of thermal monitoring for power components is to identify critical situations. If

alarm thresholds are exceeded, the user can set parameterizable response options that

enable continued operation (e.g. with reduced power) and prevent immediate shutdown. The

parameterization options, however, only enable intervention below the shutdown thresholds,

which cannot be changed by the user.

The following thermal monitoring options are available:

● i²t monitoring – A07805 – F30005

i²t monitoring is used to protect components that have a high thermal time constant

compared with semi-conductors. Overload with regard to i²t is present when the converter

load (r0036) is greater than 100% (load in % in relation to rated operation).

● Heatsink temperature – A05000 – F30004

Monitoring of the heat-sink temperature (r0037) of the power semi-conductor (IGBT).

● Chip temperature – A05001 – F30025

Significant temperature differences can occur between the barrier layer of the IGBT and

the heatsink. These differences are taken into account and monitored by the chip

temperature (r0037).

If an overload occurs with respect to any of these three monitoring functions, an alarm is first

output. The alarm threshold p0294 (i²t monitoring) can be parameterized relative to the

shutdown (trip) values.

Example

The factory setting for the alarm threshold for chip temperature monitoring is 15 Kelvin (K),

and 5 K for the heat sink and inlet air. This means that the "Overtemperature, overload"

alarm is triggered at 15 K or 5 K below the shutdown threshold.

The parameterized responses are induced via p0290 simultaneously when the alarm is

output. Possible responses include:

● Reduction in pulse frequency (p0290 = 2, 3)

This is a highly effective method of reducing losses in the power unit, since switching

losses account for a high proportion of overall losses. In many applications, a temporary

reduction in the pulse frequency can be tolerated to allow the process to continue.

Disadvantage:

As a result of the pulse frequency reduction, the current ripple is increased which can

mean that the torque ripple is increased at the motor shaft (for low moments of inertia)

and also an increased noise level. Reducing the pulse frequency does not affect the

dynamic response of the current control circuit, since the sampling time for the current

control circuit remains constant.

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Velocity Edge GX440 Instructions d'exploitation Page 406