Efficient Networks S120 manual Thermal monitoring and overload responses, Example

Monitoring and protective functions

8.2 Thermal monitoring and overload responses

8.2Thermal monitoring and overload responses

Description

The priority of thermal monitoring for power unit 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. An overload with regard to I2t is present when the converter load r0036 is greater than 100% (load in % in relation to rated operation).

●Heat-sink 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 IGBT barrier junction and the heat sink. 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). Temperature monitoring for the heat sink and inlet air is set to 5 K, that is, 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:

●Reducing the 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 pulse frequency is tolerable in order to maintain the process. Disadvantage:

Reducing the pulse frequency increases the current ripple which, in turn, can increase the torque ripple on the motor shaft (with low inertia load), thereby increasing the 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.

●Reducing the output frequency (p0290 = 0,2)

This variant is recommended when you do not need to reduce the pulse frequency or the pulse frequency has already been set to the lowest level. Further, the load should also have a characteristic similar to the fan, that is, a quadratic torque characteristic with falling speed.

292	Drive Functions
	Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4