Function descriptions 02.00
9-32 SIEMENS AG 6RX1700-0AD76
SIMOREG DC Master Operating Instructions
9.15 Dynamic overload capability of power section
9.15.1 Overview of functions
The converter rated DC current specified on the rating plate (= maximum permissible continuous direct
current when P077 = 1.00) may be exceeded in operation. The amount and permissible duration of the
overload are subject to limits which are explained in more detail below.
The absolute upper limit for the absolute value of overload currents corresponds to 1.5 times the
converter rated DC current * P077. The maximum overload period depends both on the time
characteristic of the overload current and on the load history of the converter and differs depending on
the installed power section.
Every overload must be preceded by an "underload" (load phase at load current < P077 * rated DC
current). After the maximum permissible overload period has expired, the load current must be
reduced to a value of at least ≤ P077 * converter rated DC current.
The dynamic overload period is made possible by a thermal monitoring function
(I
2
t monitor) in the
power section. This uses the time characteristic of the actual load current to calculate the time
characteristic of the thyristor temperature rise over ambient temperature. When the converter is
switched on, the calculation commences with the initial values that were calculated before the
converter power supply was last switched off/last failed. Allowance can be made for ambient conditions
(ambient temperature, installation altitude) by the setting in parameter P077.
In the delivery state, the ambient temperature is always set to the maximum permissible value
(i.e. 45°C for naturally cooled converters and 35°C for converters with forced cooling).
The I
2
t monitoring function responds when the calculated thyristor temperature rises exceeds the
permissible limit. Two alternative responses to the monitor can be parameterized:
P075 = 1: Alarm A039 with reduction of armature current setpoint to P077 * converter rated DC
current
P075 = 2: Fault F039 followed by converter shutdown
The I
2
t monitoring function can be deactivated. In this case, the armature current is limited to the
setting in P077 * converter rated DC current.
Connector K310 contains the calculated thyristor overtemperature as a % of the maximum permissible
converter-specific thyristor overtemperature:
80°C on 15A to 60A converters
85°C on 90A to 140A converters
90°C on converters of > 200A converter rated armature DC current.
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