SICROWBAR DC overvoltage protection производства Siemens

The most important components of the device are:

• Two disk-type thyristors in an anti-parallel connection
• A firing circuit, which, depending on the version, triggers a thyristor in the blocking direction at a defined voltage
• A module to detect the voltage at the de-excitation/discharge resistor, detect the current being conducted, identify when the overvoltage protection device triggers and signal the status using binary outputs.
• The power connections C, D (copper bars)
• Terminal XEW1 to connect the sensor cable from the de-excitation/discharge resistor.
• An "Optional fast de-excitation" module (Option G11).

The module allows the thyristors to be fired at any time by controlling three fast relays that are independent of one another.

The two thyristors connected in an anti-parallel connection, located between connections C and D, can briefly (approx. 5 s) conduct the pulse current. The overvoltage triggers a break-over diode (BOD) on the trigger circuit which in turn triggers the blocking thyristor and conducts the firing current past the blocking thyristor through a diode connected in an anti-parallel configuration to its gate/cathode. Independent of the polarity of the overvoltage, the break-over diode is always operated in the same direction using a bridge rectifier and the firing current is limited to between 6 and 8 A using series resistors. The thyristor fires within just a microseconds and the voltage decreases quickly down to the forward voltage (1 to 1.5 V). The load current increases the temperature of the disk-type thyristor within just a few seconds and the thyristor and the stack construction absorb the thermal energy. As a consequence, the load cycle can only be repeated after a cooling time has elapsed (see Technical specifications).

The fast de-excitation option (G11) is connected to the firing circuit in such a way that the thyristors can be triggered at any time by controlling at least one of the three fast relays - that are independent of one another. This assumes that there is sufficient voltage. Generally, this is approximately 5 % of the trigger voltage. Each of the three relays can be controlled with 24 V DC, 110 V to 125 V DC or 220 V to 240 V DC.

The voltage detection for the de-excitation/discharge resistor is connected to the external de-excitation/discharge resistor. When the voltage detection responds, the supplying converter must be blocked or the current controlled down to zero. The voltage detection module requires an external 24 V DC power supply with min. 100 mA.

The de-excitation/discharge resistor is an external device and is not included in the scope of delivery of the SICROWBAR DC overvoltage protection. Its resistance must be so low that even at the highest load current, the voltage is still under the destruction limit of the supplying converter and/or the winding to be protected. The lowest possible resistance is defined by the supply voltage and the maximum load current of the converter (dimensioning the fuses). The required de-excitation time must also be taken into account when dimensioning the value of the resistance.

The complete arrangement comprises a SICROWBAR DC overvoltage protection and de-excitation/discharge resistor.

The following device parameters that are used to select the device must be determined:

1. The firing voltage - if this is reached, then the thyristors of the SICROWBAR DC are turned-on.

2. The maximum current that flows or the maximum I²t value that occurs.

Detailed notes on the configuration, the standards that apply and the connection of the overvoltage protection are provided in the Operating Instructions, on the DVD-ROM supplied with Catalog D 23.1 or in the Internet under http://support.automation.siemens.com/WW/view/en/21690222/130000.

Typical load current characteristic for the three device power stages

Cooling-down time

Spare parts, see in the Internet under http://workplace.automation.siemens.de/sparesonweb.