Thyristor ratings & Voltage ratings of a thyristor
Thyristor ratings can be classified as
- Voltage Rating
- Current Rating
- Gate specifications
Peak Working Forward OFF state voltage (VDWM):
It specifics the maximum forward (i.e, anode positive with respect to the cathode) blocking state voltage that a thyristor can withstand during working. It is useful for calculating the maximum RMS voltage of the ac network in which the thyristor can be used. A margin for 10% increase in the ac network voltage should be considered during calculation.
Peak repetitive off state forward voltage (VDRM):
It refers to the peak forward transient voltage that a thyristor can block repeatedly in the OFF state. This rating is specified at a maximum allowable junction temperature with gate circuit open or with a specified biasing resistance between gate and cathode. This type of repetitive transient voltage may appear across a thyristor due to “commutation” of other thyristors or diodes in a converter circuit.
Peak non-repetitive off state forward voltage (VDSM): It refers to the allowable peak value of the forward transient voltage that does not repeat. This type of over voltage may be caused due to switching operation (i.e, circuit breaker opening or closing or lightning surge) in a supply network. Its value is about 130% of VDRM. However, VDSM is less than the forward break over voltage VBRF.
Peak working reverse voltage (VDWM): It is the maximum reverse voltage (i.e, anode negative with respect to cathode) that a thyristor can with stand continuously. Normally, it is equal to the peak negative value of the ac supply voltage.
Peak repetitive reverse voltage (VRRM): It specifies the peak reverse transient voltage that may occur repeatedly during reverse bias condition of the thyristor at the maximum junction temperature.
Peak non-repetitive reverse voltage (VRSM): It represents the peak value of the reverse transient voltage that does not repeat. Its value is about 130% of VRRM. However, VRSM is less than reverse break down voltage VBRR.