Claims:
WE CLAIM:
A pre-magnetizing system (100) for soft switching of a transformer (106), said transformer (106) being connected to a utility grid (102) via a circuit breaker (CB) (104), said pre-magnetizing system (100) comprising a voltage source inverter (VSI) (202) and a capacitor bank (204) adapted to facilitate:
smooth turn ON, in a first configuration, of said transformer (106), from its low-voltage (LV) side by supplying an output voltage equivalent to a rated voltage value of said transformer (106), to ensure voltage across the CB (104) is close to zero; or
smooth turn OFF, in a second configuration, of said transformer (106), from its low-voltage (LV) side by supplying an output current equivalent to no-load current value of said transformer (106), to ensure current through the CB (104) is close to zero.

The system as claimed in claim 1, wherein said CB (104) is a vacuum circuit breaker (VCB).

The system as claimed in claim 1, wherein said voltage source inverter (VSI) (202) is a full-bridge VSI.

The system as claimed in claim 1, wherein said system (100) is configured to supply a power equal to no-load power requirement of said transformer (106), wherein said no-load power requirement includes an active power requirement (Pnl) and a reactive power requirement (Qnl).

The system as claimed in claim 1, wherein said capacitor bank (204) is configured to supply half the reactive power requirement (Qnl) of said transformer (106).

The system as claimed in claim 1, wherein the power rating of said capacitor bank (204) is Pc = 0.5 x Qnl.

The system as claimed in claim 1, wherein the kVA rating of said VSI (202) is Snl =v(P_nl^2+0.25 Q_nl^2 ).

A method for soft switching of a transformer (106), said transformer (106) being connected to a utility grid (102) via a circuit breaker (CB) (104), said method involving a step of connecting a voltage source inverter (VSI) (202) and a capacitor bank (204) on a low-voltage (LV) side of said transformer (106) to facilitate smooth turn ON and smooth turn OFF of said transformer (106), wherein said CB (104) is in OFF state before initiating said smooth turn ON and said CB (104) is in ON state before initiating said smooth turn OFF.

The method as claimed in claim 8, wherein said step of smoothly turning ON said transformer (106) comprises the following sub-steps:
starting said VSI (202);
increasing an output voltage of said VSI (202) from zero to a rated value such that the voltage on a secondary side of said transformer (106) is close to a supply voltage of the utility grid (102), thereby ensuring voltage across said CB (104) is close to zero;
measuring and recording an output current of said pre-magnetization system (PMS) (100);
operating said VSI (202) in Current Controlled Mode by regulating the output current of said pre-magnetization system (PMS) (100) to a measured output current value; and
providing, a turn-ON signal to facilitate closing of said CB (104).

The method as claimed in claim 8, wherein said step of smoothly turning OFF said transformer (106) comprises the following steps:
starting said VSI (202);
increasing the output current of said VSI (202) to a value equivalent to the no-load current drawn by the transformer (106), such that the current flowing through said CB (104) is close to zero;
providing, a turn-OFF signal to facilitate opening of said CB (104); and
turning OFF and disconnecting said VSI (202) from said transformer (106).
, Description:
ABSTRACT
A PRE-MAGNETIZING SYSTEM FOR SOFT SWITCHING OF A TRANSFORMER AND A METHOD THEREOF
The present disclosure relates to the field of power electronics and discloses a pre-magnetizing system (100) and method for soft switching of a transformer (106), wherein the transformer (106) is connected to a utility grid (102) via a circuit breaker (CB) (104). The pre-magnetizing system (100) comprises a voltage source inverter (VSI) (202) and a capacitor bank (204) adapted to facilitate smooth turn-ON and smooth turn-OFF of the transformer (106). The pre-magnetizing system (100) is connected to the low voltage side of the transformer (106) and is configured to supply no-load power requirement of the transformer (106). The VSI (202) is configured to regulate its output voltage such that the voltage across the CB (104) is close to zero during turn-ON, and is further configured to regulate the output current such that the current through the CB (104) is close to zero during turn-OFF.