PASCOR Type SR-500 Surge-Suppression Resistors
PASCOR offers surgesuppression resistors for applications on 138kV, 230kV, 345kV and 500kV vertical break disconnect switches with one, two, three, or four modules respectively.
Features
Resistors are static, oil-less and maintenance free. They can be adapted to any manufacturer’s vertical break disconnect switch. Modules are pressurized at the factory with dry nitrogen, no field filling is required. Resistor assembly is easy to install.
Advantages
In the closing process, the current inrush is reduced dramatically. In the opening process, there can be high over voltage when the deenergization takes place, and with resistors this can be dampened dramatically. The opening and closing processes are dampened which prolongs transformer life. An important application is for switching platform charging current in 500kV series capacitor banks.
PASCOR’s modular resistor primary objective is to limit surge currents and transient voltage when switching transformers.
Surge-Suppression Resistor (SR-500)
As an economy measure, even rather large unloaded power transformers are frequently switched by disconnect switches. Transient overvoltages, particularly at 345kV and above, can be sever. The magnitude depends on the inductance (L) and the capacitance (C) of the system.
There are three rather distinct advantages to having the resistors when switching with a disconnect switch. That is:
- In the closing process, the current inrush is reduced dramatically. This results in a reduced mechanical shock to the transformer high voltage winding. It has been suggested that without the resistors, the inrush may be more detrimental than a through-fault. In a through-fault, the transformer design may use the forces generated in the secondary winding to brace the high voltage coil.
- As the switch opens without resistors, the transient voltage increases. This can subject the lightning arresters to a sequence of clipping requirements. With resistors, the voltage transients are well below the lightning arrester operating point plus much easier on the main concern, the transformer. For the closing process, much the same takes place.
- In the opening process there can be a rather high overvoltage when the de-energization finally takes place. With resistors, this too dampened dramatically. The exact value depends on the system parameters.
There is reason to believe the dampening processes described above will extend the life of the transformer.
