It
is experienced that one
of the causes
of overload and overstress in EHV T/F and while switching on 4-5 times of inrush current.
Sometimes
reactors and T/F were severely damaged due to heavy inrush current while
charging.
The reason for the inrush current is the random switching of the device.
The
random switching of substation equipment like power T/F, shunt/bus reactors,
capacitor banks, and transmission line& EHV power cables without proper
correlation with system voltage or current always cause unwanted overvoltage
stresses/ disturbances in the power transmission system.
These
disturbances & overvoltages may result in electrical and mechanical
stresses in associated power equipment leading to failures or reduction In
their useful lifespan.
The
re-ignitions, re-strikes and inrush currents associated with these switching
operations may also cause a disturbance in power system stability with the high
amplitude & high frequency the disturbance may lead to system outage with unexpected relay operations.
Though some traditional solutions were adapted in the past, they
could not be evaluated
for their effectiveness in controlling these disturbances on a real-time basis.
Controlled
switching or the point on wave switching technique is a versatile
and highly effective methodology to address the issues associated with the
switching of power equipment
leading to improved life expectancy & cost-effective asset management with
better power system stability.
Controlled/point
on wave switching has gained greater importance in Indian power transmission
systems with the introduction of 765 kV voltage level & downward integration with 400kv system.
Controlled
switching is one of
several technologies applied to the principle of coordinating the instant of
opening or closing of a circuit with a specific target point on an associated the voltage or current waveform.
Close
or trip command is processed through an intelligent device and
is sent to CB as
per the desired instant.
Controlled
switching CSD has
been introduced mainly for:
- to avoid re-ignitions
- to minimize inrush/magnetizing currents
- However, for reactor closing and ICT tripping operation also, the same may be utilized
- In case of CSD for tie CB where 765kv ICT and the reactor has been provided, CSD may be programmed for ICT closing and reactor tripping operation
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