Beijing Sifang CSC-241C Digital Plant/Station Transformer Protection and Control Device
1.1 Device Introduction
This device is suitable for the protection and control of station or plant transformers and can be installed locally in switchgear.
1.1.1 Protection Functions
a) Instantaneous overcurrent protection for phase-to-phase faults;
b) Overcurrent protection;
c) Overload alarm or trip function;
d) Current acceleration protection;
e) Zero-sequence current protection, operable in definite-time or inverse-time mode;
f) Undervoltage protection with current blocking;
g) Non-electrical protection;
h) F-C overcurrent blocking function.
1.1.2 Control and Monitoring Functions
a) 15-channel digital input for telemetry acquisition, device status change telemetry, and fault telemetry;
b) Remote opening and closing of normal circuit breakers;
c) Telemetry of analog quantities such as Ua, Ub, Uc, Ia, Ib, Ic, P, Q, cos?;
d) Various event SOEs, etc.;
e) 2-channel pulse P and Q inputs.
1.1.3 Other Functions
a) PT broken wire alarm;
b) Control circuit broken wire alarm;
c) Spring not charged alarm;
d) Fault recording;
e) 32 setting groups;
f) 4-20mA output.
2.2 Protection Elements
2.2.1 Overcurrent Element
Overcurrent protection current and time settings can be independently set. The starting condition is:
MAX（IΦ）> MIN(Id ); where Id is the overcurrent setting, IΦ is the phase current.
The operation conditions are:
a） IΦ>Idz; where Idz is the current setting, IΦ is the phase current;

b） is the time delay setting.
Overcurrent protection is enabled or disabled via a software setting. When tripping, it also trips the four branches of the transformer via four backup outputs. When backplane terminals X5.6
and X5.7 are used as general telemetry, a combined software-hardware setting mode can be selected, where X5.6 is the hard contact input for instantaneous overcurrent protection, and X5.7 is the
hard contact input for overcurrent protection.

2.2.2 Overload Protection
The overload element monitors the three-phase load current. If the maximum phase current exceeds the setting and the duration exceeds the time delay setting, an alarm signal is issued or the load is shed based on the control word setting. KG1.0=0: overload issues an alarm signal; KG1.0=1: overload trips and issues an alarm signal.
The operation conditions are:
a) MAX(IΦ)>Ifh, where Ifh is the overload current setting;
b) T> time setting.
The overload function is enabled or disabled via a software setting, and the control word selects whether overload acts on trip or alarm. When tripping, it also trips the four branches of the transformer via four backup outputs.

2.2.3 Current Acceleration Protection
When the transformer is manually or automatically energized into a permanent fault, if any phase current exceeds the current acceleration setting, after the current acceleration time delay setting, the device trips and also trips the four branches of the transformer via four backup outputs.
The operation conditions are:
a） IΦ>Idz; where Idz is the current setting, IΦ is the phase current;
b） Pre-closing state (circuit breaker open for 10 seconds);
c） Circuit breaker closed;
d） T>Tjs; where Tjs is the acceleration protection time delay setting.