Toshiba GRZ100 B Series, Instruction Manual, Page: 160 / 447

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3.3 Automatic Supervision
3.3.1 Basic Concept of Supervision
Though the protection system is in non-operating state under normal conditions, it is waiting for a
power system fault to occur at any time and must operate for the fault without fail. Therefore, the
automatic supervision function, which checks the health of the protection system during normal
operation, plays an important role. The numerical relay based on the microprocessor operations is
suitable for implementing this automatic supervision function of the protection system. The
GRZ100 implements the automatic supervision function taking advantage of this feature based on
the following concept:
•
The supervising function should not affect protection performance.
•
Perform supervision with no omissions wherever possible.
•
When a failure occurs, it should be able to easily identify the location of the failure.
Note
: Automatic supervision function includes automatic monitor function and automatic test
function. For the terminology, refer to IEC IEV 448.
In a fault during automatic testing, the tripping outputs are blocked for approximately 100 ms.
3.3.2 Relay Monitoring and Testing
The following items are supervised:
AC input imbalance monitoring
The AC voltage and current inputs are monitored to check that the following equations are
satisfied and the health of the AC input circuits is checked.
•
Zero sequence voltage monitoring
|Va + Vb + Vc| / 3
≥
6.35 (V)
•
Negative sequence voltage monitoring
|Va + a
2
Vb + aVc| / 3
≥
6.35 (V)
where,
a = Phase shifter of 120
°
•
Zero sequence current monitoring
|Ia + Ib + Ic
−
In| / 3
≥
0.1
×
Max(|Ia|, |Ib|, |Ic|) + k0
where,
In = Residual current
Max(|Ia|, |Ib|, |Ic|) = Maximum amplitude among Ia, Ib and Ic
k0 = 5% of rated current
These zero sequence monitoring and negative sequence monitoring allow high sensitivity
detection of failures that have occurred in the AC input circuits.
The negative sequence voltage monitoring allows high sensitivity detection of failures in the
voltage input circuit, and it is effective for detection particularly when cables have been connected
with the incorrect phase sequence.
The zero sequence current monitoring allows high sensitivity detection of failures irrespective of