Toshiba GRZ100-211B, Instruction Manual

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2.4 Protection Scheme
The GRZ100 series has the following protection schemes and is applied to transmission lines of
directly earthed networks. The function of high-speed detection and clearance of faults ensures
that the disturbance to the power system is kept to a minimum in combination with the built-in
autoreclose functions. Appendix A shows block diagrams of the GRZ100 series.
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time-stepped distance protection
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zone 1 extension protection
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command protection (distance protection using telecommunication)
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high-resistance earth fault protection
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overcurrent backup protection
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thermal overload protection
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SOTF and stub protection
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overvoltage and undervoltage protection
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broken conductor detection
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circuit breaker failure protection
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out-of-step protection
2.4.1 Time-Stepped Distance Protection
2.4.1.1 Application
Using reach and tripping time settings coordinated with adjacent lines, the GRZ100 provides up to
four steps of distance protection for forward faults and backup protection for reverse faults. These
are used as the main protection when telecommunications are not available, or as backup
protection for the protected line and adjacent lines.
The GRZ100 has maximum eight distance measuring zones for both phase and earth faults,
maximum four zones for forward faults and maximum three zones for reverse faults respectively.
There is also one non-directional zone. The zones can be defined with either mho-based
characteristic or quadrilateral characteristic. The characteristic is selected by setting the scheme
switch [ZS-C] for phase fault and [ZG-C] for earth fault to "Mho" or "Quad".
Figure 2.4.1.1 shows the mho-based characteristics. Zone 1 (Z1), Zone 1X (Z1X), Zone 2 (Z2),
additional forward Zone F (ZF) and reverse Zone R1 (ZR1) have a complex characteristic
combining the reactance element, mho element and blinder element, while Zone 3 (Z3), additional
reverse Zone R2 (ZR2) and Z4 elements have a complex characteristic combining the mho
element and blinder element. ZND elements have a complex characteristic combining the
impedance element and blinder element. Z3 is also used for detection of forward faults in
command protection. If Z3 is dedicated to command protection, ZF can be used for Zone 3 instead
of Z3 in time-stepped distance protection.
The blinder element (BFR) can be provided for each forward zone. The setting of blinder element
can be set independently or set common to forward zones by the scheme switch
[BLZONE].Figures 2.4.1.1 and 2.4.1.2 show the characteristics with an independent setting.
Since the Z4 is used for detection of reverse faults in command protection, the Z4 for phase faults
has an offset characteristic with an offset mho element which assures detection of close-up phase
faults. The operation of Z4 for phase faults in the event of internal faults is inhibited by the
operations of Z2, ZF and Z3.
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