Toshiba GR200 Series Instruction Manual page 65

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Offset characteristics in ZS

Some elements in ZS are used for the detection of faults in the reverse direction and these

elements can have an offset characteristic, which assures the detection of a close-up three-

phase fault. Offset characteristic

instructs to start the memory action at which the voltage drops to zero upon the occurrence of

a fault. That is, for dropping to zero voltage, the memory action services an important role for

deciding whether the fault is located in the forward or in the reverse direction based upon the

relay location. In the offset characteristic, its offset value is fixed at 1.5Ω for 5A rating

whereas it is fixed at 7.5Ω for 1A rating

characteristic of Z1S in the reverse direction; Figure 2.1-22 illustrates that the action of the

Quad characteristic is applied. Note that the offset characteristic in the reverse direction is not

provided in Z2S and Z3S.

Note: As a rule, Z1S, Z1XS, and Z5S are utilized for a close-up three-phase fault. For

example, the Z1S element can be instructed to operate in the reverse direction; the

operation of the Z1S element should be covered the origin (i.e., voltage=0), as

shown in Figure 2.1-21. Owing to the memory action for the close-up fault, the

Z1S element is able to detect a fault even if the memory does not hold voltage data

(say, in the memory the voltage data is set to zero for the close-up three-phase

fault). The operation of the memory action has been available for the last three-

cycles at the occurrence of the close-up fault; the memory action has not been

available for the last four-cycles. The same memory action is also provided in the

Z1XS and the Z5S.

Note: Either 1A or 5A rating is fixed to operate on a transfer modules (VCT). For more

information about the VCT, see Chapter

module for AC analog input

Figure 2.1-21 Z1S Mho element during close up fault (Offset action)

is provided in Z1S, Z1XS, and Z5S; the offset characteristic

. Figure 2.1-21 exemplifies the action of the Mho offset

Technical Description: Transformer

Static MHO characteristic

Z1S-Mho.Angle

6F2S1915 (0.46)

characteristic

during close-up fault

GRZ200 (Soft 031 & 032)