Toshiba GRZ100 B Series, Instruction Manual, Page: 92 / 447

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2.4.14 Power Swing Blocking
When a power swing occurs on the power system, the impedance seen by the distance measuring
element moves away from the load impedance area into the operating zone of the distance
measuring element. The operation of the distance measuring element due to the power swing
occurs in many points of interconnected power systems. Therefore, tripping due to the operation
of the distance measuring element during a power swing is generally not allowed. The power
swing blocking function (PSB) of the GRZ100 detects the power swing and blocks tripping by the
distance measuring element. The GRZ100 provides PSBSZ and PSBGZ for phase fault measuring
elements and earth fault measuring elements. Their functions and characteristics are same.
Once the PSB is in operation, tripping of zone 1 to zone 3 of the time-stepped distance protection,
zone 1 extension protection, additional forward zone ZF, backup protection for reverse faults and
command protection using distance measuring elements can be blocked. These tripping blocks can
be disabled by setting the scheme switches.
Tripping of the non-directional zone ZND is not blocked. If a zero-phase current has been
detected, the PSB is inhibited. This allows tripping in the event of an earth fault during a power
swing or high resistance earth fault by which the resistance at the fault point changes gradually.
GRZ100 can provide a high-speed protection for one- and two-phase faults which occur during a
power swing by using negative sequence directional element and any of the command protection
PUP, POP, UOP and BOP.
Three-phase faults during a power swing are eliminated by distance and overcurrent backup
protection.
Scheme logic
A power swing is detected by using two PSB elements PSBIN and PSBOUT. They are composed
of blinder elements and reactance elements as shown in Figure 2.4.14.1. PSBOUT encloses
PSBIN with a settable width of PSBZ.
Figure 2.4.14.2 shows the power swing detection logic. During a power swing, the impedance
viewed from the PSB elements passes through the area between the PSBOUT and PSBIN in a
certain time. In the event of a system fault, the impedance passes through this area
instantaneously. Therefore, a power swing is detected in a time which commences on operation of
the PSBOUT until PSBIN starts to operate, if longer than the set value of delayed pick-up timer
TPSB. If the residual overcurrent element EFL operates, detection of the power swing is inhibited.
The trip block signal PSB generated as a result of the detection of a power swing is reset 500 ms
after the PSBOUT is reset by delayed timer T2.
PSBZ
PSBZ
PSBZ
0
PSBZ
PSBIN
PSBOUT
R
X
Z3
Z4
ZR2
Figure 2.4.14.1 Power Swing Blocking Element