BECKWITH ELECTRIC M-3425, Инструкция

Страница: 80 / 225

Application – 2
2–43
78 Out-of-Step
The Out-of-Step function (78) is used to protect the
generator from out-of-step or pole slip conditions.
This function uses one set of blinders, along with a
supervisory MHO element. Ranges and increments
are presented in Table 2-24.
The pickup area is restricted to the shaded area in
Figure 2-18, Out-of-Step Relay Characteristics,
defined by the inner region of the MHO circle, the
region to the right of the blinder A and the region to
the left of blinder B. For operation of the blinder
scheme, the operating point (positive sequence
impedance) must originate outside either blinder A
or B, and swing through the pickup area for a time
greater than or equal to the time delay setting and
progress to the opposite blinder from where the
swing had originated. When this scenario happens,
the tripping circuit is complete. The contact will
remain closed for the amount of time set by the
seal-in timer delay.
N O I T C N U F E G N A R T N I O P T E S T N E M E R C N I
) 8 7 ( p e t S - f o - t u O
r e t e m a i D e l c r i C
0 . 0 0 1 o t 1 . 0
Ω
0 . 0 0 5 o t 5 . 0 (
Ω
)
1 . 0
Ω
t e s f f O
0 . 0 0 1 o t 0 . 0 0 1 –
Ω
0 . 0 0 5 o t 0 . 0 0 5 – (
Ω
)
1 . 0
Ω
e l g n A e c n a d e p m I 0
o
0 9 o t
o
1
o
r e d n i l B
0 . 0 5 o t 1 . 0
Ω
0 . 0 5 2 o t 5 . 0 (
Ω
)
1 . 0
Ω
y a l e D e m i T s e l c y C 0 6 1 8 o t 1 e l c y C 1
r e t n u o C p i l S e l o P 0 2 o t 1 1
t e s e R p i l S e l o P s e l c y C 0 6 1 8 o t 1 e l c y C 1
Table 2-24 Out-of-Step (78) Setpoint Ranges
Consider, for example, Figure 2-18. If the out-of-
step swing progresses to impedance Z
0
(t
0
), the
MHO element and the blinder A element will both
pick up. As the swing proceeds and crosses blinder
B at Z
1
(t
1
), blinder B will pick up. When the swing
reaches Z
2
(t
2
), blinder A will drop out. If TRIP ON
MHO EXIT option is disabled and the timer has
expired (t
2
–t
1
>time delay), then the trip circuit is
complete. If the TRIP ON MHO EXIT option is
enabled and the timer has expired, then for the trip
to occur the swing must progress and cross the
MHO circle at Z
3
(t
3
) where the MHO element drops
out. Note the timer is active only in the pickup
region (shaded area). If the TRIP ON MHO EXIT
option is enabled, a more favorable tripping angle is
achieved, which reduces the breaker tripping duty.
The relay can also be set with a Pole Slip Counter.
The relay will operate when the number of pole slips
are greater than the setting, provided the Pole Slip
Reset Time was not expired. Typically, the Pole
Slip Counter is set to 1, in which case the Pole Slip
Reset Time is not applicable.