Toshiba GR-200-5 Instruction Manual page 225

FRQ features and characteristics
2.19.1
Either an under-frequency element (UF) or an over-frequency element (OF) is used to monitor
the frequency-deviation; it is possible to set the degree of frequency deviation at each frequency.
The UF element is applied to monitor the balance between the power generation capability
and the loads. The OF element is used monitor the frequency to be within the normal range by
load shedding. The OF element is also used to protect synchronous machines from possible
damage owing to over-frequency conditions.
UF/OF characteristic
(i)
The UF and OF elements check the frequency every 5msec; they determines the frequency-
deviations whether the frequency is in under-frequency or over-frequency. Figure 2.19-1(a)
shows the UF characteristic; Figure 2.19-1(b) shows the OF characteristic; hatched area
reflects operation zone of the UF and the OF elements.
The user can select the stage 1 to detect either over-frequency state or under-frequency
state using scheme switch [FRQ1-Chara]. For example, If OverFrq is set for the scheme switch
[FRQ1-Chara], the stage 1 determines the over-frequency state when an over frequency is
observed (Figure 2.19-1 (a)); the user can set the threshold value into [FRQ1]. Conversely, if
UnderFrq is set for the scheme switch, the stage 1 determines the under-frequency state when
an under frequency is observed (Figure 2.19-1 (b)). The user can use a delay timer to postpone
to issue a trip signal using setting [TFRQ1].
Hz
o
Pickup voltage (FRQUVBLK)
a. Over frequency element at Stage 1
Figure 2.19-1 Characteristics of UF and OF elements (e.g. Stage 1 of FRQ)
Regarding the operation of the UF and OF elements, the user should notice the element
not to pick-up when the measured voltage is below the threshold value set with the
[FRQUVBLK] in positive sequence. Any operation of the FRQ function is blocked when an
OF stage 1
operation zone
- 205 -
Hz
o
V
Pickup voltage (FRQUVBLK)
b. Under frequency element at Stage 1
6F2T0207 (0.01)
UF stage 1
operation zone
V
GRE200 (5,6)