Toshiba GR-200 Series Instruction Manual page 228

DFRQ features and characteristics
2.19.2
Either a frequency-rise element (RISE) or a frequency-down element (DOWN) is used to
monitor the frequency-change. It is required for the user to select either RISE or DOWN
element at respective frequencies. The DFRQ is used to ensure the operation of load shedding
promptly when the change of frequency is very rapid.
RISE/DOWN characteristic
(i)
The RISE and DOWN elements calculate the gradient of frequency-change (Δf/Δt) every
5msec. Figure 2.19-3 shows how to calculate the gradient using Δf and Δt: the change of
frequency (Δf) over a time interval and Δt equals to 100ms. Six elements are provided for the
DFRQ function; each element can operate independently. Each stage of the DFRQ function
issues a trip signal if Δf exceeds the setting value of 50 consecutive times.
The user can set the state 1 to detect whether a frequency to be rising or to be descending
using scheme switch [DFRQ1-Chara]. For example, when Rise is set for the scheme switch
[DFRQ1-Chara], the DFRQ examines the gradient of frequency-change (Δf/Δt) in up.
Conversely, when Down is set for the scheme switch, the DFRQ examines the gradient of
frequency-change (Δf/Δt) in down. Setting [DFREQ1] is used to configure an operation
threshold; the operation threshold is configured with Hertz per second.
The operation of the RISE/DOWN elements is blocked when the FRQBLK element runs.
That is, if an obtained voltage is below the setting [FRQBLK], any operation of the DFRQ
function is blocked. The FRQBLK element is discussed in Chapter 2.19.1(i).
Figure 2.19-3 Gradient of frequency rate-of-change
Enabling DFRQ function
(ii)
The user should set On to enable the DFRQ function using scheme switch [DFRQ1-EN]. If the
user is not to operate the DFRQ function, Off should be set for the scheme switch.
DFRQ trip signal
(iii)
The DFRQ can issue a trip signal for the function of trip circuit (TRC) when Trip is set for
Hz
Δ f
Δ t
- 209 -
sec
6F2T0200 (0.15)
GRE200 (1,2)