Operation Manual 37107F
MFR 3 - Multi Function Relay
Page 116/165
© Woodward
Mains df/dt Rate Of Change Of Frequency Monitoring (ROCOF)
NOTE
The "Blocking of mains protection" input (terminal 61) disables mains monitoring and decoupling.
Function:
"Frequency change per time unit not within the permissible range"
The control unit determines a measuring value for the change in frequency per unit of time (Hz/s). In order to en-
able reliable differentiation between d
ϕ
/dt phase/vector shift and df/dt, measurement is carried out over 4 cycles.
This results in a minimum tripping time of approx. 100 ms (at 50 Hz). The breaker configured as the mains de-
coupling breaker is opened. The requirement therefore is a mains parallel operation (both GCB and MCB are
closed). An alarm is issued if a fault condition is detected.
Parameter
190
df/dt-monitoring
ON
df/dt (ROCOF)
ON/OFF
ON
................ Mains frequency monitoring is enabled, and any change in frequency
per unit of time (Hz/s) within the defined range is registered. The
subsequent screens of this function are displayed.
OFF
.............. Mains frequency monitoring is not performed. The subsequent
screens of this function are not displayed.
Parameter
191
df/dt-monitoring
release> 0.0Hz/s
df/dt (ROCOF): limit
1.0 to 9.9 Hz/s
The value to be monitored for the ROCOF is configured in this screen. If the moni-
tored frequency reaches or exceeds this level for the configured delay time, the unit
issues an alarm and opens in dependence of the setting the GCB or the MCB de-
pending on which is configured for decoupling from the mains.
Tripping of class F0 alarm
Parameter
192
df/dt-monitoring
Delay time 0.0s
df/dt (ROCOF): delay
0.1 to 9.9 s
The ROCOF monitoring threshold limit must be exceeded, without interruption, for
the time period configured here before the configured relay will be energized.
Mains Decoupling (Selection Between d
ϕ
/dt and df/dt)
Parameter
193
Mainstrip via
----------------
Mains decoupling via
Phase shift / df/dt
The opening of the GCB/MCB (refer to Parameter 115"Mains decoupling via...")
may be performed if either df/dt or phase/vector shift monitoring fault condition is
detected.
df/dt
.............. Decoupling from the mains is performed if a df/dt fault condition is
detected.
Phase shift
.... Decoupling from the mains is performed if a d
ϕ
/dt phase/vector shift
fault condition is detected.
