Basler Electric DGC-2020HD - Manual (Page 147)

9469300990 Rev B 137
Frequency Rate-of-Change
When a loss of mains occurs, it is likely that the generator load will shift abruptly since the generator is
driving everything between the generator output and the utility breaker that removed mains power. Such a
load shift is likely to cause a speed shift, which may result in the generator being out of phase with the
mains when a reclose occurs. If the generator is out of phase and connection with the mains is
established, damage could occur. The frequency rate-of-change (ROC) element trips the breaker when a
change in frequency results from a sudden change in load.
Frequency ROC protection is only active when the generator is paralleled to the mains as indicated when
the Parallel to Mains logic element is true in BESTlogicPlus. Protection is inhibited for five seconds after
the Parallel to Mains logic element first becomes true so that transients from closing onto the mains will
not cause false trips.
To minimize false trips, frequency ROC protection is disabled if any configured breakers are not closed.
Frequency ROC trips are latched. They are cleared by pressing the Reset button on the front panel or by
putting the DGC-2020HD into Off mode.
Any of the eight 81 elements can be configured for frequency ROC protection.
Source
A Source setting configures the frequency element to monitor the generator sensing input terminals or the
bus sensing input terminals.
Pickup and Trip
When the rate of frequency change (expressed in hertz per second) exceeds the threshold established by
the Pickup setting for three consecutive sensing voltage cycles, a timer begins timing towards a trip.
Pickup detection time varies according to the value of the fault frequency. When the frequency greatly
exceeds the pickup setting, pickup detection occurs very quickly. More precise and slower pickup
detection occurs when the fault frequency is much closer to the Pickup setting. Pickup detection times are
summarized as follows:
•
Faults exceeding the pickup setting by 0.57 Hz/s are detected in 2 cycles
•
Faults exceeding the pickup setting by 0.24 Hz/s are detected in 4 cycles
•
Faults exceeding the pickup setting by 0.08 Hz/s are detected in 8 cycles
•
No pickup detection time will be greater than 16 cycles
Timer duration is established by the Activation Delay. An Activation Delay of zero (0) makes the 81
element instantaneous (with the exception of the pickup detection time).
If a frequency ROC pickup condition persists for the duration of the element Activation Delay setting, the
element Trip output becomes true. In BESTlogicPlus, the Trip output can be connected to other logic
elements or a physical relay output to annunciate the condition and initiate corrective action.
If the pickup condition subsides before the element activation delay expires, the timer is reset, no
corrective action is taken, and the element is rearmed for any other occurrences of a frequency ROC
fault.
Alarm Configuration
A frequency rate-of-change annunciation can be user-selected to trigger a pre-alarm (warning) or alarm
(shutdown). It can also be user-configured to close a programmable output.
Element status is available in BESTlogicPlus programmable logic when “Status Only” is selected.
Open Mains Breaker or Gen Breaker on Trip
When Open Mains Breaker on Trip is enabled, the DGC-2020HD will request the mains breaker to open
when an 81 trip is annunciated. When Open Gen Breaker on Trip is enabled, the DGC-2020HD will
request the generator breaker to open when an 81 trip is annunciated.
DGC-2020HD Generator Protection