Defining ROCOF - Eirgrid

Defining ROCOF
Background / Proposed Modification
to Irish Grid Code

Background
• ROCOF is not currently defined in the Irish Grid
Code and is not mentioned in NI Grid Code
• Need to specify how ROCOF is calculated
– Definition will affect ultimate ROCOF capability sought
from generators
• EirGrid bringing renewed proposals to Ireland
GCRP on ROCOF
– A proposal had previously been discussed at GCRP
• SONI will also discuss ROCOF proposals at NI
GCRP

ROCOF during a 3-Phase Fault

Example 2

Proposed Modification - Background
• Generators should not trip for very high
ROCOF values seen during transient faults
– Fault ride through clauses must apply here
– There has never been a problem historically
• ROCOF value / Calculation Window should be
chosen such that electrical transient effects
are excluded
– But should be high enough to capture loss of
largest infeed / system separation type events

Proposal 1
Rate of Change of Frequency (ROCOF):
The rate of increase or decrease of Frequency as measured at the User’s Connection Point averaged
over the time period as set out in CC.7.3.1.1(d).
PROPOSED CHANGE TO CC7.3.1.1(d)
CC.7.3.1.1 Each Generation Unit, shall, as a minimum, have the following capabilities:
•remain synchronised to the Transmission System during rate of change of Transmission System
Frequency of values up to and including 0.5 Hz per second for a Rate of Change of Frequency of up to
X Hz per second averaged over Y milliseconds. Voltage dips may cause localised ROCOF values in
excess of X Hz per second for short periods, and in these cases, the Fault-Ride Through clause
CC.7.3.1.1(h) supercedes this clause;
NOTE:
X in the range 1-2Hz/sec
Y in the range 150-500ms

Proposal 2
Rate of Change of Frequency (ROCOF):
The rate of increase or decrease of Frequency as measured at the User’s Connection Point over a
time period greater than the time for the synchronous Generators on the system to reach Coherency
but no greater than 500ms in any case.
Coherency:
A group of synchronous Generators are defined as coherent after an Event if the relative
displacement between their power angles is constant.
PROPOSED CHANGE TO CC.7.3.1.1(d)
CC.7.3.1.1
remain synchronised to the Transmission System during rate of change of Transmission System
Frequency of values up to and including 0.5 Hz per second remain synchronised to the
Transmission System for a Rate of Change of Frequency of up to X Hz per second. Voltage dips
resulting in loss of coherency may cause localised ROCOFs in excess of this value for short periods,
and in these cases, the Fault-Ride Through clause CC.7.3.1.1(h) supercedes this clause;
NOTE:
X in the range 1-2Hz/sec
Y in the range 150-500ms