The North Seas Countries' Offshore Grid Initiative - Initial ... - Benelux

A normal contingency is the (not unusual) loss of one of the following elements:
generator, transmission circuit; transformer, shunt device (i.e. capacitors,
reactors), etc. This is referred to as the N-1 contingency. The N-1 security criterion
is satisfied if the network is within acceptable limits for expected transmission and
supply situations as defined by the planning cases, following a temporary (or
permanent) outage of one of the elements of the normal contingency list.
A rare contingency is the (unusual) loss of one of the following elements: a line
with two or more circuits on the same towers, a single busbar, a common mode
failure with the loss of more than one generating unit or plant, etc. These
contingencies are referred to as N-1-1, N-2 or N-G-1 contingencies, amongst
others.
An out-of-range contingency includes the (very unusual) loss of one of the
following: two lines or generation units independently and simultaneously, a total
substation with more than one busbar.
If the network is outside of acceptable limits in response to the abovementioned
contingencies for expected transmission and supply situations, then reinforcement of the
grid is planned. These measures can include, but are not limited to, the following:
Reinforcement of overhead circuits to increase their capacity (e.g. increased
distance to ground, replacing of circuits);
Duplication of cables to increase rating;
Replacing of network equipment or reinforcement of substations (e.g. based on
short-circuit rating);
Extension of substations and construction of new ones;
Installation of reactive-power compensation equipment (e.g. capacitor banks);
Addition of network equipment to control the active power flow (e.g. phase shifter,
series compensation devices);
Additional transformer capacities; or
Construction of new circuits (overhead and cable).
Initial assessment and detailed grid expansion were then benchmarked against each other
and further fine-tuned. No dynamic investigations have been carried out. Finally, the
Market modelling II step assessing a Cost-Benefit Analysis was carried out.
Page7-15