Capítulo 2: Análisis y Mejoras
2.10 Reingeniería de Procesos
Third-party damage can be a complex process which some times consists of several interdependent events. A damage event causes a specific damaged state of the cable system. The effects (the results) of the possible damaged states are also different. In many cases only the primary damage event is seen because this leads to immediate breakdown. Sometimes however, it is necessary to distinguish between short-term effect and final effect. In the following sections the terms, which will be used in the next chap-ters, are defined.
7.1 Primary and secondary damage events
When examining damage caused to cables by third parties ('damage events'), a distinction must be drawn between the first event at the time (t0) and a later damage event, mostly caused by another third party, at time t1. The second, later, event is labelled 'secondary' when there is a causal link to the first event, in other words if the second event would have caused no damage or a different kind of damage if the first event had not taken place.
Attention should first be paid to preventing the first damage event, thus ensuring a better delimitation of the scope.
In general, there is a period of time between the two events, which means that in theory it is possible to try to prevent the second event through the early detection of the damage caused by the first event.
7.2 Damaged state, short-term effect and final effect
A typical example is a protective cable plate that is removed during the primary damage event (trench damage). As a result, the cable is then left behind in a poorly protected condition. This poorly protected condition is the 'damaged state' of the cable system. There is no visible or recordable 'short-term effect' on the cable system. The short-term effect is the initial result of the damaged state.
Then, a few months later, the cable is damaged during digging operations (secondary damage event) which was caused by the first event (because there is no protection or warning above the cable). This secondary event leads to a new damaged state. The new damaged state can, for example, be damage to the cable insulation. In this example the 'final effect' on the cable system is a breakdown.
Another example of a first damage event is a damage to the outer sheath of an XLPE cable without inner metallic sheath (water barrier). The damaged state is 'damaged outer sheath'. The cable is still in service, and nobody knows that anything has happened to the cable. This first damage event with the damaged state 'damaged outer sheath' has the short-term effect on the cable that water is penetrating into the cable. After five years (example), there is an electrical breakdown at this specific spot because of poor electrical strength. The final effect was an electrical breakdown - even though there was no external sec-ondary damage event.
Further examples of short-term and final effects:
Damage event: District heat pipe close to cable Damaged state: Hot spot for cable
Short term effect: Local temperature rise in cable (over-temperature) Final effect: Accelerated ageing and possibly electrical breakdown
Damage event: Link box hit by car
Damaged state: Damage to link box for a cross-bonded cable system Short-term effect: Water ingress and imbalance in cross-bonding system Final effect: Higher losses, hot spot, accelerated ageing of insulation system
The focus must be on the first event - on how to reduce the risk of the first event. If the first event can be prevented, there will be no second event and no final damage effect. Focus must also be on the short-term effects. If the short-short-term effects can be ascertained in time, it is possible to make a repair and avoid the final effect (e.g. an electrical breakdown).
7.3 Criticality of damaged states, cable risk
Each damage event leads to a specific damaged state with a short-term damage effect on the cable sys-tem. To minimise the overall risk of the cable system it is valuable to look not only at the possible events but also at the damage effects. How severe is the damage effect for the cable system? Some damaged states will unfortunately lead to a failure (breakdown), and other damaged states are of minor impor-tance.
Damage event and damaged state represent the same situation, where the damage event is the cause and the damaged state is the result. Both terms are used.
To ensure effectiveness in the struggle against third-party damage the efforts must be prioritised in the correct order. Focus must be on the damaged states and damage events with the most severe effects and the highest probability. The combination (product) of probability (of damaged state caused by a damage event) and severity (of the short-term and final effect) is the 'Criticality of damaged states'. The criticality is the risk for the cable system. It does not say anything about the consequences for the whole network.
Criticality can change along a cable route because the surroundings are different and the threats from third parties will change. Therefore each cable system and each section in every cable system must be analysed. The same solution will not be the best solution everywhere.
To analyse the criticality of the different damaged states, the severity of effect and probability of each damaged state is shown in a criticality matrix (risk matrix).
V IV III II
I
Probability of damaged state
Severity of effect
I II III IV V
Table 7.1 Criticality matrix
The criticality matrix in Table 7.1 shall be read as follows:
Red - area where further studies must be made and something must be done to reduce the criticality Yellow - area where it must be checked whether it is possible within certain limits to do something better Green - area with low risk with no further studies being required
There are two possible ways of reducing the risk:
1. Reducing the probability 2. Reducing the severity
In the following chapters different ways of reducing the risk are discussed.
7.4 Network consequences of damaged states
Many damaged states do not make an immediate impact on the network because no failure occur. But more severe damaged states cause failures in the network with outages of power lines. This section deals with damaged states that have consequences for the network.
Transmission lines are not equally important. Some are extremely important while others are of minor interest. The consequences of a failure will therefore also be dependent on the network structure, the market situation etc.
The criticality, combined with the consequences of a specific damaged state, indicates the risk for the overall network. In Section 11.6 the 'Cable Protection Index' (CPI) is defined as the product of criticality (cable risk) and consequences for the network.