Consequences of failure
The CNAIM methodology’s second key element is the consequence of a failure. When combined with probability of failure, the consequences of failure can be used to derive the monetary network risk. Consequence of failure calculations are based on the same failure modes as probability of failure.
The consequences of failure can be divided into four:
- Financial consequences of failure
- Safety consequences of failure
- Environmental consequences of failure
- Network performance consequences of failure
The sub-consequences have an associated asset specific reference cost of failure based on the British DNOs’ experience and other objective sources. All reference costs are currently in 2012/2013 prices. The reference cost of failure for all sub-categories are scaled with respect to the specific conditions and locations of the individual asset.
Financial consequences of failure considers cost associated with replacement and repairs that returns the asset to its initial condition before the incident.
Safety consequences of failure considers the likelihood and the cost that a failure could be hazardous to a person or a worker including the likelihood that the failure could be fatal. The safety implications is taken from Electricity Safety, Quality and Continuity Regulations (ESQCR).
Environmental consequences of failure considers the cost of a potential oil spill and mitigation of the extremely potent greenhouse gas, sulfur hexafluoride.
Network performance consequences of failure considers the cost a failure imposes to the customers served by the by the asset and the number of interrupting minutes.
Example for a 6.6/11kV transformer
Assuming a transformer:
- has a rated capacity of 750 kVA
- has confined access i.e. assessed to be of a “Type B”
- is exhibiting a low risk to the public
- is exposed to a medium risk of trespassers
- is located 95 meters from a stream
- is serving 750 customers
- has an average demand of 1 kVA per customer
Financial consequences of failure
The financial reference cost of failure for a 6.6/11kV transformer is £7,739, which is scaled by the rated capacity measured in kVA and the accessibility. The financial consequences of failure are found using:
financial_cof <- f_cof_transformer_11kv(kva = 750, type = "Type B")
sprintf("The financial consequences of failure is GBP %.f", round(financial_cof))[1] "The financial consequences of failure is GBP 11125"Safety consequences of failure
The safety reference cost of failure for a 6.6/11kV transformer is £4,262, which is scaled by the location and the risk the transformer represents to the public. The function below is able to calculate the safety consequences of failure for switchgears, transformers and overhead lines:
safety_cof <- s_cof_swg_tf_ohl(type_risk = "Low",
location_risk = "Medium",
asset_type_scf = "6.6/11kV Transformer (GM)")
sprintf("The safety consequences of failure is GBP %.f", round(safety_cof))[1] "The safety consequences of failure is GBP 3836"Environmetal consequences of failure
The environmental reference cost of failure for a 6.6/11kV transformer is £3,171. The environmental consequences of failure calculation considers proximity to water courses, the asset’s rated capacity, and if the transformer is bunded or not. This function can calculate environmental consequences of failure for all types of transformers specified in CNAIM methodology:
environmental_cof <- e_cof_tf(asset_type_tf = "6.6/11kV Transformer (GM)",
rated_capacity = 750,
prox_water = 95,
bunded = "Yes")
sprintf("The environmental consequences of failure is GBP %.f", round(environmental_cof)) [1] "The environmental consequences of failure is GBP 1586"Network performance consequences of failure
The reference network performance cost of failure for a 6.6/11kV transformer is £4,862. This cost is scaled according to the number of customers connected to the transformer and kVA per customer. This function can calculate network consequences of failure for all assets with the exception EHV and 132kV asset:
network_cof <- n_cof_excl_ehv_132kv_tf(asset_type_ncf = "6.6/11kV Transformer (GM)",
no_customers = 750,
kva_per_customer = 1)
sprintf("The network performance consequences of failure is GBP %.f", round(network_cof)) [1] "The network performance consequences of failure is GBP 18232"Consequences of failure
The overall consequences of failure in our example can found using:
cof_transformer <- cof(financial_cof, safety_cof, environmental_cof, network_cof)
sprintf("The consequences of failure is GBP %.f", cof_transformer) [1] "The consequences of failure is GBP 34779"The function adds the sub-consequences together to a total consequence of a failure. For the 6.6/11kV transformer described in this example, it is now possible to derive the monetary risk.
A quick way to find the consequences of failure for the 6.6/11kV transformer in this example is:
cof_short_cut <- cof_transformer_11kv(kva = 750, type = "Type B",
type_risk = "Low", location_risk = "Medium",
prox_water = 95, bunded = "Yes",
no_customers = 750, kva_per_customer = 1)
all.equal(cof_transformer, cof_short_cut)[1] TRUE