Validating Short Circuit Studies with Short Circuit Current Measurement

From initial design there are very few electrical systems that do not change over their lifetime. During this time it would be reasonable to see changes in load, changes in source of supply, connectivity with other systems, conductor replacement and change through general equipment repair and maintenance.  As a result of these changes, updated Short Circuit Studies are needed to ensure that equipment is correctly rated, protection equipment is suitably coordinated and that personnel are protected.

With the implementation of Smart Grids – Renewable Generation, Electric Vehicles and Battery Energy Storage – the potential variability in Short Circuit Current (also known as Fault Level) can be quite significant and make traditional methods of calculation and modelling a complex engineering challenge.  Estimations, out of date information and assumptions that creep into these models as they become more and more complex can lead to uncertainty. In the worst case, this can mean under-estimating the potential Short Circuit Current which can have critical and dangerous repercussions.  More common, however, is the over estimation of these values leading to either restrictions on the system, unnecessary equipment replacement or switchgear upgrade all of which can be very costly and inefficient, both in time and money, not to mention the safety implication due to mis-operation of protection devices.

While traditional methods of calculation and modelling are very necessary aspects of fault level management, a good engineering practice is to also measure system Short Circuit Current to validate those models. The measuring of system short circuit current can be carried out using a PM7000 Fault Level Monitor (https://www.outramresearch.co.uk/fault-level-monitoring/pm7000-flm/). Installing the PM7000FLM as you would a typical three phase Power Quality Analyser you can record the Up-Stream (Half Cycle) Peak Short Circuit Current, the Down-Stream (Half Cycle) Peak Contribution and the RMS Break Short Circuit Current at 50-100ms. As well as Short Circuit Current the PM7000 FLM can also measure the same Power Quality parameters as Outram’s top of the range Power Quality Analyser the PM7000S ( ), reducing your need for further monitoring equipment.

How it works. The PM7000 FLM will work from LV to 275kV predicting the fault current on a radial network using natural voltage disturbances (not ‘faults’) of as little as 0.15%. The Outram FLM will build a population of peak (1/2 cycle) and RMS (50-90ms) Fault Level Results over time, with the confidence weighting and a time stamp as to when the result was generated. The user then analyses these results, deciding if there is a single population or multiple populations if the fault level value has in fact changed over time.

A Short Circuit Survey must be carried out whenever there is a change to the design to ensure safe operation. Use an Outram PM7000 FLM to validate these modelled values, checking that no errors have crept in and that they are up to date and accurate. The safety of you personnel may depend on it.