Study

Load flow and voltage plan

Voltages, loading and losses calculated in every operating configuration, nominal and degraded.

We calculate the voltage plan in every relevant operating configuration to find the worst case: minimum and maximum upstream voltage, outages, bus coupler positions, tap changer positions, maximum and minimum load.

Minimum load needs as much attention as maximum load. At no load, MV cables generate reactive power and the voltage rises, and the need for a shunt reactor or a limit on the tap changer often appears in this case.

These campaigns are run with in-house scripts for ETAP and PowerFactory. The script discovers the network, checks the busbars and produces a result per scenario. The assumptions are written down and the model is delivered to you.

01What we do

Calculations

Normal operation and N-1 contingencies
Voltage plan and on-load tap changer range
Power balance, losses, loading
Hosting capacity for a new load

For grid connection

Reactive power exchange at the point of delivery
P/Q and U/Q diagrams
Reactive compensation sizing

02Examples

Fig. 01Load flow of a 225 / 20 kV substation with three feeders, showing the voltage at the end of each feeder, the power flows and the transformer loading (54 %).Worked example

Fig. 02Calculated 20 kV voltage for each upstream voltage and each on-load tap changer position.Worked example

03Our offer

Usual content of an offer for this type of assignment. The exact scope, deliverables and price are set in the quotation.

Package 1Data collection and check
Data list, deviations found, assumptions agreed with you before calculation.
Package 2Modelling
ETAP or PowerFactory model, or takeover of yours after a check.
Package 3Calculation campaign
Scenario matrix set in the quotation: upstream voltage, N and N-1 configurations, maximum and minimum load, tap changer positions.
Package 4Study note
Results per scenario, deviations from criteria, conclusions and recommendations.
Package 5Presentation
Presentation of the results and incorporation of your comments.

04How we work

01Data check
Impedances, nameplates, lengths, with a source for every value.
02Scenario matrix
Upstream voltage × configuration × load × tap.
03Calculation and post-processing
Out-of-range voltages, overloads, losses, reactive power at the point of delivery.
04Conclusions
Required tap changer range, compensation, operating limits.

05References

Data centre, Île-de-France

Load flow campaign on an ETAP model

Audit of the existing scenarios and sweep of upstream voltage × configurations. The on-load tap changer range of the 225 kV transformers proved insufficient.

Integrator, West Africa

Four PV plants

Load flow, short-circuit, neutral earthing, earthing, stability and protection plan for each plant.

All references

06Frequently asked questions

How many scenarios?

As many as needed to find the worst case, combining upstream voltages, N-1, coupling arrangements and tap changers. The scope is set in the quotation.

Can you work on my existing model?

Yes, after a check of the model, quoted separately.